Selectivity of Insecticides to a Pupal Parasitoid, Trichospilus diatraeae (Hymenoptera: Eulophidae), of Soybean Caterpillars

SIMPLE SUMMARY: Lepidoptera caterpillars are important pests around the world that decrease crop production, including that of soybeans. The use of insecticides and bioinsecticides is the main control strategy for these pests. Biological control with parasitoids, in combination with insecticides, is widely used as an alternative. However, the use of insecticides with parasitoids depends on tests to assess the survival/mortality of these natural enemies for each insecticide. Trichospilus diatraeae Cherian & Margabandhu, 1942 (Hymenoptera: Eulophidae) is a polyphagous pupal parasitoid that mainly comprises defoliating lepidopterans. This study evaluated the mortality of T. diatraeae from seven insecticides (acephate, azadirachtin, Bacillus thuringiensis (Bt), deltamethrin, lufenuron, teflubenzuron and thiamethoxam + lambda-cyhalothrin). The insecticides were sprayed on soybean leaves, which were left to dry and placed in cages with 10 T. diatraeae females. The insecticides azadirachtin, Bt, lufenuron and teflubenzuron did not affect T. diatraeae survival; deltamethrin and thiamethoxam + lambda-cyhalothrin presented low toxicity; and acephate was highly toxic, causing 100% mortality in this parasitoid. Azadirachtin, Bt, lufenuron and teflubenzuron are selective for T. diatraeae. ABSTRACT: Selectivity is an important aspect of modern insecticides to be able to target pests whilst maintaining beneficial entomofauna in the crop. The present objective was to assess the selectivity of different insecticides for the pupal parasitoid of soybean caterpillars, i.e., Trichospilus diatraeae Cherian & Margabandhu, 1942 (Hymenoptera: Eulophidae). Acephate, azadirachtin, Bacillus thuringiensis (Bt), deltamethrin, lufenuron, teflubenzuron and thiamethoxam + lambda-cyhalothrin at the highest recommended concentrations for the soybean looper Chrysodeixis includens (Walker, [1858]) (Lepidoptera: Noctuidae), as well as water in the control, were used against the pupal parasitoid T. diatraeae. The insecticides and the control were sprayed on the soybean leaves, which were left to dry naturally and placed in cages with T. diatraeae females in each one. Survival data were submitted to analysis of variance (ANOVA) and the means were compared using Tukey’s HSD test (α = 0.05). Survival curves were plotted according to the Kaplan–Meier method, and the pairs of curves were compared using the log-rank test at 5% probability. The insecticides azadirachtin, Bt, lufenuron and teflubenzuron did not affect T. diatraeae survival, while deltamethrin and thiamethoxam + lambda-cyhalothrin presented low toxicity and acephate was highly toxic, causing 100% mortality in the parasitoid. Azadirachtin, Bt, lufenuron and teflubenzuron are selective for T. diatraeae and could be used in IPM programs.