Mobility of stored product beetles after exposure to a combination insecticide containing deltamethrin, methoprene, and a piperonyl butoxide synergist depends on species, concentration, and exposure time

Authors: Arthur, Franklin; ATHANASSIOU, CHRISTOS - University Of Thessaly; Morrison, William - Rob

Submitted to: Insects
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/23/2020
Publication Date: 2/29/2020
Citation: Arthur, F.H., Athanassiou, C.G., Morrison III, W.R. 2020. Mobility of stored product beetles after exposure to a combination insecticide containing deltamethrin, methoprene, and a piperonyl butoxide synergist depends on species, concentration, and exposure time. Insects. 11:151. https://doi.org/10.3390/insects11030151.
DOI: https://doi.org/10.3390/insects11030151

Interpretive Summary: Studies with susceptibility of stored product insects to insecticides often focus on direct mortality while providing little information on sublethal effects such as movement of insects after they are exposed on treated grains or a treated surface. We conducted studies by exposing adults of the lesser grain borer, the rusty grain beetle, and the rice weevil on wheat treated with an experimental formulation of deltamethrin+methoprene+piperonyl butoxide synergist. Movement and velocity of movement was assessed after 1, 24, and 72 hours of exposure to various concentrations of the insecticide ranging from 0 (untreated) to 100% of the proposed label rate. Movement was assessed through the use of a camera recording system (Ethovision). For all species, movement and velocity of movement decreased as concentration and exposure time increased. The lesser grain borer was the most susceptible species, after 72 hours movement had virtually ceased at nearly all concentrations. The rusty grain beetle was more mobile, and more tolerant, but movement still declined by 60-80% after 72 hours of exposure to concentrations of 50% or more of the proposed label rate. The rice weevil was the most tolerant species, with little decline in movement or velocity after 1 hour of exposure, but again there was a general pattern of declining movement with increasing concentration after the 24 and 72-hour exposures. Results show that sub-lethal effects can be an important component of pest management programs because insects that are less mobile after exposure to an insecticide will be less likely to colonize grain and food products. In addition, our results show the Ethovision system could be used to examine movement of adult stored product beetles after exposure to treated grains, and provide an assessment of sub-lethal effects that could also be related to direct mortality of insecticides.

Technical Abstract: Adults of Rhyzopertha dominica (Fab), the lesser grain borer, Cryptolestes ferrugineous (L.), the rusty grain beetle, and Sitophilus oryzae (L.), the rice weevil, were exposed for 1, 24, and 72 hours on wheat treated with concentrations of 0 (untreated controls) to 100% of the proposed label rate of an experimental formulation of deltamethrin+methoprene+piperonyl butoxide synergist. Movement and velocity of movement were assessed after each exposure time using a camera-based monitoring system (Ethovision®). Movement of R. dominica decreased with increasing concentration and exposure time so that movement had virtually ceased at the 72-hour exposure. Cryptolestes ferrugineous was less susceptible compared to R. dominica, but there was still a general pattern of decreased movement and velocity of movement with increasing concentration and exposure time. Sitophilus oryzae was the least susceptible species, with less differences at the 1-hour exposure interval compared to the other two species, but after 24-72 hours the patterns of declining movement and velocity were apparent as the concentration increased. Data were analyzed using curve-fit equations to show the relationship between concentration and exposure time for each species. Results show that the Ethovison system can be used to assess sub-lethal effects of exposure to grain protectant insecticides, and elucidate behavioral variation between different stored product insects.