Author
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Miliczky, Eugene |
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Calkins, Carrol |
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Submitted to: The Pan-Pacific Entomologist
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 9/6/2000 Publication Date: 1/15/2001 Citation: Miliczky, E.R., Calkins, C.O. 2001. Prey of the spider, Dictyna coloradensis, on apple, pear, and weeds in central Washington (Araneae: Dictynidae). Pan-Pacific Entomologist. 77:19-27. Interpretive Summary: Future insect pest control in orchards will rely more heavily on natural enemies of pests and less on insecticides, which pose hazards to human health and the environment. Spiders are abundant in most terrestrial habitats and all are predators, feeding primarily on insects. However, we know relatively little about the feeding habits of spiders in orchards. Dictyna coloradensis is a small (1/6") spider that was very abundant in several apple and pear orchards in south central Washington that were not treated with insecticides. Spiders built webs on the upper surface of leaves and captured a wide variety of insects. Prey from 984 webs (18,311 total prey) included at least 58 different kinds of insects. Most were smaller than the spider and weak flyers. Large numbers of pest insects (33% of all prey), such as aphids, leafhoppers, and thrips were captured. Insects considered beneficial to man comprised 24% of all prey. Some of these were known parasites of orchard pests. Thus the spider's contribution to orchard ecology includes a negative component. However, consumption of some beneficial insects and insects that have little impact on the orchard (43% of all prey), such as gnats and midges, may help the spider survive times when other prey are in short supply. Technical Abstract: The cribellate spider, Dictyna coloradensis Chamberlin, constructed webs on the upper surface of apple and pear leaves (trees not treated with insecticide), and on weeds in adjacent, uncultivated ground, at a site in south central Washington. Prey items found in D. coloradensis webs were categorized as potential pests, potentially beneficial, or neutral with respect to their impact on fruit trees. Pest taxa comprised 32%, beneficials 24%, and neutral impact groups 44% of 18,311 identified prey. Most prey were small, winged insects (length less than 5 mm) and members of 58 families in 10 orders were represented. Small spiders were occasionally trapped and four families were represented. Sciaridae and Chironomidae (Diptera) were the most numerous prey and made up 37% of the total. Most webs had one or more of these flies and occasionally had 25 or more. Alate aphids were the most frequently captured pest insects. Other pests included thrips, leafhoppers, and pear psylla. Small, parasitic Hymenoptera were the most commonly trapped beneficial insects and at least 14 families were represented. Nineteen percent of all prey were parasitic wasps. The only other taxon of beneficial insects that comprised more than 1% of total prey items was the Empididae (3%). Relatively non-mobile insects such as white apple leafhopper nymphs, pear psylla nymphs, and apterous aphids were rarely found in the webs whereas the more mobile, winged adults were regularly trapped. |
