Short‐ and long‐term effects of commercial formulations of imidacloprid, spirotetramat, and mixtures of these active ingredients on pupae of Diaeretiella rapae (Hymenoptera: Braconidae) and its progeny

Abstract

BACKGROUND: Compatibility studies of insecticides and natural enemies usually focus on short-term lethal effects, withoutconsidering the long-term sublethal effects (including progeny). Even less-explored are the effects of commercial insecticidesformulated with more than one active product. Short- and long-term lethal and sublethal effects were studied for the first timeon the progeny of commercial formulations of spirotetramat, imidacloprid and a commercial mixture of these active ingredients on pupae of Diaeretiella rapae (M´ntosh) (Hymenoptera: Braconidae), an endoparasitoid of aphids considered to be apotential biological control agent. Insecticides were exposed topically on aphid mummies in which the parasitoid was in thepupal stage.RESULTS: Imidacloprid reduced adult emergence by more than 30% and prolonged intra-host development time with respectto control from half the maximum recommended field dose (MFRD). Spirotetramat and commercial mixture only showed significant effects on these endpoints at doses above the MFRD. The tested formulations did not affect adult longevity, sex ratio, andpercentage of parasitism in the exposed generation. At low concentrations the active ingredients in the commercial mixturebehave synergistically, whereas at medium and high concentrations they behave antagonistically. Considering the 10% lethaldose (LD10), imidacloprid showed the highest hazard coefficient, whereas the commercial mixture was more hazardous whenconsidering the LD50 and LD90. The commercial mixture and imidacloprid induced higher adult emergence and altered thesex ratio in the progeny.CONCLUSIONS: The following order of toxicity onD. rapae can be established: imidacloprid > commercial mixture > spirotetramat.Joint use of this species with imidacloprid and commercial mixture should be avoided in integrated pest management programs.