Beyond polyphagy and opportunism: natural prey of hunting spiders in the canopy of apple trees

Abstract

Spiders (Araneae) form abundant and diverse assemblages in agroecosystems such as fruit orchards, and thus might have an important role as natural enemies of orchard pests. Although spiders are polyphagous and opportunistic predators in general, limited information exists on their natural prey at both species and community levels. Thus, the aim of this study was to assess the natural prey (realized trophic niche) of arboreal hunting spiders, their role in trophic webs and their biological control potential with direct observation of predation events in apple orchards. Hunting spiders with prey in their chelicerae were collected in the canopy of apple trees in organic apple orchards in Hungary during the growing seasons between 2013 and 2019 and both spiders and their prey were identified and measured. Among others, the composition of the actual (captured by spiders) and the potential (available in the canopy) prey was compared, trophic niche and food web metrics were calculated, and some morphological, dimensional data of the spider-prey pairs were analyzed. Species-specific differences in prey composition or pest control ability were also discussed. By analyzing a total of 878 prey items captured by spiders, we concluded that arboreal hunting spiders forage selectively and consume a large number of apple pests; however, spiders’ beneficial effects are greatly reduced by their high levels of intraguild predation and by a propensity to switch from pests to alternative prey. In this study, arboreal hunting spiders showed negative selectivity for pests, no selectivity for natural enemies and positive selectivity for neutral species. In the trophic web, the dominant hunting spider taxa/groups (Carrhotus xanthogramma, Philodromus cespitum, Clubiona spp., Ebrechtella tricuspidata, Xysticus spp. and ‘Other salticids’) exhibit different levels of predation on different prey groups and the trophic web’s structure changes depending on the time of year. Hunting spiders show a high functional redundancy in their predation, but contrary to their polyphagous nature, the examined spider taxa showed differences in their natural diet, exhibited a certain degree of prey specialization and selected prey by size and taxonomic identity. Guilds (such as stalkers, ambushers and foliage runners) did not consistently predict either prey composition or predation selectivity of arboreal hunting spider species. From the economic standpoint, Ph. cespitum and Clubiona spp. were found to be the most effective natural enemies of apple pests, especially of aphids. Finally, the trophic niche width of C. xanthogramma and Ph. cespitum increased during ontogeny, resulting in a shift in their predation. These results demonstrate how specific generalist predators can differ from each other in aspects of their predation ecology even within a relatively narrow taxonomic group.

High Survivorship of First-Generation Monarch Butterfly Eggs to Third Instar Associated with a Diverse Arthropod Community

“…Among polyphagous arthropod predators, diet breadth is often determined by hunting method, encounter rates, infochemical cues, and size [ 70 ]. For highly polyphagous predators, the inclusion of a prey item in the diet can be strongly associated with encounter rate [ 70 , 71 , 72 , 73 ]. When compared to many of the other potential prey items on the host plants, monarch eggs and monarch larvae up to the third instar are small and solitary.…”

The benefits of intraguild predation for a top predator spider

“…We selected only spider species that reach the desirable size and that co‐occur with philodromids in various fruit orchards (Michalko & Pekár, 2015; Michalko et al ., 2017; Mezöfi et al . 2020) and forest plantations (Michalko unpubl. data).…”

“…As measuring each prey individual would have been too labour-intensive, we assessed the size similarity visually. We selected only spider species that reach the desirable size and that co-occur with philodromids in various fruit orchards (Michalko & Pekár, 2015;Mezöfi et al 2020) and forest plantations (Michalko unpubl. data).…”

“…Philodromids are highly abundant in orchards where they reduce hemipteran pests like aphids (Lefebvre et al, 2017) and psyllids even though hemipterans are considered to be low-quality food for generalist predators (Toft, 2005). Philodromids prefer dipterans and hemipterans but other spiders represent a substantial portion of their natural diet too (Michalko & Pekár, 2015;Mezöfi et al 2020).…”

“…Philodromids prefer dipterans and hemipterans but other spiders represent a substantial portion of their natural diet too (Michalko & Pekár, 2015; Mezöfi et al . 2020).…”