Residual susceptibility of ®fth instar Plodia interpunctella to cy ̄uthrin wettable powder *

Wandering-phase ®fth instar Plodia interpuntella (HuÈ bner) were exposed at 3-week intervals for 0.5, 1, 2, and 4 h on concrete treated with sprays of 100, 150, and 200 mg 20% cy ̄uthrin wettable powder (WP) per m over a 15-week period. Pupation rate and adult emergence were not signi®cantly di€erent (Pr0.05) with respect to exposure interval at any application rate. Of the larvae exposed at week 0 (1 day after treatment) on concrete treated with 100 mg per m cy ̄uthrin WP, 8.723.8% reached the pupal stage and 3.821.5% emerged as adults, but adult emergence at all subsequent weeks was at least 63.8%. No adults emerged from larvae exposed at week 0 or week 3 on concrete treated with 150 mg cy ̄uthrin WP per m. Pupation and adult emergence for larvae exposed at week 0 on concrete treated with 200 mg cy ̄utrhin WP per m was 12.726.8 and 11.426.6%, respectively, but adult emergence at week 3 was only 1.921.0%. Residual control, de®ned as the time when pupation and adult emergence were less than 10%, exceeded 3-week only at the intermediate label rate of 150 mg cy ̄uthrin WP per m. # 1998 Elsevier Science Ltd. All rights reserved.