Observations on the Development of Neodiprion sertifer (Geoff.) within the Cocoon (Hymenoptera: Diprionidae)

Abstract

In Neodiprion sawflies the cocoon stage, which extends from the completion of larval feeding until the appearance of the adult, is of considerable ecological interest. On the basis of voltinism and the seasonal occurrence of the cocoon stage, the genus as a whole may be divided into two distinct groups, which, however, do not correspond to the two major taxonomic categories of Ross (1955). On the one hand are species that overwinter only within the cocoon (e.g. swainei, lecontei, virginianus, excitans, and others); these may or may not have more than one generation per year. On the other hand are species that overwinter primarily in the egg stage (e.g. sertifer, pratti, abietis, taedae, and others); all of these are univoltine and may remain within the cocoon for an extended period in the summer, when conditions are still favourable for further generations. The European pine sawfly, Neodiprion sertifer (Geoff.), is typical in this respect. Despite its wide distribution in Eurasia and North America, and the variety of climates that it encounters, the length of the cocoon stage is so adjusted that adults do not emerge until late summer or early autumn, regardless of when larval feeding and cocoon spinning occurred.