Level-dependent effects of predation stress on prey development, lifespan and reproduction in mites

In predator-prey interactions, non-consumptive effects of predators have been less studied than consumptive effects. However, non-consumptive effects may have significant influences on prey and can change different aspects of their life history such as development, reproduction and lifespan. The odour and other cues associated with a predator, without direct contact, could induce stress in prey, leading to phenotypic changes in life history traits. In this study, we investigate how mild and strong predator-induced stress could affect prey life history. The prey (Tyrophagus putrescentiae) was exposed, from hatching to death, to three different levels of predation stress from its predator (Neoseiulus cucumeris) (1, 3 or 5 predator adults in an adjacent cage separated by a mesh screen). Compared with the control, both males and females under predator-induced stress had longer developmental time and shorter lifespan when the level of predation stress increased, showing significant level-dependence. In addition, females had reduced fecundity under predation stress. Sex-specific response to predation stress was observed under a low level of predation stress: females had greater reduction in lifespan than males. Furthermore, the reduction in female lifespan was due more from the decrease in the post-oviposition period than the decrease in the oviposition period. Future studies applying even milder levels of predation press, such as exposure of prey to predator cues only during part of the prey lifespan, may provide additional insights.

Exploring the Kairomone-Based Foraging Behaviour of Natural Enemies to Enhance Biological Control: A Review

Kairomones are chemical signals that mediate interspecific interactions beneficial to organisms that detect the cues. These attractants can be individual compounds or mixtures of herbivore-induced plant volatiles (HIPVs) or herbivore chemicals such as pheromones, i.e., chemicals mediating intraspecific communication between herbivores. Natural enemies eavesdrop on kairomones during their foraging behaviour, i.e., location of oviposition sites and feeding resources in nature. Kairomone mixtures are likely to elicit stronger olfactory responses in natural enemies than single kairomones. Kairomone-based lures are used to enhance biological control strategies via the attraction and retention of natural enemies to reduce insect pest populations and crop damage in an environmentally friendly way. In this review, we focus on ways to improve the efficiency of kairomone use in crop fields. First, we highlight kairomone sources in tri-trophic systems and discuss how these attractants are used by natural enemies searching for hosts or prey. Then we summarise examples of field application of kairomones (pheromones vs. HIPVs) in recruiting natural enemies. We highlight the need for future field studies to focus on the application of kairomone blends rather than single kairomones which currently dominate the literature on field attractants for natural enemies. We further discuss ways for improving kairomone use through attract and reward technique, olfactory associative learning, and optimisation of kairomone lure formulations. Finally, we discuss why the effectiveness of kairomone use for enhancing biological control strategies should move from demonstration of increase in the number of attracted natural enemies, to reducing pest populations and crop damage below economic threshold levels and increasing crop yield.

Mint companion plants enhance the attraction of the generalist predator Nesidiocoris tenuis according to its experiences of conspecific mint volatiles

Mint plants enable improvement of pest management by attracting herbivore enemies to constitutively released mint volatiles. The generalist predator Nesidiocoris tenuis is used worldwide to control agricultural pests, but little is known about whether mint can serve as a companion plant that attracts this predator. To examine this, olfactory responses of N. tenuis were assessed using apple mint, candy mint, and spearmint as odor sources. Of the volatiles released by these mint species, candy mint volatiles alone were more attractive than those from undamaged eggplant, and were as attractive as volatiles from eggplant damaged with Spodoptera litura larvae. However, no prominent preference for particular volatile(s) among the mint volatiles was shown by O. strigicollis. When N. tenuis had been previously exposed to candy mint, the predator showed a stronger preference for candy mint volatiles than damaged eggplant volatiles. It was, however, irrelevant whether the predator received benefit or not by predating animal prey during the mint-experience period. In contrast, spearmint-experience increased the preference for spearmint volatiles only when the predator acquired prey during the mint-experience period. These findings suggest that previous exposure of N. tenuis to some particular mint species can increase its preference for volatiles from the conspecific mints.