Factors Affecting the Biology of Telenomus isis (Polaszek) (Hymenoptera: Scelionidae), an Egg Parasitoid of Cereal Stem Borers in West Africa A. Chabi-Olaye,* , † F. Schulthess,* H.-M. Poehling,† and C. Borgemeister† *Plant Health Management Division, International Institute of Tropical Agriculture (IITA), 08 BP 0932 Tripostal, Cotonou, Republic of Benin; and †Institute of Plant Diseases and Plant Protection, University of Hanover, Herrenha ¨ user Str. 2, 30419 Hanover, Germany Received May 22, 2000; accepted January 25, 2001 This study aimed at an assessment of the potential of the egg parasitoid Telenomus isis (Polaszek) as a bio- logical control agent of cereal stem borers. 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 modified Logan model and with eggs of the noctuid Sesamia calamistis Hampson as hosts, the lower and upper thresholds for development were estimated at 13.1 and 36°C, respectively, and the optimal temperature for development was 31°C. Female T. isis had no measur- able preoviposition period, and the oviposition period ranged from 3 to 5 days. Approximately 66% of the total lifetime complement of eggs of T. isis were pro- duced within 6 h after emergence. Average total life- time fecundity was 61.1 and 82.1 eggs per female at 21 and 28°C, respectively. Longevity of adult females was 17.1 days at 21°C and 5.2 days at 30°C. Host acceptance and suitability were tested, using nine lepidopteran borer species. Only the noctuids S. calamistis, Sesa- mia poephaga (Tam & Bowden), Sesamia botanephaga (Tam & Bowden), and Busseola fusca (Fuller) were successfully attacked by T. isis. Parasitism and emer- gence 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 significantly reduced mean parasitism from 56.7 to 23.5%. Parasitoid emergence rates and sex ratio did not vary among 1-, 2-, or 3-day- old host eggs, but both 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 fecun- dity decreased from 81.2 to 40.5 eggs per female, re- spectively, indicating resorption of eggs. The results are discussed and compared with life table parame- ters of the ubiquitous egg parasitoid Telenomus busseolae (Gahan). © 2001 Academic Press Key Words: Telenomus isis; T. busseolae; stem borer; Sesamia spp.; Busseola fusca; temperature require- ments; life history; host acceptability and suitability; host deprivation; West Africa. INTRODUCTION The most damaging field pests of cereals in Africa are lepidopteran stem and ear borers, most of which belong to the families Noctuidae, Pyralidae, and Cram- bidae (see overview by Polaszek, 1998). Most often, these borers occur as a complex of species with over- lapping spatial and temporal distributions. In West Africa, the most frequently reported maize pests are the noctuid Sesamia calamistis Hampson, the pyralid Eldana saccharina Walker (Bosque-Pe ´ rez and Mareck, 1990; Shanower et al., 1991; Gounou et al., 1994; Schul- thess et al., 1997), and, west of the Dahomey gap in countries such as Ghana and Co ˆte d’Ivoire, the noctuid Sesamia botanephaga Tams and Bowden (Endrody- Younga, 1968). The noctuid Busseola fusca (Fuller) is generally of little importance in West Africa, but is the predominant species across all ecozones in Cameroon in Central Africa (Cardwell et al., 1997; Ndemah, 1999). The crambid Coniesta ignefusalis Hampson, a pest of millet in the Sahelian and savanna regions (Nwanze, 1991), is occasionally found on maize in all ecozones. Other species found in the system are Sesa- mia poephaga Tams and Bowden, a minor pest of sor- ghum in the Guinea and Sudan savanna mainly (Schulthess et al., 1997), and Chilo spp. (Moyal and Tran, 1991; A. Chabi-Olaye, unpublished data). Spe- cies such as the pyralid Mussidia nigrivenella Ragonot and the torticid Cryptophlebia leucotreta (Meyrick) feed only in the maize ear and are common in all zones (Moyal, 1988; Se ´tamou et al., 2000). In West Africa, maize yield losses due to ear and stem borers vary from 10 to 100%, depending on eco- Biological Control 21, 44 –54 (2001) doi:10.1006/bcon.2001.0922, available online at http://www.idealibrary.com on 44 1049-9644/01 $35.00 Copyright © 2001 by Academic Press All rights of reproduction in any form reserved.