Pullus impexus(Muls.) (Coleoptera, Coccinellidae), a Predator ofAdelges piceae(Ratz.) (Hemiptera, Adelgidae), with notes on its Parasites

Abstract

The biology ofPullus impexus(Muls.), a Coccinellid beetle predacious onAdelges piceae(Ratz.) in Switzerland, Germany and France, was studied during 1950–1952. The present work is a part of the research on the complex problem of factors in the control of the Balsam Woolly Aphid in Canada.The morphology of both the larva and the adult has been studied. Some information has been provided on the probable distribution of the species.P. impexushas only one generation a year. The eggs are deposited during the late summer or early autumn on infested trees and the larvae hatch in April. The larvae develop and adults appear in May. The adults of the new generation are to be found in June together with adults of the old generation. In the biology, particular attention has been directed to the diet of the insect in each of its stages, in order to establish the value of the species from the standpoint of biological control.Two new species of Hymenopterous parasites were found in Switzerland and in Germany,Scymnophagus mesniliFerr., a parasite of pupae, andCentistes scymniFerr., a parasite of the imagines. The life history of these species has been briefly studied. A cephaline gregarine species was noted in the mesenteron of adults ofP. impexusand a nematode in the abdominal cavity of a female. The two Hymenopterous species provide an important limiting factor in the increase of the population ofP. impexus.