Conservation biocontrol of the coffee berry borer in coffee farms through ant predation

Abstract

Pesticides threaten biodiversity in farms and the any matrices where they are used. In the coffee system, conservation biocontrol is a sustainable agriculture practice that has the potential to ameliorate the effects of pesticide by encouraging the presence of natural enemies. The coffee berry borer (CBB) remains the most important insect pest in coffee around the world. Spending the majority of its life cycle within coffee berries, CBB evades topical applications of pesticide. Ants have been shown to be important predators of the coffee berry borer in field and laboratory settings. We measured CBB damage in low, medium and high coffee bush branches, and assessed the ability of ants to prey on adult CBB before and after entering berries in coffee farms in Puerto Rico. This was done by assessing the proportion of damaged berries and survival of adult beetles within the berries at the time of sampling. Over 20,000 coffee berries were assessed from 220 plants in two farms in Puerto Rico. Ant identity and activity was determined via tuna fish baits in individual coffee bushes. Fifteen ant species were observed within the two farms, but only five species were abundant enough to assess their impact on the CBB. Top branches had significantly less damage than medium and low branches. 73% of the plants surveyed had some level of CBB damage, and average damage on a per plant basis was 6.4%. Of those berries with damage, 41% had live adult beetles inside. Plants with W. auropunctata and Solenopsis invicta had lower CBB damage than plants where these species were not present, although for W. auropunctata this effect was significant only for one of the farms. Contrary to expectations, plants with Pheidole moerens and Monomorium floricola had significantly more CBB damage than plants without these species. With respect to survival (adult CBB that were alive and inside the berries at the time of sampling), CBB had a significantly lower survival in plants with W. auropunctata, while it has a significantly higher survival in plants with S. invicta. Our results suggest that the effect of ants on CBB damage and survival is highly contextual depending on the ant species that occupy the coffee plants. Nonetheless, this study identified two species that had a significantly negative effect on damage by the CBB in coffee plants, S. invicta and W. auropunctata, but only W. auropunctata also had a negative effect on the survival of the CBB adults once they penetrated the berries. Understanding the distribution of ant species within farms can be important for implementing conservation biocontrol of the CBB.