EVOLUTION OF PSYLLA-PYRI (L) AND PSYLLA-PYRISUGA (FOERSTER) [HOMOPTERA, PSYLLIDAE] PARASITOID COMPLEX IN PEAR ORCHARDS OF SOUTHEASTERN FRANCE IN WINTER, SPRING AND SUMMER

The pear psylla, Psylla pyri (L.) is the key pest of pear orchards in France and many European countries. Among beneficial insects, we have studied the influence of the parasitoid complex on the pest population dynamics. The pest populations are estimated by visual assessment of twigs. The host larvae are caged in the laboratory for estimating the prevalence. The parasitoid complex includes parasitoid and hyperparasitoid micro-hymenoptera of 4th and 5th psyllid instar larvae. Trechnites psyllae (Ruschka), and in a lesser proportion Prionomitus mitratus (Dalman) are the primary parasitoids which ensure the pest regulation from the 1st generation. Hyperparasitism, essentially due to Syrphophagus mamitus (Walker), appears later on the host species Psylia pyrisuga Foerster acting as a relay between the 1st and 2nd generation of P. pyri. The other hyperparasitoids, Pachyneuron muscarum (L.), Pachyneuron aphidis Bouche, Dendrocerus psyllarum Dessart, Dilyta subclavata Foerster and Dilyta talitzkii Belizin appear even later. Hyperparasitis, is not recorded on the 1st generation of P. pyri. This supports the idea of a successful early release practice of parasitoids for reducing as soon as possible the pest populations.