Effects of release site on the early establishment of the mirid bug, Nesidiocoris tenuis Reuter (Hemiptera: Miridae), on greenhouse tomato: A comparison between an alternative host plant and tomato crop

To evaluate the potential enhancement of establishment speed and abundance of the generalist zoo-phytophagous natural enemy, Nesidiocoris tenuis (Hemiptera: Miridae) on tomato (Solanum lycopersicum (Solanales: Solanaceae)) under greenhouse conditions, we compared the effect of release site on tomato crop and an alternative host plant (garden verbena, Verbena×hybrida variants (Lamiales: Verbenaceae) (V.×hybrida cv. Tapian in 2017, V.×hybrida cv. Hanatemari-aya in 2018), which is a common release site. We monitored baseline prey populations of greenhouse whitefly Trialeurodes vaporariorum (Hemiptera: Aleyrodidae) on tomato plants without natural enemy release in 2016, and with release in 2017 and 2018. The experiment consisted of two separate greenhouses with both the host plants and 15 individuals of N. tenuis were released three times on the tomato crop in one of the greenhouses and on the garden verbena in the other greenhouse. Based on this experiment, we were able to draw several conclusions. Approximately two weeks after initial release, N. tenuis individuals were initially observed on the garden verbena in both greenhouses, and subsequently on the tomato plants. Once N. tenuis individuals were observed on tomato plants for aproximately 40 days after release, the number of observed individuals on tomato plants and garden verbena showed a similar seasonal prevalence. This seasonal prevalence did not differ regardless of release site for both years. The absolute number of N. tenuis individuals observed on both the tomato and garden verbena was higher when N. tenius was released on garden verbena than that on tomato plants in 2017. Notably, after release in 2017, numerous ants [Lasius hayashi (Hymenoptera: Formicidae)] were observed in the vicinity garden verbena plants, and they seemed to carry N. tenuis nymphs around. In 2018, the greenhouses were switched to reduce environmental variation, and N. tenuis individuals were re-lesased on the tomato and garden verbena. However, just before release, packages of granular ant insecticide were placed in the greenhouses. The number of N. tenuis individuals observed in both greenhouses in 2018 was very similar between the tomato and garden verbena and also showed a similar seasonal prevalence. These results indicate that N. tenuis on tomato plants provides little to no enhancement of establishment speed or population size. The poupulation of greenhouse whiteflies in the greenhouses remained low during the growing season of the tomato plant, suggesting that N. tenuis is an effective biological control agent of greenhouse whiteflies on tomato plants although the experimental location is not a natural distributing area of the species.