Nature's Own Little Exterminators

Here's a shot of my first wasp of the season:

Earinus limitaris, Van Patten Woods Forest Preserve,
Lake Co, IL  4/9/2014

This little guy's in the family Ichneumonidae -- one of the largest families of animals in the world. There are an estimated 5,000 known species in North America, with perhaps 3,000 or so left to be described. Given the astounding level of convergent evolution in color and structure in the family, I may never know which of those 8,000 this one belongs to.

(Update, 4/10: Well, the folks at Bugguide.net came through again -- and I was wrong, this isn't an ichneumonid, it's in a smaller, related family called Braconidae. This particular Braconid is Earinus limitaris. They're still parasitoids, though.)

Ichneumonids are parasitoids, with the larvae feeding on arthropods. In many cases, the mother stings the host to paralyze it before dragging it to a burrow and laying an egg on or in it. In other cases, the host (typically a larva of some sort in these cases) continues to develop after the female lays her egg. Either way, though, the host is doomed.

Frequently, the host is an herbivorous insect. Plants apparently take a dim view of the practice of herbivory, given the number of chemicals they produce for no reason other than to make them hard to eat. As a result, many herbivores are specialized to deal with those chemicals (think Monarch caterpillars and Milkweed), often by sequestering them. This then makes the herbivore less attractive to predators -- again, like Monarchs.

Barbosa, et al. looked at the effects of one such chemical, nicotine, on a couple of species of ichneumonids. Or rather, they looked at the effects of feeding on larval hosts that had consumed nicotine. What they found was that wasps that developed on nicotine-feeding hosts developed more slowly and died more often than wasps that developed on nicotine-free hosts. Furthermore, they found that of the two ichneumonid species that they examined, the impacts of nicotine were significantly stronger on the generalist parasitoid than on the more specialized one. (1)

This suggests that the evolution of secondary compounds in plants may have played an important role in the diversification of both herbivorous insects and the wasps that parasitize them, an interesting chain of events indeed.

This interaction, unfortunately, has it's darker side -- when we apply insecticides, we not only impact the pests we don't want but the wasps that prey on them. Hill & Foster examined this, finding that many of the common insecticides that kill Diamondback Moths also killed the ichneumonid Diadegma insulare. (2) On the other hand, Idris & Grafius found that planting the right sorts of wildflowers could increase the survival and parasitic activities of D. insulare, suggesting a way of manipulating the parasite's abundance to control moths without pesticides. (3)

Louis Pasteur convinced the scientific world that diseases are caused by things too small for us to see. It seems that it's taken us 150 years or so to be convinced that the critters we can see can be partners instead.

(1) Barbosa, P., Saunders, J. A., Kemper, J., Trumbule, R., Olechno, J., & Martinat, P. (1986). Plant allelochemicals and insect parasitoids effects of nicotine on Cotesia congregata (say)(Hymenoptera: Braconidae) and Hyposoter annulipes (Cresson)(Hymenoptera: Ichneumonidae). Journal of Chemical Ecology, 12(6), 1319-1328.

(2) Hill, T. A., & Foster, R. E. (2000). Effect of insecticides on the diamondback moth (Lepidoptera: Plutellidae) and its parasitoid Diadegma insulare (Hymenoptera: Ichneumonidae). Journal of economic entomology, 93(3), 763-768.

(3) Idris, A. B., & Grafius, E. (1995). Wildflowers as nectar sources for Diadegma insulare (Hymenoptera: Ichneumonidae), a parasitoid of diamondback moth (Lepidoptera: Yponomeutidae). Environmental Entomology, 24(6), 1726-1735.