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