Effects of temperature on eggs, fecundity, and adult longevity of Hylobiustransversovittatus Goeze (Coleoptera : Curculionidae), a biological control agent of purple loosestrife

Oviposition, egg development, and adult longevity of Hylobius transversovit tatus Goeze (Coleoptera: Curculionidae), a biological control agent of purp le loosestrife (Lythrum salicaria L.), were studied at several temperatures . Adults reared at constant temperatures of 12.5, 15, 20, 25, and 30 +/- 1 degrees C showed large differences in longevity and oviposition response to temperature. Preoviposition and oviposition periods increased with decreas ed temperature. The preoviposition period ranged from 8.4 days at 25 degree s C to 77.9 days at 12.5 degrees C, and the oviposition period was 143.2 da ys at 30 degrees C and 891.7 days at 12.5 degrees C. Oviposition per female per day increased from 0.34 eggs at 12.5 degrees C to 2.92 at 25 degrees C . The highest total number of eggs per female (701.3) was observed at 25 de grees C. At 30 degrees C, total eggs laid per female decreased to 139.0. Ad ults lived for over 3 years at the lower temperatures, and longevity was in versely proportional to temperature. For the range of temperatures tested, females survived six times longer at the lowest temperature (1149.3 days at 12.5 degrees C) compared with the highest temperature (185.4 days at 30 de grees C). Based on regression analysis, minimum threshold temperature for d evelopment was 9.5, 12.7, and 11.6 degrees C for eggs, preoviposition, and oviposition, respectively. Eggs were reared at 10, 15, 20, 25, 27.5, 30, 32 .5, and 35 degrees C and had hatch rates of >90% at 20, 25, and 30 degrees C but only 5% hatch at 32.5 degrees C, and zero at 10 and 35 degrees C. Dev elopmental rate of eggs increased with temperature between 15 and 30 degree s C but decreased at 32.5 degrees C. Egg developmental time increased from 8 to 36 days with temperatures decreasing from 30 to 15 degrees C, respecti vely. These data indicate that 25 degrees C is the optimum temperature for oviposition and egg development. (C) 1999 Academic Press.