Effects of imidacloprid on Harmonia axyridis (Coleoptera : Coccinellidae) larval biology and locomotory behavior

The effects of imidacloprid on 1-day-old third instars of Harmonia axyridis were assessed by topical treatment and contact with treated glass plates i n laboratory bioassays. When 5 mul of imidacloprid solutions were applied t opically, the LD50 was 0.085 g/l per insect after 24 h. Contact with imidac loprid-treated plates had little effect on the number of third instars that became adults. Average duration of larval development was not significantl y affected by duration of contact and imidacloprid concentrations. There we re no significant differences in maximal larval weight, weight gain and day at maximum larval weight. There were significant differences in average we ight gain per day (from third instar to prepupa) after treatments with diff erent imidacloprid concentrations. A temporary knockdown effect was observe d with higher concentrations and longer durations of contact with treated p lates. Compared with untreated third instars, contact with imidacloprid-tre ated plates caused an increase in time spent (in seconds) on the glass plat es resulting from an increase in number of stops (per second) and angular s peed (degrees per second) and a decrease in linear speed excluding stops (m m/second). The changes in locomotory behavior (i.e., duration of stay on un treated plate, number of stops and angular speed) lasted up to 24 h after c ontact with imidacloprid-treated plates.