New primary resource increases predation on a pest in a banana agroecosystem
Résumé
1 Primary resources may affect the structure of species assemblages in upper trophic levels of food webs. These bottom-up effects may involve important ecological processes that affect pest control. For example, population densities of natural enemies may increase when alternative preys are favoured by a new resource. 2 Ants, particularly Solenopsis geminata Forel (Myrmicinae), are recognized as effective predators of herbivores eggs. In the present study, we tested the hypothesis that the addition of a primary resource in a banana agroecosystem will increase pest control of the banana weevil Cosmopolites sordidus Germar (Coleoptera, Curculionidae) by ants. 3 Using stable isotope analyses, we showed that S. geminata used the new resource pathway provided by the addition of a cover crop. This change was revealed by increased d13C values (13C/12C) in a cover crop treatment (C4 plant) compared with a banana (C3 plant) in bare soil treatment. 4 We also showed that the abundance of S. geminata, as measured with pitfall traps, was 4.85.4-fold higher in the cover crop treatment than in the bare soil treatment. Estimation of egg predation rates was in the range 7.870.3%, which occurred in plots with the lowest and highest S. geminata numbers, respectively. 5 The addition of a new primary resource in this system changed the origin of the carbon consumed by predators and increased their densities. The increased ant abundance resulted in increased predation of weevil eggs, which was consistent with our hypothesis. These results will be useful for the design of cropping systems that enhance the biological regulation of pests.