The effects of insecticide seed treatments on green peach aphid Myzus persicae (Sulzer) (Homoptera: Aphididae) parasitism by Aphidius colemani Viereck (Hymenoptera: Aphidiidae) and predation by Mallada signatus (Schneider) (Neuroptera: Chrysopidae)

AbstractThe green peach aphid, Myzus persicae (Sulzer) (Homoptera: Aphididae), is a major pest of Brassica L. species in Australia, where it can transmit >100 viruses. Globally, this species has evolved resistance to 74 insecticides from numerous chemical groups. Although Integrated Pest Management (IPM) strategies are being implemented, chemical treatment remains the predominant method used to control aphids. Insecticide seed treatments are viewed as a softer alternative to chemical sprays and are widely used in Australian canola fields. The effects of imidacloprid, thiamethoxam, and a mixture of thiamethoxam & lambda-cyhalothrin canola seed treatments were investigated on the parasitoid, Aphidius colemani Viereck (Hymenoptera: Aphidiidae) and the predator, the green lacewing Mallada signatus (Schneider) (Neuroptera: Chrysopidae); both important natural enemies of M. persicae. The number of mummies formed by A. colemani on the untreated plants was lower than those formed on the thiamethoxam & lambda-cyhalothrin and imidacloprid treated plants. The number of A. colemani reared from mummies on thiamethoxam & lambda-cyhalothrin plants was higher than those reared from thiamethoxam and untreated plants. Significant effects of insecticide seed treatments were only noted for mummies produced while the parent parasitoids were on the plants, not for those mummies produced after their removal. This suggests seed treatment effects were immediate but not long lasting. Based on cumulative parasitoid survival days for two generations, A. colemani exposed to thiamethoxam & lambda-cyhalothrin and imidacloprid treatments had a greater fitness than those exposed to the thiamethoxam and untreated controls, possibly due to the phenomenon of insecticide hormoligosis. Despite the treatment effects observed, we did not detect any behavioural differences in M. persicae or A. colemani. Mallada signatus were not negatively affected by feeding on M. persicae on insecticide seed treated plants, suggesting they are more tolerant of seed treatments than A. colemani. The findings from this study provide a useful platform for further experimentation on the effects of seed treatments on natural enemies of M. persicae.