Lethal impacts of insecticides and miticides on three agriculturally important aphid parasitoids

Abstract

Globally, agricultural industries are contending with escalating insecticide resistance evolution among a number of arthropod pests. The Australian grains industry is no exception, with the indiscriminate use of broad-spectrum insecticides contributing to the rise of resistant aphid populations. As such, there is a growing appreciation for the need to harness the full potential of biological control offered by aphid parasitoid wasps, yet few studies have quantified the non-target effects of pesticide use on these taxa using Australian populations and rates relevant to the grains industry. With this in mind, we followed IOBC protocols and tested the acute toxicity of 20 insecticides and miticides against three important aphid parasitoids: Diaeretiella rapae (M’Intosh), Aphidius colemani Viereck, and Aphelinus abdominalis (Dalman). We found toxicities across the three species were generally consistent for many of the active ingredients tested, however notable differences for paraffinic oil, diafenthiuron, indoxacarb, and thiodicarb were observed. Overall, the aphelinid, A. abdominalis, showed greater tolerance to several active ingredients, with lower IOBC toxicity rating categories compared with the two braconid species, D. rapae and A. colemani. Of the eight active ingredients tested that are currently registered to control aphids in Australian grain crops, only two (flonicamid and afidopyropen) had low toxicity across all three parasitoid species, with four active ingredients resulting in very high toxicity for one or more species. We additionally found that the toxicity of synthetic pyrethroids differed between chemical types, with type I pyrethroids (bifenthrin) found to be more toxic than type II (gamma-cyhalothrin and lambda-cyhalothrin) pyrethroids. Taken together, these results highlight the risks of making generalised toxicity inferences across active ingredients and species. We recommend further toxicity testing be undertaken in the field, in addition to quantifying the sub-lethal effects of insecticides and miticides on aphid parasitoids.