Hymenoepimecis argyraphaga

Those who have been reading this blog for a while realise that August is the month when I featured some guest posts written by students from my Evolutionary Parasitology  (ZOOL329/529) class.  One of the assessment I set for the students is for them to summarise a paper that they have read, and write it in the manner of a blog post. The best blog posts from the class are selected for re-posting (with their permission) here on the Parasite of the Day blog. I am pleased to be presenting these posts from the ZOOL329/529 class of 2015. To kick things off, here's a post by Alison Cash on a paper published in 2001 about a parasitoid that uses its spider host to weave a tangled web.

Left: The usual web constructed by a Plesiometa argyra. Right: A web constructed under Hypmenoepimecis' influence
Photo from this paper.

The parasitoid wasp Hymenoepimecis argyraphaga can be considered to be pretty unremarkable at first glance. However, the life history of this killer insect contains more drama and intrigue than an episode of Game of Thrones - maybe with just a little less incest. This wasp is found in the tropical forests of Costa Rica. Here, when an expectant mother wasp is prepared to lay her solitary egg, she seeks out one particular species of orb-weaver spider - Plesiometa argyra.

This spider is known for its elaborate web-spinning abilities, with which it uses to capture its prey. Each day, it meticulously recreates its skilled masterpieces and for this talent H. argyraphaga targets it with the burden of raising its life-sucking young. The larva of this wasp not only makes a meal of the spider, it also turns the unfortunate arachnid into its personal slave via mind control - using it to create a perfect haven to pupate.

When the female wasp locates a P. argyra, it temporarily paralyses its victim with a sting before it glues an egg on the spider and leaving. After 10-15 minutes, the spider wakes out of its stupor, and resume life as normal, apparently unaware of its new and sinister backpack. The egg soon hatches and the larva anchors itself to its spider host, riding it triumphantly for the next two weeks, all while feeding on the spider's blood (call hemolymph) from small holes it has punctured in the host's abdomen.

Once the larva has matured and is ready to begin its transformation into an adult wasp, the relationship becomes more menacing. The larva injects the spider with a cocktail of chemicals that alters its web-weaving behaviour. Under this influence, the spider custom-build a unique reinforced web, fit to encase the wasp larva in its a cocoon while it metamorphoses. Once the spider had completed this highly altered web, the spider moves to the center of the web where it remains somewhat dazed. The wasp larva then dismount from its naive eight-legged steed, then kills it and suck the corpse dry for its last supper as a larva. It then weaves a cocoon which nestles securely in the middle of the web, suspended away from potential threats. After ten days, the adult emerges to begin the grisly cycle once again.

What sets this wasp apart from many other parasitoids is that it modify the host's behaviour, via an injected chemical cocktail, in such a specific and detail manner. Instead of weaving the usual intricate five-step web, P. argyra is reduced to repeated the first two step of web construction. The scientist who conducted this study observed that by blocking the ability to construct the multi-step web, the result was a "custom-built" structure which is more durable and less likely to be damaged by falling debris. Even when the larva is removed from the spider before it is able to kill its host, the webs made by the previously parasitised spiders are still malformed for the following few days, but eventually return to normal, which suggest that the behavioural change is induced by a chemical rather than just physical interference by the parasitoid larva.

By chemically inducing this altered host behaviour, H. argyraphaga ensures that it will successfully raise another generation of spider-enslaving wasps.

Reference:
William G. Eberhard. (2001). Under the influence: Webs and building behavior of Plesiometa argyra (araneae, tetragnathidae) when parasitized by Hymenoepimecis argyraphaga (hymenoptera, ichneumonidae). Journal of Arachnology, 29(3), 354-366.

This post was written by Alison Cash

Lysibia nana

Lysibia nana photo by Nina Fatouros
Used with permission
from BugsinthePicture 

In order to live, a parasite must find its host. Whereas some parasites take a passive approach and simply wait for a chance encounter, many species are more proactive. In the case of parasitoid insects that have free-flying adults, they have various adaptations for tracking down their hosts. But what about the hyperparasites - parasites that infect other parasites? How do they find their host, which themselves are hidden within the body of a host animal? It seems as if they would need to have X-ray vision in order to complete their life cycle.

The parasite we are featuring today is Lysibia nana, a hyperparasitoid that infects Cotesia glomerata - the parasitoid wasp which lays its eggs inside caterpillars. It turns out that L. nana does not rely on superpowers like X-ray vision, but a far more parsimonious ability. To find out how L. nana finds a host, first of all, we have to ask; how does C. glomerata itself find its hosts? A few months ago, we featured a parasitoid fly that uses sound to track down its prey, but most parasitoid wasps use scent to sniff our their hosts. But this scent does not come directly from the host itself, but rather, the host's food.

When a plant comes under attack by herbivores like caterpillars, they emit volatile chemical signals call kairomones that acts like a dinner bell for parasitoid wasps, which have evolved to use those chemicals to guide them to their prey. Feeding by different species of caterpillars elicit different chemical emissions from the plant, which provides a signature of their presence and attract different species of parasitoids.

Parasitoid wasps are master body-snatchers, they don't just consume their hosts from within; while they are in residence they also change the caterpillar's physiology, altering its growth pattern and behaviour - so much so that on some levels the parasitised caterpillar can be considered as almost a different animal. But they have their own enemies in the form of hyperparasitoids like L. nana.

A research group in the Netherlands conducted a series of experiments to figure out how this hyperparasitoid tracks down its hidden prey. They first tested how wild cabbage plants responded when they come under attack by two different species of caterpillar - Pieris brassicae and P. rapae.

Dead caterpillar with Cotesia glomerata cocoons
Photo by Hectonichus

They found that two caterpillars induce very different blends of chemical volatiles from the plant. But it is a different story when those caterpillars are parasitised by C. glomerata. The physiological alteration that the parasitoid imposed on their host was reflected in how the caterpillar's food plant responded. Cotesia glomerata manipulated their hosts to such a degree that once parastisied, both P. brassicae and P. rapae elicited a far more similar blends of chemical emissions from the plant.

This is where the hyperparasitoid L. nana comes in. The researchers put some female hyperparasitoids in a Y-maze and exposed them to combinations of different volatile chemical released by; caterpillar-free plants, plants which had been chewed on by caterpillars, or plants which have been chewed on by parasitised caterpillars. They noticed that given the choice between the chemicals of plants damaged by parasitoid-free and parasitised caterpillars, the hyperparasitoids preferred overwhelming to go in the direction of the latter - regardless of what species the host caterpillar might be. To L. nana, whether those caterpillars had parasitoid babies onboard is far more important than their species identity, and they showed no clear preference for either caterpillar species as long as they were parasitised by C. glomerata.

The researchers also conducted a field-based study that corroborated the results from the behavioural experiment. They did so by attaching C. glomerata cocoons to some wild cabbage plants that they have grown in an experimental plot. Some of the plants had previously been munched on by parasitoid-free caterpillars, others by parasitised caterpillars. After 5 days, they checked the parasitoid wasp cocoons for signs of L. nana and found that cocoons on plants which have been chewed on by parasitised caterpillar attracted far more L. nana than those munched on by parasitoid-free-caterpillars

So while parasitoid wasps like C. glomerata may have masterful control over their host body's physiology, this also leaves a calling card to their own hyperparasitoids. For the hyperparasitoids, it's what's inside that counts.

Reference:
Zhu, F., Broekgaarden, C., Weldegergis, B. T., Harvey, J. A., Vosman, B., Dicke, M., & Poelman, E. H. (2015). Parasitism overrides herbivore identity allowing hyperparasitoids to locate their parasitoid host using herbivore‐induced plant volatiles. Molecular Ecology 24: 2886–2899.

P.S. I will be attending the New Zealand Society for Parasitology and Australian Society for Parasitology joint conference in Auckland, New Zealand. So watch for tweets with highlights from conference at my Twitter @The_Episiarch! All tweets related to that conference will have the #NZASP15 hashtag.

Coccipolipus hippodamiae

Today we feature a guest post by Katie O'Dwyer who recently completed her PhD at the Evolutionary and Ecological Parasitology group at Otago University. She has previously written for Parasite of the Day about  Phronima - a parasitic crustacean that turns gelatinous salps into floating zombies. This time she has written a story about why "Promiscuous ladybirds pay the price when it comes to parasites".

A pair of mating two-spot ladybirds (photo by Richard001)

For most of us when we hear any mention of sexually transmitted infections (STIs) we think of humans, herpes and the variety of public service announcements we see about practicing safe methods in order to avoid contracting STIs. However STIs are rife in the animal kingdom. They can be found in any animals that require internal fertilisation for reproduction. And it seems that one group which can really benefit from advice on safe methods to avoid STIs are the ladybirds.

Who would have known (well, probably some entomologists) that these beautiful beetles are highly promiscuous and not very choosy about who they mate with? This makes them an extremely efficient host for any sexually transmitted parasite. Today’s post is about a sexually transmitted mite Coccipolipus hippodamiae and its host - an European ladybird.

These mites are transmitted when ladybirds are mating and they migrate to the wing case (called elytra) of the beetles. Here they latch on using their mouthparts and feed on the hosts blood (known as haemolymph) before metamorphosing into adults. What quickly follows is the development of a large mite colony on a single ladybird. The presence of these mites can reduce the fertility and reproductive capacity of female ladybirds.

A female Coccipolipus hippodamiae mite with eggs.
Scale bar = 100 µm (photo from here)

There are some measures that can be taken when faced with high levels of STIs, such as switching the mating system to monogamy and being choosier when it comes to potential partners. However, studies have found no evidence for C. hippodamiae having any effects on mate choice in ladybirds. Luckily for the mites, female ladybirds are unable to detect if their male partners are infected.

However, there are other factors that limit the success of these parasites. Timing is an important aspect of STI transmission in this system. Ladybirds overwinter and refrain from mating regularly during this season. Following the period of overwintering, these highly promiscuous bugs travel across plants on a mating spree, hooking up indiscriminately, and triggering an epidemic of mite infections. A key aspect in this process is the overlap between generations.  In order for the mite population to be maintained mating must occur between consecutive generations of ladybirds. The mites have evolved to take advantage of those hosts with overlapping generations and unfortunately for the two-spot ladybird, Adalia bipunctata, it has one of the longest periods of overlap between generations. Therefore it is also the most common host for these mites.

These miniature mites have also adapted to infect other ladybird species with up to four species of European ladybirds in its repertoire of hosts. Interestingly, one of these ladybird species does not have an overlap in generations because a period of diapause is required during development, whereby one generation dies off before the next one metamorphoses into adults.  Luckily for the mite, these ladybirds appear free and easy when it comes to mating, even across different species. So even this ladybird species without overlapping generations can become reinfected during such hybrid mating sessions.

This picture gets even more complicated when the invasive Asian harlequin ladybird gets involved. This beetle has invaded the UK and is out-competing the native ladybirds (of which there are up to 46 species!). As a method of control some researchers have decided it might be a good idea to introduce the mites as a biological control agent. However, up to now, C. hippodamiae has not been found in ladybirds in the UK as they do not overlap in generations in the same way that continental European ladybirds do. This is currently an active area of research and not much is known about the effect the mites could have on the UK’s naïve ladybird hosts. In their struggle against the feisty harlequin ladybird, can a foe of European ladybirds become a friend of the UK’s native ladybirds? Only further research will tell…

References:

Hurst, G.D.D., Sharpe, R.G., Broomfield, A.H., Walker, L.E., Majerus, T.M.O., Zakharov, I.A., Majerus, M.E.N. (1995) Sexually transmitted disease in a promiscuous insect, Adalia bipunctata. Ecological Entomology 20, 230-236

Webberley, K.M., Hurst, G.D.D., Husband, R.W., Schulenberg, J.H.G.V.D., Sloggett, J.J., Isham, V., Buszko, J., Majerus, M.E.N. (2004) Host reproduction and a sexually transmitted disease: causes and consequences of Coccipolipus hippodamiae distribution on coccinellid beetles. Journal of Animal Ecology 73, 1-10

Rhule, E.L., Majerus, M.E.N., Jiggins, F.M., Ware, R.L. (2010) Potential role of the sexually transmitted mite Coccipolipus hippodamiae in controlling populations of the invasive ladybird Harmonia axyridis. Biological Control 53, 243-247

Post written by Katie O'Dwyer

Mermis nigrescens

Photo by Haseeb Randhawa & Ken Miller here

New Zealand is a land known for its unique animals and plants, but over the centuries it has also become home to many introduced species which have become invasive and disruptive to its natural ecology. While many of the introduced species are recognisable larger animals such as pigs, possums, and rats, some of them tiny creepy-crawlies - insects and other invertebrates. And some of those have passengers living inside them which have largely been hidden out of sight

Meet Mermis nigrescens, a nematode worm which arrived in New Zealand inside European earwigs (Forficula auricularia). Mermis nigrescens is a species which had been known since 1842, and it is likely that it might have even been discovered earlier than that in 1766, but was mistakenly identified as Gordius - a genus of hairworm - which despite superficial resemblance and a similar life cycle, belongs to a different phylum. Its host, the European earwig, first arrived in New Zealand during the 19th century, but it was only recently noticed that these insects have also brought along a parasite from their original home range.

Photo of earwig host with M. nigrescens from this paper

Like other nematodes from the family Mermithidae, M. nigrescens are aquatic as adults and only parasitise earwigs during their juvenile stage. An earwig can be hosting anything from a single worm up to as many as seven of those parasite. When M. nigrescens reaches maturity, it needs to get into a water body to mate and reproduce. And if they're anything like the hairworms and other species of mermithids, it would commandeer the earwig and steer it to water, where the worm can evacuate its host xenomorph-style and leaves the now hollowed-out earwig to drown.

So how do we know this parasite is an introduced species and isn't one that the earwig had simply acquired in its new home?

Molecular analysis looking at three genetic markers from M. nigrescens showed that the closest relatives of these particular nematodes are found in Canada - M. nigrescens appears to be well-travelled, and is found all over the world. But it does not seem to be as abundant in Dunedin, New Zealand as seen elsewhere in world. In the population that was examined for this study, only 19 out of the 198 earwigs examined were infected with M. nigrescens, whereas a study in Tasmania, Australia found the parasite in half of the earwigs examined, and it was even more common in Ontario, Canada where infection prevalence reached 63%. It is currently unknown why M. nigrescens does not seem to be as abundant in New Zealand as it is elsewhere in the world, though it could just be something about this particular bunch of earwigs and that there are more heavily parasitised earwig populations elsewhere in New Zealand.

But where did the M. nigrescens population in New Zealand originate? While its closest living relatives are found in Canada, did it arrive to New Zealand from there? After all, the original home of M. nigrescens is Europe, so the Canadian population was not native to that region either. The missing piece of this puzzle is genetic sequences of M. nigrescens specimen from its original range in Europe, which might resolve where this newly discovered New Zealand population originated - from Europe or elsewhere. For all we known, this supposedly widespread species may in fact be composed of a complex of closely-related cryptic species, with each species found in a different region of the world.

Just goes to show that even in the common earwig, there are natural history secrets waiting to be revealed.

Reference:
Presswell, B., S. Evans, R. Poulin, and F. Jorge. 2015. Morphological and molecular characterization of Mermis nigrescens Dujardin, 1842 (Nematoda: Mermithidae) parasitizing the introduced European earwig (Dermaptera: Forficulidae) in New Zealand. Journal of Helminthology 89: 267-27

Edhazardia aedis

When two different parasites find themselves in a small host animal like a mosquito, there is only so much of the host to go around. So there is a pretty good chance that those co-occurring parasites are going to fight it out, and there's no guarantee that there will be a winner out of this conflict.

Photo of E. aedis spores from here

Edhazardia aedis is a microsporidian parasite that specialises on infecting Aedes aegypti - also known as the mosquito that can act as the main vector for a variety of viruses include those that causes degnue fever, yellow fever, and Chikungunya. Edhazardia aedis can spread through the mosquito population via two methods; (1) the parasite can proliferation throughout the mosquito's body until it ultimately overwhelms the host, which dies and dissolves into a cloud of infective spores, or (2) if an infected female mosquito survives the ordeal to adulthood and still manage to produce offspring, her mosquito babies will inherit E. aedis from her (gee, thanks a lot mum!).

But E. aedis can sometimes run into a competing species - Vavraia culicis. It is also a microsporidian, but unlike E. aedis, it is a generalist that can infect many different species of mosquitoes. It is also a mosquito-killer which has the same general modus operandi as E. aedis, where the parasite's spores are released when the host finally succumbs. This study found that mosquito larvae which have less access to food and are infected by both parasites tend to die earlier - and when the host dies, the spores are dispersed for both E. aedis and V. culicis - so everyone wins, right? Well not quite.

While host death does release the spores which allow them to infect more mosquito larvae, the parasites get more spores for their bucks by keeping their host alive for longer - so a host that ends up keeling over too early is not very cost effective. This applies to both E. aedis and V. culicis. Even before host death, the cost of co-infection starts manifesting itself. Regardless of whether the host dies sooner or later, both parasites produce less spores in co-infections. If E. aedis is sharing a host, it produces half as many spores as it would have if it had the host all to itself. But co-infection is even more costly for V. culicis, which manages to produce only a bit over a quarter of the spore it would have in single infections.

It is unknown how these two parasites duke it out in the mosquito, or why E. aedis has a competitive edge over V. culicis. Perhaps by being a specialist of A. aegypti, E. aedis has some sort of home ground advantage when it comes to getting the most out of its host. So it seems that some parasites just don't like sharing, and when it comes to living with others, sometimes it pays for a parasite to be a specialist.

Reference:
Duncan, A. B., Agnew, P., Noel, V., & Michalakis, Y. (2015). The consequences of co-infections for parasite transmission in the mosquito Aedes aegypti. Journal of Animal Ecology 84: 498-508.

Emblemasoma erro

During summer the air is filled with the rattling ruckus of cicada songs. Male cicadas produce this summer choir using a pair of noise-making organs located in their abdomen, with the aim of getting attention from any prospective mates. But in some cases, they can also end up with some unwanted attention.

Top: Male Tibicen dorsatus cicada
Bottom: Female Embelmasoma erro fly
Photos from Figure 1 & 2 of this paper

The species we are featuring today is an "acoustically hunting" parasitoid fly - it eavesdrops on the male cicada's flirtatious serenading and uses it to home in on its target. This fly is commonly found on the Great Plains of North America and is a scourge to male cicadas, especially male Tibicen dorsatus.

Most of what is known about such acoustically hunting parasitoids are based on flies from the Tachinidae family - one of which targets crickets (I talked about how crickets on Hawaii evolved to become silent due to the presence of one such parasitoid fly here). But this fly belongs to a different family (Sarcophagidae). Only one species of Emblemasoma is well-studied - E. auditrix- and even though Emblemasoma is widely use in the study of insect hearing, not much is known about how they actually live out in the wild. Until now, the only information available on E. erro are based on two scientific papers - one published in 1981 and the other published in 2009. The paper we are featuring today provides some much-needed update on key aspects of this parasitoid's ecology and life history.

This paper reports on a series of field surveys and laboratory experiments that documented the parasitoid's occurrence, abundance, behaviour, and developmental cycle.

The field surveys were conducted at study sites located across Kansas and Colorado. The surveys found that a bit over a quarter of male cicadas were infected with E. erro larvae, and because of how the flies track down their host, almost all the infected cicadas were male - except for one very unlucky female cicada, which most probably got infected because she was responding to the call of a male, ran into a larvae-ladened E. erro that had the same idea, the latter decided that any cicada will do. Talk about a case of fatal attraction!

And it is indeed the sound of the male cicada's serenade that draws in those flies - a loudspeaker playing the recordings of cicada calls is sufficient to attract the attention of E. erro, but a female fly need more than that to commit to dropping off her precious offspring. In outdoor cage experiments where flies and cicadas were housed together and allowed to mingle freely, the researcher observed that even if an E. erro finds herself perched next to a cicada, she will only attack when the host makes any sudden movements. So E. erro uses two separate signals to track down its prey; an acoustic signal at long range in the form of the cicada's call to guide them in, and a visual signal at close range in the form of cicada movement to confirm the host's identity

Emblemasoma erro larva emerging from a cicada
From Figure 6 of this paper

Once she has confirmed her target, the female fly makes an attack run, and very quickly drops off between 1-6 maggots (usually 3) on the base of the cicada's wings. As soon as the maggots land, they immediately start burrowing between the segments and into the cicada's body. The maggots then start devouring its host alive from the inside. Depending on the temperature and clutch size, they take about 88 hours to reach a large enough size to start pupating. At the end of this period, the maggots use teeth-like "oral hooks" to chew their way to freedom, fall onto the soil below to become pupae, and leaving the cicada an empty husk.

So while the aim of the male cicada's singing is to attract the attention of female cicadas, some of them may instead end up getting attention from females of a very different species, and become reluctant incubators for the broods of some keen-eared, cicada-hunting flies.

Reference:
Stucky, B. J. (2015). Infection behavior, life history, and host parasitism rates of Emblemasoma erro (Diptera: Sarcophagidae), an acoustically hunting parasitoid of the cicada Tibicen dorsatus (Hemiptera: Cicadidae). Zoological Studies, 54: 30.

Gelis agilis

It's a bug-eat-bug world out there and the same applies to parasitic wasps - even parasites can themselves become parasitised - which is why some parasitoids recruit their dying host as defence. The parasitoids that go after other parasitoids are call "hyperparasitoids" and the species we are featuring today is Gelis agilis, a tiny wingless wasp that lays its eggs in the cocoons of parasitic wasps such as Cotesia glomerata.

Photo of Gelis agilis by Christophe Quintin

This hyperparasitoid wasp has more to contend with than just overcoming their host's reluctant bodyguard. It is after all a small insect which equates to a handy mouthful for many potential predators. The adult G. agilis is a tiny (3-5 mm) and seemingly defenceless - it doesn't even have wings to fly away from any danger. But G. agilis makes up for that with a clever masquerade

If there is a group of tiny insect which are generally regarded as pretty unpalatable, it is ants (except for animals that specialise on eating ants), so many other creatures have evolved to mimic them in one way or the other. When it comes to playing the part of an ant, G. agilis is a method actor - not only does it look and act like an ant, it even smells the part. When agitated, it emits a volatile chemical call sulcatone, which is the same chemical used by ants as alarm pheromone to rally colony members to their defence.

This "full spectrum mimicry" pays off. Spiders that normally pounce straight onto similarly-sized insects such as fruit flies or parasitic wasps like C. glomerata would hesitate or back right off when confronted with Gelis. A species related to G. agilis - G. aerator - looks and acts like an ant but lacks the distinctive "antsy" smell. When G. aerator was put through experimental trials up against hungry wolf spiders, most spiders back off due to its ant-like appearance. But the lack of matching ant BO was enough for a few more daring (or desperate) spiders to get the jump on G. aerator.

By playing the part to its fullest capacity - behaviour, appearance, and scent - G. agilis is better able to evade its predators to survive another day, and go on to make life a living hell for other body-snatchers

Reference:
Malcicka, M., Bezemer, T. M., Visser, B., Bloemberg, M., Snart, C. J., Hardy, I. C., & Harvey, J. A. (2015). Multi-trait mimicry of ants by a parasitoid wasp. Scientific Reports 5: 8043

Columbicola columbae

You would think that of all living things, parasites would have the least need to move around. After all, it is sitting in its ideal habitat and is already (in a way) surrounded by food. Why would it need to go anywhere else? But most parasites usually reside at a very specific part of the host's body - at some stage, it would have had to makes its way there somehow, even if it stays in one spot after that. Furthermore for some parasites, where they live on the host is not the same as where they eat, so they have to commute regularly in order to get their meal ticket.

Photo by Vince Smith at phthiraptera.info

One such parasite is the humble pigeon louse (Columbicola columbae), which is usually found hanging out on the wing feathers of pigeons. It has evolved a narrow body that allows it to fit snugly between the barbs of the flight feathers and safe from the preening beak of the host. But while wing feathers are a nice place to seek shelter, they do not make for such an appetising meal - they are far too tough for C. columbae to chew on. So when the pigeon louse gets hungry, it needs to make a move to the body region where the more palatable, downy feathers are found.

So how does C. columbae find its way from the wing to the body? It's not like it can just look up Google Pigeon or something like that and get directions. Well, based the study we are featuring today on this blog, they use temperature to find their way.

Like us, birds are homeotherms - which means they keep a consistent body temperature, regardless of the outside environment. But even for a homeothermic animal, the temperature is not consistent across the body. For example, the temperature at the wings and tail of a pigeon is about 32 °C (89.6 °F), whereas the body region temperature is approximately 36 °C (96.8 °F). So are the lice using temperature differentials across parts of the pigeon's body as a cue for navigation? To find out, a pair of researchers did a series of experiments to determine what temperature the lice preferred under different circumstances.

They did a choice experiment where they put some pigeon lice in a glass petri dish with one end resting on top of a heated metal block. They also did another experiment where they placed some lice on a piece of filter paper sit on a heating apparatus that they built to generate a radial temperature gradient. In both experiments, they recorded where the lice moved to and found while the lice did respond according to the temperature differences, it was also dependent on whether they were hungry or not.

Lice which had a full belly prefer to hang out at 32 °C (wing region temperature), but those that have been experimentally starved for 18-20 hours tend to move to where it is 36 °C (body region temperature). But if down feathers are so tasty, why don't they just hang out there all the time? While the pigeon's main body is covered in tastier feathers, it is also more exposed to the murderous beak of a preening host. Whereas on the wings, the skinny body of C. columbae allows it to tuck itself between the barbs of the pigeon's flight feathers, and stay safe and sound.

So some lice like it hot, but only if they are hungry.

Reference:
Harbison, C. W., & Boughton, R. M. (2014). Thermo-orientation and the movement of feather-feeding lice on hosts. Journal of Parasitology 100: 433-441.

Ampulex compressa

This is the sixth post in a series of blog posts written by students from my third year Evolutionary Parasitology unit (ZOOL329/529) class of 2014. This particular post was written by Holly Cooper about how the Emerald Cockroach Wasp acquired the skills needed to wrestle and zombifies a cockroach into submission (you can read the previous post about how Sarcocystis makes their vole host more vulnerable to death from above via kestrel here).

Photo by Jen R

Of all the creatures in the animal kingdom, cockroaches are generally not looked upon all that favourably. Largely seen as pests for their suspected transmission of pathogens, the thought of these critters being forcibly removed from play evokes little compassion from most people. However, zombification followed by a slow death via being consumed from the inside may be enough to shed a sympathetic light upon these hapless victims of parasitism.

The culprit of this gruesome attack is the Emerald Cockroach Wasp (Amuplex compressa), a 2-3 centimetre long insect of a startling blue-green colour with vibrant red upper legs. Remarkable in its colouring and delicate in build, the beautiful, fragile female wasps can single-handedly and viciously attack their sturdy cockroach victim. Targeting specifically the American cockroach (Periplaneta Americana), the wasp undertakes a complex sequence of behaviours involving a brutal wrestling match followed by two consecutive stings to the midsection and head of the prey. The latter of these stings penetrates directly into the nervous system, the venom injected seeping into that organ to throw the cockroach into a daze. What follows is a brief feed by the wasp upon the victim’s haemolymph (the insect’s blood) by tearing off the antennae to access the nutritious fluids. Upon eating her fill, the female conducts a puppet master-like act of nudging the now zombified cockroach into a burrow where it is buried alive with a single egg glued to its belly. When the larva emerges, it proceeds to nibble into the fresh prey, even crawling inside the roach to continue obtaining nourishment. Gradually, as its internal organs are consumed, the cockroach dies and its hollowed out body become a shell in which the larval wasp spins a cocoon to undergo pupation. At a point of 6 weeks after initial burial, the new wasp breaks out of the carcass and emerges from its burrow.

This complex and potentially dangerous sequence of behaviours conducted by the female wasp involves a certain amount of skill and apparent calculation. From overcoming the cockroach to injecting venom directly into the nervous system to ensure maximum effect, and finally burying the host with their larva, each step is essential in ensuring optimal development of the offspring. How did such a small creature acquire the skills to perform this violent yet evidently effective attack? A team of researchers conducted a study to determine whether such efficiency is a product of learning, and as such improving with experience, or whether the knowledge was wired into wasps before birth. The researchers observed the successive attack and burial of cockroaches by 10 individuals in 4 instances each, observing the efficiency and precision of the wasps' behaviours.

The consistency of this highly complex and specific set of behaviour was found to change little with experience. That is, gaining experience did not improve the performance of the female wasps. The time taken to attack and bury did not become more refined, though at times the ordering of the sequences was altered. The viciousness and efficiency of the behaviours is not learned but innate; these wasps were born with all the knowledge they needed.

This demonstration of skill is just one example of the incredible abilities of insects. Despite lacking in parental care after birth, and hence not afforded the chance to learn from their parents, the newly born wasps are gifted with the ability to continue in the behaviours required for survival and reproduction. Emerald Cockroach Wasps has become a specialist in the most effective method of subduing their target; an evolutionary triumph for the wasp, though not in the least bit positive from the perspective of the cockroach.

Reference:
Keasar, T., Sheffer, N., Glusman, G., & Libersat, F. (2006). Host handling behaviour: An innate component of foraging behaviour in parasitoid wasp Ampulex compressa. Ethology 112: 699-706

This post was written by Holly Cooper

Culicoides anopheles

This is the fourth post in a series of blog posts written by students from my third year Evolutionary Parasitology unit (ZOOL329/529) class of 2014. This particular post was written by Sarah Prammer she had titled "The Mosquito's Karma" on a midge that sucks blood the belly from mosquitoes (you can read the previous post about how leaf-cutter ants defend themselves against parasitoid flies here).

Photo from Figure 1 of the paper

Very few people are lucky enough to escape the bloodsucking appetite of a mosquito - most would have been bitten by those insects at some point in their life. It seems now, however, we can say the same of the mosquitoes themselves. A type of midge, scientifically known as Culicoides anopheles, has been recorded feeding on the blood of at least nineteen different species of mosquito. It only attacks mosquitoes that are already engorged with blood, so typically leaves males and ‘empty’ females alone. Although this study was located on the Chinese island province of Hainan, these midges have also been found in Papua New Guinea, Sri Lanka, Myanmar, Thailand, Vietnam, Indonesia, and on almost three quarters of Anopheles stephensi mosquitoes in India.

This particular study took place last year (2013) in Haikou, a populous city in Hainan. An unfortunate cow was used as bait inside a net trap to capture mosquitoes. Upon examining the caught mosquitoes, the researchers noticed that one of them, an Anopheles sinensis specimen, was being parasitised by the midge. This happened again the next day. The researchers chloroformed the animals and videotaped their behaviour underneath a microscope. The midge had pierced the front of the mosquito’s abdomen with a specialised tube-like mouthpart called a proboscis, and its own abdomen increased in size as it stole the stolen blood directly from the mosquito. It was significantly smaller than the host which probably gave it easier access and prevent the mosquito from pulling it off.

Notably, the midge had trouble detaching itself; it had to rotate its body a few times in order to unscrew itself from the host. The researchers hypothesised that the midge’s proboscis has evolved to remain firmly inside the mosquito, which allows it to continue feeding at leisure even while the host is flying. This is supported by other studies which show that the midge can hang off the mosquito for almost two and a half days. A paper about a study done in Papua New Guinea described one midge still embedded in its mosquito even after being sedated, killed, and preserved. Although the mosquitoes can tolerate the midges for a few hours with apparent indifference, they appear to eventually grow agitated of being a blood meal, sometimes flying about erratically when infected. One mosquito was observed to suffer organ damage from this type of parasitism. Up to three midges have been found on a single mosquito.

Because mosquitoes are often carriers of disease, the midge is considered a component in further spreading pathogen in both humans and other animals; it is effectively a transmitter between transmitters. The pathogens it can potential spread include the Bluetongue, Oropouche, and Schmallenberg viruses, which are transferred by the midges themselves, as well as the Dengue, West Nile, and Japanese encephalitis viruses, which carried by the mosquitoes. It is not known just how much the Culicoides anopheles midges contribute to the spread of these diseases. Similarly, there is little other information on their behaviour or genetics.

Reference:
Ma, Y., Xu, J., Yang, Z., Wang, X., Lin, Z., Zhao, W., Wang, Y., Li, X. & Shi, H. (2013). A video clip of the biting midge Culicoides anophelis ingesting blood from an engorged Anopheles mosquito in Hainan, China. Parasites & Vectors, 6: 326.

This post was written by Sarah Prammer

Apocephalus attophilus

This is the third post in a series of blog posts written by students from my third year Evolutionary Parasitology unit (ZOOL329/529) class of 2014. This particular post was written by Jon Schlenert on a paper published in 1990 about a way that leaf-cutter ants defend themselves against parasitoid flies (you can read the previous post about a tardigrade-killing fungus here).

Photo by Norbert Potensky

Leaf cutter ants are well known for their important ecological role as herbivores of tropical forests. The ants harvest large quantities of leaf material which they use as garden beds to grow a highly specialised, symbiotic fungus which is eaten by the ants. Less well known is that leaf cutter ants exhibit a peculiar behaviour  whereby smaller ants of the same species called minims, hitchhike on the leaves being carried back to the colony by the larger foraging ants.

Observations of this hitchhiking behaviour provoked much speculation about its purpose, and two alternative hypotheses arose to explain it. The first hypothesis, dubbed the energy conservation hypothesis, suggested that the smaller ants undertook important roles at the foraging site, and would then hitchhike back to the colony on the leaves to reduce energy costs. The second hypothesis, the ant protection hypothesis, posited that hitchhiking behaviour was a defensive response to pressures from parasitic flies.

The flies belong to the family Phoridae and mostly parasitise hymenopterans: ants, bees wasps. The reproductive strategy of parasitic phorids involves the female laying eggs inside the bodies of living insects. The parasitised insects are kept alive whilst the larvae hatch from the egg and begin to consume the host’s tissue. Eventually the larva is ready to leave the host and become a free living adult, when it emerges the host is left mortally wounded or in some cases is already dead beforehand.

Leaf cutter ants have their share of parasitic flies. Foragers are particularly vulnerable to attacks from the flies as they are unable to defend themselves whilst carrying leaves back to the colony. A female fly will land on the leaf fragment being carried, and make its way down towards the joint between the cephalon (head) and cephalothorax (first thoracic segment) of the ant. The fly, using it’s long ovipositor, injects an egg between the armoured plates and quickly absconds.

In the paper, researchers set out to quantitatively assess whether the hitchhiking behaviour in leaf cutting ants is a response to attack from parasitic flies. Research was carried out on Barro Colarado Island in Panama; an important research location for studying tropical ecosystems. The two species looked at were the ant species Atta colombica and its parasitic fly Apocephalus attophilus. The study found strong evidence in favour of the ant protection hypothesis and concluded that hitchhiking behaviour is driven by parasitism rather than energy conservation. The study also found that flies require leaf fragments to stand on whilst they inject their eggs, thus only leaf carriers were susceptible to parasite attack. The presence of hitchhikers significantly reduced the probability of attack from the flies and represents a major investment into parasite defence. Furthermore, the researchers observed that the ants were able to adjust the level of hitchhiking behaviour displayed in response to daily and seasonal changes in parasite abundance.

The highly specialised defensive response of leaf cutter ants represents a significant cost to the colony, as ants are diverted from undertaking other important tasks. Consequently, there is a trade-off between investing in parasite defence or other areas such as caring for offspring. This demonstrates that parasitism from phorids has shaped the evolutionary responses of leaf cutter ants, and is a strong influence on their ecology and behaviour.

Reference
Feener Jr, D. H., & Moss, K. A. (1990). Defence against parasites by hitchhikers in leaf-cutting ants: a quantitative assessment. Behavioral Ecology and Sociobiology 26:17-29.

This post was written by Jon Schlenert

Controrchis sp.

Extreme weather events can cause significant changes to ecosystems and their inhabitants. When Hurricane Iris made landfall at Belize, it caused widespread devastation in its wake. The study we are featuring today was a part of a larger project to look at how Hurricane Iris affected a population of black howler monkeys (Alouatta pigra) which has been monitored since 1998. In the aftermath of the hurricane, the number of monkeys in the forest decreased by 78 percent until their population began to stablise and increase three and a half years later. But aside from such outwardly visible impacts, there were also other changes afoot within the monkeys themselves.

Photo of black howler monkey by Ian Morton

A team of scientists interested in monitoring the recovery carried out a study to see how this has affected the monkeys' parasites. It is possible that these primates are harbouring higher parasite loads than they did before the hurricane due to the stress of living in a disturbed habitat. The scientists collected samples of monkey fece over the course of 3 years and look for parasite eggs. They also measured the level of cortisol, a hormone associated with stress, present in the fecal sample, and collected data on other aspects of the monkey's behaviour to see if they were associated with their parasite burden.

Photo of Controrchis eggs
from here

The black howler monkeys were found to have five species of roundworms and a species of digenean fluke (based on the presence of their eggs in the monkey poop), but the prevalence and abundance of those parasites were not associated with the level of stress hormones. Instead, nematode (roundworms) prevalence was heavily dependent on population density and the size of the groups in which the monkeys gathered. This is to be expected as these worms are transmitted via accidental ingestion of eggs or larvae from the host's feces. The more monkeys there are around in a given area, the more opportunities for these particular parasites to be passed on. This is similar to what has previously found in other studies on primate parasites. But the only factor that successfully predicted the occurrence of the digenean trematode fluke Controrchis was the amount of leaves the monkeys consumed.

While black howler monkeys usually prefer a diet filled with fruit, in the aftermath of Hurricane Iris there were no fruit-bearing plants in the forest for 18 months. So the monkeys were forced to go on a leaf-based diet instead of the fruit-based one they enjoyed before the hurricane, and the plant most readily available and palatable to the monkeys was Cecropia. These fast-growing leafy plants usually happens to be the first on the scene in the wake of such habitat disturbances. They do not contain as much fibre as other plants and have little in the way of noxious defensive chemicals - which makes Cecropia excellent fodder for the black howler monkeys. Cecropia also contains a lot of what these monkeys need in a balanced diet, so in the absence of fruits, the howler monkeys munched readily on these nutritious greens

But why is the consumption of Cecropia associated with the prevalence of Controrchis? The fluke does not use leaves and vegetation as a mean of transmission (unlike Fasciola the liver fluke), instead, Controrchis uses ants as a go-between to get in their vertebrate host. But these monkeys don't really have a taste for ants, so why is Controrchis prevalence linked to the amount of leaves they have consumed? That is because Cecropia also happens to be myrmecophtyes, or ant-plants. Monkeys that are chowing down those leafy greens are also inadvertently swallowing a lot of ants, which means taking onboard a lot of Controrchis waiting to make a connection with a suitable monkey host.

For another more detailed take on this paper, from the lead author herself, see this post here. 

Reference:
Behie, A. M., Kutz, S., & Pavelka, M. S. (2014). Cascading Effects of Climate Change: Do Hurricane‐damaged Forests Increase Risk of Exposure to Parasites?. Biotropica 46: 25-31.

Gordionus chinensis

Hairworms are known for their ability to make their host go for an impromptu (and terminal) swim in a stream or a pond, but by doing that they are not just sending ripples through the water, but also into the surrounding ecosystem. The paper we are looking at today features a species of hairworm from Japan call Gordionus chinensis - this parasite infects three different species of forest-dwelling camel crickets from the genus Diestrammena.

Photo by Danue Sachiko from here

The scientists who conducted the study that this paper is based on wanted to find out what happens to the the cricket population and their hairworm parasites after their home forest has been cut down. They conducted an observational field study at an experimental forest in the upper parts of the Totsu River at Nara Prefecture, Japan. The forest was originally clear-cut in 1912 and 1916 and since then, parts of it have been replanted and cut down at different point in time over the last century. Each study site corresponds with a different replanted forests of Japanese cypress ranging from 3 to 48 years old.

These scientists found that the camel crickets began returning a few years after a forest has been replanted, their abundance steadily increasing and eventually reaching a peak after the forest has been standing for at least 30 years. But their hairworm parasites did not return with similar gusto. In fact, they estimated that only second-growth forests that are more than 50 years old have hairworm populations that are as abundance as those found at undisturbed sites.

One possible reason for the hairworms' slow recovery is their complex life cycle which requires infection of more than one host. The replanted forest might be lacking some of the other host G. chinensis needs to complete its life cycle. Because parasites has such a negative public image, a forest which is free of parasites (or at least a specific parasite) might sound good to most people. But these hairworms actually play a very vital role in the ecosystem.

By causing their cricket host to jump into a stream, they actually serve as a kind of fast food delivery service for the fish living in those streams. A cricket infected with a hair worm is 20 times more likely to stumble into a stream and become fish food than an uninfected cricket - so fish which would not usually get to feed on such large land-loving insects on a regular basis can now do so thanks to the hairworm, and it has calculated that this straight-to-your-stream food delivery service accounts for 60% of the trout population's energy intake in some watersheds.

For hairworms, new forests just do not have the same creature comforts of old forests. And if you are a keen angler or simply appreciate a fish-rich stream - you have a parasite to thank for all the fishes.

Reference:
Sato, T., Watanabe, K., Fukushima, K., & Tokuchi, N. (2014). Parasites and forest chronosequence: Long-term recovery of nematomorph parasites after clear-cut logging. Forest Ecology and Management, 314: 166-171.

Sphaerularia vespae

Hornets can put fear into the minds of many people, but today meet the parasite that the hornets fear (if they are capable of fear). Sphaerularia vespae is a parasitic nematode that infects the Japanese yellow hornet (Vespa simillima) and as far as infection goes, this one is quite a doozy. It specifically invade and resides in the gaster (abdomen) of female hornets where it grows and develop. The nematode ends up sterilising the host (much like other parasitic castrators we have featured on this blog), turning her into a cozy nursery for baby worms. But a new study has shown that they are capable of doing more than just castrate the hornet.

Photo of a queen hornet (from Fig. 2 of the paper)

In a previous study, a group of scientists noticed that the majority of overwintered hornet queens caught in bait traps were infected with S. vespae, so there is something about these nematode-infected hornets which seems to make them more likely to end up in those traps. During autumn/fall, queen hornets fortunate enough not to be infected with S. vespae would visit and poke around various nooks and crannies (usually decayed logs) in the forest to find a spot to hibernate. When the hornet find a place she likes, she will start excavating a hibernacula ( a place to hibernate) and line it with plant fibres that serve as nesting material. But queens that are parasitised and sterilised by S. vespae start visiting decaying logs much earlier during early to mid-summer.

A team of scientists in Japan decided to find out just what those infected queens are up to. For three months between May and August, they made regular weekly visits to a predesignated sites in a forest at the foot of Mount Moiwa and set up a video cameras to observe the decayed logs in the morning and afternoon.

Photo of a hornet releasing
some S. vespae juveniles
(from Fig. 2 of the paper)

They saw that unlike other hornets, the nematode-infected queens never dig nor gather nesting material. They simply crawl inside a decayed log, hang out for a while, then fly off. That is because they have become sterilised couriers that visited potential hibernation sites only to drop off a special package in the form of S. vespae juveniles. A quarter of the infect queens they saw landing on decayed logs offloaded some nematodes (there were some hornets that moved out of sight so the scientist couldn't see what they were up to). But in addition to those observations, the scientists also captured some hornet queens and brought them back to the laboratory for further examination. They kept them in vials and noticed that over two-third of the infected hornets ended up releasing juvenile worms.

When they dissected hornets to see how many of them were infected and to check the developmental stage of their parasites, they found a seasonal pattern to the infections. Queens caught during May and June were mostly infected with fully-mature female worms and their eggs, while queens caught between July and throughout August were filled with juvenile worms that were ready to disembark and infect a new host - which just so happen to be the period when parasitised queens start making regular visits to potential hibernation sites.

So that is S. vespae's game - use the hornet as a mobile incubator/nursery, fly her around during summer to scope out the best pieces of real estate around the forest, then drop off a bundle of worms that can lie in wait like a booby-trap for an uninfected hornet queen to come along and settle in for winter. To complete its life cycle, S. vespae simply take advantage of a preexisting behaviour (seeking out hibernation sites) from the host's repertoire, and "switch it on" at a different time of year to fit the developmental schedule of the parasite's own offspring. Parasite manipulation isn't necessarily about teaching an old host new tricks, but to get the host to perform the tricks that it already knows in a brand new context.

Reference:
Sayama, K., Kosaka, H., & Makino, S. (2013) Release of juvenile nematodes at hibernation sites by overwintered queens of the hornet Vespa simillima. Insectes Sociaux 60: 383-388.

Ascosphaera apis

This is the second post in a series of blog posts written by students from my third year Evolutionary Parasitology unit (ZOOL329/529) class of 2013. This particular post was written by Karen McDonald on a paper published in 2008 on how bees use resin to protect their hive against fungal parasites (you can read the previous post about toxic birds and their lice here).

Animals have evolved many different strategies to fight parasite infections; from eating tough or poisonous leaves (which would normally never be chosen as part of their diet), dirt bathing, grooming themselves with plants that contain chemicals that kill parasites, living in hostile environments that parasites can't tolerate, to drinking toxic substances like alcohol to kill internal parasites. Animals in general are individuals and care only for their own personal well-being and so the parasite-ridding strategies animals use really only affect their own health and well-being. But bees, on the other hand, are different.

SEM photo of Ascosphaera apis sporeball from here

Bees are communal animals and each bee is an important part of the hive community. The article I am going to talk about today shows that bees don't act on a self-motivated level where they are only concerned with their own well-being, instead bees work only to improve and support the whole hive community. Wild bees always smother the inside of their nests with sticky plant resin and the reason for this was never really understood. Domesticated bees don't use much, if any resin at all. They have been selectively bred to not use it because the sticky resin makes opening the hive and removing the honey and combs very difficult. But domestic bees are also plagued by many, often destructive, parasites.

In 2008 researchers decided to document whether the amount of plant resin that domestic bees use in their hives has an effect on fungal parasite levels in that hive. Two groups of hives were set up; the first group of 12 had the inside of each box painted with thick resin to replicate the nests of wild bees, the second group of 11 boxes were only painted with the type and quantity of resin used by commercial apiaries. Bees from both groups were fed with pollen infected with Chalkbrood, which they ate and/or carried back to their hives.

Photo of chalkbrood-infect larvae from here

Chalkbrood (Ascosphaera apis) is a fungal infection of bee larvae, causing them to die and mummify in the nest (see photo on the right). Adult bees are not affected by the parasite but they do carry it in their bodies and drop spores throughout the nest infecting young bees. Normally, as mentioned above, infected animals are usually only concerned with their own well-being and so the researchers were interested in seeing whether the adults would react to the threat to the larvae or ignore the parasite menace because it did not affect them personally.

Within days, the bees immediately began collecting more resin for their nests. Normally, there are only a few bees in each hive that forage for resin, the majority forage for pollen or nectar. Bees do not eat resin; its only function is to line the nest, so not much energy is used by the hive community to collect it. But when the hive is under threat from a parasite like Chalkbrood, more bees begin to forage for resin and a lot of energy is used to find it.  The nests painted with resin, although infected at the same level, also had a reduced level of infection compared to the commercial standard nests, but the level of infection in all nests dropped as the amount of resin in the nest increased. The bees were using the resin as a form of  social immunity rather than self-immunity.

References:
Simone-Finstrom M.D., Spivak M., (2012) Increased Resin Collection after Parasite Challenge: A Case of Self-Medication in Honey Bees? PloS One, 7(3): e34601. Doi: 10.1371/journal.pone.0034601

This post was written by Karen McDonald

Toxic Birds Make For Sad Lice

It has been a while since we had a guest post at the Parasite of the Day blog (in fact the last guest-contributed post date back to May 2011), but in the next few weeks I will be bringing you a series of posts from guest contributors. Earlier this year, I ran my third year Evolutionary Parasitology unit (ZOOL329/529) for the first time. One of the assessments I set for the students who took that unit was for them to summarise a paper that they have read, and write it in the manner of a blog post, much like the ones you see on this and other blogs. 

I also told them that the best blog posts from the class will be selected for re-posting (with their permission) here on the Parasite of the Day blog. I am pleased to be presenting these posts from the ZOOL329/529 class of 2013. To kick things off, here's a post by Bianca Boss-Bishop on a paper published in 1999 on toxic birds and their lice.

Photo by John Dumbacher from
the California Academy of Sciences

Birds are host to an impressive diversity of external parasites, from insects (including lice, fleas, bugs and flies) to mites, ticks and even fungi and bacteria. These parasitic organisms can have severe negative effects on host fitness. Therefore, it is not surprising that birds invest a lot of time engaged in behaviours such as grooming, preening, dusting and sunning in attempts to rid themselves of their ectoparasites. A handful of unique birds from the genus Pitohui have an interesting physiological adaptation that may assist in the fight against parasite infestation: feather toxins.

Yes, toxic birds. The six species of Pitohui, which are endemic to New Guinea have been found to carry toxin in their skin and plumage. These are the same potent toxins as those found in the skin of poison dart frogs (Phyllobates spp.) and are some of the most toxic natural substances known. The toxin present in the Pitohui is known as homobatrachotoxin and like all batrachotoxins is a neurotoxic steroidal alkaloid capable of depolarising nerve and muscle cell membranes. The level of toxins present in Pitohui tissue varies between species and geographic location. The most toxic species is the hooded pitohui (Pitohui dichrous), from which merely handling an individual can cause numbness, sneezing, and irritation of the eyes and sensitive mucous membranes. It has been hypothesised that the high proportions of toxin present in the Pitohui skin and feathers could provide the bird with a barrier from ectoparasites that live and feed on skin, feathers and subdermal blood supplies.
batrachotoxins

SEM photograph from phthiraptera.info

John Dumbacher, current curator and department chair of Ornithology and Mammology at the California Academy of Sciences was the first to test if the presence of toxins in Pitohui feathers and skin would deter or kill chewing lice (order Phthiraptera). In order to investigate this he conducted a series of choice and lifespan experiments. Dumbacher found that when individual lice in the laboratory were given a choice of two feathers (one toxic Pitohui feather and one non-toxic non-Pitohui feather) there was a statistically significant preference against feeding or resting on the toxic feathers. Lice exposed to the highly toxic feathers of P. dichrous rarely showed signs of eating, with many becoming immobile and inactive. In some cases the louse would simply drop off the toxic feather. In a natural setting, immobility and lower feeding rates reduces the damaging effect of the lice and may even allow the birds to more easily remove or dislodge the parasites mechanically by preening or flying. Since this part of the study showed that the lice exhibited an active choice against the naturally toxic Pitohui feathers we can conclude that homobatrachotoxin has the potential to act as a repellent against these parasites.

Dumbacher also determined that the natural levels of homobatrachotoxin in Pitohui feathers greatly increased louse mortality. The results of the lifespan experiments showed that the mean lifespan of lice exposed to feathers of either high or low level toxicity was half that of those on nontoxic feathers. Interestingly, the mean lifespan of the lice on the toxic feathers was similar even though the toxin levels in P. ferrugineus are ten times lower than P. dichrous. Therefore, Pitohui feathers with lower toxin levels may not have been potent enough to repel lice during the choice experiments but were as effective in increasing louse mortality as the highly toxic feathers. Increased mortality in lice could have many benefits for the host. Less time spent on the host will reduce the negative effect of each individual louse.

One observation from the study was that non-toxic feathers showed obvious damage from lice feeding. This may be due to the extended life span offering additional feeding time, or the lice simply find nontoxic feathers more palatable. Further investigations may provide insight into additional  benefits, for example whether or not the potent toxin is able to reduce louse fecundity. If mating in lice is decreased then subsequent generations of lice are also reduced. Smaller populations would cause less irritation to the host and also be less visible to potential mates. Additionally, less ectoparasites would reduce time spent mechanically removing them and more time to invest in other activities. The results of Dumbacher's study suggest that the naturally occurring homobatrachotoxin found in the skin and feathers of the Pitohui repels and kills lice. The presence of a powerful toxin in skin and feathers has the potential to create a formidable barrier and protect the bird against infestation from ectoparasites.

Reference:
Dumbacher, J. P. (1999). Evolution of toxicity in Pitohuis: I. effects of homobatrachotoxin on chewing lice (order: Phthiraptera). The Auk, 116: 957-963.

This post was written by Bianca Boss-Bishop

Asobara japonica

Drosophila suzukii is a fruit fly like no other. Native to Asia, it is related to that common lab workhorse(fly) Drosophila melanogaster, but unlike most Drosophila, which lay their eggs on overripe and rotting fruit, D. suzukii has a saw-like ovipositor that allows it to lay its eggs in fruits that are still ripening. Recently D. suzukii has been spreading its wings over the American and European continents, earning the title of being a pest species as it attacks a wide range of soft-skinned fruits including strawberries, cherries, grapes, nectarines, pears, and peaches.

The usual adversary of fruit flies is Leptopilina heterotoma, a parasitoid wasp that can devaste Drosophila maggots. It is such a threat that some maggots resort to imbibing alcohol to stave off this parasitoid. But while L. heterotoma is a menace to most fruit fly maggots, the maggots of D. suzukii is the first Drosophila found to stop that wasp in its tracks. The secret lies in the fly's blood. Insects and other invertebrates have blood cells called hemocytes that patrol their bodies, clotting wounds and entombing foreign invaders in hardened capsules. Leptopilina heterotoma disables those defensive cells by unleashing a virus that destroys them.

Asobara japonica photo from here 

However, this feat of biological warfare doesn't seem to work on D. suzukii. In the study we are featuring today, researchers exposed a group of D. suzukii to some L. heterotoma that were eager to lay their eggs in some suitable victims. But while the wasps readily injected their eggs into D. suzukii as they would with any other fruit flies, most of the eggs ended up being trapped in hemocyte coffins and none of the parasitic larvae ever made it out of a D. suzukii maggot alive. When they looked at the blood of D. suzukii, they found that it has five to ten-fold more hemocytes than D. melanogaster, making it a tough adversary for any would be parasite. Furthermore, not only were the hemocytes of D. suzukii not destroyed by L. heterotoma's "pet" virus, their numbers actually increased in response.

But D. suzukii is by no mean invincible; it has its own parasitoid to watch out for and it is also the species we are featuring today - the parasitic wasp Asobara japonica. This wasp is one nasty customer; it would have to be seeing as it has coevolved with D. suzukii. When the researchers unleashed egg-bearing A. japonica upon both D. suzukii and D. melanogaster, the exposed D. suzukii were able to entomb very few of the A. japonica eggs - a quarter of them at most. In comparison, D. melanogaster did not stand a chance - none them were able to entomb the A. japonica eggs that had been laid inside them.

While both L. heterotoma and A. japonica are both parasitic wasps of fruit flies, they have very different methods for subduing their host's immune system. Whereas Leptopilina heterotoma wages biological warfare on its host, A. japonica is a chemical warfare specialist. It injects at first glance what appears to be a peculiar cocktail into its host; a deadly venom and its antidote. Yet this mixture allows A. japonica to manipulate the host's physiology, but only when both serums are injected in combination. The venom alone will disrupt the host's immune system, and then induce paralysis, which is followed by death. But A. japonica also injects the antidote along with it which mitigates some of the venom's effects - it keeps the host alive, but at the same time allows the immune system to be ravaged. So in effect this wasp brings its host to the edge of death, enough to disable its defences, then cures it - but only so that it can then act as a living incubator for its babies.

Reference:
Poyet, M. et al. (2013). Resistance of Drosophila suzukii to the larval parasitoids Leptopilina heterotoma and Asobara japonica is related to haemocyte load. Physiological Entomology. 38: 45-53.

Strelkovimermis spiculatus

If you don't like mosquito bites, then you will like today's parasite as it is a mermithid nematode which infects mosquitoes. We have previously featured worms from that family of nematodes - they all infect arthropods as larvae but have adults that live free in the environment. The larval worm develops inside the host's body and once it is fully mature, it exits its host by drilling a hole through the body wall, killing the host in the process (you can see this in action here).

Image taken from a screenshot of this video by Manar Sanad

Not only is Strelkovimermis spiculatus a scourge for mosquito larvae, it is also easily cultured in laboratories, and is not very picky about which species of mosquito it infects. So not surprisingly, S. spiculatus is also currently being considered as a biological control for mosquitoes. But how does S. spiculatus infect the mosquito in the first place? Mosquito larvae can live in just about any waterbodies, ranging from permanent ones such as lakes or dams, to more ephemeral bodies of water such as puddles or rainwater that collect in cavities such as car tires. Because mosquitoes can breed opportunistically in just about any pool of water, parasites that infect their larvae must also be prepared to be equally opportunistic and S. spiculatus has adaptations to do just that.

Firstly, the eggs of S. spiculatus are able to survive being dried out; this allows them to simply wait in empty ponds or puddles for them to fill up and become colonised by mosquito larvae. Secondly, even in more permanent water bodies S. spiculatus eggs can stay dormant in the environment for several months. The reason is that once the parasite larvae hatch, they have a very short window of 24-48 hours to find and infect a host before they die, therefore they have evolved to hatch only if suitable hosts are available. So what is it about the presence of mosquito larvae that trigger these dormant eggs into hatching at just the right moment?

To find out, a group of scientists exposed some S. spiculatus eggs to both chemicals and vibrations that are associated with mosquito larvae. They exposed S. spiculatus eggs to "mosquito-conditioned water" (which is basically water which had mosquito larvae in them for a while) as well as vibrations generated by artificial mosquito larvae that mimic the behaviour of real ones. To make these artificial mosquito larvae, they took tiny strips of iron wire and coated them in hot glue. They then placed those coated bits of wire in the assay container and rested the container on a magnetic stirring plate (common in laboratories) to make their little "artificial mosquito larvae" move.

They found that while the vibrations generated by those fake mosquito larvae did not provoke the eggs into hatching, the scent of mosquito larvae in the water induced about a third of the eggs to hatch. But that was not as good as the presence of actual live mosquito larvae that send the eggs into a hatching frenzy. Furthermore, the eggs of S. spiculatus are also most likely to be set off by the presence of second-instar mosquito larvae and they trigger almost twice as many eggs into hatching than any other mosquito stages. It just so happens that mosquito larvae at this developmental stage are also the most vulnerable to infection by S. spiculatus.

By having hardy eggs that can survive being dried out, remain dormant for extended periods of time, and hatch only when presented with the right signals, S. spiculatus can simply lurk in the environment, ready to launch into action whenever mosquito larvae might appear.

Reference:
Wang Y, Lutfi Z, Dong L, Suman DS, Sanad M, and Gaugler R. (2012) Host cues induce egg hatching and pre-parasitic foraging behaviour in the mosquito parasitic nematode, Strelkovimermis spiculatus. International Journal for Parasitology 42: 881-886