Submitted to: Journal of Stored Products Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/8/2019
Publication Date: 8/15/2019
Citation: Arthur, F.H., Scheff, D.S., Brabec, D.L., Bindel, J. 2019. Aerosol concentration, deposition, particle size, and exposure interval as mortality factors Tribolium confusum Jacquelin du Val (Coleoptera: Tenebrionidae). Journal of Stored Products Research. 83:191-199. https://doi.org/10.1016/j.jspr.2019.06.005.
Interpretive Summary: Aerosol insecticides are being increasing used as an alternative to the fumigant methyl bromide for control of insects in wheat and rice mills. Previous research has provided some data regarding effects of particle size on insect control, but additional data were needed on effects of intermediate droplet sizes and sublethal impacts on insects that recover from exposure. Studies conducted using adult confused flour beetles treated directly with a combination aerosol of pyrethrin and the insect growth regulator methoprene, showed that as exposure time (5, 10 and 20 minutes) and particle size (4 to 16 microns) increased effectiveness of the aerosol increased as well, but when adults were provided with a food source after exposure effectiveness decreased. When late-stage larvae of the confused flour beetle were exposed on concrete arenas previously exposed to the combination aerosol, and as exposure time and particle size increased the ability to develop and emerge as a normal appearing adult decreased. Aerosol particle size, and not aerosol concentration, is the most important factor in assessing the effectiveness of aerosols. Aerosol application equipment could be adjusted to spray at particle sizes which give the most effective deposition and control of stored product insects.
Technical Abstract: A series of experiments was conducted in which adults of Tribolium confusum Jacquelin du Val, the confused flour beetle, were exposed on concrete arenas and treated with a combination aerosol of pyrethrin+methoprene dispensed for 5, 10, and 20 minutes at particle sizes of 4, 8, 12, and 16 µm, inside an aerosol exposure chamber. Nearly all adult T. confusum were knocked down when removed from the chamber. Among all the exposure time and particle size combinations, recovery increased as the post-exposure holding period increased from one to seven days and when adults were transferred to untreated dishes with flour. A second experiment evaluated the residual effect of the aerosol on concrete arenas at 1, 3, and 6 weeks using 3-4- week-old larvae of T. confusum. Adult emergence of exposed larvae decreased with increasing particle size and exposure time. A third set of experiments investigated effects of particle size on adult fecundity for the 10-minute exposure time. A biological index that assessed development of exposed larvae to the pupal and adult stages was also related to particle size and exposure interval, and this index was correlated with adult emergence. Male and female adults were cross-mated: exposed female with exposed male, exposed female with unexposed male, exposed male with unexposed female, and unexposed female and unexposed male. Progeny production was reduced as particle size increased, and there were indications that females were affected more than males by the aerosol exposure. This research could be used to improve insect pest management programs by emphasizing sanitation when using aerosols to control adult stored product insects. Adjusting application equipment to dispense aerosols at particle sizes that give optimum control of exposed adults and residual control of immatures would also benefit pest management programs.