Seasonal abundance of western flower thrips and its natural enemies in different French bean agroecosystems in Kenya

The seasonal abundance of western flower thrips (WFT) [Frankliniellaoccidentalis (Pergande) (Thysanoptera: Thripidae)] and its natural enemies on French beans in two agro-ecological zones (AEZs) (high and mid altitude) in Kenya, was studied in three growing cycles from January to December 2009. French beans were sampled every 2 weeks for WFT and natural enemies. Results show that colonization of French beans with WFT in both farm scales studied in the two AEZs started at 2- to 3-leaf stage. There was an increase in the population density of WFT from budding stage to podding/flowering stage, and it declined at crop senescence. The population densities of WFT on French beans were lower in the first compared with the second growing cycle and the highest in the third growing cycle. Two natural enemies of thrips, Orius spp. (Hemiptera: Anthocoridae) and Ceranisus menes (Walker) (Hymenoptera: Eulophidae), were recorded on French beans. The population density of C. menes was positively correlated with thatof WFT, while the population densities of Orius spp. and WFT were not correlated. The population density of WFT was not correlated with temperature and relative humidity, but was negatively correlated with rainfall. Our results suggest that the population density of WFT in the two AEZs differs along growing cycles and plant phenological stages. Management strategies targeted at WFT would need to start at early crop stages (3-leaf to budding stage), depending on growing cycle, to prevent further build-up of thrips population.