John E. Dunley

Effect of Pesticides on Colpoclypeus florus (Hymenoptera: Eulophidae) and Trichogramma platneri (Hymenoptera: Trichogrammatidae). Parasitoids of Leafrollers in Washington

Abstract Pesticides were evaluated for their effect on two parasitoid species, Colpoclypeus florus and Trichogramma platneri, that are potential biological control agents of leafrollers in apple orchards. Organophosphate and carbamate insecticides were highly toxic to both parasitoids in topical applications, but foliar residues of some products were nontoxic after 7 d. At reduced rates, topically applied pyrethroids were low in toxicity to C. florus were highly toxic to T. platneri, and foliar residues were nontoxic after about 7 d. Imidacloprid and abamectin were highly toxic when applied topically to both parasitoids but were not toxic as 1-d-old residues. Insect growth regulators did not cause mortality either as topical applications or residues; however, diflubenzuron caused severe sublethal effects, completely blocking the production of C. florus offspring. Biorational pesticides, such as soap, oil, and B. thuringiensis products, caused no toxicity to C. florus but had a direct impact on T. platneri as topical applications through physical immobilization. The potential to integrate different pesticides with biological control of leafrollers and the need for a step-wise approach to evaluate the impact of pesticides against natural enemies is discussed.

Lethal, Sublethal, and Behavioral Effects of Sulfur-Containing Products in Bioassays of Three Species of Orchard Mites

ABSTRACT The effects of three sulfur products (calcium polysulfide [ = lime sulfur], dry flowable sulfur, and ammonium thiosulfate, a plant nutrient), were tested in bioassays against a predatory mite, Galandromus occidentalis (Nesbitt), and two species of tetranychid (pest) mites, twospotted spider mite (Tetranychus urticae Koch) and European red mite [Panonychus ulmi (Koch)]. Calcium polysulfide and ammonium thiosulfate were acutely toxic on contact to adult females of all three mite species, causing 58–100% mortality in 48 h. Dry flowable sulfur, in contrast, was nontoxic to adults of all three species. Fresh residues of the sulfur products were essentially nontoxic to females of G. occidentalis and T. urticae. Galandromus occidentalis consumed 8.2 and 4.0× fewer prey contaminated with residues of calcium polysulfide and ammonium thiosulfate; dry flowable sulfur had no effect on prey consumption. Higher posttreatment temperatures (32 versus 18°C) did not affect the toxicity of dry flowable sulfur to G. occidentalis and T. urticae. The toxic effect of the sulfur products was not related to the concentration of elemental S but rather to some intrinsic characteristic of the compound itself. There were substantial differences in the responses of different stages of G. occidentalis. Residues that were nontoxic to adult females were highly toxic to hatching larvae, including those of dry flowable sulfur. In addition, all three products were highly repellent to adult female G. occidentalis. The lethal effect of calcium polysulfide on larvae was still present when the laboratory-aged residues onbean leaves were 8–9 d old. Field-aged residues on apple (Malus spp.) leaves were highly toxic (89% mortality) after 7 d, but mortality declined to 50 and 17% after 14 and 22 d, respectively. The increasing use of sulfur-containing products is detrimental to predatory mites and may play a role in the diminishing effectiveness of integrated mite control in Washington apple orchards.

Resistance and cross-resistance in populations of the leafrollers, Choristoneura rosaceana and Pandemis pyrusana, in Washington apples

Abstract Insecticide bioassays of the leafrollers, Choristoneura rosaceana (Harris), and Pandemis pyrusana Kearfott (Lepidoptera: Tortricidae), were used to investigate resistance and cross-resistance between azinphosmethyl and other insecticides. Comparisons of field-collected populations with susceptible laboratory colonies of both leafroller species were made in 1996–97, prior to registration and field introduction of several of insecticides, and were re-tested in 2000–2001 following several years of use in the field. Insecticides tested included azinphosmethyl, chlorpyrifos, methyl parathion, tebufenozide, methoxyfenozide, spinosad, indoxacarb, acetamiprid, Bacillus thuringiensis, and azadirachtin. Azinphosmethyl-susceptible laboratory colonies were used for comparison to field populations. Resistance to azinphosmethyl was found in all populations of C. rosaceana (5.2–26.8 fold) and P. pyrusana (8.4–24.9 fold) collected from commercial orchards. Cross-resistance between azinphosmethyl and the insect growth regulators tebufenozide and methoxyfenozide was found in all but one population of the two leafroller species. No cross-resistance was found to chlorpyrifos. Some of the populations tested were cross-resistant to spinosad and indoxacarb, but the responses to these materials were more variable.

Influence of Timing and Prey Availability on Fruit Damage to Apple by Campylomma verbasci (Hemiptera: Miridae)

Abstract Campylomma verbasci Meyer is a zoophytophagous mirid that feeds on small arthropods as well as apple (Malus domestica Borkhausen) fruits, causing economic damage to some cultivars. The influence of timing and prey availability on the amount of fruit damage was studied to determine whether either factor could be used to refine a management program. C. verbasci nymphs were caged on branches of fruiting ‘Golden Delicious’ apple trees during the period from bloom through early fruit set. The greatest amount of fruit damage occurred during the bloom period; little or no damage occurred after fruit reached ≈13 mm in diameter. The availability of prey did not reduce the incidence of fruit damage by C. verbasci, nor did it influence the survival of nymphs. Nymphal survival was higher, however, in cages where a blossom or fruitlet was present versus a vegetative spur. These data support the hypothesis that post petal fall insecticide applications (those made after the fruit is greater than ≈10–13 mm in diameter) are not useful in preventing economic levels of fruit damage in Washington State, and that petal fall applications would only prevent a fraction of the total amount of damage by this pest. The data from this study do not support the hypothesis that manipulating arthropod prey species of C. verbasci will prevent fruit damage. There was evidence to support the hypothesis that nymphs can survive a relatively short period (7 d) without arthropod prey.

Optimal sampling and spatial distribution of Ixodes pacificus, Dermacentor occidentalis and Dermacentor variabilis ticks (Acari: Ixodidae)

A common method for sampling tick populations is flagging, which is a method of dragging a white cloth over a plant substrate for a fixed distance along a transect. Flagging over rough physical surfaces or using long subtransect lengths could lead to the underestimation of tick densities. Using estimates of the drop-off rates of adult Ixodes pacificus in flag sampling, optimal sampling schemes (the length and number of subtransects) were examined using the relationships between the tick drop-off rates (c), the tick density and distribution patterns and the roughness of the sampled plant substrate. It was found that the optimal number of subtransects and Lmax, the longest subtransect length which did not significantly underestimate the tick density from c, were affected by the tick density, substrate roughness and tick distribution pattern. This study also showed that the density and distribution of I. pacificus and Dermacentor occidentalis varied greatly over time in the populations sampled, while the Dermacentor variabilis densities were low and showed no significant changes over time. Both I. pacificus and D. occidentalis had clumped distributions along trails and these clumps were aggregated. However, the clump sizes (or individual clump areas) changed significantly over time because of density fluctuation or the movement of ticks. Finally, a positive association between the number of I. pacificus and D. occidentalis adults was observed from 2 m subtransect flag collections in March 1995; no relationship was found in 1994.

Mineral Oil Inhibition of White Apple Leafhopper (Homoptera: Cicadellidae) Oviposition

Various rates, types and residue ages of horticultural mineral oils were tested for inhibition of oviposition by white apple leafhopper, Typhlocyba pomaria McAtee, in laboratory bioassays. The numbers of nymphs produced from females exposed to treated apple leaf surfaces were used to determine the behavioral effect. No differences in effect were found among the three oils tested (Orchex 796, Orchex 692, and Orchex 892). Inhibition of oviposition was found in concentrations of Orchex 796 as low as 1% vol:vol (2-fold reduction in nymphs), with complete inhibition at 4%. The inhibitory effect of this material at 1% vol:vol persisted for at least 3 d, with no difference between the 7-d-old residues and the check.