Aerial dispersal ability does not drive spider success in a crop landscape

Authors: Hogg, Brian; DAANE, KENT - University Of California

Submitted to: Ecological Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/23/2018
Publication Date: 9/3/2018
Citation: Hogg, B.N., Daane, K.M. 2018. Aerial dispersal ability does not drive spider success in a crop landscape. Ecological Entomology. 43:683-694.

Interpretive Summary: Crop fields are often hostile environments for natural enemies of pests. Many natural enemies are unable to survive in crops on a long-term basis, and must recolonize crop fields during the growing season from remaining patches of natural habitat. Thus, only good dispersers may reach crop fields in high numbers. Spiders can help control a wide range of pests, and can disperse into crop fields by floating on wind currents using strands of silk, a behavior known as “ballooning”. Spiders that build webs to capture prey tend to be the most prolific ballooners. We monitored ballooning spiders in California vineyards and surrounding woodland, to identify spiders that were ballooning in these habitats, and to examine whether the best ballooners were also the most successful in vineyards. As expected, most ballooners in both habitats were web-building spiders, although hunting spiders (active hunters that do not build webs) also ballooned frequently. Ballooning spiders in woodland appeared to live in this habitat, while most of the ballooning spiders in vineyard failed to establish in high numbers. Although most ballooning spiders were small web-builders, most of the spiders in vineyard were large hunting spiders that may not balloon long distances. Web-building spiders ballooned on bright sunny days, whereas hunting spiders ballooned when temperatures were high. This study shows that spiders that establish in crop fields are not always the best dispersers, and that adaptability or competitive ability may be more important.

Technical Abstract: Although spiders can colonize crop fields by ballooning, dispersal capabilities are likely to differ between spider species. Web-building spiders typically balloon at higher rates than hunting spiders. Most studies of spider ballooning have focused on open habitats where meteorological conditions may favor ballooning, and few have documented the aerial spider faunas of both crop fields and putative source habitats. We monitored spiders in the air and in the foliage of California vineyards and adjacent oak woodland, to compare ballooning spider faunas between these disparate habitats, and to determine whether highly dispersive species contributed disproportionately to the spider community in vineyards. Results show that the majority of ballooners in both habitats were web-building dwarf spiders, Erigone spp. (Linyphiidae), although hunting spiders were also well represented in the air, especially in oak woodland. Most ballooning woodland spiders appeared to be residents of oak woodland. Conversely, only a subset of the aerial spider fauna appeared to establish in vineyard in high numbers. Most of the spiders that dominated the aerial fauna were underrepresented in vineyard foliage, whereas several hunting spiders ballooned at low rates but dominated vineyard spider composition. The same meteorological variables appeared to trigger ballooning in both habitats; insolation and maximum daily temperature were correlated with numbers of web-building and hunting spiders, respectively. Results suggest that aerial dispersal ability may allow spiders to reach vineyards, but that establishment depends on habitat preferences and/or competitive ability.