Evaluating Pachycrepoideus as a potential biological control agent for silk flies in sweet corn

Four species of picture-winged flies (a.k.a. silk flies, Diptera: Ulidiidae) infest sweet and field corn ears in southern Florida.  Control tactics rely almost exclusively on insecticides and there is little information on silk fly natural enemies.  In 2013, the polyphagous parasitoid Pachycrepoideus vindemiae (Rondani) (Hymenoptera: Pteromalidae) was identified from a laboratory colony of silk flies, and investigations were begun to determine its potential as a biological control agent.  The parasitoids completed development in healthy, refrigerated, and frozen silk fly pupae.  After determining that silk fly larvae burrow to an average soil depth of 2.5 cm for pupation, pupae covered by 2.5 cm of soil were presented to the parasitoids, but P. vindemiae did not parasitize them.  Finally, insecticide residue assays were performed to determine if the parasitoids could survive in insecticide treated corn fields.  Methomyl and chlorpyrifos were highly toxic to the adult parasitoids while zeta cypermethrin was less toxic.  Given the intensity of insecticide sprays, and that P. vindemiae do not appear to dig, its greatest impact on silk flies would be in field and organic sweet corn fields against the few silk fly larvae that pupate in dried silk at the apex of corn ears.