Spillover of crop herbivores into adjacent desert habitats

Spillovers of crop herbivores from cultivated areas are likely to have important effects on the structure and function of food webs in adjacent natural areas. In the Arava agroecosystem in the south of Israel, preliminary studies suggested that crop herbivore species disperse into nearby desert areas. The objective of the present study was to investigate the occurrence and timing of crop herbivore spillovers in this hyper-arid agroecosystem and the potential for survival and reproduction of these herbivores in the desert environment. In this region, the arable lands constitute productive islands embedded in an extreme desert matrix. We studied the dispersal of the sweetpotato whitefly, Bemisia tabaci (Gennandius) (Hemiptera, Aleyrodidae), and the western flower thrips, Frankliniella occidentalis Pergande (Thysanoptera, Thripidae), into surrounding desert habitat. Using sticky traps, we recorded the timing of their dispersal with respect to the cropping season and their presence at increasing distances from cultivated areas. Then we investigated the ability of these two crop herbivore species to establish themselves on selected desert plants by testing their survival and reproduction on these plants. We caged plants in situ, seeding them with adult herbivores, and recorded numbers of young and second generation adults. We found that both species disperse into desert areas to considerable distances from the crops, but whiteflies do this mainly in a short, single-pulse spillover event, while thrips disperse in small numbers over the crop season. Both species were shown to survive and reproduce on some desert plant species within this habitat. These results suggest that both crop herbivore species could affect the desert food web and that desert plants may serve as a refuge for them to survive the harsh summer and a source from which to re-colonize the crops in the next season.