Biologia e exigências térmicas de Zagreus bimaculosus (Mulsant) (Coleoptera : Coccinellidae).

Abstract

The cactus pear (Opuntia ficus-indica Mill) is one of the most important bases of supply for ruminants during the dry season in the semiarid region of northeastern Brazil. The major problem faced by cactus producers is the high incidence of scale insects in culture. In Brazil, the species most commonly found infesting the crop are: Diaspis echinocacti (Bouché) (Hemiptera: Diaspididae) and Dactylopius opuntiae (Cockerell) (Hemiptera: Dactylopiidae), known as carmine cochineal. Zagreus bimaculosus (Mulsant) (Coleoptera: Coccinellidae) is a native predator of D. echinocacti and often has been found in areas infested with carmine cochineal, which has raised interest in using it against this pest. Thus, this study aimed to compare biological aspects of Z. bimaculosus reared on D. opuntiae and D. echinocacti and to study its biology reared at 18, 22, 25, 28, 30, 32 and 34°C. The results of comparative biology showed better development of Z. bimaculosus when fed on D. opuntiae, with means values of egg- adult period of 52.25 and 55.72 days and the viability values of 60.6% and 60%, respectively, for individuals reared on D. opuntiae and D. echinocacti. The developmental period of Z. bimaculosus was reduced as temperature increases. The egg-adult period ranged from 27.92 to 84.68 days from 32 to 18°C and showed viability greater than 50% between the temperatures 22 and 30°C. The lower temperature threshold and thermal requirement for egg-adult period were 12.9°C and 543.5 degree days,respectively. Based on thermal requirement, Z. bimaculosus can develop 8.6 generations per year in the semiarid region of Pernambuco State, Brazil.