Michael J. Smirle

Partial inhibition of pheromone production inDendroctonus ponderosae (Coleoptera: Scolytidae) by polysubstrate monooxygenase inhibitors

Female and male mountain pine beetles,Dendroctonus ponderosae Hopkins, were treated topically with piperonyl butoxide or sesame oil, both of which are known to inhibit poly substrate monooxygenase activity. Beetles then exposed to vapors of the host monoterpenes α-pinene and myrcene were found to contain reduced levels of the pheromonestrans-verbenol and ipsdienol, as well as a buildup of monoterpene precursors. Polysubstrate monooxygenase enzymes appear to be at least partially responsible for the detoxification of host monoterpenes and for the production of terpene alcohol pheromones in this species.

The influence of a queen-produced substance, 9HDA, on swarm clustering behavior in the honeybeeApis mellifera L.

The effect of enantiomers of the queen-produced substance, 9-hydroxy-(E)-2-decenoic acid (9HDA) on swarm clustering behavior of the honeybeeApis mellifera was studied. Caged queens were removed from the swarms at the start of each test and were replaced with small Petri dishes containing one of the following treatments: 100 μgS(+) enantiomer of 9HDA, 100 μgR(-) enantiomer of 9HDA, 200 μg racemic (R, S) 9HDA, and a vehicle-treated control. Each swarm was considered to have dispersed when it had lost 50% of its starting weight. All treatments with 9HDA resulted in significantly longer swarm aggregation when compared with the control. Enantiomers were not shown to have different effects at theP ≤ 0.05 level of significance. However, observations on swarm behavior indicated that theR(-) enantiomer was the most active in retarding swarm dispersal.

The influence of colony population and brood rearing intensity on the activity of detoxifying enzymes in worker honey bees

Abstract. Cohorts of worker honey bees from a single parental hive, cross‐fostered into colonies which differed in population and other colony parameters, were assessed for activities of enzymes involved in metabolic detoxication. Activities of glutathione S‐transferase and mixed‐function oxidase enzymes were negatively correlated with foster colony population, but positively correlated with the ratio of larvae (brood)/adult workers. Worker bees which had begun foraging had enzyme activity levels higher than any found in bees which were still performing in‐hive duties. Elevated levels of detoxifying enzymes in colonies with low populations and high ratios of larvae/adults may be a protective mechanism to prevent poisoning of larvae by toxins brought to the colony by foragers.

Relationship of Insecticide Tolerance to Esterase Enzyme Activity in Aphis pomi and Aphis spiraecola (Hemiptera: Aphididae)

ABSTRACT Green apple aphid, Aphis pomi De Geer, and Aphis spiraecola Patch (both Hemiptera: Aphididae), are sympatric aphid species that are pests of apples (Malus spp.) and other crops, A. spiraecola has been shown to be significantly more tolerant to several insecticides compared with A. pomi. To establish the mechanisms contributing to this difference in insecticide response, clones of both species were collected from British Columbia, Canada, and Washington state. Dose—response bioassays were conducted to determine relative tolerances to the insecticides pirimicarb, dimethoate, and imidacloprid; these results have been reported previously, Samples of adult aphids from each clone were assayed for the activity of esterase enzymes often involved in the detoxification of insecticides. A. spiraecola had higher esterase activity compared with A. pomi; this was apparent for two model substrates, &agr;-naphthyl acetate (&agr;-NA) and &agr;-naphthyl butyrate (&agr;-NB), Aphid clones of both species collected from Washington had higher esterase activity than clones collected from British Columbia. Clones from both species and locations hydrolyzed &agr;-NA to a greater extent than &agr;-NB. Esterase activity measured with both substrates was significantly positively correlated with the relative response to pirimicarb and dimethoate; a significant positive correlation also was found for hydrolysis of &agr;-NB and imidacloprid. The apparent involvement of esterases in the differential response of A. pomi and A. spiraecola to insecticides indicated that the choice of control chemicals for A. spiraecola should not involve chemistries that are metabolized predominantly by esterases.

Baseline Susceptibilities to Imidacloprid for Green Apple Aphid and Spirea Aphid (Homoptera: Aphididae) Collected from Apple in the Pacific Northwest

Abstract Susceptibilities to the neonicotinyl insecticide imidacloprid were determined for clones of apple aphid, Aphis pomi De Geer, and spirea aphid, Aphis spiraecola Patch, collected from conventional and organic apple orchards and from crab apple and wild apple in Washington state and British Columbia over a period of 6 yr. For aphids collected during 1996–1998, adults were dipped in test solutions by using the Food and Agriculture Organization protocol, and third instars and adults were reared on treated apple leaf disks. During the final 3 yr of study, bioassays involved only third instars on treated leaf material. Tests showed that A. spiraecola was significantly more tolerant to imidacloprid compared with A. pomi. Depending on the bioassay method and aphid developmental stage, average LC50 values for A. spiraecola were 4.4–5.7 times higher than those for A. pomi established under the same test conditions. Clones of both species from Washington were marginally more tolerant to imidacloprid than clones from British Columbia, but the differences were generally not significant. Average measures of susceptibility for clones from organic orchards or unsprayed trees also did not differ from those for clones from conventional orchards, and there was no evidence for increasing LC50 values over the 6 yr of study. Differences in susceptibility to insecticides between these two anatomically similar species should be considered during the testing of new products for use on apple.