Submitted to: CDFA Pierce's Disease Control Program Research Symposium
Publication Type: Proceedings
Publication Acceptance Date: 10/19/2005
Publication Date: 12/5/2005
Citation: Leopold, R.A., Chen, W., Morgan, D.J. 2005. The influence of temperature on development and reproduction of the egg parasitoid, Gonatocerus ashmeadi Girault (Hymenoptera: Mymaridae). Proceedings of 2005 CDFA Pierce's Disease Control Program Research Symposium. Dec. 5-7, 2005. San Diego, CA. pp. 349-353.
Technical Abstract: The effect of temperature on the development and reproduction of Gonatocerus ashmeadi Girault within eggs of its host, Homalodisca coagulata, was studied in environmentally-controlled chambers set at 12, 16, 20, 24, 28 and 32 deg. C. Our results showed that the parasitoid developed the fastest at 28 deg. C. The parasitoid took 27.1 at 16 deg. C and 9.5 deg. C days at 28 deg. C to complete the development from egg to adult. At 12 deg. C, the embryonic stage was 6.3 days, about 2 days at 16-20 deg. C, and 1 day at 24-32 deg. C. At 16-32 deg. C, the length of the first instar larval stage was about 1 day, but 6 days at 12 deg. C. The development of the second and third instars also varied with temperature. At 16 deg. C, the second and third instars were approximately 2 and 3 days in length, respectively, and 1 and 1.5 days at 28 deg. C. Continued exposure to 32 deg. C arrested the development of the third instar larvae. Prepupae developed faster as temperature increased, but slowed down when held at 32 deg. C. Pupae also developed faster as the temperature increased, but without slowing at 32 deg. C. Linear regression analysis showed that the threshold temperature for development was 5.5, 3.4, 8.3, 5.2, and 5.4 deg. C for embryos, first, second, third instar larvae, prepupae and pupae, respectively. The lower temperature threshold was 8.2 deg. C for egg to adult development. A total of 219.2 degree days above the minimum temperature threshold were needed to complete the development from egg to adult. Temperature also affected the emergence pattern of the G. ashmeadi adults. At 16 and 20 deg. C, adult emergence lasted 10 days and 5 days at 28 and 32 deg. C. The maximum emergence occurred on the first day of emergence at 20-32 deg. C while the emergence peaked on the second day at 16 deg. C. At 28 and 32 deg. C, about 92 and 88% parasitoids emerged within first two days. At 20 and 24 deg. C, nearly 84 and 85% parasitoids emerged within the first three days. Temperature did not influence the sex ratio of the emerging G ashmeadi, but significantly affected the longevity of both sexes. At 16 deg. C, the life spans of female and male adults were 27 and 19 days, respectively, while at 28-32 deg. C, their life spans ranged from 6 to 8 days. The maximum lifetime fecundity of the female parasitoid occurred at 24 deg. C, with an average total of 105 eggs deposited. High temperature shortened parasitoid longevity and reduced lifetime fecundity. At 4 and 32 deg. C, G. ashmeadi deposited >10 eggs/day. At 16 and 20 deg. C, parasitoid oviposition was 3 and 7 eggs/ day, respectively.