Dinâmica populacional do piolho-de-São José Quadraspidiotus perniciosus (Comstock, 1881) (Homoptera: Diaspididae) em pessegueiro, no município de Jacuí - Minas Gerais

Abstract

This work was carried out in Jacuí, Minas Gerais, from August 1994 to July 1995, with objective of evaluating the population dynamics of San José Scale Quadraspidiotus perniciosus (Comst.) on peach orchard, the weathereffects and its natural enemies. The samples were taken fortnightly from branches of peach trees in untreated and treated areas with convencional inseticides and fungicides. The results indicated that the occurrence of Q. perniciosus in peach trees was detected during the whole period of the experiment, reaching the highest peaks in August (winter), January and February (summer) in untreated area and in January, February (summer) and April (autumn) in treated area. The occurrence of Q. perniciosus was higher in treated area, showing that the inseticides used for its control were not efficients. The natural enemies, parasitoids and the fungus Fusarium coccophüum (Desm.) showed to be more efficient in unteated area, with 9.5% of parasitized scales and 29.4% of infected scales. To average temperature, the relative humidity and the precipitation showed significant effects on San José Scale population, with more influence observed 30 days later the occurrence of these factors. In this study, untreated area showed more equilibrium, that is to say, there was a maintenance of Q. perniciosus population to lower levels because of the action of its natural enemies, mainly parasitoids and F. coccophüum (Desm.). The control of Q. perniciosus has to be done in the first fortnight of August or between the first fortnight of October and the second fortnight of November when the crawlers appear, considering the use of seletive insecticides to its natural enemies.