Eric J. Hoffmann

Reduction of Mosquito (Diptera: Culicidae) Attacks on a Human Subject by Combination of Wind and Vapor-Phase DEET Repellent

Abstract In a Central Michigan wetland setting, air drawn through a DEET-impregnated screen using an electric fan and projected toward a human subject significantly reduced mosquito orientation by 74%, landing by 75%, and probing by 70%, relative to no applied wind or DEET. The DEET vapor effect was significant as revealed by a statistically significant wind/DEET interaction. The wind speed at the downwind human subject was 0.6 m/s and the DEET vapor concentration was estimated at 2 μg/liter air. We suggest a combination of directed wind and volatile repellent might be developed as a mosquito deterrent strategy for the backyard setting.

Reassessment of the Role and Utility of Wind in Suppression of Mosquito (Diptera: Culicidae) Host Finding: Stimulus Dilution Supported Over Flight Limitation

Abstract In a Central Michigan wetland setting, with abundant Aedes vexans (Meigen), Anopheles walkeri (Theobald), and Coquillettidea perturbans (Walker), electric fan-generated wind strongly reduced mosquito catches in Centers for Disease Control and Prevention light traps releasing carbon dioxide at 650 or 1,950 ml/min. This relationship was negatively logarithmic over the range of velocities tested (0 m/s to 3.7 m/s; 0–8.3 mph) and closely matched the theoretical dilution function predicted to occur with increasing wind flows over a constantly releasing point source of volatile chemical. Tripling the carbon dioxide release rate consistently doubled the number of mosquitoes caught across the range of wind velocities tested. Neither applied wind velocity nor carbon dioxide release rate was correlated with mosquito body mass across the range of wind velocities tested. Collectively, these data support the conceptual model that applied wind diminishes mosquito catches primarily by diluting attractants rather than by exceeding mosquito flight capability. Previously published estimates of maximum air speeds of which mosquitoes are capable may now need to be reassessed if they were based upon shut-down of catches in traps baited with chemical attractants. Addition of DEET vapor significantly reduced the number of mosquitoes caught relative to equivalently moving air without repellent. We recommend that fan-generated wind should be pursued as a practical means of protecting humans or pets from mosquitoes in the backyard setting.

Curative Activity of Insecticides Against Plum Curculio (Coleoptera: Curculionidae) in Tart Cherries

ABSTRACT Tart cherry, Prunus cerasus L. variety Montmorency, fruit were infested with plum curculio, Conotrachelus nenuphar (Herbst) (Coleoptera: Curculionidae), and treated with insecticides to target late instars, neonates, and eggs. The organophosphates azinphos-methyl and phosmet and the neonicotinoid thiamethoxam reduced larval emergence rates by >90% for all life stage targets; after >30 d, few surviving larvae were found inside fruit. Acetamiprid and thiacloprid also had curative activity and yielded >75% reductions in emergence and few surviving larvae in the fruit after >30 d. The juvenile hormone analog pyriproxyfen reduced larval emergence, but 66% of fruit that was treated to target late-instars still had live larvae inside of them after >30 d. Novaluron, chlorantraniliprole, and esfenvalerate had no curative activity. Indoxacarb had limited curative activity, and all targeted life stages had larval emergence. Internal and external residues were analyzed and are discussed in relation to their penetration and curative potential. The curative activity of azinphos-methyl has played an important role in meeting federal standards for infestation-free tart cherries at processing. Regulatory changes are eliminating the use of this compound, and new integrated pest management programs for plum curculio will need to address the loss of azinphos-methyls curative activity.

Imidacloprid in Melon Guttation Fluid: A Potential Mode of Exposure for Pest and Beneficial Organisms

ABSTRACT ELISA techniques were used to detect imidacloprid in guttation fluid of young cantaloupe plants in Arizona. Imidacloprid was detected at up to 4.1 µg/ml (ppm) in a coincidental guttation collection 3 d after a top label rate soil application and at 37 µg/ml one d after a separate top label rate soil application study. These imidacloprid titers exceed reported median oral toxicities for several insect species by factors of 10 or more. Pesticides in guttation fluid are a relatively unexplored route of exposure for both pest and beneficial insects, and could represent an important risk for both of these groups in guttation-prone environments.

Ovicidal activity of organophosphate, oxadiazine, neonicotinoid and insect growth regulator chemistries on northern strain plum curculio, Conotrachelus nenuphar

Abstract An in vitro method was developed for assessing ovicidal effects of the organophosphate azinphos-methyl, the neonicotioids thiacloprid, thiamethoxam and clothianidin, the oxadiazine indoxacarb and the insect growth regulators novaluron and pyriproxifen on the plum curculio, Conotrachelus nenuphar (Herbst)(Coleoptera: Curculionidae). The baseline survivorship of this method was 88 percent. Plum curculio eggs were most sensitive to azinphos-methyl. Thiacloprid, clothianidin and the chitin synthesis inhibitor, novaluron, had LC50 values below 100 ppm. Thiamethoxam, indoxacarb and pyriproxifen were not ovicidal at 100 ppm. Octanol-water partitioning coefficients, log Kow, appeared to be an important indicator of ovicidal activity within the neonicotinoids. This new bioassay method eliminates the confounding of the insect-chemical and plant-chemical interactions and the results highlight the utility of a post-infestation curative approach to plum curculio management.

Penetrative and Dislodgeable Residue Characteristics of 14C-Insecticides in Apple Fruit

Infinite- and finite-dose laboratory experiments were used to study the penetrative and dislodgeable residue characteristics of (14)C-insecticides in apple fruit. The differences in dislodgeable and penetrated residues of three radiolabeled insecticides ((14)C-thiamethoxam, (14)C-thiacloprid, and (14)C-indoxacarb), applied in aqueous solution with commercial formulations, were determined after water and methanol wash extractions. The rate of sorption and extent of penetration into the fruit cuticles and hypanthium of two apple cultivars were measured after 1, 6, and 24 h of treatment exposure, using radioactivity quantification methods. For all three compounds, 97% or more of the treatment solutions were found on the fruit surface as some form of non-sorbed residues. For indoxacarb, sorption into the epicuticle was rapid but desorption into the fruit hypanthium was delayed, indicative of a lipophilic penetration pathway. For the neonicotinoids, initial cuticular penetration was slower but with no such delay in desorption into the hypanthium.

Plum Curculio (Coleoptera: Curculionidae) Adult Mortality and Associated Fruit Injury After Exposure to Field-Aged Insecticides on Tart Cherry Branches

ABSTRACT Plum curculio, Conotrachelus nenuphar (Herbst) (Coleoptera: Curculionidae), adults were exposed to field-aged residues of thiamethoxam, acetamiprid, thiacloprid, indoxacarb, or azinphos-methyl on tart cherry, Prunus cerasus L. variety Montmorency. At 1, 3, 7, and 14 d postapplication, fruit were sampled for chemical residues, and bioassays were used to assess beetle mortality and plant tissue injury. Azinphos-methyl had lethal activity within 1 d of exposure at all postapplication intervals and significant fruit protection extended to 14 d postapplication. All of the neonicotinoids had lethal activity at 3 d posttreatment, with acetamiprid activity extending to 7 d. Antifeedant and oviposition deterrent effects were seen with thiamethoxam and thiacloprid; damage incidence was significantly reduced in the absence of significant beetle mortality or intoxication. Thiamethoxam and acetamiprid penetrated into leaf and fruit tissue and were detected in the interior tissues at 14 d postapplication, but interior thiacloprid residues were not detected after day 1. Indoxacarb provided some fruit protection out to 7 d postapplication, and 14-d-old residues intoxicated beetles, but the slow action of this compound allowed significant damage to occur before beetles were incapacitated. Indoxacarb was only detected as a surface residue after the first day postapplication. These data on the plant— insect—chemistry interactions will support use and management decisions as compounds with acute contact activity are phased out.