Influence of integrated control practices on the population dynamics of diamondback moth, Plutella xylostella (Linnaeus), and its ichneumonid parasitoid, Diadegma insulare on cabbage

Studies were conducted to evaluate toxicity of insecticides to adult Diadegma insulare (Cresson) and its host, the diamondback moth, Plutella xylostella (Linnaeus). Leaf-dip and direct-dip bioassays for diamondback moth larvae, and residual bioassays for adults of diamondback moth and D. insulare were used to assess mortalities. Larval mortalities at field rates were significantly higher with carbaryl, permethrin, spinosad, and tebufenozide when compared with B. thuringiensis, or imidacloprid in the larval-dip bioassay 72 h after treatment. In leaf-dip and residual bioassays, both permethrin and spinosad caused 100% mortalities to diamondback moth larvae and adults, respectively, 72 h after treatment. Only B. thuringiensis and tebufenozide were not toxic to D. insulare 24 h after treatment. Spinosad was not toxic to D. insulare 30 min after treatment, however, 100% mortality was observed 8 h after treatment. Effects of insecticides on diamondback moth and D. insulare were also evaluated in the field. Ideally, pesticides used in an integrated control program should be effective against target organisms, but largely harmless to beneficial organisms used in biological measures. Insecticides applied for control of diamondback moth caused variations in parasitism by D. insulare ranging from 20–84%. Permethrin applications were highly toxic to diamondback moth populations, although D. insulare levels were adversely affected. Spinosad applications also reduced diamondback moth levels, however percent parasitism was higher than in untreated plots and over 4X higher than in permethrin treated plots. The diamondback moth is a highly pesticide-resistant species, possessing resistance to a variety of insecticide classes. Selective materials which conserve D. insulare populations and maintain diamondback moth populations below economic thresholds can be used which may reduce the frequency of application, thus prolonging the efficacy of these materials. Pest management strategies were evaluated for effects on diamondback moth and D. insulare. Insecticides used were combinations of Bacillus thuringiensis, permethrin and spinosad. Data from this study demonstrate that use of economic thresholds for management of lepidopterous pests on cabbage is as effective as weekly sprays of permethrin, and that revenues exceed those of weekly permethrin applications. Proper timing of more expensive selective materials may still provide an economic benefit