Different behavioral responses in specialist and generalist natural enemy interactions (predators and fungi) in a strawberry-mite pest system

Abstract: Natural enemies like arthropods and entomopathogenic fungi contribute to the natural regulation of pests in many crops. Arthropod natural enemies are a part of a complex multitrophic system and they exist alongside species of entomopathogenic fungi. Their regulation of prey will depend not only of their direct interactions but also of their interactions with each other. For example some of these entomopathogenic fungi may actually also be a potential threat to arthropod natural enemies. Both arthropod predators and entomopathogenic fungi are important biological control agents of the two spotted spider mite, Tetranychus urticae in strawberry. Previous studies on the interactions between these two types of natural enemies show variable results in regards to synergistic/antagonistic effects. We speculated if the degree of specialization of the predator or the fungus could affect the response. Therefore a behavioral study was conducted to investigate the behavior of predators (two species tested) in the presence of entomopathogenic fungal spores (two species tested). The predator species used in this study were the generalist predatory bug, Orius majusculus and the specialist predatory mite, Phytoseiulus persimilis. The entomopathogenic fungal species used was the generalist Metarhizium brunneum and the specialist Neozygites floridana. Predator behavior was recorded by observations in an experimental setup where the predator was given a choice between two strawberry leaf discs; one with entomopathogenic fungal spores and one without, and both with healthy T. urticae. Results suggest that searching and feeding times of both predator species was affected by the presence of entomopathogenic fungal spores and varied depending on the level of specialization of both the predator and the fungal species. Searching time was lower on leaf discs with presence of M. brunneum spores compared to no fungal spores and higher on leaf discs with presence of N. floridana spores compared to no fungal spores. Results indicate that the degree of specialization of the beneficial organisms plays a role in the interaction between arthropods and entomopathogenic fungi. Such interactions are important to consider when biological control using several biological control agents is developed.