Toxicity of insecticides on various development stages of pear psylla (Cacopsylla pyri L.)

摘要

In France, C. pyri is a dreaded pest in pear tree orchards. The control of this insect includes, on the one hand, post-winter treatments on adults and eggs, and on the other hand, spring treatments on young larvae. The withdrawal of nitrated dyes and the resistance of C. pyri to the pyrethrinoids used against the psylla adults at the end of winter make the post-winter control more difficult, involving the presence in spring of significant larval populations with, sometimes, failures in this control. In this study, we tested the effectiveness, on the various psylla development stages, of several insecticides and mineral oil used alone or combined. Materials and methods. Various psylla populations sampled on several dates in various French southeastlocalities were treated in the laboratory alter migration of the larvae on young pear tree seedlings. Insecticide sprayings were applied to eggs and to various L1-1.2, L3-L4 and L5 larval stage's whereas the adult stage was treated by topical applicationand tarsal test, in particular with pyrethrinoids, abamectin, amitraze and mineral oils. Results. The abamectin and amitraze effectiveness was maximum on the L1 to L4 stages, and it slightly dropped on the 1.5 stage larvae. The lethal dose of these twoinsecticides varied according to the localities and the sampling dates. Whatever the psylla development, the pyrethrinoids only had a low effectiveness. The tests with oils revealed their effectiveness with tarsal contact on adults, which, added to theiralready described effectiveness on young larvae, shows the interest of their introduction into programs of protection against C. pyri.