Bichang’a, Gladys


Titre de la thèse (en anglais) : Identification of kairomones mediating host recognition and acceptance by Cotesia spp. in Kenya

Résumé (en anglais): Lepidopteran stemborer is one of the major constraints to the increased food production in sub-Saharan Africa due to the crop losses they cause. FAO and CIMMYT predict that by the year 2020, there will be a 50% increase in the demand of maize. In order to improve food safety in that region, an increasing capacity to reduce the problem of stemborers in maize is very essential. Cotesia spp. are one of the key parasitoids that have been used in control of cereal stemborers. For example, in eastern Africa, the braconid larval endoparasitoid, Cotesia flavipes Cameron was introduced in a classical biocontrol programme for the control of the invasive stemborer Chilo partellus (Swinhoe) (Lepidoptera: Crambidae), to complement the action of the predominant indigenous larval endoparasitoid Cotesia sesamiae (Cameron) (Hymenoptera: Braconidae). One of the major problems affecting the efficacy of exotic parasitoids is the suitability of indigenous stemborer species and the host plant they are feeding on. For successful biological control, the ability of the natural enemy to locate, accept, parasitise and develop successfully in their host is crucial. Most recent studies indicates that contact host examination is more crucial for Cotesia spp. To determine the suitability of the stemborer and to induce the host recognition and acceptance. Furthermore, from these studies it has been hypothesized that water soluble stemborer regurgitant kairomones may be involved in eliciting host recognition and acceptance. The stimuli eliciting host recognition and acceptance are coming from a water-soluble compounds most likely protein(s) of the regurgitant. Apart from a 30 kD, protein revealed from a noctuid host species, there are very few examples in the literature showing the involvement of proteins from the host involved in host recognition and acceptance by endoparasitoids. Those which have been revealed are frequently non-proteins e.g. lipids phenols and alcohols. The work will focus on the use of a bioassay guided quantitative and analytical (LC-MS and GC MS) techniques as the reference methodology to identify, for the first time, the kairomones from the lepidopteran stemborer involved in host recognition and acceptance by three Cotesia species. The study will describe also the origin of the kairomones their structure/chemical variability according to stemborer species/population and the Cotesia species/population association. The data obtained will be used to explain the varied results seen in biological control systems. This will allow policy makers in the country to implement measures and to advice the agricultural sector on the better pest management systems using biological control programs. This will contribute to improve food security in Kenya and across sub- Saharan Africa through increasing trade and agriculture productivity hence meeting the millennium development goal and the Kenya vision 2030.