Spatial dynamic and spillover of the polyphagous pest Bemisia tabaci is influenced by differences in farmland habitats on tropical organic farms

The interplay between natural, non-cropped, and cropped habitats affects insect movement in the landscape. Polyphagous, highly mobile pests are more likely to cross habitat-edges and colonize crops. However, local differences within habitats can affect pest populations and modulate their broad response to the landscape. We investigated how different habitat types influence the spatiotemporal dynamics and spillover of a polyphagous pest on tropical organic vegetable farms. We simultaneously sampled the abundance of the worldwide pest Bemisia tabaci (Hemiptera: Aleyrodidae) on crops, fallow areas, agroforests, and forests fragments on five farms for two years. This whitefly species achieved higher population growth rates in open-field habitats (mostly crops), where resources are more easily found and concentrated. The lack of density dependence on population growth suggests that migration drives habitat occupancy. Crops were the main source of individuals to other habitat types, while agroforests and forest fragments (both sink and stepping-stones habitats) are most likely temporary habitats for whiteflies where they face a populational bottleneck. Regardless of habitat features, higher precipitation and low temperatures independently regulated population densities throughout seasons. Fragmented agricultural landscapes reduced bottom-up effects of forests and facilitated whitefly infestation on crops due to edge effects. In summary, the source-sink dynamics of whiteflies was largely determined by sink habitats that differ in local characteristics and management but was also influenced by landscape type. These findings indicate that the farmland habitat scale was adequate to integrate the scale-dependent processes operating on different spatial (local and landscape) and temporal (seasonality) scales on pest populations.