Temporal patterns in the abundance and species composition of spiders on host plants of the invasive moth Epiphyas postvittana

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

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/3/2017
Publication Date: 3/30/2017
Citation: Hogg, B.N., Mills, N.J., Daane, K.M. 2017. Temporal patterns in the abundance and species composition of spiders on host plants of the invasive moth Epiphyas postvittana. Environmental Entomology. doi: 10.1093/ee/nvx065.

Interpretive Summary: The invasive light brown apple moth, Epiphyas postvittana, recently arrived in California, where it poses a threat to agriculture. The moth attacks an extremely wide range of plant species, including many crop plants. It has yet to reach outbreak levels in California, however, and may be suppressed by predators and parasitic wasps that were present in California before its arrival. Predators such as spiders may play a crucial part in keeping newly introduced herbivores in check. Spiders can feed on a wide range of prey, and their indiscriminant feeding habits and long life spans may allow them to persist when numbers of pests are low, and to prevent pest populations from increasing to outbreak levels. We examined whether spiders are likely to suppress populations of the light brown apple moth in two plants that are commonly attacked by the moth, Australian tea tree, Leptospermum laevigatum, and the weed French broom, Genista monspessulana. Spiders were present throughout the year, during periods of high and low moth abundance. The most abundant spiders at most sites were wandering spiders, which search actively for prey without using a web, and are likely to be particularly effective predators of the relatively immobile moth larvae. Adult wandering spiders were rare at all times of the year, however, and these are likely to consume the most larvae. Nevertheless, the high year-round numbers of spiders suggest that they are likely to play a crucial role in mitigating the impacts of the light brown apple moth in California.

Technical Abstract: Generalist predators such as spiders may help mitigate the spread and impact of exotic herbivores. The lack of prey specificity and long generation times of spiders may allow them to persist when pests are scarce, and to limit the growth of pest populations before they reach damaging levels. We examined whether resident spiders are likely to play a role in maintaining populations of the recently introduced light brown apple moth, Epiphyas postvittana (Walker) (Lepidoptera: Tortricidae), below outbreak levels in California. We surveyed the spider community on two E. postvittana host plants, the ornamental Australian tea tree, Leptospermum laevigatum, and the weed French broom, Genista monspessulana, to characterize spider abundance and species composition throughout the year in relation to changes in densities of E. postvittana larvae. Spider densities and species composition showed slight seasonal changes. Spiders were present during periods of high and low E. postvittana abundance. Anyphaenid hunting spiders, Anyphaena aperta Banks in Australian tea tree and Anyphaena pacifica Banks in French broom, dominated spider species composition at four of five sampled sites, and showed only slight seasonal variation in abundance. Adult A. aperta were rare at all times of the year, suggesting that high mortality among juvenile A. aperta limits the potential of this species as a predator of E. postvittana. Nevertheless, high year-round densities of spiders suggest that the resident spider community is likely to play a key role in reducing E. postvittana populations in California.