Traps for Gauging Fumigation Effectiveness in Commercial Facilities James F. Campbell USDA ARS CGAHR, Manhattan Kansas
Evaluation of Treatment Efficacy Question: what impact does a management tactic such as fumigation have on pest populations in mills Problem: Difficult to accurately measure pest population Difficult to replicate, have adequate controls, or isolate impact from other concurrent tactics
In Depth Analysis from Two Mills Use results of red flour beetle monitoring projects from two flour mills in the same geographic area Six or more years of monitoring data Total of 23 fumigations performed Evaluate impact of fumigations and IPM on pest populations as measured using pheromone trapping Immediate reduction following treatment Rebound after treatment Determine what factors impact fumigation efficacy Determine if risk thresholds can be developed for flour mills based on monitoring data
Mill #1 Monitored continuously - July 2002 - December 2008 Eleven structural fumigations performed, with ten complete inter-fumigation periods of monitoring data Nine with methyl bromide Two with sulfuryl fluoride Starting in November 2004, IPM program improved Regular aerosol treatments (1% or 3% synergized pyrethrins and methoprene) Enhanced sanitation Targeted sanitation and residual insecticide application in areas where pheromone trap captures were elevated
Mill #2 Monitored continuously between March 2003 - December 2008 Twelve structural fumigations were performed, with 11 complete inter-fumigation periods of monitoring data 12 with methyl bromide
Pheromone Trapping Program Tribolium castaneum – red flour beetle Dome Traps Mill #1: 55 traps Mill #2: 32 traps
Mill #1 – Mean Trap Capture
Mill #1 – Mean Trap Capture
Mill #1 – Mean Trap Capture Change in Mill Management Aerosol treatments Enhanced sanitation Targeting trap hot spots
Mill #1 and #2 – Mean Trap Capture Mean Trap Capture – Mill #1 Change in Mill Management Aerosol treatments Enhanced sanitation Targeting trap hot spots Mean Trap Capture – Mill #2
Percent Reduction in Mean Beetle Capture Mean capture (beetles/trap/2 week period) last monitoring period before 92±2% 78±8% fumigation compared to mean capture first monitoring after fumigation
Fumigation Efficacy – Initial Reduction in Beetle Captures Two mills did not differ from each other in reduction in trap capture after fumigation 85±5% reduction in beetles/trap/period (23 fumigations) 11±3 beetles/trap/period immediately before fumigation 1±0 beetles/trap/period immediately after fumigation Only 3 fumigations had no captures immediately after fumigation
Effect of Season on Efficacy Fumigations sorted into spring (April - June) (n=9) and fall (October – December) (n=11) periods Temperature during fumigation for combined mills Outside temperature differed between seasons ( F =8.90; d.f.=1,16; P =0.0083) Fall (11.8 1.8 C) cooler than spring (18.9 1.2 C) Inside temperature did not differ between seasons ( F =0.03; d.f.=1,16; P =0.8625) Spring (24.6 1.2 C) and fall (24.4 0.6 C)
Impact of Season on Fumigation Efficacy: Reduction in Mean Trap Capture Also no difference in the mean number captured immediately after fumigation ( F =2.86; d.f.=1,18; P =0.1083)
Mechanism Beetle capture immediately after fumigation could result from: Survival within structure Prediction: number captured after fumigation should be proportional to number present before fumigation Test: positive correlation between captures before and after fumigation (Pearson Correlations, P <0.05)
Mechanism Beetle capture immediately after fumigation could result from: Movement into structure after treatment Prediction: captures after fumigation should be greater after warm season fumigations then after cool season fumigations Test: no significant difference between seasons (GLM: P>0.05)
Rebound after Treatment How numbers captured change over time after treatment – rate of increase or rebound Rebound influenced by… Survival within the structure Immigration Recolonization by individuals driven out during treatment Colonization by new individuals (own movement or infested inbound products) Reproduction - impacted by environmental conditions and management tactics
Fumigation Efficacy – Rebound in Beetle Captures Mill #1 Mill #2 spring summer fall Time after Fumigation (Days)
Population Growth Different simple models for population growth with and without competition Tested how well trap captures after fumigation fit models, but none explained results well for either combined or individual fumigations Logistic Growth to Exponential Carrying Capacity Growth from Price (1984)
Fumigation Efficacy – Rebound in Beetle Captures Developed threshold value to compare rebound rates – 2.5 beetles/trap/2 wk period (= median trap capture prior to fumigation) Mill #1 Mill #2 spring summer fall Time after Fumigation (Days)
Fumigation Efficacy – Rebound in Trap Captures Two mills did not Combined Mills and Seasons differ from each other in the time required to reach 174±33 days (n=21, 8 did not reach) threshold (Kaplan- Meier log-rank test: Z =0.702, P =0.402) Mill #1 did not reach threshold two times, but Mill #2 did not reach on six Time after Fumigation (Days) occasions
Fumigation Efficacy – Rebound in Beetle Captures Significant effect of season on rebound to mean beetle capture threshold ( Z =10.389, P =0.006) Sorted by Season Proportion of Post-Fumigation Periods Mean Trap Capture Threshold that had Not Reached 248±50 days (n=9, 5 did not reach) 104±21 days (n=9, 3 did not reach) Time after Fumigation (Days)
Before and After Management Changes (Mill #1) GLM: F 1,166 =64.91, P<0.0001
Before and After Management Changes (Mill #1) GLM: F 1,9 =0.04, P=0.8438
Before and After Management Changes (Mill #1) Change in management increased rebound time Reduced from 2-3 fumigations/year to 1 fumigation – just in the fall Mean Threshold 246±71 days (n=5, 2 did not reach) 49±15 days (n=5, 0 did not reach) Time after Fumigation (Days)
Mechanism Slower post-fumigation rebound time after change in IPM program could result from: Reduction in founder population Prediction: reduced number captured after fumigation increases rebound time Test: 1. number captured immediately after fumigation lower after IPM change (GLM, P <0.05) 2. significant negative correlation between rebound time and number after treatment (Pearson Correlations, P <0.05)
Mechanism Slower post-fumigation rebound time after change in IPM program could result from: Change in season when fumigation performed Prediction: cooler temperatures inside mill after fall fumigations results in slower population growth Test: comparing change in capture from one monitoring period to the next: season was significant factor (GLM, P <0.05)
Mechanism Slower post-fumigation rebound time after change in IPM program could result from: Increased mortality due to enhanced IPM Prediction: aerosol treatments, extra sanitation, and targeted responses reduce pest population size and colonization ability Test: comparing change in capture from one monitoring period to the next: IPM program and interaction between IPM and season were not significant (GLM, P >0.05)
Management Thresholds based on Trapping Focused on change in trap capture from one monitoring period to the next If rebound in beetle captures fits an exponential function, size of increase should increase with increasing mean trap capture Goal to keep beetle captures Exponential Growth in the relatively flat portion of the rebound curve – where potential increases will be smaller
Risk Thresholds – Mean Trap Capture Positive correlation No correlation between between number captured number captured and and change from the change in number in next previous period (Pearson monitoring period ( P =0.151) Correlation Coefficient, P <0.001)
Risk Thresholds – Mean Trap Capture Above and below the 2.5 beetles/trap/monitoring period Overall - below: 0.34±0.08 above: 1.76±0.8 (Not significantly different Mann-Whitney rank sum test, P=0.607) Just intervals with increase - below: 0.9±0.2 above: 5.4±1.2 (Significantly different, P<0.001)
Expand Dataset to Include More Mills (Twelve Wheat or Rice Mills) 691 monitoring -0.37±0.12 1.31±0.72 periods in 12 mills Significant difference in captures in next monitoring period above and below threshold (Mann-Whitney Rank Sum Test, P <0.001)
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