Bioassays and methodologies for insecticide tests with larvae of Trogoderma granarium (Everts), the khapra beetle

Authors: Arthur, Franklin; DOMINGUE, M - Kansas State University; Scheff, Deanna; MYERS, S - Animal And Plant Health Inspection Service (APHIS)

Submitted to: Insects
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/14/2019
Publication Date: 5/22/2019
Citation: Arthur, F.H., Domingue, M.J., Scheff, D.S., Myers, S.W. 2019. Bioassays and methodologies for insecticide tests with larvae of Trogoderma granarium (Everts), the khapra beetle. Insects. 10(5):E145. https://doi.org/10.3390/insects10050145.
DOI: https://doi.org/10.3390/insects10050145

Interpretive Summary: The khapra beetle is a potentially invasive stored product insect that is subject to quarantine actions if it is detected by USDA-APHIS during inspections of inbound goods and seaports and airports. Control recommendations are out of date, and new insecticides are needed to replace older organophosphate insecticides for use as surface treatments. However, testing methodologies often affect results of insecticide treatments. In one study, a new formulation of deltamethrin (Polyzone) was assessed for residual efficacy when treated arenas were stored outside, inside a shed, or on a laboratory counter. Survival of khapra beetle larvae was high on the arenas held outside compared to those arenas held inside the shed or inside the lab, suggesting rapid degradation of residues so that the insecticide efficacy was compromised. Also, the highest label rate was more effective than a low-midrange label rate. In a second test, residual efficacy was evaluated on concrete arenas treated with a new formulation of the insect growth regulator methoprene plus deltamethrin plus the synergist piperonyl butoxide. When larvae were exposed on the treated arenas few were able to complete development to the adult stage, but there was evidence that food material absorbed the residues from the insecticide. Results how that the new deltamethrin Polyzone and the new methoprene formulation could be incorporated into management plans to assist in eliminating infestations of khapra beetle should they be detected in APHIS inspections.

Technical Abstract: New insecticide treatment options would be beneficial to control programs for Trogoderma granarium Everts, the khapra beetle, in the United States. Two insecticides were evaluated, the Polyzone® formulation of deltamethrin, and a formulation of the insect growth regulator methoprene combined with deltamethrin and the synergist piperonyl butoxide. In the test with Polyzone deltamethrin, concrete arenas were treated with a low and high rate, and held outside, inside a shed, or inside a lab. Compared to storage in the lab, residue degradation increased slightly in the shed, and then further outside, as evidenced by greater larval survival and adult emergence. Across all environmental treatments, the high rate was more effective than the lower rate. For the combination methoprene product, the effect of food contact with treated surfaces was examined. When treating arenas with food, and transferring the food to clean dishes, there was not an immediate effect on larval survival, but there was a reduction in survival and emergence to the adult stage after one month. For both tests, larvae apparently often went into diapause after they were introduced to particular treatment arenas. Both treatments could be utilized in management programs if T. granarium infestations are detected.