Reproductive potential of Eupelmus orientalis (Crawford) and Eupelmus vuilleti (Crawford) (Hymenoptera : Eupelmidae), two parasitoids of Bruchidae (Coleoptera) during the harvest and storage of cowpea pods (Vigna unguiculata(L.) Walp.)

Eupelmus orientalis (Crawford) and Eupelmus vuilleti (Crawford) are two clo sely related ectoparasitoids that parasitize the larvae and pupae of Bruchi dius atrolineatus Pic and Callosobruchus maculatus (Fabricius) (Coleoptera: Bruchidae) in the Niamey Region of Niger, West Africa. In this Sahel Regio n, these solitary parasitoids occur sympatrically in the field crop of cowp ea, Vigna unguiculata, (L.) Walp. (Leguminosae), and during subsequent stor age in granaries. In the Niamey Region the storage of cowpea seeds correspo nds to the period of transition from summer (23-33 degreesC) to winter (15- 25 degreesC). With C. maculatus as host, the reproductive potential (number of eggs laid, hosts parasitized and offspring produced) was similar in bot h parasitoid species in the summer, the only major difference between the t wo being the sex ratio of the progeny. In E. orientalis 50% of the offsprin g were females compared to 60 % in E. vuilleti. In cooler winter conditions , all aspects of reproductive potential were greater in E. orientalis femal es than in E. vuilleti. Under these conditions development times were short er for E, orientalis than for E. vuilleti, although E. or had a longer life span. Eupelmus orientalis females were more effective than E. vuilleti at parasitizing their common host. This advantage was confirmed by their intri nsic growth rate (r(m)) during both seasons. Despite this, the population o f E. orientalis decreased during storage, and disappeared within two months , while the population of E. vuilleti became dominant. The disappearance of E. orientalis during storage cannot be attributed directly to a temperatur e-related loss of reproductive potential with the advent of the cooler seas on.