Non-consumptive predator effects on a primary greenhouse pest: Predatory mite harassment reduces western flower thrips abundance and plant damage

Abstract

Prey react to the presence of predators in suite of ways that reduce predation risk, but may also negatively affect fitness. Non-consumptive effects (NCEs) of predators on prey are likely important components of biological control and moderators of plant damage in agricultural systems. Yet, few studies have investigated their effects in crops relying on augmentative release of natural enemies for protection. Here, we investigated NCEs of the predatory mite Neoseiulus cucumeris on a non-prey life stage of western flower thrips (Frankliniella occidentalis), one of the most damaging pest of greenhouse crops in the world. Second instar thrips were exposed to 2 adult female mites on a leaf disk for 24h. Over a 20min observation period, we saw a 22% reduction in thrips feeding behavior in the presence of predatory mites compared to thrips alone. Thrips feeding was often interrupted by attempted mite attacks, which averaged 4 attacks per thrips over 20min. After 24h, this reduced leaf damage by 51% in the predator treatment compared to the control. This result held true in experiments on whole plants, with damage reduced by 38% in the presence of mites. No significant reduction in feeding activity or damage was observed when larval thrips were exposed to non-predatory mites, conspecifics, or leaves which had previously held large numbers of predatory mites. The presence of mites did not alter thrips development time or final adult size. However, survival to adulthood was decreased by 54–78% in the presence of mites, suggesting a lack of nutritional reserves necessary to complete development. This study demonstrates that NCEs of predatory mites can induce a trophic cascade by reducing pest feeding and fitness. Such beneficial effects of natural enemies are often overlooked in simple predation and efficacy studies.