Incidence and distribution of insect pests in rain-fed wheat in eastern Africa

Abstract

Insect pests are some of the major constraints limiting yield of wheat ( Triticum aestivum L.) in East Africa. The objective of this study was to determine the species composition and distribution of insect pests, and their natural enemies associated with wheat in Eastern Africa. A survey was conducted in farmers’ fields in Ethiopia, Kenya and Uganda during 2013 and 2014 cropping season. Wheat fields along roadsides were randomly selected at approximately 2 to 10 Km intervals, and in each field, several wheat plants in a cross diagonal line were examined for presence or absence of insect pests and associate natural enemies. Also, the type of insect was identified to species level and in situ population counts recorded. In Ethiopia, only 39% of the fields were infested by tef epilachna, Chnootriba similis Thurnberg (Coleoptera: Coccinellidae); while the remaining wheat fields were free of insect infestation. The Russian Wheat Aphid (RWA), Diuraphis noxia Kurdijumov (Hemiptera: Aphididae), was the most prevalent insect pest of wheat in Kenya and Uganda. The maximum number of RWA per tiller was 58 in Kenya and 38 in Uganda. Moreover, in Kenya the rose wheat (grass) aphid ( Metopolophium dirhodum Walker), oat-bird-cherry aphid ( Rhopalosiphum padi Walker) and corn leaf aphid (R. maidis Fitch) were prevalent, though at low densities ranging, from 0.1 to 9 per tiller. The greenbug ( Schizaphis graminum Rondani) and the green stink bug ( Nezara viridula L.) were recorded only in Uganda. The general aphid predators Cheilomenes spp., spiders, lacewings and the parasitoid Aphidius spp. were the natural enemies of aphids found in Kenyan wheat. However, the density of these natural enemies was too low to bring the aphid population to a level that causes economic damage. Key Words: Russian Wheat Aphid, Triticum aestivum