Tree spatial structure, host composition and resource availability influence mirid density or black pod prevalence in cacao agroforests in Cameroon

PLoS One. 2014 Oct 14;9(10):e109405. doi: 10.1371/journal.pone.0109405. eCollection 2014.

Abstract

Combining crop plants with other plant species in agro-ecosystems is one way to enhance ecological pest and disease regulation mechanisms. Resource availability and microclimatic variation mechanisms affect processes related to pest and pathogen life cycles. These mechanisms are supported both by empirical research and by epidemiological models, yet their relative importance in a real complex agro-ecosystem is still not known. Our aim was thus to assess the independent effects and the relative importance of different variables related to resource availability and microclimatic variation that explain pest and disease occurrence at the plot scale in real complex agro-ecosystems. The study was conducted in cacao (Theobroma cacao) agroforests in Cameroon, where cocoa production is mainly impacted by the mirid bug, Sahlbergella singularis, and black pod disease, caused by Phytophthora megakarya. Vegetation composition and spatial structure, resource availability and pest and disease occurrence were characterized in 20 real agroforest plots. Hierarchical partitioning was used to identify the causal variables that explain mirid density and black pod prevalence. The results of this study show that cacao agroforests can be differentiated on the basis of vegetation composition and spatial structure. This original approach revealed that mirid density decreased when a minimum number of randomly distributed forest trees were present compared with the aggregated distribution of forest trees, or when forest tree density was low. Moreover, a decrease in mirid density was also related to decreased availability of sensitive tissue, independently of the effect of forest tree structure. Contrary to expectations, black pod prevalence decreased with increasing cacao tree abundance. By revealing the effects of vegetation composition and spatial structure on mirids and black pod, this study opens new perspectives for the joint agro-ecological management of cacao pests and diseases at the plot scale, through the optimization of the spatial structure and composition of the vegetation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cacao* / growth & development
  • Cacao* / microbiology
  • Cacao* / parasitology
  • Cameroon
  • Crops, Agricultural
  • Heteroptera / physiology*
  • Host-Pathogen Interactions / physiology*
  • Models, Statistical
  • Phytophthora / physiology*
  • Plant Diseases / microbiology
  • Plant Diseases / parasitology
  • Population Density
  • Population Dynamics
  • Principal Component Analysis

Grants and funding

The authors thank the West African Scientific Partnership Platform on diversity of production systems and agroecological management of pests and diseases of the French Agricultural Research Centre for International Development (CIRAD) and the research project "Search for trade-offs between production and other ecosystem services provided by tropical agroforestry systems" (SAFSE) for funding. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.