Efficiency of Gryon fulviventris (Hymenoptera : Scelionidae) as an egg parasitoid of Clavigralla tomentosicollis (Hemiptera : Coreidae) in northern Nigeria

Field surveys were conducted on cowpea and pigeon pea in 1995 and 1996 to a ssess the effect of indigenous egg parasitoids on populations of Clavigrall a tomentosicollis Stal in northern Nigeria. From the egg masses of C. tomen tosicollis, three species of Hymenoptera belonging to three families, namel Anastatus sp. (Eupelmidae), Ooencyrtus utetheisae (Risbec) (Encyrtiidae), and Gryon fulviventris (Crawford) (Scelionidae), were recorded. Among them, G. fulviventris was found to be the most abundant parasitoid. Of a total o f 3,502 egg masses-collected on cowpea from four geographical locations, 2, 587 (73.9%) were found to contain at least one egg parasitized by G fulvive ntris. From 56,072 eggs discovered, it parasitized 38,935 (69.4%). Overall, 74,724 eggs were collected from the four different locations and of these 52% were parasitized by G. fulviventris. However, parasitism rates varied w ith time and location. At one of the study sites (Minjibir, Kano) where wee kly samples were collected throughout the growing season, the discovery eff iciency, exploitation efficiency, and overall percentage parasitism increas ed significantly from July to November. Also, the proportion of eggs parasi tized was found to be inversely related to the size of the egg mass. These findings are discussed in relation to the potential contribution of biologi cal control in the integrated pest management of this economically importan t pest.