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United States Department of Agriculture

Agricultural Research Service

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2010 Annual Report

1a. Objectives (from AD-416)
Evaluate efficacy of potential alternatives to the use of methyl bromide as a structural treatment and improve Integrated Pest Management (IPM) programs for stored-product insect pests in food facilities such as wheat flour mills, rice mills, pet food facilities, and their associated warehouses with the goal of reducing the number of methyl bromide critical use exemptions (CUEs) requested or the amount of methyl bromide used.

1b. Approach (from AD-416)
A four part approach, based on priorities identified by stakeholders at the NP308 program review, will be used to meet this objective. (1) Obtain information on the field efficacy of alternative structural treatments, such as sulfuryl fluoride or heat, compared with methyl bromide. (2) Evaluate the impact of some alternative tactics, such as reduced-risk aerosol insecticides or targeted treatment with residual contact insecticides, as part of an IPM or systems approach to eliminate the need for, or reduce the frequency of, fumigations or other structural treatments. (3) Develop improved monitoring tools and strategies to evaluate the need for and effectiveness of different management tactics to improve the implementation of an IPM program (in association with Gainesville). (4) Develop models using the above information with which to determine optimal management strategies using methyl bromide alternatives.

3. Progress Report
Progress has been made on the three objectives of the project reported here, all of which fall under National Program 308, Component 2, Post-Harvest Alternatives. Progress made in this project has focused on Problem 2A, developing alternatives to methyl bromide for disinfestation of post-harvest food processing facilities. Under Objective 1, significant progress was made in understanding stored-product insect population dynamics and the relative impact of structural fumigations with methyl bromide and the alternative treatment, sulfuryl fluoride. We conducted monitoring of stored-product insects, emphasizing the red flour beetle, in commercial food facilities and used this information to determine the impact of structural fumigations on pest populations. This research also revealed potential management thresholds and is being used to supply information needed to validate population models developed in Objective 4. Under Objective 2, significant progress has been made on evaluating the impact of reduced-risk aerosol insecticides on stored-product insects such as the red flour beetle and the Indianmeal moth. Effective use of these insecticides could reduce the need to conduct structural fumigations, facilitating the phaseout of methyl bromide. Our research focused on how aerosol insecticide applications are distributed when applied in food facilities, determining how different commercially reduced-risk insecticides impact pest insect survival, and how long this impact persisted after treatment. We also evaluated how obstructions and food material impact aerosol insecticide effectiveness, and showed the importance of sanitation programs in enhancing insecticide impact. Long-term studies in experimental sheds were initiated to determine the impact of repeated aerosol insecticide applications on red flour beetle populations. Progress was made on Objective 4, with population models for two major pests developed, and the model for red flour beetle in flour mills was used to simulate the impact of fumigations with methyl bromide and sulfuryl fluoride. Initial analysis of the red flour beetle population model for flour mills was consistent with the real world monitoring data obtained in a mill. Treatment with high temperature is being incorporated into the model as well. This research will contribute to the development of more effective pest management programs with the potential benefit of reducing the number of methyl bromide critical use exemptions (CUEs) requested or the amount of methyl bromide used.

4. Accomplishments
1. Impact of season and structural fumigation on red flour beetle trap captures in flour mills evaluated. Red flour beetle management in flour mills has relied on fumigation with methyl bromide, but use of this fumigant is being phased out worldwide under the Montreal Protocol. Data on the impact of fumigation on pest populations is limited, and this has hampered the adoption of alternative treatments. ARS scientists in Manhattan, KS, and Gainesville, FL, analyzed red flour beetle monitoring data collected over multiple years from two flour mills to determine the impact of fumigations on pest populations and the influence of season on efficacy. Average percentage reductions were calculated, and it was shown that allowing high pest populations before fumigations resulted in greater abundance after treatment because percentage reduction was similar. Reduction in beetle captures was also not significantly affected by season. Results provide baseline information on pest populations and fumigation efficacy to which methyl bromide alternatives can be compared and provides information that can be used to help optimize fumigation and IPM programs.

2. Simulation model for red flour beetle in flour mills used to evaluate fumigation efficacy. Red flour beetle contamination of flour has many negative impacts on the milling industry including damage to brand identity, failure to pass inspections, and the cost of product returns. With the phase-out of methyl bromide for fumigation, new alternatives and treatment strategies need to be evaluated. ARS scientists in Manhattan, KS, developed a computer model for the red flour beetle in flour mills that can be used to predict the effects of various insect control procedures. The model was used to investigate several fumigation strategies. Insect population rebound following fumigation was much longer in mills that were fumigated in the fall compared to spring fumigations. Simulated fumigations with sulfuryl fluoride resulted in faster population rebound compared to methyl bromide because of reduced egg mortality in the former. Findings from this study will be used to develop optimal treatment programs for flour mills using alternative methods such as heat and sulfuryl fluoride.

3. Flour deposits and obstructions impact aerosol insecticide efficacy against red flour beetle. Stored-product insect infestation in food processing facilities and storage warehouses is a serious problem, and pest management professionals have begun using aerosolized insecticide applications more frequently to mitigate these infestations, although limited information is available on their efficacy. Pilot-scale tests were conducted by ARS scientists in Manhattan, KS, to determine the effects of two aerosolized insecticides (pyrethrins and esfenvalerate) on all life stages of the red flour beetle. Insect mortality generally decreased as the amount of residual food (flour) increased, and mortality was reduced if the insects were sheltered. Because differences in beetle mortality between insecticides were considerably less than differences attributed to flour deposits, this suggests that sanitation and removal of obstructions prior to aerosol insecticide treatments was more important than choice of a particular insecticide.

4. Rebound in red flour beetle trap captures following flour mill structural fumigations determined. The rate at which pest populations recover following structural fumigations of food processing plants is influenced by both the fumigant treatment and the management and environmental conditions following treatment. More effective management of this rebound could reduce the need to perform fumigations and make methyl bromide alternatives more viable. ARS scientists in Manhattan, KS, and Gainesville, FL, evaluated rebound over time after fumigation in red flour beetle captures in pheromone traps, a measure of pest abundance, using data from 21 fumigations in two mills. Evaluation of the time it took for beetle captures to increase to different thresholds indicated that both time of year fumigation was performed and integrated pest management practices performed within the mill after fumigation affected rebound time. A new monitoring threshold was developed that might be useful as a management target to reduce risk. These findings provide baseline information on methyl bromide efficacy, but also illustrate how population growth can be manipulated to reduce the need to fumigate.

5. Differences in aerosol insecticide residual control among pest species suggest different application rates should be used. Aerosol insecticide applications of pyrethrin mixed with an insect growth regulator (IGR) methoprene are being used with increasing frequency inside flour mills, but residual efficacy of these insecticidal mixtures was not known. ARS scientists in Manhattan, KS, and University cooperators exposed flour in petri dishes to applications of either low (1%) or high (3%) rates of pyrethrin + the IGR methoprene and then measured the survival of immature red flour beetle and the confused flour beetle at two week intervals. This showed that there was residual activity of the insecticide mixture and that confused flour beetle was the more tolerant species. Results show that if the red flour beetle is the target species, the low rate of pyrethrin + methoprene was sufficient, but if the confused flour beetle is the target pest the higher rate would be preferable.

6. Indianmeal moth simulation model developed and tested in stored corn. The Indianmeal moth is a common pest of stored corn. ARS scientists in Manhattan, KS, and Gainesville, FL, developed a computer model to simulate population development of the Indianmeal moth in stored corn. The model accurately simulated population development of Indianmeal moths in corn stored during fall and winter of three separate storage seasons in South Carolina, but did not accurately predict populations in the spring. Despite this, the model should be useful from a management perspective because the corn is being sold off or used up after winter, and the observed Indianmeal moth populations never reached damaging levels after winter. The model will be useful for predicting Indianmeal moth population levels in stored corn to time management actions and will be evaluated for its applicability to populations in food processing facilities.

7. New insect growth regulator controls stored-product insects. Pyriproxyfen (trade name NyGard®) is a new insect growth regulator that was recently labeled by the US-EPA for use as an aerosol and as a surface treatment inside mills and food storage warehouses. An ARS scientist in Manhattan, KS, demonstrated that even though applied at a lower rate, NyGard gave generally greater residual control, as determined by reduced adult emergence of four beetle species and the Indianmeal moth, than Gentrol®, which is also an insect growth regulator. Residual activity of an insecticide can be impacted by the substrate to which it is applied, but NyGard performed better than Gentrol on plywood, metal, and tile treated surfaces. The Indianmeal moth larvae were generally more tolerant to both insecticides than the beetle larvae, but there were variations in susceptibility among the different beetle species. The overall results showed that NyGard was effective and it could be used as a residual surface treatment in management programs for control of stored-product insects.

Review Publications
Campbell, J.F., Toews, M.D., Arthur, F.H., Arbogast, R.T. 2010. Long Term Monitoring of Tribolium castaneum Populations in Two Flour Mills: Rebound After Fumigation. Journal of Economic Entomology. 103: 1002-1011. DOI: 10.1603/EC09348.

Campbell, J.F., Toews, M.D., Arthur, F.H., Arbogast, R.T. 2010. Long Term Monitoring of Tribolium castaneum in Two Flour Mills: Seasonal Patterns and Impact of Fumigation. Journal of Economic Entomology. 103: 991-1001. DOI: 10.1603/EC09347.

Jenson, E.A., Arthur, F.H., Nechols, J.R. 2009. Efficacy of Methoprene Applied at Different Temperatures and Rates to Surface Substrates to Control Eggs and Fifth Instars of Plodia interpunctella. Journal of Economic Entomology. 102: 1992-2002.

Jenson, E.A., Arthur, F.H., Nechols, J.R. 2010. Efficacy of an Esfenvalerate plus Methoprene Aerosol for the Control of Eggs and Fifth Instars of Plodia interpunctella (Lepidoptera: Pyralidae). Insect Science. 17: 21-28.

Last Modified: 06/23/2017
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