Novel Fumigants and Heat Treatments for Flour Mills

The efficacy of methyl bromide fumigations in mills (6 mills) was compared to heat treatments (3 mills), sulfuryl fluoride (ProFume®) (4 mills) and phosphine (ECO2FUME®), heat and carbon dioxide combination treatment (2 mills). The efficacy of treatments was estimated in three ways: Tribolium castaneum adults and eggs in vials during treatment, pheromone traps and rebolt sifter tailings counts. Almost all treatments were effective in killing 100% of adult T. castaneum put out in vials. There was more survival of eggs. In the sulfuryl fluoride treatments, egg mortality ranged from 35 to 99.6%. The other treatments had egg mortalities over 98%. Insect populations in the mills were estimated using pheromone traps. In methyl bromide treatments, the range of times that it took insect populations to rebound to pre-treatment levels was between 3 weeks or over 30 weeks. For sulfuryl fluoride the rebound took from as little as 1 week to never rebounding within the 18-week study. Phosphine combination treatment saw populations rebound within seven to 29 weeks. In all three heat treatments, none of the populations returned to the original levels by 19 weeks posttreatment. Adult and larva flour beetles were monitoring in the tailings from rebolt sifters. For the most of the mills, there is a good correlation between insects found in the pheromone traps and insects found in the rebolt sifter tailings. However, on several occasions pheromone traps were not a good predictor of insect numbers in the rebolt sifter tailings. In methyl bromide treatments, the rebound of insect populations to pre-treatment levels occurred between 13 and over 31 weeks. For sulfuryl fluoride, the rebound occurred between 9 and over 18 weeks. The phosphine combination treatment saw populations rebound within 1 to 33 weeks. In all three heat treatments, the mills either did not sample rebolt sifter tailings or no insects were found in the tailings.