PHOSPHINE AND ITS EFFECT ON SOME COMMON INSECTS IN CUT FLOWERS

The most effective fumigant for insect disinfestation of cut flowers i s currently methyl bromide, which will soon be unavailable in several countries. The toxicity of an alternative fumigant, phosphine (2% PH3 and 98% N-2), was tested at 24 degrees C on adult greenhouse thrips (H eliothrips haemorrhoidalis), adult aphids (Myzus persicae) and lightbr own apple moth larvae (LBAM; Epiphyas postvittana). These are commonly found as insect pests on many cut flower crops. Thrips were exposed t o phosphine concentrations ranging from 20-600 mu l/l for 1 or 2 h. Al l thrips were killed within 18 h of exposure after a treatment of 300 mu l/l phosphine for 2 h. Adult aphids and fifth instar LBAM larvae we re more resistant to phosphine, and trials were therefore conducted us ing higher phosphine concentrations (> 500 mu l/l) combined with atmos pheric (0.035%) or elevated (33%) CO2. The most effective treatment fo r aphids was 1000 mu l/l phosphine +33% CO2 for 4 h, which killed all insects within 36 h of exposure. Under atmospheric CO2 levels, 92% of aphids were killed within 36 h after exposure to 1000 mu l/l phosphine for 6 h, with 100% kill attained after exposure to 5000-8000 mu l/l p hosphine for 6 h. Elevated CO2 levels did not improve the efficacy of phosphine on LBAM larvae. The optimal treatment was 2000-2500 mu l/l p hosphine for 4 or 6 h, which killed 96 or 100% of the larvae, respecti vely. Under atmospheric CO2 levels, 4000 mu l/l phosphine killed 74% o f LBAM larvae after 4 h. and 94% after 6 h exposure. (C) 1997 Elsevier Science B.V.