Diversity and phenology of predatory arthropods overwintering in cardboard bands placed in pear and apple orchards of Central Washington State

Abstract

Overwintering shelters composed of cardboard bands were placed on pear and apple trees located in central Washington state to monitor overwintering by predatory arthropods and by two pest taxa. A subset of bands was sampled at regular intervals between late summer and mid-December to determine when taxa began to enter bands. The remaining bands were left undisturbed until collection in mid-December to determine the numbers and types of arthropods overwintering on tree trunks in these orchards. More than 8,000 predatory arthropods were collected from bands left undisturbed until mid-December, dominated numerically by Acari (Phytoseiidae) [Galendromus occidentalis (Nesbitt), Typhlodromus spp.], Araneae, and Neuroptera (Hemerobiidae, Chrysopidae). Predatory mite numbers were higher in bands placed in apple orchards than bands placed in pear orchards. The Araneae were particularly diverse, including >3,000 spiders representing nine families. Less abundant were Heteroptera, including a mirid [Deraeocoris brevis (Uhler)] and three species of Anthocoridae [Anthocoris spp., Orius tristicolor (White)]. Coleoptera included Coccinellidae, dominated by Stethorus picipes Casey, and unidentified Staphylinidae and Carabidae. The bands that were collected at regular intervals to monitor phenology provided >15,000 predatory arthropods, dominated numerically by spiders, Dermaptera [Forficula auricularia (F.)], lacewings, and predatory mites. Some well-defined phenological patterns were apparent for some taxa. Brown lacewing adults (Hemerobius) began appearing in bands in late October, coinciding with leaf fall in orchards. Cocooned larvae of green lacewings (Chrysopa nigricornis Burmeister), conversely, were most abundant in bands in September, which was well before leaf fall. Predatory mites began to appear in bands in late September before onset of leaf fall. Patterns for predatory Heteroptera were less clear, but results showed that D. brevis and O. tristicolor were active in the orchards well into the period of leaf fall. Two pest taxa, spider mites (Tetranychus spp.) and pear psylla [Cacopsylla pyricola (Foerster)], were also monitored. Spider mites entered bands beginning in September and finished movement at the beginning of leaf fall, similar to patterns shown by Phytoseiidae. Pear psylla moved into bands very late in the season (November and December). Our results suggest that postharvest applications of chemicals, as made by some growers, would occur before most predatory taxa have entered overwintering quarters.