Effects of four insecticides on the two-spotted ladybird Adalia bipunctata using a“Microcosm” test design

Abstract: The effects of four insecticides, the two aphid-feeding inhibitors pymetrozine andflonicamide, the systemic insecticide thiacloprid and the contact insecticide pirimicarb wereassessed on larvae of the two spotted ladybird A. bipunctata with the help of an extended lab-test.The larvae were held on French bean seedlings infested with aphids in units surrounded by atreated metal frame in order to prevent both ladybird larvae and aphids to escape. 2-3 day oldlarvae were introduced on the aphid infested plants and left to distribute on the vegetation canopyseveral hours before treatment. The units were then treated with the insecticide with the help of aknapsack sprayer with a flat-fan nozzle. Units were kept 8-9 subsequent days in the laboratorywithout food addition and were dismantled when first larvae started to pupate in the control. Thelarvae and pupae were counted and surviving larvae were kept individually in plastic petri dishes.They were fed with aphids till pupation. Development time, fecundity and fertility of the adultswere then assessed. This method combines different aspects of toxicity, with direct toxicity byspray, contact toxicity with treated plants, toxicity by ingestion of contaminated aphid and bystarvation due to the elimination or reduction in food availability by the insecticides.One of the four insecticides tested, pymetrozine, was harmless with only 12% larval mortality.Flonicamide, thiacloprid and pirimicarb led to 65%, 80% and 84% corrected mortality,respectively. Thiacloprid, pirimicarb and flonicamide significantly increased the developmenttime to reach adult stages. Total egg production by surviving female was not affected by the fourtested product but flonicamide significantly affected emergence with 35% of egg hatchingcompared to 70% in the control and reduced by more than 50% the mean viable egg productionby female, compared to control.