Tailoring insect biocontrol for high tunnels

Abstract

Augmentation biocontrol is an effective tool for managing greenhouse pests, but typically fails in open-field settings where dispersal and/or harsh environmental conditions prevent natural enemy establishment. Here, we provide the first experimental evaluation of biocontrol in high tunnels, a new and increasingly popular tool for season extension as part of the local food movement. High tunnels are a hybrid growth environment with characteristics of both greenhouse and field production; thus, the success of augmentation biocontrol in these structures is unclear. Using tomato and cucumber as focal crops, we tested the retention and effectiveness of four commercially available insect predators: Hippodamia convergens (Coleoptera: Coccinellidae), Orius insidiosus (Hemiptera: Anthocoridae), Podisus maculiventris (Hemiptera: Pentatomidae), and Chrysoperla rufilabris (Neuroptera: Chrysopidae). Further, two tactics were evaluated to reduce emigration: i) installing fine mesh screen to tunnel openings; and ii) incorporating flowers with herbivore-induced plant volatile (HIPV) lures. Overall, predator recapture rates were relatively low (<10% of released individuals) and failed to elicit strong impacts on sentinel prey, aphids (Aphis gossypii, Myzus persicae) or hornworm caterpillars (Manduca sexta). The two experimental treatments had contrasting effects on predator establishment. Flowers + HIPVs dramatically increased retention of O. insidiosus (ca. 10–20% recapture vs. 0–1% in control or screened tunnels). Screening, however, mostly failed to retain predators and likely increased mortality due to higher temperatures from reduced ventilation. The abundance of naturally occurring predators (e.g., berytids, syrphid flies, spiders) and parasitoids was highest in flower + HIPV tunnels, intermediate in controls, and lowest in the screened treatment. These data suggest that diversifying high tunnel vegetables with additional sources of nectar/pollen and providing an attractant can simultaneously enhance both augmentation and conservation biocontrol. Screening, on the other hand, may induce pest outbreaks and was not shown to increase retention of augmented natural enemies.