Parasitic wasp

Diglyphus isaea

Diglyphus isaea is a small parasitic wasp that attacks the larval stages of at least 9 different

species of leaf-mining flies (primarily Liriomyza species) on various crops including tomatoes, cucumbers, eggplant, peppers, Chrysanthemum and Gerbera. This wasp is most effective at warmer temperatures (approximately 25-33°C (77—91°F)). Adults of D. isaea range in size from approx. 1 to 2.5 mm. with males being slightly smaller than females. The body is generally  dark with a metallic greenish sheen, while the legs show variable patterns of dark and light bands.

The adult females attack second and third instar host larvae within mined leaves. Each host larva may be penetrated by the wasp’s ovipositor (egg-laying apparatus) from one to several times, during which a toxin is injected that paralyzes the host larva and prevents it from feeding. The adult wasp may either feed directly on the fluids seeping from the wounded host (‘host feeding’), or lay eggs beside it. Both processes eventually result in the death of the host larva. On hatching from the egg, the wasp larvae feed externally on the paralyzed host, undergoing 3 larval instars and becoming blue-green in color as they mature. Shortly before pupating, the wasp larvae move a short distance from the dead host and construct six dark-colored ‘pillars’ of frass (fecal material) between the upper and lower surface of the leaf mine; these dark spots are visible through the leaf surface and surround the papa, which is initially bluish-green, becoming much darker just prior to adult emergence.

Diglyphus isaea seems to tolerate a relatively wide range of humidities, but performs best at warmer temperatures; fastest development occurs between 30-35°C (86-95°F). At the latter temperature, the life-cycle (egg to adult) can be compIeted in 6-7 days (13-15 days at 20°C/68°F). Adults live approximately 10 days at 25°C(77°F) and 30 days at 20°C (68°F). With each female producing a total of approximately 200 eggs during that time.
Temperatures at or below 10°C {50°F) or above 40°C (104°F) do not support development.

When scouting for evidence of this insect, look for short mines where paralysis of the host has prevented further damage; within the mine, wasp eggs or larvae may be observed next to parasitized hosts, while fly larvae killed by host-feeding often show multiple dark puncture wounds. Pupating wasp larvae can be detected by looking for the surrounding dark spots of fecal matter.