| Abstract: | An on-demand, uniform droplet generator was used to apply 120 μm diameter drops of formulated permethrin either directly onto 3rd-instar Plutella xylostella, of two Ohio populations, or onto the abaxial surface of leaf discs (1-1000 drops cm?2) to which those larvae were subsequently exposed. Incorporating a fluorescent tracer (Saturn Yellow GT-17N) in the spray mixture confirmed that ?direct hit”? larvae had received a topical dose from a single droplet. There was little difference in the LC50/LD50 for either population of P. xylostella when 24 and 48 h mortality assessments from direct hits were compared, but the LD50 of Celeryville larvae was 6-8 times greater than that of Fremont larvae. Residual deposits of 120 μm drops containing approximately the LC50, based on the topical assays, revealed that a droplet density providing a dose per cm2 leaf surface of more than 1000 times the LD50 was required to cause median mortality. The efficiency of utilisation, based on the topical LD95 values, was 0.0006% and 0.072% for Fremont and Celeryville larvae, respectively. |
