ROLE OF PEACH [PRUNUS PERSICA (L.) BATCSH] EXTRAFLORAL NECTARIES IN MEDIATING NATURAL ENEMY-HERBIVORE INTERACTIONS
Mathews, Clarissa Ruth
Bottrell, Dale G.
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Extrafloral nectaries (EFNs) are reported to benefit some plants when ants (Hymenoptera: Formicidae) use their secretions and fend off herbivores. The significance of peach [Prunus persica (L.) Batcsh] EFNs in mediating natural enemy-pest dynamics was studied for the 'Lovell' cultivar with EFNs present and absent. The first phase of the research tested the hypothesis that peach EFNs contribute indirectly to plant defense from herbivores. Trees with EFNs experienced a 6-fold increase in predators (predominantly ants), fewer herbivores, and less folivory compared to trees without EFNs. Ant exclusion techniques further revealed that trees with EFNs benefited from reduced folivory in the spring and increased vigor (trunk circumference, leaf surface area, and terminal carbon composition) only when ants were permitted in their canopies. It was concluded that the EFNs do have a defensive role with regard to foliage feeders. The next research phase explored the impact of EFNs on biological control of a key economic pest, Grapholita molesta (Busck) (Lepidoptera: Tortricidae), in peach orchards. Experiments revealed that trees with EFNs had higher parasitoid densities in the spring and increased parasitism of larval G. molesta later in the season. Ant exclusion from mature peach trees with EFNs increased G. molesta fruit injury by > 4-fold, indicating that EFNs have a protective role for the fruit as well. The potential for competitive interactions between ants and other natural enemies associated with EFNs was explored in the final research phase. Studies revealed that several natural enemy groups contribute to reductions in G. molesta eggs, larvae, and pupae in peach orchards. Although ants antagonized the G. molesta egg parasitoid Trichogramma minutum (Riley) on trees with EFNs, the ants were crucial in reducing G. molesta in both the larval and pupal stages. The implications of EFN-natural enemy-pest interactions to orchard-level biological control will likely depend on local herbivore population dynamics. However, the EFNs clearly benefit P. persica indirectly, through enhancement of ants and other natural enemies. Thus, EFNs are an important host-plant characteristic that should be retained in future peach cultivars in order to maximize conservation biological control.