The efficiency of phosphine against diapausing larvae of Ephestia elutella (Lepidoptera) over a wide range of concentrations and exposure times

Abstract

Diapausing larvae of Ephestia elutella (Hübner) were fumigated at 20 C with phosphine at concentrations of 0.014–4.0 mg/l, and exposure periods of 3 1 2 hr to 43 days. Phosphine achieved peak efficiency at concentrations of 0.04–0.10 mg/l, a concentration-time (CT) product of 14 mg hr/l being adequate for 100% kill. At 0.7 mg/l, nearly 10% of larvae survived 20 mg hr/l, while at 4.0 mg/l, one in eight larvae survived 56 mg hr/l. For 90 or 99% kill, concentrations less than 0.04 mg/l were not fully efficient, and CT products increased very sharply to about 100 mg hr/l for the LD 99 at 0.02 mg/l. The CT products required for 50% kill, however, varied little. For concentrations between 0.04 and 0.35 mg/l, the LD 50, LD 90 or LD 99 was constant for C 0.9T. As concentrations were increased beyond this range the CT products required for the LD 90 and LD 99 increased more rapidly and from 0.7 mg/l the more rapid increase was also evident at the LD 50 level.