Reproductive compatibility of several East and West African Cotesia sesamiae (Hymenoptera: Braconidae) populations and their crosses and backcrosses using Sesamia calamistis (Lepidoptera: Noctuidae) as the host

The relative importance of the braconid Cotesia sesamiae, a gregarious larval parasitoid of lepidopteran stemborers, varies greatly with region in Africa; while the most common parasitoid of noctuid stemborers in eastern Africa, it is rare in western Africa. Thus, several strains of C. sesamiae from Kenya are envisaged for introduction into western Africa. The present study investigates the reproductive compatibility between four populations of C. sesamiae from West Africa and Kenya with the noctuid Sesamia calamistis as the host using reciprocal crosses as well as backcrosses of hybrid females with males of the parental populations. Searching time of the male for the female and mating period varied significantly with couple and ranged between 0.78-1.9 min and 3.4-12.8 s, respectively. Crosses that involved females from inland Kenya (KI) did not yield any female offspring. However, backcrosses of hybrid female bearing a KI male genome with a KI male yielded both female and male offspring. Thus, there was a partial reproductive incompatibility between KI and West African populations which suggested that the latter were infected with Wolbachia sp. However, this should not affect the efficacy of a population introduced from East into West Africa, as there is a high degree of sib-mating in this gregarious parasitoid species. It was concluded that the regional differences in the relative importance of C. sesamiae was due to differences in the insect and plant host range of the different populations.     

Calyx fluid proteins of two Cotesia sesamiae (Cameron) (Hymenoptera: Braconidae) biotypes in Kenya: implications to biological control of the stem borer Busseola fusca (Fuller) (Lepidoptera: Noctuidae)

Cotesia sesamiae (Cameron) (Hymenoptera: Braconidae) is an indigenous larval endoparasitoid of Busseola fusca (Fuller) (Lepidoptera: Noctuidae) in sub-Saharan Africa. In Kenya, reports suggest that C. sesamiae occurs as two biotypes. Biotype avirulent to B. fusca gets encapsulated by haemocytes in this host and is unable to complete development. Biotype virulent to B. fusca is able to overcome immune defences. Factors present in the calyx fluid such as the PolyDNAviruses (PDV), venom and calyx fluid proteins have been implicated in the variation of C. sesamiae virulence against B. fusca. In the present study, calyx fluid proteins of the two C. sesamiae biotypes were compared using 2-D gel electrophoresis. More protein spots were observed in the virulent parasitoid calyx fluid, but some proteins were specifically observed in the avirulent parasitoid calyx fluid while others were observed in both. To study changes in proteins due to parasitism of B. fusca larvae by the two strains, SDS-PAGE gel were performed on fat body tissues and the haemolymph at three time points. Differences between the two strains were observed in both the fat body and haemolymph tissues. Parasitism-specific protein bands were detectable in fat body tissues of B. fusca larvae parasitized by the two C. sesamiae strains. These proteins were absent in unparasitized larvae. Implications for using C. sesamiae as a biocontrol agent of B. fusca in Africa are discussed.     

The effect of neem (Azadirachta indica A. Juss) oil on oviposition, development and reproductive potentials of Sesamia calamistis Hampson (Lepidoptera: Noctuidae) and Eldana saccharina Walker (Lepidoptera: Pyralidae)

Abstract 1 The effect of different treatments of neem oil (0, 0.075, 0.1 and 0.15 mL/plant) and their persistence (0, 5 and 10 days after application; DAA) on the oviposition behaviour and the bionomics of the noctuid Sesamia calamistis and the pyralid Eldana saccharina were tested in laboratory and greenhouse experiments. 2 For most variables, no difference was found between DAA, showing that the treatments had a long‐term effect, and pooled analyses across DAA were performed. Compared with the control (0 mL/plant), mean reductions due to neem in numbers of egg batch and eggs laid were 70 and 88% for S. calamistis and 50 and 49% for E. saccharina, respectively, but no differences were found among neem concentrations. 3 For both species, larval and pupal development time was shortest in the control and longest with the highest oil concentration. Immature survival, larval weight and fecundity were highest in the control and similar in the neem treatments. 4 No differences were found in sex ratios. Egg viability was highest in the control (approximately 87%) and lowest (72%) with the highest oil concentration. As a result of lower fecundity and longer developmental time, on average, the intrinsic rates of increase in the neem treatments were 30% lower than in the control. 5 In view of the low oviposition rates, immature survival, fecundity and egg viability in the neem treatments, and the relatively high persistence of neem oil, it can be expected that the reduction in densities of the two borers species in the field will be considerable.     

Multiple Parasitism by Cotesia sesamiae and Cotesia flavipes (Hymenoptera: Braconidae) on Busseola fusca (Lepidoptera: Noctuidae)

Busseola fusca (Fuller) is one of the most important pest of cereals in sub-Saharan Africa. Cotesia sesamiae (Cameron) is the predominant parasitoid attacking B. fusca larvae in many parts of Africa. An exotic parasitoid, Cotesia flavipes Cameron, was introduced into Kenya in 1993 for the control of Chilo partellus (Swinhoe). Laboratory studies indicated that although C. flavipes would search for, and attack B. fusca , it was not able to complete its development in this host. The aim of the present study was to investigate the outcome of multiple parasitism of B. fusca by the two Cotesia species. The study showed that when both parasitoid species stung a B. fusca larva at the same time, both parasitoids emerged from more than half of the host larvae, C. flavipes alone emerged from 17%, and C. sesamiae alone emerged from 9%. When the larvae were parasitized by C. sesamiae first, and then 2 h later by C. flavipes , and vice versa, most of the progeny were C. flavipes . However, when B. fusca larvae were stung by C. sesamiae three days before oviposition by C. flavipes , significantly more C. sesamiae emerged from the larvae. When C. flavipes oviposited first, no larvae produced C. flavipes only. The interaction of parasitoids and the host immune system, and the implications of these results for the biological control of stem borers in East Africa are discussed.     

Effects of Bacillus thuringiensis on Adults of Cotesia plutellae (Hymenoptera: Braconidae), a Parasitoid of the Diamondback Moth, Plutella xylostella (Lepidoptera: Plutellidae)

To complement existing information on the mortality of larvae of the wasp Cotesia plutellae attacking moth caterpillars infected with Bacillus thuringiensis (Bt) we tested the direct and indirect effects of the bacterium on adult wasp longevity and oviposition behaviour. In one experiment with female parasitoids, mean longevity (SEM) was not significantly different between females exposed to Bt (1.98 +/- 0.08 days) and those not exposed (2.18 +/- 0.13 days). In a second experiment with both males and females, Bt treatment did not significantly effect either male or female parasitoids exposed to Bt. To observe the possible effects of Bt on oviposition behaviour of C. plutellae each of 10 females were given five larvae that had been treated with Bt and five untreated larvae at the same time. All parasitoids were observed to make oviposition attempts in both untreated and treated larvae. Upon dissection of the host larvae, one or more C. plutellae eggs were found in each of the larvae in which a parasitoid attempted oviposition. There was no effect of Bt treatment on parasitoid oviposition. The mean number of ovipositions in treated larvae (4.3 +/- 0.3) was not significantly different from untreated larvae (4.7 +/- 0.2).