Bionomics of the Spruce Web-spinning Sawfly Cephalcia-arvensis Panzer (hym, Pamphiliidae) In Northeastern Italy

The life history of the spruce web-spinning sawfly Cephalcia arvensis has been studied from 1987 to 1991 in two outbreak areas of the Venetian Prealps. The populations of the pest are composed of individuals characterized by a different length of the life cycle, annual and biennial, the latter including in a few cases also triennial individuals. The two parts of the population differ as the emergence period, the distribution of the larvae (nymphs) in the soil, the fecundity and the weight of the mature larvae are considered. Longterm diapausing individuals seem to be heavier and more fertile than annual individuals; they are more deeply distributed in the soil and later in the emergence. These and other characteristics (adult behaviour, oviposition and egg features, larval feeding) are described and compared with those known in literature for other populations of the pest, with particular reference to the ''forms'' of C. arvensis recently described from Czechoslovakia.