Temperature and Diapause Development in the Egg of Diabrotica barberi (Coleoptera: Chrysomelidae)

Abstract

Three independent studies were conducted on the effects of constant temperatures (0, 3, 6, 9, 12, 15, 18, and 25°C) with numerous exposure 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 temperahlres 15 and 18°C appeared to enhance diapause development and subsequent diapause termination when compared with the lower temperatures (O–3°C). However, the temperature range 9–12°C was optimum for minimum mortality and maximum hatch at nearly all exposure times used. At this range and in particular 9°C, hatch was as high as 60% after 180 d exposure. Exposures 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 for all temperatures. Eggs exposed only to the developmental optima of 25°C had <20% hatch in all studies, and ≥50% of the eggs were still in the diapause state at the conclusion of the studies. We concluded that most D. barberi embryos require low temperature to terminate diapause and complete embryogenesis. These studies support the hypothesis that D. barberi has a propensity to be continuously variable in diapause length. Also, variable diapause length has allowed this species to adapt to natural and artificial perturbations, in particular, crop rotation.