Ant-psyllid mutualism and its effect on the abundance of natural enemies and predation by lady beetle larvae

Many species of ants have mutualistic relationships with honeydew producing hemipterans in which ants protect these hemipterans against their natural enemies, and in return, receive honeydew, thus disrupting biological control. However, current understanding of this food-for protection mutualism between ants and Asian citrus psyllid (ACP) is limited. We hypothesized that ants tending psyllids interferes with predation of ACP by natural enemies. In this study, we focused on an ant-psyllid mutualism, and how this relationship would affect the abundance of natural enemies as well as predation by ladybird larvae. We conducted a field experiment where replicated, 12 tree (Citrus sinensis, va. Valencia) were randomly assigned two treatments: ants present or absent. We recorded natural enemy populations by 2 min. visual observations, and with sticky cards deployed twice per month. We sampled five young flushes per tree to record ACP nymph densities, and sampled adults with stem tap sampling. Similarly, we released 3^rd or 4^th instar larvae of lady beetle, Harmonia axyridis, on flush containing either only ACP nymphs or combination of ACP nymphs and ants to observe direct interactions between ants and ladybeetle larvae. We expect that abundance of natural enemies will be lower, and ACP survival will be higher, in trees containing ants than in trees without ants. In addition, we predict that predation of ACP nymphs by ladybeetle larvae will be reduced due to the interference by ants. Improved understanding of ant-psyllid relationships should improve incorporation of biological control as a component of ACP management.