The chemical and biological properties of methoxyfenozide, a new insecticidal ecdysteroid agonist.

Methoxyfenozide [N-tert-butyl-N'-(3-methoxy-o-toluoyl)-3,5-xylohydrazide; RH-2485] is the newest diacylhydrazine insecticide to reach the marketplace. It binds with very high affinity to the ecdysone receptor complex (EcR:USP) in lepidopteran insects [Kd = 0.5 nM (Plodia)], where it functions as a potent agonist, or mimic, of the insect molting hormone, 20-hydroxyecdysone (20E). Methoxyfenozide exhibits high insecticidal efficacy against a wide range of important caterpillar pests, including many members of the family Pyralidae, Pieridae, Tortricidae and Noctuidae. It is most effective when ingested by the target caterpillar, but it also has some topical and ovicidal properties. It is modestly root systemic, but not significantly leaf-systemic. Evidence collected to date indicates that methoxyfenozide has an excellent margin of safety to non-target organisms, including a wide range of non-target and beneficial insects.

Baseline monitoring of codling moth (Lepidoptera: Tortricidae) larval response to benzoylhydrazine insecticides.

A diet-incorporation larval bioassay was developed to measure the response of codling moth, Cydia pomonella (L.), to the benzoylhydrazine insecticides tebufenozide and methoxyfenozide. The bioassay tested neonates and third, fourth, and fifth instars from a laboratory colony and neonates and fourth instars from a pooled population collected from five certified-organic apple orchards. Bioassays were scored after 6 and 14 d. No differences between the laboratory and field population were found for either insecticide. Significant differences were found in the response of third and fifth instars between the 6 and 14 d bioassays, primarily due to a high proportion of moribund larvae in the shorter assay. Larval age had a significant effect in bioassays and was more pronounced in 6- versus 14-d tests. Fifth instars were significantly less susceptible to both insecticides than other stages, while responses of third and fourth instars were similar. The response of neonates was significantly different from third and fourth instars to tebufenozide but not with methoxyfenozide in the 14-d test. Field bioassays excluded the use of fifth instars and were scored after 14 d. LC50s estimated for 18 field-collected populations varied five- and ninefold for tebufenozide and methoxyfenozide, respectively. The responses of all but six field-collected populations were significantly different from the laboratory strain. Five of these six populations were collected from orchards with no history of organophosphate insecticide use. The LC50 for methoxyfenozide of one field-collected population reared in the laboratory for three generations declined fourfold, but was still significantly different from the laboratory population. These data suggest that transforming current codling moth management programs in Washington from a reliance on organophosphate insecticides to benzoylhydrazines may be difficult.

Monitoring the susceptibility of citrus rust mite (Acari: Eriophyidae) populations to abamectin.

A citrus leaf disk bioassay was developed to monitor the susceptibility of citrus rust mite, Phyllocoptruta oleivora (Ashmead), populations to abamectin. Disks from leaves of several citrus cultivars were equally suitable bioassay substrates, and there was no difference in mortality when mites were sprayed directly or exposed to dry abamectin residue. The concentration-response relationship was determined at intervals over 2 yr for a reference population of citrus rust mites that had been maintained in culture and never exposed to acaricides. Three diagnostic concentrations of abamectin were selected based on the response of the reference population and were used to test the susceptibility of 15 populations of mites from commercial citrus groves. Comparisons with the reference population showed reduced levels of susceptibility in some populations. Populations of citrus rust mites from 6 commercial groves were sprayed twice in 1997 with combinations of acaricides designed to exert different intensities of selection pressure from abamectin. None of these populations showed a change in their response to abamectin in pre- and postspray bioassays, although their susceptibility was usually less than that of mites from the susceptible reference population. Biweekly counts of rust mites on fruit in these 6 groves suggested that, relative to groves which received no abamectin or 1 abamectin spray, mite control was not adversely affected in the groves sprayed twice with abamectin. The bioassay method is discussed in relation to factors that affect the interpretation of results from its use, and factors that may affect the development of resistance to abamectin in citrus rust mite populations are presented. This study has provided baseline data with which the results of ongoing tests of the response of citrus rust mite populations to abamectin can be compared.

Potential of foliar, dip, and injection applications of avermectins for control of plant-parasitic nematodes.

Studies were conducted to determine the potential of two avermectin compounds, abamectin and emamectin benzoate, for controlling plant-parasitic nematodes when applied by three methods: foliar spray, root dip, and pseudostem injection. Experiments were conducted against Meloidogyne incognita on tomato, M. javanica on banana, and Radopholus similis on banana. Foliar applications of both avermectins to banana and tomato were not effective for controlling any of the nematodes evaluated. Root dips of banana and tomato were moderately effective for controlling M. incognita on tomato and R. similis on banana. Injections (1 ml) of avermectins into banana pseudostems were effective for controlling M. javanica and R similis, and were comparable to control achieved with a conventional chemical nematicide, fenamiphos. Injections of 125 to 2,000 mug/plant effectively controlled one or both nematodes on banana; abamectin was more effective than emamectin benzoate for controlling nematodes.

Curative and Residual Efficacy of Injection Applications of Avermectins for Control of Plant-parasitic Nematodes on Banana.

Studies were conducted to determine the curative and residual efficacy of avermectins at controlling plant-parasitic nematodes when injected into the pseudostem of banana, Musa acuminata cv. Cavendish. In addition, we determined the lowest concentration of avermectins that provided satisfactory efficacy as protectants when injected into banana pseudostems. Experiments were conducted with a root-knot nematode, Meleidogyne javanica, and the burrowing nematode, Radopholus similis. Injections (1 ml) of >/= 100 mug a.i./plant of abamectin into pseudostems were effective at controlling M. javanica and R. similis, and were comparable to control achieved with a conventional chemical nemaficide, fenamiphos, in a protectant assay. Abamecfin injections of 250 and 500 mug a.i./plant were effective at reducing nematode infections 28 to 56 days after inoculation. Abamectin was more effective than ivermectin at controlling nematodes after nematode populations were established in banana roots. Injections of between 100 and 1,000 mug a.i./plant were effective at controlling nematodes for at least 56 days after treatment. These studies confirmed earlier results and demonstrated that abamecfin has potential for controlling nematode parasites on banana when injected into the pseudostem.

Sampling range of male sweetpotato weevils (Cylas formicarius elegantulus) (Summers) (Coleoptera: Curculionidae) to pheromone traps: Influence of pheromone dosage and lure age.

Studies were conducted to determine the effects of sex pheromone dosage and lure age on movement of male sweetpotato weevils (SPW),Cylas formicarius elegantulus (Summers), using mark-release-recapture techniques. SPW trap counts from various downwind distances were compared for dosages ranging from 0.01 to 10.0 µg and lure ages ranging from fresh (0 days old) to 64 days old. The percentages of male SPW recaptured decreased with an increase in release distance and decreased with a decrease in dosage at each corresponding distance. Most SPW were caught within the first 16-hr period. Slopes of percent recapture vs. release distance for the two higher dosages (10 µg and 1.0 µg) differed from those of the two lower dosages (0.1 and 0.01 µg) but did not differ from each other. Intercepts were similar among the three higher dosages. Slopes did not differ among the five lure ages examined. Intercepts differed between fresh (0 days old) and 24-day-old septa at 16 hr and between fresh (0 days old) and 34-day-old septa at 40 hr. Previous exposure to pheromone (conditioning) did not increase percentages of SPW recaptured. Results indicate that male SPW are capable of traversing distances of at least 280 m in 16 hr. The pheromone tested in this study appears to be effective at dosages lower than any other coleopteran sex-pheromone system. Incorporation of this pheromone into a SPW management system may effectively reduce the use of insecticides.