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