Submitted to: Environmental Entomology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/26/2006
Publication Date: 10/1/2006
Citation: Chen, W., Leopold, R.A., Morgan, D.J., Harris, M.O. 2006. Development and reproduction of the egg parasitoid, Gonatocerus ashmeadi Girault (Hymenoptera: Mymaridae) as a function of temperature. Environmental Entomology. 35(5):1178-1187. Interpretive Summary: The development, fecundity and a number of demographic variables of the egg parasitoid, Gontocerus ashmeadi, were measured at six different temperatures ranging from 12 to 32°C. This very small wasp is a parasite of the glassy-winged sharpshooter (GWSS), a vector of Pierce's disease in a range of high value agricultural crops and ornamental plants. At 12°C the 3rd stage larvae of this wasp could not develop unto the pupal stage and 1st and 2nd stages developed very slowly. Development time from the egg stage to adult emergence varied from 27 days at 16°C to 9.5 days at 28°C. The minimum temperature required for one stage to develop to the next stage was lowest for the egg and 1st larval stages (4°C) and highest for pupae (12.8°C). Survival from egg to adult was the highest (ca. 85%) between 20-32°C. Adult females and males lived the longest at 16°C (27 and 19 days) and died fastest when held at 32°C. Adding honey to diet of adult females maintained on water did not increase their longevity. After completing the development at 20-32°C, the greatest number of adults came out on the 1st day of emergence, but when completing development at 16°C, it was greatest on the 2nd day. The male to female sex ratio, while strongly female, did not change when the wasps were reared within egg hosts from 16-32°C. The greatest number of eggs obtained during the female lifespan occurred at 24°C, and lowest at 32°C, with the maximum net reproduction also occurring at 24°C. The greatest rate of population increase, doubling time and mean generation time was gained when these wasps were reared and maintained at 28°C. This information is relevant to research programs where maintaining colonies of this beneficial insect is an essential practice, in mass-rearing programs for maintenance of economy and efficiency, and for predicting their seasonal fluctuations and geographical distribution in control programs.
Technical Abstract: The development, fecundity and life table parameters of Gonatocerus ashmeadi Girault, an egg parasitoid of the glassy-winged sharpshooter, Homalodisca coagulata, were studied in the laboratory at six constant temperatures between 12 and 32°C. At 12°C, the parasitoid failed to develop beyond the 3rd instar and durations of the egg stage and the 1st and 2nd instars were prolonged. Development from the egg stage to adult emergence varied from 27.1 d at 16°C to 9.5 d at 28°C. Temperature thresholds for development were estimated at 4.0, 3.8, 9.1, 6.2, and 12.8°C and thermal constants were 29.9, 35.0, 26.7, 32.3 and 75.4 degree days for the egg, 1st through 3rd instars, and pupal stages, respectively. To complete development from egg to adult, 206.7 degree days were required above the lower temperature threshold of 8.5°C. The optimum temperature for egg to adult development was 29.2°C. Survival from egg to adult was 67.4% at 16°C and ranged from 83.4-86.7% between 20-32°C. At 16-32°C, the population had a Type I survivorship pattern. At 16°C, longevity of adult females and males averaged 27.1 and 19.0 d respectively, but declined to 6.4 and 6.9 d at 32°C. Adding honey to the diet of mated females did not increase their longevity. At 20-32°C, peak adult emergence occurred on the 1st day of emergence, but at 16°C, it was greatest on the 2nd day. When exposed to temperatures ranging from 16-32°C, the female: male sex ratio was similar, ranging from 3.4 to 5.6. Lifetime fecundity was greatest at 24°C, and lowest at 32°C, with the maximum net reproduction also occurring at 24°C. Greatest intrinsic and finite rates of increase, shortest population doubling time, and mean generation time occurred when G. ashmeadi was held at 28°C.