Susceptibility of two diamondback moth parasitoids, Diadegma insulare (Cresson) (Hymenoptera; Ichneumonidae) and Oomyzus sokolowskii (Kurdjumov) (Hymenoptera; Eulophidae), to selected commercial insecticides

In summer and fall 2004, insecticide toxicity bioassays were conducted on adults of Diadegma insulare and Oomyzus sokolowskii, two important parasitoids of diamondback moth, Plutella xylostella in the southeastern United States. The toxicity bioassay utilized a cabbage leaf dip method and serial dilution concentrations of various labeled insecticides on crucifer crops. Results showed that all insecticide treatments, including spinosad, indoxacarb, esfenvalerate, methomyl, acetamiprid, acephate, emamectin benzoate, and methoxyfenozide were toxic to the adult stage of D. insulare or O. sokolowskii or both. The broad-spectrum insecticides esfenvalerate, methomyl, and acephate as well as the more IPM-compatible insecticides, spinosad, indoxacarb, and emamectin benzoate at their field rate concentrations resulted in 100% mortality to either D. insulare or O. sokolowskii or both after 72 h of exposure. Moreover, LC50 values for all of these insecticides were only a fraction (<2%) of the actual field rate concentration. The neonicotinoid, acetamiprid was less toxic than the other insecticides but still killed 77% of D. insulare adults and 91% of O. sokolowskii adults after 72 h of exposure. The insect growth regulator, methoxyfenozide, though considerably less toxic than the other insecticides based on LC50 levels, still resulted in substantial (62%) mortality of O. sokolowskii adults after 72 h. Results of these studies suggest that field applications of any of the aforementioned insecticides would impact biological control of diamondback moth.