Foraging behaviour of the egg parasitoid Uscana lariophaga : towards biological control of bruchid pests in stored cowpea in West Africa

Seed beetles cause considerable losses in traditionally stored cowpea ( <em>Vigna unguiculata</em> Walp.) under subsistence farming conditions in West Africa. The indigenous egg parasitoid <em>Uscana lariophaga</em> Steffan (Hymenoptera; Trichogrammatidae) is evaluated as a candidate for a conservation strategy of biological control against the major pest <em>Callosobruchus maculatus</em> Fab. (Coleoptera; Bruchidae). Different aspects of <em>U. lariophaga</em> 's searching efficiency, such as host habitat location, host cluster location, the functional response, egg laying capacity and egg load, host handling time, arrestment response, photo- and geotaxis, dispersal and walking behaviour, have been investigated and results are reported in this thesis. <em>Uscana lariophaga</em> uses odour of uninfested cowpea seeds and of <em>C. maculatus</em> eggs to locate host habitats and host clusters therein. Host clusters with many eggs are more frequently located than clusters with few eggs, probably through olfaction. The parasitoid demonstrates a Holling Type II functional response, and the maximum number of hosts parasitized is determined by her ovarial egg load. Due to a strong arrestment response within host clusters, and area restricted searching behaviour after an oviposition, <em>U. lariophaga</em> parasitizes more eggs in host clusters with an even or clumped distribution than in clusters with a low density random distribution. <em>Uscana lariophaga</em> is positive phototactic and negative geotactic, and can move through cowpea stock over several meters a day. Under optimal conditions, <em>U. lariophaga</em> can significantly reduce losses in stored cowpea by <em>C. maculatus</em> . Further progress towards biological control of cowpea storage pests is discussed.