Sublethal exposure of Trogoderma granarium everts (Coleoptera: Dermestidae) to insecticide-treated netting alters thigmotactic arrestment and olfactory-mediated anemotaxis.

Long-lasting insecticide treated netting (LLIN) has a number of potential uses for the control of insect pests. Using such netting, stored products may be protected from insects including the khapra beetle (Trogoderma granarium Everts, Coleoptera: Dermestidae) a widespread pest of many agricultural commodities. Here we first examined whether brief exposures of larvae to LLIN, for less than 30 min, decreased the chance of eventual adult emergence compared to larvae exposed on untreated netting. Next, we observed the responses of larvae that were either not exposed to any netting, exposed to untreated netting, or exposed to LLIN for 10 min and then placed in a wind tunnel and monitored for movement toward a stimulus. The wind-tunnel assay was performed either with or without a lure containing kairomones and pheromones known to be attractive to larvae of this species. There was little effect of the LLIN on adult emergence of exposed larvae. However, there were interacting effects of untreated netting and LLIN relating to thigmotaxis and anemotaxis. Larvae not exposed to netting showed increased likelihood of walking upwind if the semiochemical lure was provided, as expected. A similar pattern was observed when the untreated netting was used, but the larvae became more likely to remain stationary in the assay after acclimating to the net. When LLIN was used, the larvae became more likely to move and there was a baseline increase in the likelihood of moving upwind. However, upwind walking was no longer related to semiochemical presentation. These observations suggest that particular care should be used in relation to the airflow patterns and semiochemical landscape of the warehouse settings in which LLIN is deployed.

Effects of Flour and Milling Debris on Efficacy of Beta-Cyfluthrin for Control of Tribolium castaneum (Coleoptera: Tenebrionidae).

Laboratory and field studies were conducted to determine if accumulation of a flour food source or milling debris affected residual efficacy of beta-cyfluthrin for control of Tribolium castaneum (Herbst), the red flour beetle. In the laboratory study, the high label rate of 20 mg active ingredient (AI)/m2 gave effective control for 8 wks, regardless of whether or not the concrete was sealed prior to application or the presence of flour contamination. However, with the low label rate of 10 mg AI/m2, the flour apparently absorbed the insecticide residues from the treated surface, and sealing the concrete did not have a beneficial effect on efficacy. Two field studies with the low label rate were conducted during autumn of 2012 and 2013 and summer of 2013, using only unsealed concrete. Accumulated milling debris caused a reduction in efficacy in the autumn studies, as shown by increased time to 100% knockdown, decreased mortality, and decreased residual efficacy. There was no such corresponding decrease in residual efficacy in the summer study. Overall, results of both studies show that accumulated food and milling debris can absorb residue of beta-cyfluthrin from a treated surface and have a negative impact on residual efficacy, particularly with the low label rate of 10 mg AI/m2.

Efficacy of Deltamethrin Against Stored-Product Beetles at Short Exposure Intervals or on a Partially Treated Rice Mass.

Stored-product insects can potentially be exposed to grain protectants for variable time periods. Adults of three species, the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae), the granary weevil Sitophilus granarius (L.) (Coleoptera: Curculionidae), and the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) were exposed for 1, 4, 8, and 24 h on brown rice treated with the pyrethroid deltamethrin at the label rate of 0.5 ppm, then removed and placed on untreated rice. Adults of these same species plus the rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae), the maize weevil, Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae), and the warehouse beetle, Trogoderma variabile Ballion (Coleoptera: Dermestidae) were exposed on treated brown rice mixed with varying amounts of untreated rice to assess progeny production. Immediate and delayed mortality of exposed adults did not exceed 7% for any exposure interval, but progeny production for T. castaneum was generally lower in comparison with that for the other species. Increasing the amount of treated rice decreased progeny production of R. dominica but not for any Sitophilus species. Mixed results were obtained for T. castaneum and T. variabile. Results show that long exposure times and treatment of an entire rice mass may be necessary to give complete control of stored-product beetles.

Economic Analysis for Commingling Effects of Insect Activity in the Elevator Boot Area.

Boot areas in commercial grain elevators and feed mills contribute to commingling of insects with grain that moves through the elevator leg. A partial budget and stochastic dominance model were developed to improve pest management decision-making and risk analysis assessment from commingling effects of insect activity in the boot area. Modified pilot-scale bucket elevator legs, containing residual wheat or corn, were infested with varying insect pest densities prior to clean grain transfers. Appropriate grain discounts were applied to grain samples obtained from clean grain transfers over either: 1) insect-free and untreated boots, 2) infested and untreated boots, or 3) infested and chemical-treated (ß-cyfluthrin) boots. The insect-free boots simulated performing clean-out of the boot area. Partial budget analysis and stochastic dominance modeling indicated that boot sanitation (cleanout) about every 30 d, avoiding costly grain discounts from insect commingling, is the preferred choice. Although chemical spray treatments of the empty boot may reduce insect populations of some boot residual grains, boot cleanout always had lower and usually zero insect pest populations in the boot residual grain, providing higher facility operational net income without the use of chemicals.

Susceptibility of Tribolium confusum (Coleoptera: Tenebrionidae) to Pyrethrin Aerosol: Effects of Aerosol Particle Size, Concentration, and Exposure Conditions.

A series of laboratory studies was conducted to assess the effect of droplet size on efficacy of pyrethrin aerosol against adults of Tribolium confusum Jacqueline DuVal, the confused flour beetle. A vertical flow aerosol exposure chamber that generated a standardized particle size diameter was used for these trials. In the first experiments, adults were exposed in the chamber for 2.5-45 min to aerosol dispensed at a volumetric median particle size diameter (VMD) of 16 µm, and then held in the arenas in which they were exposed or transferred to new arenas with or without a flour food source. All adults were initially knocked down when removed from the chamber. Recovery from knockdown decreased as exposure interval increased, but the presence of a food source enhanced recovery at the lower exposure intervals. In the second experiment, the aerosol was applied at a VMD of 2 µm and adults were exposed for between 5 and 75 min. Knockdown of adults was ≤10% when adults were removed from the chamber regardless of exposure time and afterward there was essentially complete recovery of adults. In the third and final experiment, the same 2-µm VMD particle size and exposure times were used, but the concentration of aerosol was increased by ≍4× compared with the previous experiment. In this test, initial knockdown was greater at the higher exposure intervals, but by 3 and 4 d posttreatment, recovery was again essentially 100%. This is the first published test assessing the efficacy of specific aerosol particle sizes on a stored product insect. Results indicate that particle size was a more important factor in conferring toxicity than the actual concentration or number of aerosol particles.

Spatial pattern in aerosol insecticide deposition inside a flour mill.

Aerosol insecticides are commonly used for management of stored-product pests inside food facilities, but the physical complexity of the interior of most food facilities may influence the dispersal and deposition of droplets and create spatial variation in dosage. The spatial pattern in aerosol deposition was evaluated inside a flour mill using a high density grid of bioassay insects. Three insecticides, Aerotech with NyGuard and Pyrocide 100 + Diacon II, both pyrethrin and insect growth regulator combinations, and Vap20, an organophosphate, were evaluated at normal (27 degrees C) and high (40 degrees C) target temperatures. Using a newly developed efficacy index, there was spatial pattern to aerosol deposition detected for the pyrethrin insecticides and the pattern differed between aerosols and temperatures. Walls and corners, especially behind the direction of application, were especially vulnerable to zones of lower efficacy, and open areas in center of the room tended to have the highest efficacy. The organophosphate insecticide provided complete efficacy at all bioassay dish locations, probably due in part to its vapor toxicity. Using boxes 1 m in depth and 5, 10, or 20 cm in height and open on only one end, it was shown that aerosol dispersal under horizontal surfaces could be impacted by gap height, aerosol, and temperature. These results show the potential for spatial variation in aerosol efficacy within a food facility and identify locations with the potential to receive a lower insecticide dosage. To increase overall efficacy, these locations may be targeted for additional interventions to provide more uniform pest population suppression.

Efficacy of aerosol applications of methoprene and synergized pyrethrin against Tribolium castaneum adults and eggs.

Experiments were performed to determine the efficacy of a single aerosol application of the insecticides methoprene and piperonyl butoxide-synergized pyrethrin, alone or in combination, and the insecticide carrier, Isopar M, against Tribolium castaneum (Herbst), the red flour beetle. The initial test exposed adults to insecticide treatments and placed male/female pairs in flour. All adults exposed to synergized pyrethrin were knocked down for at least 24 h after exposure but they recovered. High adult survival and similar average numbers of living F1 progeny were produced regardless of treatment exposure. In a separate test, insecticide treatments were directly applied to newly laid eggs, which resulted in the suppression of egg hatch. Synergized pyrethrin was the most effective insecticide (P < or = 0.001) for suppressing egg hatch. The effect of flour on insecticide activity to eggs and consequent insect development was also evaluated. An amount of 0.01 g of flour in the exposure arena, 62-cm2 area, was not sufficient for individuals to develop beyond the early larval stages, regardless of the treatment. As the flour amount in the arena increased from 1 to 5 g, the number of eggs that could develop to the adult stage increased, but this number was significantly lower in the insecticide treatments than in the control or carrier treatments. The results of the later tests indicate a high efficacy of the insecticides alone or in combination on T. castaneum egg hatch and development to the adult stage.

Residual efficacy of chlorfenapyr for control of stored-product psocids (Psocoptera).

The residual effect of chlorfenapyr (Phantom) was evaluated for residual control of three stored-product psocid species: Liposcelis bostrychophila Badonnel, Liposcelis entomophila (Enderlein), and Liposcelis paeta Pearman (Psocoptera: Liposcelididae). Chlorfenapyr was applied to individual arenas with a concrete surface at rates of 0, 2.8, 13.8, 20.6, 27.5, 55, and 110 mg active ingredient (AI)/m2. Adults were exposed on the treated arenas and mortality assessed after 1, 2, and 3 d. The procedures were repeated weekly on the same treated arenas for 3 wk to assess residual efficacy. At each week, mortality of all species was low after 1 d of exposure but notably increased after 2 or 3 d. L. entomophila was the most susceptible species, with 99-100% mortality at rates of 13.8 mg/m2 or higher. Similarly, mortality of L. paeta after 3 d of exposure at the same concentration ranged from 92 to 100%. L. bostrychophila was the least susceptible species, with mortality of < 60% during the third week after application at rates < or = 27.5 mg/m2. However, even for this species, mortality after 3 wk was 90% or higher at rates > 27.5 mg/m2. Complete mortality of all species occurred after 3 d exposure at the highest rate tested of 110 mg/m2. Thus, our results show that chlorfenapyr is effective against major psocid species at the application rates evaluated in this study.

Evaluation of synergized pyrethrin aerosol for control of Tribolium castaneum and Tribolium confusum (Coleoptera: Tenebrionidae).

Aerosol insecticides are being used in flour mill pest management programs, but there is limited information on their efficacy on different insect life stages. In this study, we evaluated the efficacy of synergized pyrethrin applied as an aerosol against eggs, larvae, pupae, and adults of the red flour beetle, Tribolium castaneum (Herbst), and the confused flour beetle, Tribolium confusum Jacquelin du Val. Effects of direct and indirect exposure were evaluated by exposing each life stage to the aerosol and then transferring to untreated flour, transferring untreated insects to treated flour, or exposing both the insects and the flour to the aerosol. The aerosol produced >88% mortality of both species and all life stages when insects were directly treated and transferred to either treated or untreated flour. Mortality was significantly reduced when insects were either treated together with flour or untreated insects were transferred to treated flour (indirect exposure to the aerosol). Larvae and adults of both species were more tolerant compared with eggs and pupae. Recovery of moribund adults in the indirect exposure treatments was greater compared with recovery of moribund insects in the direct exposure treatments. Good sanitation before aerosol application could facilitate direct exposure of insects and thus increase aerosol efficacy inside flour mills.

Combination Insecticide Treatments with Methoprene and Pyrethrin for Control of Khapra Beetle Larvae on Different Commodities.

Trogoderma granarium Everts, the khapra beetle, is a serious pest of stored products throughout the world. Larvae pose a significant threat to stored products because they feed on >100 different commodities, possess the ability to enter facultative diapause, and are difficult to detect. Control methods for T. granarium include fumigation, contact insecticides, trapping, and insecticide-incorporated packaging. The objective of this study was to determine the residual efficacy of two insecticide formulations (methoprene + deltamethrin + piperonyl butoxide synergist Gravista® and methoprene + deltamethrin, DiaconIGR®Plus). These insecticides were evaluated on three stored product commodities, corn, wheat, and brown rice, by exposing T. granarium larvae during a 12-month testing period. Both formulations significantly reduced adult emergence on corn and wheat for 12 months and on brown rice for up to 6 months. Adult emergence was highest at month 12 for corn (8.41%), and brown rice (85.88%), and month 9 for wheat (39.52%), treated with DiaconIGR®Plus or Gravista®, respectively. A biological index used to measure the development of exposed larvae on the treated grain from the larval stage (low values) to adult emergence (high values) was lower (fewer adults) on corn and wheat compared to controls. Despite differences in formulations, each of these grain protectants could be utilized by stored commodity managers to protect commodities during storage and transportation for T. granarium when and if this pest is detected at USA ports of entry.

Variation in susceptibility of field strains of three stored grain insect species to spinosad and chlorpyrifos-methyl plus deltamethrin on hard red winter wheat.

Spinosad and chlorpyrifos-methyl plus deltamethrin efficacy at labeled rates on hard red winter wheat were evaluated against 11 field strains of the red flour beetle, Tribolium castaneum (Herbst); six strains of the sawtoothed grain beetle, Oryzaephilus surinamensis (L.); and two strains of the lesser grain borer, Rhyzopertha dominica (F.), collected mostly from farm-stored grain in Kansas. Adults were exposed to wheat treated with spinosad at 1 mg (active ingredient)/kg or chlorpyrifos-methyl plus deltamethrin at three plus 0.5 mg (active ingredient)/kg. Adult mortality was assessed after 7 and 14 d and progeny production after 42 d. Spinosad did not provide complete mortality or progeny suppression of T. castaneum and O. surinamensis field strains, but was effective against R. dominica strains. Chlorpyrifos-methyl plus deltamethrin produced complete mortality and progeny suppression of field strains all three species. The two least susceptible T. castaneum and O. surinamensis strains and the two R. dominica strains were chosen for dose-response tests only with spinosad. The LD99 values for T. castaneum and R. dominica field strains were similar to that of the corresponding laboratory strains. Corresponding values for the two O. sturinamensis field strains were significantly greater (approximately 6 times) than the laboratory strain. The effective dose for progeny reduction (ED99) of only one R. dominica field strain was significantly greater (approximately 2 times) than the laboratory strain. The baseline susceptibility data of field strains of three insect species to spinosad will be useful for monitoring resistance development when this product is commercially released as a grain protectant.

Efficacy of a combination of beta-cyfluthrin and imidacloprid and beta-cyfluthrin alone for control of stored-product insects on concrete.

The insecticidal effect of Temprid, a formulation that contains beta-cyfluthrin and imidacloprid, was tested on concrete for control of seven stored-product insect species: the rusty grain beetle, Cryptolestes ferrugineus (Stephens); the sawtoothed grain beetle, Oryzaephilus surinamensis (L.); the red flour beetle, Tribolium castaneum (Herbst); the confused flour beetle, T. confusum Jacquelin du Val; the hide beetle, Dermestes maculatus (DeGeer); and the psocids Liposcelis bostrychophila Badonnel and L. paeta Pearman. Temprid, which contains 10.5% beta-cyfluthrin and 21% imidacloprid, was tested at the rate of 17.2 ml of formulation/4.1 liters of water/100 m2. Adults were exposed for 4, 8, 14, and 24 h, and then daily for 7 d, on untreated dishes or dishes treated with Temprid. In the untreated dishes, mortality of C. ferrugineus and O. surinamensis was lower when food was present, but food did not affect mortality of the other species. Presence of food did not affect mortality of any of the species tested in the treated dishes. C. ferrugineus, O. surinamensis, and the two psocid species were very susceptible to Temprid, with mortality of 97-100% after 7 d of exposure. In contrast, D. maculatus, T. castaneum, and T. confusum were tolerant to Temprid, as mortality did not exceed 57, 25, and 17%, respectively, at the 7-d exposure. A separate series of similar bioassays with Tempo, a formulation that contains 11.8% beta-cyfluthrin alone, which was applied at the same dose rate as Temprid, was conducted using O. surinamensis and T. castaneum as the target insect species, and results showed that Tempo was at least as effective as Temprid. Our results indicate that the simultaneous use of beta-cyfluthrin with imidacloprid is not more effective on concrete than beta-cyfluthrin alone, and efficacy of both formulations varies with the target species.

Economic feasibility of methoprene applied as a surface treatment and as an aerosol alone and in combination with two other insecticides.

Economic evaluations of integrated pest management strategies are becoming increasingly important as restrictions on conventional insecticides continue to become more stringent and chemical control costs rise. Aerosol treatments with insect growth regulators alone and in combination with conventional contact insecticides may be a feasible alternative to expensive and highly toxic fumigants such as methyl bromide for control of the Indianmeal moth (Plodia interpunctella (Hübner)). Average calculated mortality of Indianmeal moth eggs exposed to surface applied methoprene, aerosol methoprene alone and in combination with esfenvalerate and synergized pyrethrins is 55.0, 69.0, and 94.6%, respectively. Temperature effects on development time makes frequency and timing of insecticide applications very important as evidenced by simulations of population levels in response to a variety of treatment dates by diet, and become critical in situations where survival of Indianmeal moth is high. Using a measurement of risk that is equal to deviations below a target mortality goal (99%), we are able to optimize cost and frequency of application using simulated mortality data for each of the treatment strategies. Optimal timing of each insecticide treatment depends heavily on the rate of development by diet. This type of analysis helps pest control operators and managers by showing consequences of treatment scenarios in time and cost.

Competition of Rhyzopertha dominica and Sitophilus oryzae on six sorghum varieties.

We tested the effect of simultaneous infestation by adults of the lesser grain borer, Rhyzopertha dominica (F.) and the rice weevil, Sitophilus oryzae (L.) on six sorghum varieties. For this purpose, vials containing sorghum and either each species alone or both species were placed at 30 °C and 65% relative humidity. After ten days, all parental adults were removed and the vials were returned to the same conditions. Five weeks later the vials were emptied, to record adult emergence, the percentage of insect damaged kernels (IDK), and frass weight. Our results indicated that progeny production capacity for both species was not affected by the simultaneous presence of R. dominica and S. oryzae, and that adult emergence was more of a variety- mediated parameter. Both species had previously shown similar preferences towards specific sorghum varieties. IDK and frass were higher in vials containing R. dominica alone rather than S. oryzae alone, but these indicators were not always related to progeny production. Specifically, the most and the least frass production was noted on Sumac and PE sorghum varieties for both species, respectively. When the two species were placed together in the same vial, the most frass production was noted in the Non-Waxy Burgundy and Sumac varieties. Our results suggest that varietal resistance in sorghum could be utilized to help reduce post-harvest infestations by S. oryzae and R. dominica.

Development and Immature Mortality of the Sawtoothed Grain Beetle (Coleoptera: Silvanidae), on Different Sorghum Fractions and Different Temperatures.

Developmental ability of Oryzaephilus surinamensis (L.) (Coleoptera: Silvanidae) was examined on six different sorghum milling fractions: Bran, Shorts, Cgrits, Fgrits, Red dogs, Flour, and also on a standard diet of Oat Flakes. For this purpose, a 1-day-old egg was placed in a vial containing 1 g of one of the sorghum fractions and exposed to three temperatures: 25, 30, or 32°C. All vials were checked daily for pupal and adult emergence and mortality of immatures. The developmental time was significantly affected by the type of sorghum fraction. After two weeks, for most of the temperatures examined, the longest developmental times in most cases for both pupation and adult emergence were observed in Flour and Oat flakes. Increasing the temperature from 25 to 30 accelerated the development, while adult emergence time did not differ between 30 and 32°C for all fractions except Flour. Egg mortality ranged from 11 to 78%, while larval and pupal mortality ranged from 0 to 22 and 0 to 45%, respectively for all sorghum fractions and different temperatures tested. Moreover, the mean overall immature mortality occurred at 30°C was 49.2, 39.7, and 65.1% at 25, 30, and 32°C for all the diets examined. The findings of the present work show that O. surinamensis can develop and survive in sorghum milling fractions and that the optimal temperatures for growth enhancement are 30 and 32°C. The temperatures within sorghum milling facilities could support O. surinamensis development on milling fractions if they are not addressed through phytosanitary measures.

Immediate and delayed movement of resistant and susceptible adults of Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) after short exposures to phosphine.

BACKGROUND: During the last decade, the evaluation of certain behavioral attributes has been utilized as an indicator of resistance to phosphine. In this context, an underappreciated challenge may be the development of behavioral traits that are related with resistance to phosphine such as the movement to refugia and recovery of stored product insects after short exposures. Thus, the aim of the current study was to track the movement of phosphine-resistant and -susceptible adults of the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), which is a major pest of stored products, after brief exposures to phosphine. Exposures were followed for extended intervals to assess the recovery patterns and how those patterns are related to known resistance to phosphine. A video-tracking procedure coupled with Ethovision software was used to assess movement after exposure. RESULTS: Overall, we found baseline movement was less for phosphine-resistant T. castaneum, suggesting resistance comes at a considerable fitness cost. In the presence of phosphine (1000 or 3000 ppm), there was a much greater reduction in movement for phosphine-susceptible than phosphine-resistant T. castaneum adults immediately after brief 5-min exposures. Twenty-four hours later, these effects were more variable and less apparent, regardless of the susceptibility level. CONCLUSIONS: The initial knockdown associated with successful fumigation may just be a temporary state whereafter insects shortly resume movement and may be able to seek out refugia from phosphine, thereby promoting the development of resistance. Our results strengthen a growing consensus that it is the speed to knockdown that truly matters, with quick knockdown indicating slow recovery and a reduced likelihood for the occurrence of resistance. © 2023 Society of Chemical Industry. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Aerosolized Insecticide Spray Distributions and Relationships to Efficacy against Stored Product Pests.

Aerosol insecticides are widely used in stored product insect management programs in food facilities. Previous research has shown spatial variation in aerosol efficacy within facilities, but information on how spatial patterns of aerosol droplet concentration, size distribution, dispersal, and deposition contribute to this variation in efficacy is limited. This study involved two aerosol application systems: a high-pressure cylinder containing TurboCide Py-75® with pyriproxyfen IGR (ChemTech Ltd., Des Moines, IA, USA) and a hand-held fogger containing Pyrocide 100® (MGK, Minneapolis, MN, USA) with Diacon II which contains methoprene IGR (Wellmark, Schaumburg, IL, USA). These systems were used at single or multiple application locations. The spray trials were conducted in a small-scale flour mill, Hall Ross Flour Mill (Kansas State University, Manhattan, KS, USA). The droplet size distributions were monitored at multiple positions within the room using nine aerodynamic particle sizing (APS, TSI Incorp, Shoreview, MN, USA) instruments. The APS data collected over the treatment period were summarized into a mass concentration index (MCI), which ranged from 155 to 2549 mg/m3 for Turbocide and 235-5658 mg/m3 for Pyrocide. A second parameter called the Deposition Index (Dep.Idx) was derived to estimate potential insecticide depositions on the floor and has units of g/m2. The Dep.Idx was below 5.3 g/m2 for most Turbocide applications, while the Dep.Idx was below 8.4 g/m2 for most Pyrocide applications. The MCI and Dep.Idx values varied with APS position and spray application location, with proximity to the aerosol application location and degree of obstruction between the release point and APS position contributing to this variation. We assessed the relationship between aerosol droplet parameters and insect efficacy using Tribolium confusum Jacqueline DuVal, the confused flour beetle. The adults were treated directly, while the larvae were treated two weeks later during the residual test (previously published). For Turbocide, efficacy against adults increased with MCI and Dep.Idx values, but for residual efficacy of the IGR, efficacy was high at all aerosol droplet values, so no relationship was apparent. In contrast, the relationship between Pyrocide deposition and adult insect efficacy was highly variable. But with larval insect efficacy, residual larvae control was directly related to increases in Pyrocide MCI and Dep.Idx. Contour plots of Dep.Idx values were developed, which could be used to predict areas of the mill that are not receiving an adequate application rate, and this could be used to develop more effective application strategies for aerosol insecticides in food facilities.

Residual efficacy of methoprene for control of Tribolium castaneum (Coleoptera: Tenebrionidae) larvae at different temperatures on varnished wood, concrete, and wheat.

The residual efficacy of the juvenile hormone analog methoprene (Diacon II) was evaluated in bioassays using larvae of Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) exposed on unsealed concrete or varnished wood treated with a liquid formulation and held at different temperatures. When these two types of surfaces were stored at 20, 30 or 35 degrees C for 0-24 wk, the percentage of adult emergence on concrete increased with time. In contrast, there was no adult emergence from larvae exposed to varnished wood at 24 wk after treatment at any of these temperatures. The presence of flour reduced residual efficacy of methoprene on concrete, but not on varnished wood, with no differences between cleaning frequencies. Methoprene was also stable for 48 h on concrete held at 65 degrees C and wheat, Triticum aestivum L., held at 46 degrees C. Results show that methoprene is stable at a range of temperatures commonly encountered in indoor food storage facilities and at high temperatures attained during insecticidal heat treatments of structures. The residual persistence of methoprene applied to different surface substrates may be affected more by the substrate than by temperature.

Residual activity of methoprene and novaluron as surface treatments to manage the flour beetles, Tribolium castaneum and Tribolium confusum.

The juvenile hormone analog methoprene, and the chitin synthesis inhibitor novaluron, were evaluated by exposing late-stage larvae of Tribolium castaneum (Herbst) or Tribolium confusum (Jacqueline DuVal) (Coleoptera: Tenebrionidae) to it. The larvae were exposed to it in food material, on concrete, on plywood, and on floor tile. Larvae of T. castaneum were more susceptible than T. confusum larvae to both methoprene and novaluron on all surfaces. A further evaluation was done by exposing adult T. confusum to methoprene and novaluron through food placed on concrete treated with methoprene and novaluron, and then assessing resulting progeny production. The emergence of adults with normal morphology was reduced for both chemicals, with more malformed adults appearing in the methoprene treatment, and fewer adults of any form emerging in the novaluron treatment. The results show direct exposures to larvae, or determining progeny production from exposed adults, are valid methods for assessing the susceptibility of flour beetles to insecticides.

Susceptibility of stored-product psocids to aerosol insecticides.

The efficacies of commercial methoprene and esfenvalerate aerosols for control of stored-product psocid pests were evaluated in simulated field studies. The efficacies of methoprene, esfenvalerate EC, the carrier Isopar-M™, and a combination of methoprene and esfenvalerate aerosols for control of Liposcelis decolor (Pearman) (Psocoptera: Liposcelididae) and Liposcelis entomophila (Enderlein) nymphs were assessed, and the effects of direct and indirect exposure of Liposcelis bostrychophila Badonnel, L. decolor, and Liposcelis paeta Pearman adults to esfenvalerate EC aerosol were evaluated. The greatest nymphal mortality attained was 76%, indicating that the four aerosols tested were ineffective against L. decolor and L. entomophila nymphs. In the direct and indirect exposure studies, the greatest adult mortalities attained for the three psocid species were 62 and 32%, respectively. Based on these data, esfenvalerate aerosol is ineffective for control of L. bostrychophila, L. decolor, L. entomophila, and L. paeta psocid species. This study shows that methoprene, esfenvalerate EC, and a combination of methoprene and esfenvalerate aerosols were ineffective against the four psocid species tested when applied at rates that are usually effective against other stored-product insect pests.