نامه انجمن حشرهشناسی ایران (Feb 2011)
Biological parameters of the egg parasitoid Trissolcus grandis (Hym.: Scelionidae) on Eurygaster integriceps (Hem.: Scutelleridae)
Abstract
Trissolcus grandis Thomson is a solitary egg parasitoid of Sunn pest, Eurygaster integriceps Puton. Although widely distributed, it has often been overlooked in field surveys. Our objectives were to develop an efficient rearing technique for T. grandis, and to determine the basic bionomics and demographic parameters, necessary for future augmentative biological control programs. Exposure of 0-4 h-old Sunn pest egg masses to parasitoids at 1:1, 2:1 and 3:1 host-parasitoid ratios resulted in a parasitism rate of > 80%. The results demonstrated that the age of the host and the exposure time affected parasitism rate. However, parasitism rate did not differ significantly among 24, 48 and 72 h-old Sunn pest eggs. The percent of emerged parasitoids during the 24-h host exposure period was relatively high when host eggs were 24 h old. Moreover, the mean sex ratio showed a definite trend, suggesting that host age had an effect on the sex ratio of the T. grandis offspring. The mean developmental time obtained as 11.091 ± 0.1 and 9.68 ± 0.15 d. for female and male progenies, respectively. The longevity of females was ~ 30% lower compared to that of males. The average net fecundity reached 181.83 eggs per female. On the other hand, a female laid averagely ~ 7 eggs per day. Similarly, the daily population increase and mean generation time were 34.2%, and 14.61 d, respectively. The developing population consisted of 99% immature (egg, larvae, pupa), and only 1% adults. The importance of these findings to the population biology of this parasitoid is discussed.
