Laboratory evaluation of tween 20 for potential use in control of cacopsylla pyri l. eggs and nymphs (Homoptera: Psyllidae)

Abstract

The toxicity of the Tween 20, also known as polyoxyethylene (20) sorbitan monolaurate, was evaluated against the summerform pear psylla Cacopsylla pyri (L.) (Homoptera: Psyllidae) under laboratory conditions. Tween 20 was applied at 1, 2, 3, 7, 10, 20 and 30 ml/l concentrations onto eggs and nymphs of C. pyri on pear shoots. Water was used as a control treatment. The toxic effect on eggs and nymphs was determined by counting treated eggs and nymphs, live or dead. Despite low toxicity to psyllid eggs, Tween 20 showed significant toxic effects against nymphs. The mortality rates of eggs were 3.2%, 2.1%, 1.0%, 12.8%, 13.5%, 100.0%, 100.0% at 1, 2, 3, 7, 10, 20 and 30 ml/l concentrations, respectively. The highest toxic activity was recorded at concentrations of 20 and 30 ml/l. The mortality rates of nymphs were 7.2%, 21.0%, 49.9%, 96.5%, 100.0%, 96.5%, and 100.0% at above concentrations in the same order, respectively. Tween 20 at 3, 7, 10, 20 and 30 ml/l concentrations showed the highest toxic activity to psyllid nymphs, while concentrations of 1 and 2 ml/l had the lowest toxicity compared to water control. No significant phytotoxic effect was observed at all concentrations except for concentrations at 20 and 30 ml/l. In conclusion, Tween 20, either alone or in combination with pesticides, may provide an effective alternative to control pear psylla nymphs.