Antagonism between two natural enemies improves biological control of a coffee pest: The importance of dominance hierarchies

• Infection of Coccus viridis by Lecanicillium lecanii is reduced in the presence of Azya orbigera.
• Predation has a negative effect on pathogenesis.
• Predator was dominant control agent in field survey.
• Pathogen was dominant control agent in experiment.
• Presence of both enemies improves biological control only when predator is dominant.

The relationship between two natural enemies of Coccus viridis (green coffee scale), an important hempiteran coffee pest was determined using a combination of experimental and observational approaches. Adult and larval forms of Azya orbigera, a coccinellid beetle predator were included on leaves of coffee plants with healthy scale populations resulting in lower proportions of scales infected with the second natural enemy, an entomopathogenic fungus (Lecanicillium lecanii). C. viridis populations on leaves where A. orbigera were excluded exhibited twice as much fungal infection by L. lecanii. In addition, field surveys of C. viridis populations on whole coffee plants corroborated experimental findings with eight times less fungal infection for coffee plants where A. orbigera was present than for plants where the predator was absent a month prior to surveys of L. lecanii. Despite a reduction in fungal infection in both the experiment and survey, the presence of the beetle reduced overall biological control of the pest only in the experiment where the receiver of the antagonism (L. lecanii) was more dominant in controlling C. viridis than the instigator of the antagonism (A. orbigera). In the survey, A. orbigera was dominant over L. lecanii, resulting in equal to greater levels of biological control depending on the degree to which A. orbigera was dominant over L. lecanii. Our results indicate that a negative relationship exists between A. orbigera and L. lecanii, but that contrary to expectations, this antagonism may in some cases improve overall biological control of the shared pest target.

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