The Gall of That Midge!

Tiny wasps discovered by Agricultural Research Service (ARS) scientists in Poplarville, Miss., may help Gulf Coast blueberry growers put the sting on their crop's top insect pest: the gall midge.

As larvae, gall midges feed on the blueberry plant's buds, deforming them and endangering the fruition of up to 10 berries per bud. In Gulf Coast states like Florida, the midges are so prevalent some blueberry growers have abandoned rabbiteye varieties, which the pests commonly attack.

But blueberry growers take heart: The pests themselves are fed on—from the inside out.

Entomologist Blair Sampson made the discovery while working at the ARS Southern Horticultural Laboratory in Poplarville. He and a research assistant were examining a gall midge larva under a microscope when a pair of tiny jaws appeared, tearing at the specimen.

As it turned out, the jaws belonged to an immature wasp—one of four parasitic species that Sampson was to discover. The wasps belong to the genera Synopeas, Inostemma and Platygaster, but Sampson has yet to assign them a species name.

In blueberry fields, a female wasp seeks out midge larvae hiding inside buds and stings them. She then injects her eggs into her prey's stomach and brain.

There, the eggs develop into immature wasps that fight for the chance to feast on their midge host. It's a mandible-on-mandible slugfest that ends when only one wasp remains.

Needless to say, the real losers are gall midges. Sampson has determined that a natural population of the wasps in blueberry fields can kill 40 percent of all midges, controlling them for about 200 days.

Sampson will explore the possibility of rearing the wasps for release into areas where years of insecticide use have diminished the insect's natural populations.

Read more about this research in the January 2008 issue of Agricultural Research magazine.

ARS is the U.S. Department of Agriculture's chief scientific research agency.