Influence of temperature and artificially-created physical barriers on the efficacy of synergized pyrethrin aerosol

https://doi.org/10.1016/j.jspr.2014.10.004Get rights and content

Highlights

  • Barriers limit dispersion of pyrethrin aerosol and cause reduced efficacy of pyrethrin aerosol.

  • Recovery of adult Tribolium confusum from initial exposure increases when barriers are present.

  • Temperature variation did not affect aerosol efficacy.

Abstract

The dispersal of aerosol insecticides within a flour mill may be hampered by barriers created from machinery and other equipment that block dispersion. Additionally, seasonal temperature variations may influence aerosol dispersion and subsequent effectiveness against stored product insects. The influence of barriers and temperatures on the efficacy of synergized pyrethrin aerosol against adults and pupae of the confused flour beetle, Tribolium confusum (Jacquelin du Val), was evaluated in experimental sheds. Insects were exposed to the aerosol at target temperatures of 22, 27, and 32 °C. Wooden boxes 1 m in length, 20 cm in width, and 5, 10, or 20 cm in height were used for creating different open and concealed areas for exposing insects. Results showed that exposing adults of T. confusum in open areas produced more moribund adults (those knocked down and unable to move except for reflex twitching or unable to respond when touched with a probe) at all temperatures, while survival increased with increasing distance from the front to the back of the boxes. Given the decreased survival, it would appear that more aerosol dispersed under the box height of 20 cm compared to 5 and 10 cm box heights because survival was generally less under the 20 cm box compared to the other two. Less than 2% of the pupae exposed in the open emerged as adults, but as the distance increased from the front to the back of the box adult emergence from these exposed pupae increased. Synergized pyrethrin aerosol can provide good control of T. confusum pupae and adults and may not be affected by seasonal temperature variations, but aerosol dispersion into obstructed or concealed areas may affect control.

Introduction

The confused flour beetle, Tribolium confusum Jacquelin du Val, along with the related species Tribolium castaneum (Herbst), are important pests of flour mills in the United States of America (USA) (Arthur, 2008, Arthur and Campbell, 2008). The constant availability of flour patches and the structural complexity created by different types of processing equipment can create areas inside of flour mills that are conducive for growth and development of both species (Good, 1937, Cotton, 1958, Campbell and Runnion, 2003). Also, T. castaneum adults can fly whereas T. confusum adults do not appear to fly (Rees, 2004).

Historically fumigation with methyl bromide as a whole-plant treatment was the primary strategy used to control insect infestations inside flour mills in the USA. Options for whole-plant treatment of mills include alternative fumigants such as sulfuryl fluoride, cylinderized phosphine, or heat treatments. However, heat treatment may not be suitable for many older facilities and can be cost-intensive, while fumigants require facility shutdown, and phosphine could cause potential damage to equipment and structural components (Fields and White, 2002, Brijwani et al., 2009, Subramanyam et al., 2011).

Synergized pyrethrin has the potential to be a technically and economically feasible alternative to fumigants or heat. Aerosols can be used to target a portion of a facility, which makes them a cost effective and desirable option for many commercial operations (Boina and Subramanyam, 2012). However, dispersal of aerosol inside a flour mill may be limited by barriers such as milling equipment and structural components. Movement underneath concealed and obstructed areas and resulting particle deposition may be reduced compared to more open areas (Boina and Subramanyam, 2012).

Bernhard and Bennett (1981) reported lower dispersion of synergized pyrethrin aerosol in open and partly open cabinets, and in closed areas compared to completely exposed areas. Similarly, Toews et al. (2010) reported less than 75% mortality in all life stages of T. castaneum exposed under wooden pallets as opposed to at least 80% mortality when these life stages were exposed in open areas without obstructions. Campbell et al. (2014) conducted a study whereby T. confusum were exposed within a flour mill in areas that would be open or obstructed to the aerosol, such as underneath equipment, along walls and corners, and beside structural beams. There was variation in efficacy for two formulations of aerosol pyrethrin, which led to greater recovery in obstructed sites and along the walls and in corners compared to the more open areas. However, mortality of adults was almost 100% when exposed to the organophosphate dichlorvos (Campbell et al., 2014, Subramanyam et al., 2015).

Additionally, ambient temperature inside a facility during aerosol application may influence insecticidal efficacy. Campbell et al. (2010) conducted a study in which they monitored temperature within a flour mill and in a wheat-processing facility. They reported average daily temperature inside the facilities to be about 24 and 30 °C during cool and warm seasons, respectively. Although pyrethrin insecticide has a negative temperature coefficient, the addition of the synergist piperonyl butoxide increases its toxicity at higher temperatures (Blum and Kearns, 1956). Higher temperatures may also facilitate dispersion of aerosols into hidden and obstructed areas. In general, there is a lack of published data regarding the distribution and efficacy of synergized pyrethrin aerosol at different temperatures. The only recent results are described in Campbell et al. (2014), in which the evaluations described in the preceding paragraph were conducted at target temperatures of 27 and 40 °C (low and high, respectively). There was greater 24 h knockdown of adult T. confusum exposed to the pyrethrin aerosols at the high versus low temperature, but after 2 weeks the reverse had occurred, indicating a greater recovery of at the high versus low temperatures.

In previous tests conducted inside small-scale experimental sheds, larvae and adults of T. confusum were more tolerant to a commercial formulation of pyrethrin aerosol compared to pupae and (Kharel et al., 2014ab). Therefore, T. confusum pupae and adults were selected for the present study to represent tolerant immobile and an active stage, respectively. The objectives were to evaluate the efficacy of synergized pyrethrin aerosol at temperatures of 22, 27, and 32 °C against T. confusum adults and pupae, and to observe effects of dispersion of the insecticide underneath a barrier.

Section snippets

Materials and methods

This study was conducted in six experimental sheds at the USDA-ARS Center for Grain and Animal Health Research (CGAHR), Manhattan, KS, USA. The experimental sheds were 6 m long, 2.9 m wide and 2.6 m high, and each was equipped with a heating/air conditioning unit that could be set at different temperatures. The target temperatures for the study were 22, 27, and 32 °C. A treatment and control shed was designated for each temperature, and the thermostats were set to the desired temperatures.

Results

Temperature data for replicates 1 and 2 were lost due to an error in launching the HOBO data recorders, however; actual temperatures in the sheds during the designated time blocks for replicates 3–6 for the target temperatures of 22, 27, and 32 °C averaged 19.5 ± 0.1, 26.5 ± 0.2, and 31.6 ± 0.1 °C. The combination of the thermostatic controls on the heating/air conditioning units plus timing the sprays with specific time periods during the day allowed us to obtain desired temperatures within

Discussion

Our results indicated that when adults of T. confusum were exposed to pyrethrin aerosol in an open area compared to the obstructed positions underneath the boxes, there was little survival of adults exposed at all three test temperatures of 22, 27, and 32 °C. Campbell et al. (2014) reported that mortality of adult T. confusum exposed to two different pyrethrin formulations (Aerotech, 0.7% AI pyrethrin and Pyrocide, 1% AI pyrethrin), was greater in open than in obstructed positions inside a

Acknowledgments

We would like to express our sincere thanks to B. Barnett, R. Hammel, and K. Hartzer for technical assistance. We thank Entech Corporation for providing the insecticide used in this study. This research was partially funded by the Department of Agriculture, National Institute of Food and Agriculture (NIFA) Methyl Bromide Transitions program (grant number 2010-51102-21660). Insect voucher specimens were deposited at the Kansas State University Museum of Entomological and Prairie Arthropod

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