BIONOMICS OF NEODIPRION-GILLETTEI (HYMENOPTERA, DIPRIONIDAE) ON PINUS-PONDEROSA

The biology and life history of Neodiprion gillettei (Rohwer) are described. N. gillettei overwinters as eggs in the needles of ponderosa pine, Pinus ponderosa. N. gillettei is unique among ponderosa pine-feeding sawflies because of its preference for trees < 60 cm tall. The larvae eclose in spring and develop through four male and five female larval feeding instars in almost-equal-to 4 wk. Ultimate instars do not feed and crawl to the ground to spin cocoons, where they remain for the summer. They have a short-day diapause response. Adults emerge in the fall, mate, and lay eggs in ponderosa pine needles. Lab rearing under various photoperiods indicates that the critical photoperiod for larval diapause induction is 14:10 (L:D). Females laid an average of 48.5 eggs, 3.5 eggs per needle, and cut preslits on only 4% of the needles. A greater number of eggs are laid in the bottom-south compared with the top-north quadrant of the tree. Eggs need to be chilled at least 6 wk at 4-degrees-C before eclosion.