TEMPERATURE AND DIAPAUSE DEVELOPMENT IN THE EGG OF DIABROTICA-BARBERI(COLEOPTERA, CHRYSOMELIDAE)

Three independent studies were conducted on the effects of constant te mperatures (0, 3, 6, 9, 12, 15, 18, and 25-degrees-C) with numerous ex posure times (15 to 240 d) on diapausing embryos of the northern corn rootworm, Diabrotica barberi Smith and Lawrence. All three studies had similar results. The temperatures 15 and 18-degrees-C appeared to enh ance diapause development and subsequent diapause termination when com pared with the lower temperatures (0-3-degrees-C). However, the temper ature range 9-12-degrees-C was optimum for minimum mortality and maxim um hatch at nearly all exposure times used. At this range and in parti cular 9-degrees-C, hatch was as high as 60% after 180 d exposure. Expo sures of 15 and 30 d produced minimal hatch, <20%, at any temperature. Days to hatch tended to decrease as temperature increased but varied with experiment. Hatching time also decreased as exposure increased fo r all temperatures. Eggs exposed only to the developmental optima of 2 5-degrees-C had <20% hatch in all studies, and greater-than-or-equal-t o 50% of the eggs were still in the diapause state at the conclusion o f the studies. We concluded that most D. barberi embryos require low t emperature to terminate diapause and complete embryogenesis. These stu dies support the hypothesis that D. barberi has a propensity to be con tinuously variable in diapause length. Also, variable diapause length has allowed this species to adapt to natural and artificial perturbati ons, in particular, crop rotation.