oa African Entomology - 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 closely related ectoparasitoids that parasitize the larvae and pupae of Bruchidius atrolineatus Pic and Callosobruchus maculatus (Fabricius) (Coleoptera: Bruchidae) in the Niamey Region of Niger, West Africa. In this Sahel Region, these solitary parasitoids occur sympatrically in the field crop of cowpea, Vigna unguiculata, (L.) Walp. (Leguminosae), and during subsequent storage in granaries. In the Niamey Region the storage of cowpea seeds corresponds to the period of transition from summer (23-33 0c) to winter (15-25 DC). With C. maculatus as host, the reproductive potential (number of eggs laid, hosts parasitized and offspring produced) was similar in both parasitoid species in the summer, the only major difference between the two being the sex ratio of the progeny. In E. orientalis 50 % of the offspring were females compared to 60 % in E. vuilleti. In cooler winter conditions, all aspects of reproductive potential were greater in E. orientalis females than in E. vuilleti. Under these conditions development times were shorter for E. orientalis than for E. vuilleti, although E. orientalis had a longer life span. EupeImus orientalis females were more effective than E. vuilleti at parasitizing their common host. This advantage was confirmed by their intrinsic growth rate (rm) during both seasons. Despite this, the population of 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 temperature-related loss of reproductive potential with the advent of the cooler season
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