Quantitative relationship between potato tuber damage and counts of Pacific coast wireworm (Coleoptera: Elateridae) in baits: seasonal effects

Experimental plots of potatoes were baited with rolled oats in spring to assess the relationship between counts of Pacific coast wireworm, Limonius canus (Coleoptera: Elateridae), and end-of-the-season damage to potato tubers. Baiting was done at seven intervals beginning before planting of potatoes and ending following plant emergence. Injury (percentage of tubers damaged or number of holes per tuber) showed a curvilinear relationship with increasing wireworm counts in baits. Damage increased rapidly with increasing wireworrn numbers at lower densities, eventually flattening out at very high counts. Wireworm counts in baits fluctuated seasonally, increasing from lows obtained during pre-planting samples to a peak just before plant emergence, followed thereafter by declines in counts. Thus, baiting efficiency varied seasonally. Low counts in baits during the pre-planting interval may have been due primarily to low soil temperatures, while declining counts following plant emergence may have been due to the presence of competing food sources (i.e., the seed piece and developing potato plant). I also assessed depth of wireworms in the soil profile between late-March and mid-May, and found that a relatively large percentage (approaching 25% on two dates) of wireworms occurred very deep in the soil (61-91 cm) until soil temperatures at 31 cm approached 17 °C in early- to mid-May. Thus, low counts in baits during the pre-planting samples may also have occurred in part because a proportion of the population was deep in the soil during this time interval. Seasonal variation in baiting efficiency led to date-to-date differences in predicted damage for a given wireworm count. Low efficiency during the preplanting interval would complicate efforts to use pre-planting baiting as a means to predict end-of-the-season tuber damage

Phenology of emergence from artificial overwintering shelters by some predatory arthropods common in pear orchards of the Pacific Northwest

The phenology of emergence from artificial overwintering shelters that had been placed in pear orchards located near Yakima, Washington, was determined for the green lacewing Chrysopa nigricornis Burmeister, the predatory mirid Deraeocoris brevis (Uhler), and the brown lacewing Hemerobius ovalis Carpenter. Cumulative emergence from shelters was determined in 2001 and 2002 on both a calendar-date and degree-day basis. Similar data for a major pear pest, pear psylla, Cacopsylla pyricola (Förster), were also collected for these same shelters. Pear psylla and H. ovalis emerged earliest, both taxa completing emergence by early March (120 degree-days accumulated from early January). Deraeocoris brevis emerged beginning in late February and finished emergence by early April (150 degree-days for 90% emergence). Chrysopa nigricornis emerged considerably later than the other species, and completed emergence by late May or early June. Calendar-date emergence is also shown for spiders (Araneae) and Anthocoridae (Heteroptera), which occurred at lower numbers in the shelters. The anthocorids, Orius tristicolor White and three species of Anthocoris, emerged from shelters in February and March, while spiders emerged over a long interval between March and May

Occurrence of the Western Flower Thrips, Frankliniella occidentalis, and potential predators on host plants in near-orchard habitats of Washington and Oregon (Thysanoptera: Thripidae)

One hundred thirty species of native and introduced plants growing in uncultivated land adjacent to apple and pear orchards of central Washington and northern Oregon were sampled for the presence of the western flower thrips (WFT) Frankliniella occidentalis (Pergande, 1895) and potential thrips predators. Plants were sampled primarily while in flower. Flowering hosts for WFT were available from late-March to late-October. Adult WFT occurred on 119 plant species and presumed WFT larvae were present on 108 of 119 species. Maximum observed WFT density on several plant species exceeded 100 individuals (adults and larvae) per gram dry weight of plant material. The most abundant predator was Orius tristicolor (White, 1879) (Heteroptera: Anthocoridae). It was collected on 64 plant species, all of which were hosts for WFT. The second most abundant predators were spiders (Araneae). Small spider immatures (first and second instars) of several species were common on certain host plants, and are likely to feed on WFT

Numbers and types of arthropods overwintering on common mullein, Verbascum thapsus L. (Scrophulariaceae), in a central Washington fruit-growing region

Densities and types of arthropods overwintering on common mullein, Verbascum thapsus L., in a fruit-growing region of Central Washington were determined. Over 45,000 arthropods were collected from 55 plants (5 plants from each of 11 sites), dominated numerically by Acari and Thysanoptera. Insects representing 8 orders and 29 families were identified, distributed both in the basal leaf rosettes and in the stalk material of the plants. One specialist insect herbivore of mullein, the mullein thrips, Haplothrips verbasci (Osborn), was abundant at all sites. Several pest and predatory taxa that commonly occur in orchards were also collected, suggesting that mullein may be a source of overwintered pests or predators moving into orchards in early spring. Pest taxa included primarily western flower thrips (Frankliniella occidentalis (Pergande)), Lygus spp., and tetranychid spider mites. Common predators included phytoseiid mites and minute pirate bugs (Orius tristicolor (White)). Sites that were geographically close to one another were not more similar (in taxonomic composition of overwintering arthropods) than more distantly separated sites

Spatial patterns of western flower thrips (Thysanoptera: Thripidae) in apple orchards and associated fruit damage

Western flower thrips, Frankliniella occidentalis (Pergande), is an economic pest of apples in orchards of North America. Western flower thrips causes damage (“pansy spot”) to apples by its egglaying activities during the bloom and immediate post—bloom periods. Difficulties in monitoring this pest and incomplete understanding of its biology during the bloom period have complicated control efforts in apple orchards. Densities of western flower thrips were monitored in seven (2003) or eight (2004) apple orchards at each of four bloom stages; in each orchard, thrips counts in blossom clusters were estimated at four to six distances into the orchard from an orchard edge that abutted native sagebrush-steppe habitat. We hypothesized that numbers of thrips in blossoms would decline with increasing distance along transects into orchards if the native habitat acted as a source of thrips. Thrips numbers in blossom clusters peaked at full bloom and petal fall. Densities showed a linear drop with increasing distance into the orchard, which we interpreted as evidence that the native habitat adjacent to each orchard did indeed act as a source of thrips moving into the orchards. Pansy spot incidence declined with increasing distance into the orchard. The major drop in damage occurred between the border row trees and samples taken at the adjacent distance (nine m away), suggesting that border rows adjacent to native habitats should be monitored with particular care. Regression analyses showed that damage and thrips density were positively correlated, albeit with substantial levels of unexplained variation in levels of damage