Uscana lariophaga (Hymenoptera: Trichogrammatidae), an egg parasitoid of bruchid beetle (Coleoptera: Bruchidae) storage pests in West Africa: host-age and host-species selection

Uscana lariophaga Steffan is an egg parasitoid of bruchid species in West Africa. The hosts are Callosobrucbus maculatus (Fabricius) and Bruchidius atrolineatus Pic, insect pests of stored cowpea. Experiments were carried out to study the selection between hosts of different ages and of different species in choice and no-choice situations. Results were obtained through parasitization studies and by direct behavioural observations. A description of the parasitization behaviour of Uscana lariophaga is given. At 30°C, C. maculatus eggs of 0–2 day old are readily accepted for parasitization, but in a choice situation the 0 day old eggs are preferred. Of the older eggs only those of 3 days old are parasitized but significantly less than those of 0–2 days. At 30°C, B. atrolineatus eggs older than 24 hours are significantly less parasitized than younger eggs also in the no-choice situation. When eggs are older than one day, the time needed for penetrating the egg increases with host age. Both bruchid species are suitable hosts for U. lariophaga. In a choice situation B. atrolineatus is the preferred host and especially so when U. lariophaga has been reared on this species. However, in a no-choice situation the highest rate of successful parasitization is obtained on hosts of the species from which they have been reared. The higher parasitization rate of C. maculatus in the field in Niger can be explained by the difference in the susceptible period between the two host species.