Factors affecting the biology of Telenomus isis (Polaszek) (Hymenoptera : scelionidae), an egg parasitoid of cereal stem borers in West Africa

This study aimed art an assessment of the potential of the egg parasitoid T elenomus isis (Polaszek) as a biological control agent of cereal stem borer s. Therefore, the effects of temperature, host species, host age, and time of host deprivation on the development and the reproductive potential of T. isis were studied in the laboratory, By use of linear regression and a mod ified Logan model and with eggs of the noctuid Sesamia calamistis Hampson a s hosts, the lower and upper thresholds for development were estimated at 1 3.1 and 36 degreesC, respectively, and the optimal temperature for developm ent was 31 degreesC. Female T. ist's had no measurable preoviposition perio d, and the oviposition period ranged from 3 to 5 days. Approximately 66% of the total lifetime complement of eggs of T. isis were produced within 6 h after emergence. Average total lifetime fecundity was 61.1 and 82.1 eggs pe r female at 21 and 28 degreesC, respectively. Longevity of adult females wa s 17.1 days at 21 degreesC and 5.2 days at 30 degreesC, Host acceptance and suitability were tested, using nine lepidopteran borer species. Only the n octuids S. calamistis, Sesamia poephaga (Tam & Bowden), Sesamia botanephaga (Tam & Bowden), and Busseola fusca (Fuller) were successfully attacked by T. isis. Parasitism and emergence did not, differ among those species, but the sex ratio (expressed as proportion of female progeny) was significantly lower on S. calamistis. An increase of the host age from 1 to 4 days signi ficantly reduced mean parasitism from 56.7 to 23.5%. Parasitoid emergence r ates and sex ratio did not vary among 1-, 2-, or 3-day-old host eggs, but b oth parameters were significantly lower on 4-day-old eggs. With increasing duration of host deprivation from 0 to 17 days, longevity increased from 8. 5 to 18.5 days, whereas average lifetime fecundity decreased from 81.2 to 4 0.5 eggs per female, respectively, indicating resorption of eggs. The resul ts are discussed and compared with life table parameters of the ubiquitous egg parasitoid Telenomus busseolae(Gahan). (C) 2001 Academic Press.