Cross-mating and oviposition behaviour between strains of cotesia sesamiae. Cameron (hymenoptera: braconidae) from kitale, Mombasa and Mount Kenya.

Abstract

Stemborers cause 50% yield losses in cereal crops including maize, sorghum and sugarcane. In Kenya, stemborers include Busseola fusca, B. phaia, Sesamia calamistis, Eldana saccharina, Chilo orichalcociliellus and C. partellus. Control options for the various stem borers include use of pesticides, early planting, intercropping with noncereals and host plant resistance. In addition to being expensive, pesticides are environmentally unfriendly and are not fully effective due to the cryptic feeding behavior of the larvae. Thus the search for more efficient and convenient control methods for these pests is still ongoing. One of the other methods still being researched on is biological control where natural enemies, predators, parasitoids and pathogens, are used to lower the population of the pest to below economic injury level. Predators cannot keep the stem borers below economic injury levels, as pathogens and nematodes do not regulate the stem borer numbers. Parasitoids feed on immature stages of other insect host stages and kill them in the process. In Kenya C. sesamiae is one of the parasitoids that has been studied in regard to the control of stem borer pests. The relative importance of Cotesia sesamiae Cameron (Hymenoptera: Braconidae), a gregarious larval parasitoid of lepidopteran stem borers, varies significantly between regions. Two biotypes of the parasitoid have been described in Kenya: the coastal biotype, which is unable to develop in the noctuid B. fusca (Fuller) and the western biotype, which develops successfully in this host. Thus several strains of C. sesamiae from Kenya are envisaged for introduction into regions where B. fusca is the main pest icluding certain parts of Kenya such as Wundanyi (Taita- Taveta District,), and Central, and western Africa. In this study the reproductive compatibility of three populations of C. sesamiae was investigated using the noctuid S. calamistis and B. fusca as hosts. The effect of cross mating on the mating and oviposition behavior of C. sesamiae strains as well as the influence of parental strain of C. sesamiae on the fitness and sex ratio of their hybrid progeny was investigated. Further, the effect of Wolbachia treatment on the reproductive compatibility of the three strains was assessed. The three strains of C. sesamiae from coastal regions, central (Mt Kenya) and western (Kitale) were cross-mated among themselves giving rise to homogenic and heterogenic crosses. The mated females (whether cured or not) oviposited in fourth instar larvae of S. calamistis and B. fusca as hosts. Duration of searching, courting, foraging, mating and ovipositing was recorded. Data on searching, mating time and cross mating parameters were analyzed using analysis of variance (ANOY A). Means were separated by the Student-Newman-Keuls (SNK) test. The results showed that homogamic crosses of Mombasa uncured and Mt Kenya cured took a long time to mate (20.27±0.63a and 12.28±0.27) respectively. The number of Progeny produced varied among the crosses with cured Mombasa male mated with cured Kitale female having the highest with (33.0±0.la) and a sex ratio of 8% compared with uncured Mombasa male mated with uncured Kitale female having the lowest with (9.3±0.Ic) and a sex ratio ofO.6±0.labcd, therefore curing affects mating behavior, progeny and sex ratio. The FI individual were neither compatible among themselves nor with the parents. All parameters were highly significant apart from mean number of cocoons. The output of this work has helped to determine the effect of cross mating and oviposition behaviour of C. sesamia strains and the influence of crossing on sex ratio and progeny size and has helped to understand the possible consequences of the introduction and redistribution of C sesamiae for the sustainable control of stem borers in Africa.