The Presence of Flour Affects the Efficacy of Aerosolized Insecticides used to Treat the Red Flour Beetle,Tribolium castaneum

Abstract

Experiments were conducted in tightly sealed pilot scale warehouses to assess the efficacy of common aerosolized insecticides on all life stages of Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) when exposed in dishes containing 0 to 2 g of wheat flour either under pallets or out in the open. Petri dishes containing 0, 0.1, 1, or 2 g of flour were prepared with 25 eggs, 3rd instars, pupae, or adults and then immediately treated with aerosolized solvent, Pyrethrins, or esfenvalerate. Twenty-four h after insecticide exposure, the dishes were brought to the laboratory and placed in a growth chamber and held for a 3 day moribund (knockdown) assessment and a 21 day mortality assessment. Mortality in untreated controls was generally less than 10%, with the exception of the 21 day counts of adults and eggs. Solvent-treated replications followed similar trends, except that additional mortality was observed in exposed larvae and pupae. In the insecticide-treated dishes, mortality of T. castaneum provisioned with flour generally showed a linear decrease with increasing flour deposits. Regardless of life stage, mortality did not exceed 60% when individuals were exposed in petri dishes containing 2 g of flour. Exposure location also made a significant difference in observed mortality. While mortality never exceeded 75% in dishes positioned under pallets, there was never less than 80% mortality in dishes exposed in the open. Although there was a perceptible increase in mortality with esfenvalerate compared to Pyrethrins, these differences were considerably less than the variation observed among flour deposits. The study suggests that sanitation and preparation prior to aerosol insecticide treatments were more important than choice of a particular insecticide.

Insect Management with Aerosols in Food-Processing Facilities

“…The recovery and survival were positively correlated with post-exposure time and the amount of flour present in dishes (Arthur and Campbell 2008). Similar observations of knockdown and recovery of T. castaneum life stages exposed to synergized pyrethrins and esfenvalerate applied separately at label rates in pilot scale warehouses were made in the presence of flour as food, both in open and concealed locations (under wooden pallets) (Toews et al 2010). Arthur and Campbell (2008) noticed that T. confusum adults exposed to the synergized pyrithrins in Petri dishes with flour during application and later transferred to new Petri dishes along with the same flour showed increased survival.…”

“…This discrepancy was partly explained by the fact that the nozzles delivering aerosol particles were directed to the front of the experimental room (Arthur and Campbell 2008), suggesting non-uniform distribution throughout the empty warehouse. Toews et al (2010) observed that exposure to synergized pyrethrin and esfenvalerate applied separately as aerosols at label rates resulted in higher mortality of all life stages of T. castaneum in open locations than in concealed locations (under wooden pallets).…”

“…Similarly, methoprene applied alone at the label rate was highly toxic to larvae of T. confusum (open locations) and T. castaneum (open and concealed locations) but moderately toxic to eggs of P. interpunctella exposed in media (Arthur 2008, Jenson et al 2010b). Gillenwater et al (1971), Arthur and Campbell (2008), and Toews et al (2010) showed that both exposure location and presence of flour as the food source in a facility influenced insect control. Synergized pyrethrins applied at the label rate in an empty warehouse resulted in a wide variation in mortality (20-94%) of T. confusum adults exposed in Petri dishes without flour in the rear part of the warehouse whereas more than 80% mortality occurred in Petri dishes that were placed in the front part of the warehouse (Arthur and Campbell 2008).…”

Spatial Pattern in Aerosol Insecticide Deposition Inside a Flour Mill

“…This improved coverage increases the chance of a stored-product insect encountering the insecticide either during application or afterwards through contact with a treated surface. However, because at a given point in time most of the pest population is located in hidden areas (e.g., inside equipment, accumulated food in cracks and crevices, under pallets, inside packaged food), only a small percentage of individuals are likely to be directly exposed during an aerosol application (Toews et al 2010. The structural complexity of many food facility interiors may also inßuence the dispersal and deposition of aerosol droplets, creating spatial variation in dosage.…”

“…The majority of the research on efÞcacy has been under laboratory conditions simulating aerosol applications made directly to the insects Arthur 1988Arthur , 1993Arthur and Gillenwater 1990;Tucker et al 2014) or aerosol applications conducted in small rooms (Jenson et al 2010a, Toews et al 2010. Data on the efÞcacy of aerosol insecticides applied at the scale and under the conditions typically found in commercial applications are much more limited.…”