Side effects of diflubenzuron on a pear psylla predator:Forficula auricularia

A series of laboratory, semi-field and field tests showed the high toxicity of diflubenzuron toForficula auricularia L. nymphs, at concentrations of 15 and 20 g a.i./hl registered in various European countries and the United States to controlCydia pomonella L. Diflubenzuron proved more selective using the 10 g/hl concentration registered in France, but several sublethal effects have been observed: morphological abnormalities, reduced weight increase and mobility. Unexpectedly for a chitin-deposit inhibitor, intake was reduced, which became apparent from the beginning of exposure to the insecticide, before the onset of the moulting process. In the semi-field tests, and despite diflubenzuron's slowing down effect on psylla nymphs, the earwig's reduced predatory activity due to the product resulted in greater growth of the psylla populations than without treatment. The field-test confirmed the efficacy ofF. auricularia as a psylla predator, and the relative selectivity of diflubenzuron at the lowest concentration.