Climbing ability of Trogoderma granarium larvae on artificial household and insecticide-treated materials

Authors: DOMINGUE, MICHAEL - Animal And Plant Health Inspection Services (APHIS), National Wildlife Center; Scheff, Deanna; LEVA, NATASHA - Animal And Plant Health Inspection Services (APHIS), National Wildlife Center; MYERS, SCOTT - Animal And Plant Health Inspection Services (APHIS), National Wildlife Center

Submitted to: Journal of Stored Products Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/17/2021
Publication Date: 12/23/2021
Citation: Domingue, M.J., Scheff, D.S., Leva, N., Myers, S.W. 2021. Climbing ability of Trogoderma granarium larvae on artificial household and insecticide-treated materials. Journal of Stored Products Research. 95. https://doi.org/10.1016/j.jspr.2021.101922.
DOI: https://doi.org/10.1016/j.jspr.2021.101922

Interpretive Summary: The khapra beetle is a serious pest of stored grains throughout the world. This insect is not established in the United States and is considered a quarantine pest. Currently, monitoring programs are in place throughout the country to detect and intercept this species before it becomes established. Traditionally, traps for this species are placed on vertical walls, but there is limited information on the movement of khapra beetle larvae across different surface types and angles and how this could impact trap efficiency. We found that rougher surfaces, such as plywood, sheetrock, tile, cement, and netting were much more easily climbed compared to slick surfaces like plastic, painted cement, and metal. Angle of the surface was also an important factor and as the surface increased from 0° to 90°, fewer larvae were able to climb upwards. Adding tape strips to provide a corridor for larvae to climb to reach the trap improved the ability of the larvae to climb. Tape with a rough or paper like surface promoted more effective climbing compared to smoother tapes. When traps need to be mounted on smooth or slick surfaces, use of tape corridors could improve ability of larvae to reach the traps, but this needs to be confirmed with field testing. The results of this study can help to improve trap placement recommendations for monitoring programs, particularly at ports of entry into the United States where detection is especially critical.

Technical Abstract: The khapra beetle, Trogoderma granarium is a serious pest of stored grains in many nations. Larvae of T. granarium may be persistent in warehouse conditions due to the ability to enter facultative diapause. Thus, a better understanding of their behavior with respect to movement as they seek places of refuge or food may lead to improvements in the development of monitoring tools and control technologies. The distance that khapra beetle larvae walk on a variety of surfaces at different angles was examined for 10-minute intervals. Certain surfaces such as plywood, sheetrock, tile, cement, and netting were much more easily climbed than plastic, painted cement, and metal. Movement would often increase when the surface inclination increased from 0° to 30°, but then decrease at 60° or 90°. Tape corridors promoted climbing, and those with paper-like surfaces such as masking tape or lab labeling tape provided the most benefit. Other tapes with slippery or textured surfaces did not promote climbing. We also tested the ability to move on plastic bag and netting material impregnated with insecticide at different angles. Regardless of insecticide treatment, plastic bags were much less amenable to larval movement than netting. At the same time, there was little effect of the insecticide on slowing movement in these brief trials. The results suggest that optimal placement of wall traps should include and assessment of the surface, and that incorporating insecticide-treated nets or bags into new technologies must account for larval mobility on such surfaces.