Increasing plant diversity does not always enhance the efficacy of omnivorous mirids as biocontrol agents

The plant matrix influences the performance of omnivorous mirids as biocontrol agents and increasing plant diversity has been hypothesised to enhance pest control. This research aimed to determine the effect of using calabash, Lagenaria siceraria , as a companion plant on the population dynamics and whitefly control efficacy of Dicyphus argensis in tomato greenhouses. The response of D. argensis was also compared with that of Nesidiocoris tenuis. Four treatments were assayed in a complete randomised block design with three replicates each: (1) Bemisia tabaci , (2) B. tabaci + D. argensis , (3) B. tabaci + D. argensis + calabash and (4) B. tabaci + N. tenuis . Calabash harboured high populations of D. argensis , but its abundance on tomato plants was significantly lower in the presence of calabash than in its absence, and in both treatments, it reached lower numbers than N. tenuis . Dicyphus argensis reduced the whitefly density on tomato plants relative to the compartments with no mirids, but the whitefly density was higher in the presence of companion plants, and N. tenuis was more effective in reducing whitefly populations. Calabash served as a host for the multiplication of whitefly and increased the pest density on tomato. In this research, increasing plant diversity in crops did not enhance pest control because: (1) the aggregation of D. argensis in calabash reduced its abundance in tomato plants; (2) the pest populations multiplied. This contrasts with the diversity hypothesis and confirms the importance of the plant context for predatory dicyphines.