New primary resource increases predation on a pest in a banana agroecosystem

Abstract

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 ?13C 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 4.8-5.4-fold higher in the cover crop treatment than in the bare soil treatment. Estimation of egg predation rates was in the range 7.8-70.3%, 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. (Résumé d'auteur

Response of pest control by generalist predators to local‐scale plant diversity: a meta‐analysis

“…An increase in plant diversity can contribute to an increase in the abundance of predators by providing a broader range and greater abundance of prey (Mollot et al. ), of nectar sources, and of suitable microclimates (Landis et al. ).…”

“…), and banana plantations (Mollot et al. ). In the case of herbaceous annual crops, most options involve the integration field margins and the management of hedgerows (Marshall and Moonen ; Gaba et al.…”

“…Increases in plant diversity usually cause increases in plant biomass and in habitat diversity, both of which can benefit predators (Hector et al 1999;Marshall and Moonen 2002). An increase in plant diversity can contribute to an increase in the abundance of predators by providing a broader range and greater abundance of prey (Mollot et al 2012), of nectar sources, and of suitable microclimates (Landis et al 2005). Interestingly, there was a contrasted effect of plant diversity on herbivore diversity (positive) and herbivore abundance (neutral).…”

Field evaluation of sweet corn varieties for their potential as a trap crop forHelicoverpa zeaunder tropical conditions

“…Symondson et al (2002) reported that ants are predators of Lepidoptera, and Pfannenstiel (2005) observed ants feeding on H. zea eggs. We also expected to find Solenopsis geminata (Fabricius) in our sweet corn plots since our study site was the same as that used for a study by Mollot et al (2012) on the banana weevil, in which S. geminata was abundant, and the species is commonly found on corn (Litsinger et al 2007). Holway et al (2002) reported that S. geminata is a predator of Lepidoptera and so we expected it to be a predator of H. zea in the sweet corn plots.…”

Tracing dietary origins of aphids and the predatory beetle Propylea japonica in agricultural systems using stable isotope analyses

“…Stable isotope signa-tures can be used directly using natural differences in the isotopic abundances in the landscape, or in enrichment studies, where isotope-labeled supplements are added to the system. Natural abundance studies use naturally occurring differences in isotopic signatures to follow flows and processes (Hood-Nowotny & Knols, 2007;Girard et al, 2011;Mollot et al, 2012). For example, prey origins and colonization behavior of the lady beetle Hippodamia convergens (Gu erin-M eneville) in agricultural systems were examined by analysis of carbon stable isotope values (Prasifka et al, 2004).…”