Semiochemical basis of feeding preferences on waterbuck kobus defassa, buffalo syncerus caffer and ox, by some glossina morsitans group of Tsetse

Abstract

This study was carried out based on the speculation that gradation of hosts as sources of blood meal by tsetse flies is due to the absence and/or presence of specific semiochemicals. The study was carried out to establish whether kairomones and/or allomones from waterbuck Kobus defassa (nonhost of tsetse), buffalo Syncerus caffer and ox (hosts) emanate from the skin surface of the animals and whether these semiochemicals are responsible for the relative refractoriness ofthe waterbuck to tsetse flies. The behavioural responses of caged individual teneral Glossina morsitans morsitans on waterbuck and ox and on feeding membranes with and without smears of different doses of water buck sebum, were compared. No significant difference was found in the initial landing behaviour on the two animals (waterbuck and ox), nor on treated and control parts of the membrane. However, the subsequent behaviours of the flies were significantly different. Whereas none of the flies that landed on the ox showed any escape behaviour, more than a third of those that initially landed on waterbuck escaped. Similar results were obtained on feeding membranes treated in part with the waterbuck sebum. Moreover, flies that landed on waterbuck or its sebum changed probing sites more often, probed significantly longer and showed a general delay in initiation of feeding. Comparison of the behaviour of flies that landed on control zones of the membrane and those on untreated (double control) membrane also showed significant differences, indicating that the insect's behaviour was affected by a more volatile chemical signal in addition to a less volatile contact signal associated with the sebum. Analysis of the waterbuck sebum by gas chromatography-linked electroantennographic detector (GC-EAD) revealed the presence of two electrophysiologically (EAG) active constituents of relatively high molecular weights which may have a role in the close-range/contact effects. The compounds were identified from their mass spectral data as the diacylglycerol, glyceryll-butanoate-3myristate and the triacylglycerol, glyceryl I-butanoate-3-hexanoate-2-myristate. An effective technique for trapping odour from a specific area on the body surface of a live animal was developed. The odour from the waterbuck body surface was trapped on various adsorbents including activated charcoal, glass wool and