Role of shade trees in conserving beneficial arthropods of biocontrol importance in tea ecosystem

Naturally or artificially created diverse vegetation habitats often promote natural enemies of crop pests. The abundance of natural enemies increases with response to increasing habitat complexity at various spatial scales. Against this backdrop, we assessed the contribution of shade trees to conserve beneficial predatory and parasitoid arthropods at local scale in a subtropical tea agroecosystem in Bangladesh. Arthropods viz., predators and parasitoids were captured using Malaise traps in plots with shade trees and in those without shade trees having three different densities of tea bushes due to naturally created gaps (large-gap, small-gap and control). The number of arthropods captured in each plot corresponded to shade-tree and tea-bush densities, such that arthropod abundance in the shade-tree plot was twice that of the control plot, which had similar tea-bush density but no shade trees. Predators were least abundant in the large-gap plot, which had the lowest tea-bush density and no shade-trees, while 2.4–3.8 folds predators were captured in the control and shade-tree plots. There was a negative correlation between mean light intensity and number of predators in the four plots. Similar trends were observed for parasitoids. Relative abundance of predatory Staphylinidae was more than twice in the shade-tree and small-gap plots compared to control and large-gap plots. Relative abundance of parasitoid Ichneumonidae was ranked as small-gap > shade-tree > control > large-gap plots. Our results suggested that shade trees may help conserve and promote beneficial arthropods such as predators and parasitoids in tea agroecosystems.