Lawrence C. Wright

Effect of secondary plant substances on winter wheat resistance to grain aphid

The association between the concentrations of hydroxamic acids, total phenols, and indole alkoloids in winter wheal cultivars with their antibiotic resistance to the grain aphid Sitobion avenae (F.) (Homoptera: Aphididae) was studied. The antibiosis was measured under field conditions using the intrinsic rate of natural increase (rm). The content of the studied allelochemicals was estimated in flag leaf at the anthesis growth stage. Highly significant negative correlations were found between the rm values and the concentrations of hydroxamic acids (r = –0.905) and total phenols (r = –0.946), but not with indole alkaloids (r = –0.380). The contribution of these allelochemicals to the resistance of winter wheat to S. avenae is discussed.

Mite abundance and phenology on commercial and escaped hops in Washington State, USA

Abstract The abundance and phenology of two-spotted spider mite (Tetranychus urticae) and its phytoseiid and nonphytoseiid predators, were monitored monthly on commercial (pesticide-treated) and escaped (pesticide-free) hops in the Yakima Valley, Washington over two seasons. Mean abundance of T. urticae for both seasons was generally low (2.8-27.7 mites/leaf) and did not differ significantly between commercial and escaped hop sites, despite application of up to four miticides at commercial sites. Miticide control of T. urticae failed at three hop yards in 1999 producing substantial populations (300/leaf) in August. Six phytoseiid species (Galendromus occidentalis, Neoseiulus fallacis, Typhlodromus pyri, Amblyseius andersoni, Typhlodromus caudiglans, Proprioseiopsis lindquisti), were identified with G. occidentalis and N. fallacis accounting for > 95% of phytoseiids sampled. Mean abundance of phytoseiids for both seasons did not differ significantly between commercial and escaped hops. Six nonphytoseiid predators of T. urticae were recorded with the mite-eating ladybird, Stethorus picipes, most abundant. The incidence of nonphytoseiid predators was more than three times greater in escaped than in commercial hops. The possible importance and utilization of an assemblage of natural enemies containing phytoseiid and nonphytoseiid predators for biological control of T. urticae populations in Washington hops, is discussed.

Effects of Powdery Mildew Fungicide Programs on Twospotted Spider Mite (Acari: Tetranychidae), Hop Aphid (Hemiptera: Aphididae), and Their Natural Enemies in Hop Yards

ABSTRACT Twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), and hop aphid, Phorodon humuli (Schrank) (Hemiptera: Aphididae), are the most important arthropod pests of hop (Humulus lupulus L.) in the Northern Hemisphere. A potential barrier for greater adoption of conservation biological control strategies for spider mites and hop aphid is the extensive use of fungicides for management of hop powdery mildew, Podosphaera macularis (Wallr.:Fr.) U. Braun & S. Takamatsu. Field studies conducted in experimental plots in Oregon and Washington in 2005 and 2006 quantified the effects of powdery mildew fungicide programs (i.e., sulfur, paraffinic oil, and synthetic fungicides) on arthropod pests and natural enemies on hop. Fungicide treatment signifi-cantly affected spider mite populations in all four studies. Multiple applications of sulfur fungicides applied before burr development resulted in 1.4-3.3-fold greater spider mite populations during summer. Near the cessation of the sulfur applications, or after a lag of 20–30 d, spider mite populations increased significantly faster on sulfur treated plants compared with water-treated plants in three of four experiments. The effect of paraffinic oil on spider mites was varied, leading to exacerbation of spider mites in Oregon and Washington in 2005, suppression of mites in Oregon in 2006, and no significant effect compared with water in Washington in 2006. Significant relative treatment effects for cone damage due to spider mite feeding were detected in Oregon in 2005 in plots treated with sulfur and paraffinic oil compared with water and synthetic fungicides. Mean populations of hop aphids were similar among treatments in Oregon, although sulfur treatment suppressed hop aphid populations in Washington in 2005 and 2006. Populations of individual predacious insect species and cumulative abundance of macropredators were not consistently suppressed or stimulated by treatments in all trials. However, predatory mite abundance in Washington was affected by fungicide treatments, with plots treated with sulfur consistently having 10-fold fewer phytoseiids per leaf compared with the other treatments. Based on the results of these studies, powdery mildew fungicide programs that minimize or eliminate applications of sulfur and paraffinic oil would tend to conserve predatory mites and minimize the severity of spider mite outbreaks. However, mechanisms other than direct or indirect toxicity to phytoseiid mites likely are associated with exacerbation of spider mite outbreaks on hop.

Identity, Abundance, and Phenology of Anagrus spp. (Hymenoptera: Mymaridae) and Leafhoppers (Homoptera: Cicadellidae) Associated with Grape, Blackberry, and Wild Rose in Washington State

Abstract In 2001 and 2002, we monitored densities of western grape leafhopper, Erythroneura elegantula Osborn, and Virginia creeper leafhopper, Erythroneura ziczac Walsh (Homoptera: Cicadellidae), eggs from June through September in managed and nonmanaged vineyards in Washington state. Anagrus parasitoids (Hymenoptera: Mymaridae) were reared from sampled parasitized leafhopper eggs. Densities of nonparasitized and parasitized E. elegantula eggs, and nonparasitized E. ziczac eggs, were significantly higher in nonmanaged grapevines, although this pattern was not consistent for the latter two groups. Densities of parasitized E. ziczac eggs were consistently low across management regimes. Anagrus erythroneurae S. Trjapitzin & Chiappini, Anagrus daanei S. Triapitsyn, and Anagrus tretiakovae S. Triapitsyn emerged from parasitized E. elegantula eggs, whereas latter two mymarid species also parasitized E. ziczac eggs. Of these species, A. tretiakovae was the most common parasitoid of Erythroneura leafhopper eggs within sampled vineyards. From 2001–2003, we used yellow sticky traps to collect Anagrus wasps and potential leafhopper hosts from blackberry, grape, and wild rose sites, because these habitats might serve as refugia for the wasps. All three Anagrus species collected within vineyards and a fourth species, A. atomus L., were found on traps in these plant habitats. Several leafhopper taxa that could serve as potential alternative hosts for Anagrus spp. also were collected. Our collection of A. daanei, A. tretiakovae, and A. atomus in Washington represents range extensions for these species, revealing several novel candidate species for conservation. Because we consistently found Anagrus species of agricultural importance within rose and blackberry patches, cultivation of these plants close to vineyards may enhance colonization by Anagrus and thus improve grape leafhopper biocontrol.

Effects of generalist phytoseiid mites and grapevine canopy structure on spider mite (Acari: Tetranychidae) biocontrol

Abstract Specialist-feeding phytoseiid mites have a well-documented role in biological control of phytophagous spider mites. However, although there is evidence for the importance of generalist-feeding phytoseiid mites in spider mite suppression, their role is less clear than that of specialists. The effectiveness of generalists as biocontrol agents and their interactions with specialists might be directly influenced by canopy structure or indirectly affected by altering plant microclimate. We manipulated densities of generalist phytoseiid mites and canopy size (large and small) in open-field experiments in an abandoned vineyard. In the first experiment, we increased generalist densities by transferring grapevine foliage housing robust generalist populations, whereas in the second experiment, we lowered generalist densities using the broad-spectrum insecticide chlorpyrifos. In both experiments, we also altered canopy size by tying grapevine shoots. Increasing densities of generalists resulted in lower spider mite densities. Generalists initially decreased densities of specialist phytoseiid mites as well, although specialist densities rebounded as spider mite densities increased later in the experiment. Lowering generalist densities appeared to slightly increase densities of both spider and specialist mites, consistent with the first experiment. However, these effects were not statistically significant, possibly because the reduction in generalist densities through chlorpyrifos application was not as dramatic as our generalist augmentation in the first experiment. Canopy size did not significantly affect pest or predatory mite densities in either experiment. These field experiments demonstrate that generalists can slow spider mite population growth in grapes. In contrast, canopy architecture appeared to have little impact on spider mite biocontrol.

Pheromone Trapping of Synanthedon tipuliformis (Lepidoptera: Sesiidae) in Washington Red Currants

Abstract Collections of volatiles, ovipositor extracts, and electoantennography showed the sex pheromone of female currant borer moths, Synanthedon tipuliformis (Clerck), from Washington to be a 2-component (100:3) blend of (E,Z) -2, 13-octadecadienyl acetate and (E,Z) -3, 13-octadecadienyl acetate. Pheromone-baited sticky traps (rubber septa dispensers) captured male S. tipuliformis at one abandoned and two commercial red currant sites (one treated with insecticide, one untreated) in south central Washington from 19 May to 16 August 2000. Peak catches occurred during late May and June with up to 200–300 moths/trap/wk. Lowest numbers (overall mean: 4.8 ± 0.9 moths/trap/visit) were recorded at the insecticide-treated site and largest numbers (39.6 ± 5.5 moths/trap/visit) occurred at the untreated, commercial site.

Mixture of Synthetic Herbivore-induced Plant Volatiles Attracts More Stethorus punctum picipes (Casey) (Coleoptera: Coccinellidae) than a Single Volatile

We compared the attractiveness of a mixture of cis-3-hexen-1-ol, cis-3-hexenyl acetate, and methyl salicylate (MeSA), and of each of these compounds singly, to a predacious ladybird beetle, Stethorus punctum picipes (Casey), to make it clear whether mixture of several volatiles may attract more natural enemies at different spatial scales. In an olfactometer experiment, S. p. picipes females were attracted to the volatile mixture, but not to single volatiles. Male S. p. picipes were not attracted to the mixture. In a small-scale open-field test using sticky cards, S. p. picipes were attracted to the volatile mixture and to MeSA alone. In a vineyard trapping test, significantly more S. p. picipes were trapped on sticky cards baited with a mixture of volatiles than on single-volatile-baited cards.

Population Density and Phenology of Tetranychus urticae (Acari: Tetranychidae) in Hop is Linked to the Timing of Sulfur Applications

ABSTRACT The twospotted spider mite, Tetranychus urticae Koch, is a worldwide pest of numerous agronomic and horticultural plants. Sulfur fungicides are known to induce outbreaks of this pest on several crops, although mechanisms associated with sulfur-induced mite outbreaks are largely unknown. Studies were conducted during 2007–2009 in Oregon and Washington hop yards to evaluate the effect of timing of sulfur applications on T. urticae and key predators. In both regions, applications of sulfur made relatively late in the growing season (mid-June to mid-July) were associated with the greatest exacerbation of spider mite outbreaks, particularly in the upper canopy of the crop. The severity of mite outbreaks was closely associated with sulfur applications made during a relatively narrow time period coincident with the early exponential phase of spider mite increase and rapid host growth. A nonlinear model relating mean cumulative mite days during the time of sulfur sprays to the percent increase in total cumulative mite days (standardized to a nontreated plot) explained 58% of the variability observed in increased spider mite severity related to sulfur spray timing. Spatial patterns of spider mites in the Oregon plots indicated similar dispersal of motile stages of spider mites among leaves treated with sulfur versus nontreated leaves; however, in two of three years, eggs were less aggregated on leaves of sulfur-treated plants, pointing to enhanced dispersal. Apart from one experiment in Washington, relatively few predatory mites were observed during the course of these studies, and sulfur-induced mite outbreaks generally occurred irrespective of predatory mite abundance. Collectively, these studies indicate sulfur induces mite outbreaks through direct or indirect effects on T. urticae, mostly independent of predatory mite abundance or toxicity to these predators. Avoidance of exacerbation of spider mite outbreaks by sulfur sprays was achieved by carefully timing applications to periods of low spider mite abundance and slower host development, which is generally early to mid-spring for hop.

Trapping hop looper moths, Hypena humuli Harris (Lepidoptera: Erebidae), in hop yards with acetic acid and 3-methyl-1-butanol

Hop looper moths, Hypena humuli Harris, in commercial hop yards (Humulus lupulus L.) were captured in traps baited with a combination of acetic acid plus 3-methyl-1-butanol (AAMB). The two chemicals were synergistic in attracting hop looper moths. In a comparison of the lure chemicals, most moths were trapped with AAMB as the lure, while very few moths were captured in traps baited with acetic acid alone or 3-methyl-1-butanol alone. Female and male hop looper moths were trapped with AAMB, with an overall sex ratio through the year of 44% females to 56% males. Moths were trapped in all months of the growing season, from April into October. From April through September, most females captured in traps were mated, whereas in October most females trapped had been unmated. Most of the mated females, we trapped contained one spermatophore, indicating a single mating. The numbers of moths trapped were low from April through June, and increased greatly in July, and at one site again in late August. AAMB-baited traps may be a useful tool for monitoring hop looper moths in commercial hop yards, to determine their presence, and potentially to assess the risk of damaging infestations.

Identification of prey consumed by Stethorus punctum picipes (Casey) (Cleoptera: Coccinellidae) in tree fruit and vines in Washington State, USA

ABSTRACT To determine the type of prey consumed by the predatory coccinellid, Stethorus punctum picipes (Coleoptera: Coccinellidae), we identified food remains, based on body parts or whole bodies of mites, in the guts of adults collected in two fruit orchards (apple and cherry) and one vineyard in Washington State, United States in August and September 2009. Various plant-inhabiting mites, including species in the families Stigmaeidae, Eriophyidae, Phytoseiidae, and Tetranychidae, were found in guts of S. p. picipes collected on grapevine where no tetranychids were observed. On apple, where tetranychids were abundant, gut contents contained Tetranychidae, Stigmaeidae, and Eriophyidae. On cherry, where tetranychids were abundant, only Tetranychidae were found in gut contents. These results indicate that S. p. picipes adults can feed on alternative plant-inhabiting mites, in particular, when tetranychids are scarce.