Winsome invaders, lose some invaders

Of the thousands of invasive Japanese beetles that I see each summer, a small number have white ovals stuck to them.  These white ovals, which are the eggs of the parasitic "winsome fly" (Istocheta aldrichi), are usually attached to a beetle's pronotum (just behind the head) or sometimes to its elytra (the hard coverings over the wings).  Although the eggs do not look like much, they mean that the beetle has only a few more days to live.

Mating Japanese beetles (Popillia japonica); these beetles are unlikely to have any offspring, however, since the female has several winsome fly (Istocheta aldrichi) eggs glued to her.

About a day after the eggs are laid, larvae hatch from them and bore into their beetle host.  After a few more days, the beetle dies, eaten from the inside by the fly larvae.  Like the Japanese beetles themselves, winsome flies were introduced into North America from Japan.  Unlike the Japanese beetles, the flies were introduced intentionally -- in the hope that they would restrict the growth of the Japanese beetle populations.  However, it has now been more than 90 years since the flies were first introduced, and the Japanese beetle remains a growing problem.

Explore Some More: Biological Control of Japanese Beetles