MEAN TERM EFFECTS OF PESTICIDES ON BENEFI CIALS IN PEAR ORCHARD - A FIELD TRIAL EVALUATION

A field trial was performed to test the side effects of pesticides in a pear tree orchard, near Avignon The experiment was carried out under a small plot design allowing statistical analysis, and followed good agricultural practice. The treatments were applied in April and May to reach the first generations of the pear leaf rolling gall midge, Dasy neura pyri Bouche. The observations were carried out for 15 days after each two treatments, and concerned the gall midge, pear psylla Psylla pyri L., pear aphid Dysaphis pyri L., and the main beneficials presen t. This design allowed a good evaluation of the effect of pesticides o n phytophagous insects. Specific sampling methods gave informations on different groups of beneficials: funnels, measuring 0.5 m2 hung under the trees were equipped with soil collectors, which allowed us to sep arate dead and live organisms; corrugated paper band traps allowed the capture of coccinelids and syrphid larvae, and mainly earwigs. The de ferred mortality of these insects, after a period of exposure to pesti cides in the field could be recorded in the laboratory. In the same wa y, the collection of infested shoots gave indications on the effect of pesticides on aphid parasitoids. These observations were completed by visual controls. It appeared that the earwig Forficula auricularia L. plays a prevailing role in the regulation of P. pyri populations: the analysis by multiple range correlation indicated that the toxicity of pesticides on this predator determined the variability of P. pyri pop ulations, prior to the own susceptibility of this pest to pesticides. Using appropriate sampling methods, this design, recommended tor biolo gical evaluation of pesticides on pests, appeared to be suitable to ev aluate simultaneously side effects on some beneficials.