Influence of bifenthrin spray deposit quality on the mortality of Trichoplusia ni (Lepidoptera: Noctuidae) on cabbage

Abstract

A uniform droplet generator was used to apply precise deposits of aqueous bifenthrin to the abaxial surface of cabbage leaf sections. These deposits were defined in terms of droplet size, droplet density (drops/cm 2), concentration of active ingredient (a.i.) and quantity of a.i./cm 2. Three droplet sizes (60 μm, 90 μm and 120 μm in-flight diameter) were examined at bifenthrin concentrations between 0·0075 and 7·5 g a.i./l. Cabbage looper ( Trichoplusia ni Hübner) first-instar larvae were exposed to the dried deposit and, 24 h later, mortality and the location of the larvae were recorded. Significant reductions ( P < 0·01) in dose/cm 2 for median mortality (LQ 50) were associated with decreasing concentration. At each concentration, doubling the droplet diameter, from 60 μm to 120 μm, also doubled the LQ 50. The insecticide utilization efficiency extremes were represented by 60 μm drops at 0·0075 g a.i./l where 0·3 ng/cm 2 (374 drops/cm 2) caused 50% mortality, compared with 15·8 ng/cm 2 in two drops, 120 μm diameter, containing 7·5 g a.i./l.