Uncovering the relationship between two ant species and the coffee berry borer in Chiapas, Mexico

Background/Question/Methods

The coffee berry borer (CBB) is currently the most important insect pest of coffee plantations worldwide. In highly diversified farms natural enemies (such as ants) appear to limit CBB and potentially prevent outbreaks. Recently, evaluations on the effects of ants on the CBB population density have arisen, as well as the mechanisms that ants use to attack the CBB. This research aimed to determine the relationship between the presence of ants and the level of damage in berries, and the behavior of Azteca instabilis and Pheidole syananthropica in the presence of the CBB on coffee berries. To these ends, an ant survey was conducted in a 2500m² plot within a shaded coffee farm in Chiapas, Mexico. A 4 x 4m coordinate system was established and the coffee plant or shade tree closest to the coordinate point was sampled using tuna fish for a total of 168 coffee plants and 46 shade trees sampled. Additionally up to 100 berries were harvested from 138 coffee plants to measure damage and verify the presence of the CBB. Behavior was determined in the field by placing live CBB adults on berries and video recording all attacks. Ethograms were constructed using The Observer XT v10.

Results/Conclusions

Eighteen ant species and eleven genera were recorded, in which seven of them CBB predators have been reported. Results showed that 7.21% of the berries sampled (n=10,488) had CBB damage. Although this percentage is higher than generally suggested for this pest (3-5%), plants with ants (particularly plants with P. synanthropica and A. instabilis) had less percentage of damaged berries (mean ± s. e.) (23.34% ± 0.44%) than plants without ants (33.8% ± 1.2%) (p=0.05). The length of CBB galleries was significantly smaller (p=0.01) in plants with ants (0.34cm ± 0.28cm) than in plants without ants (0.40cm ± 0.34cm), however, the longitude of galleries in plants with A. instabilis showed no significant differences (p>0.05) from plants without ants. P. synanthropica was observed carrying CBB to the nest in 50% of the cases, while A. instabilis threw CBB off of the coffee plant in 79% of the cases. Results indicate that the presence of these ant species reduce CBB damage and suggest that different behaviors could explain the non devastating status of the CBB in this agroecosystem. Additionally A. instabilis may limit the CBB before entering the berry but also it may create an enemy-free space once it is inside.