Publication Type

Journal Article

Journal Name

Insect Science and its Application

Publication Date

1-1-2001

Abstract

Studies to determine the relative abundance and distribution of stemborer species and their associated parasitoids in maize and sorghum were carried out during the 1995-1996 and 19992000 cropping seasons on Unguja and Pemba, the two main islands of Zanzibar. Three stemborer species were found on both islands in maize and sorghum, with the exotic species Chilo partellns (Swinhoe) (Crambidae) being the most abundant and widely distributed species, accounting for 75.3 % of stemborer attack. It was followed by Sesamia calamistis Hampson (Noctuidae) and C/i. oriclialcociliellus Strand (Crambidae). Stemborer abundance was significantly higher in Pemba (1.47 ± 0.20) than Unguja (0.85 ±0.05). Overall stemborer density in Zanzibar, during the period of study, was 1.03 ±0.08 stemborers per plant. Stemborer infestation was significantly higher during the short rainy season than long rainy season but it did not vary between maize and sorghum or coral rag and plantation areas. The indigenous parasitoids recorded included ten larval parasitoids: Bossus sp., Chelomis sp., Cotesia sp., Cotesia sesamiae (Cameron), Cotesia nificrits (Haliday), Dolichogenidea sp., Dolichogenidea aethiopica Wilkinson, Dolichogenidea polaszeki Walker, Megaselia sp. and an unidentified Tachinidae. Among these, the braconid Co. sesamiae was the most common parasitoid, attacking all the stemborer species and recorded from 85.2 % of parasitised larvae. However, parasitism was low- 3.9 % on Unguja and 1.9 % on Pemba. In addition, the efficiency of Co. sesamiae was reduced by two hyperparasitoids-Aphagnomus fijiensis Fernere and Elasmus sp. Seven pupal parasitoids were recorded, namely Dentichasmias bnsseolae Heinrich, Brachymeria sp. Westwood, Brachymeria olethria Waterston, Pediobins fiirvus Gahan, Psilochalcis soudanensis Steffan, Syzenclus riiberrimns Benoît and an unidentified Chalcididae. The differences in species diversity between the two islands are discussed in the context of the equilibrium theory of biogeography and the geographical size. Classical biological control of the introduced stemborer C/z. partellus using the exotic parasitoid Co.flavipes to supplement the indigenous parasitoids in population regulation is proposed as a potentially useful option for Zanzibar. © 2001 ICIPE.

Keywords

Biological control, Chilo orichalcociliellns, Chilo partellus, Cotesia sesamiag, Hyperparasitism, Indigenous parasitoids, Maize, Sesamia calamistis, Sorghum, Stemborer, Zanzibar

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