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

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-min 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 degrees to 30 degrees, but then decrease at 60 degrees or 90 degrees. 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 an assessment of the surface, and that incorporating insecticide-treated nets or bags into new technologies must account for larval mobility on such surfaces.