Effects of irrigated and rain fed conditions on infestation levels of thrips (Thysanoptera: Thripidae) infesting Dolichos lablab (L.) in Eastern Kenya

Dolichos lablab (L.) is a neglected crop species in Kenya, grown only for subsistence where they are highly adapted to a small range of ecological niches. It is grown under irrigation and rain fed conditions, where production is limited by insect pests such as thrips (Genera: Megalurothrips and Frankliniella). However, the effects of irrigation and rain fed conditions on infestation levels of these thrips in Kenya are unknown. This study aimed at investigating the levels of infestation of thrips on D. lablab (L.) grown under rain fed and irrigated conditions in Meru Central and Yatta sub-counties, Kenya.  Sampling was conducted biweekly from June, 2009 to February, 2010. In each sub-county, eight farms (four each irrigation and rain-fed) were randomly selected. The infestation levels were monitored using 5 quadrats (30 cm × 30 cm), placed randomly at each farm in every sampling session. The thrips population within each quadrat was estimated from 3 randomly selected shoots of D. lablab.  Thrips samples were placed in 30 ml vials and transported in a cool box to the International Centre for Insect Physiology and Ecology (ICIPE) labs for sorting and identification. The abundance of thrips varied significantly between the irrigated and rain fed farms at both sub-counties. In Meru sub-county, thrips numbers averaged 352.3±36.1 for irrigated farms as compared to 199.1±26.3 for rain fed. In Yatta sub-county, the mean abundance for rain fed farms was 265.5±42.0 as compared to 235.4±37.2 for irrigated farms. D. lablab for irrigated farms were significantly more infested (Anova: p=0.05) than in rain fed farms.    Key words: Infestation levels, sampling, irrigated, rain fed, quadrats.