Foraging behaviour of the egg parasitoid Uscana lariophaga : towards biological control of bruchid pests in stored cowpea in West Africa
1996
van Alebeek, F.
Seed beetles cause considerable losses in traditionally stored cowpea ( Vigna unguiculata Walp.) under subsistence farming conditions in West Africa. The indigenous egg parasitoid Uscana lariophaga Steffan (Hymenoptera; Trichogrammatidae) is evaluated as a candidate for a conservation strategy of biological control against the major pest Callosobruchus maculatus Fab. (Coleoptera; Bruchidae). Different aspects of U. lariophaga '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. Uscana lariophaga uses odour of uninfested cowpea seeds and of C. maculatus 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, U. lariophaga parasitizes more eggs in host clusters with an even or clumped distribution than in clusters with a low density random distribution. Uscana lariophaga is positive phototactic and negative geotactic, and can move through cowpea stock over several meters a day. Under optimal conditions, U. lariophaga can significantly reduce losses in stored cowpea by C. maculatus . Further progress towards biological control of cowpea storage pests is discussed.
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