The effect of the presence of dead adults with different susceptibility to phosphine in pitfall traps with four different stored product insect species

Authors: SAKKA, MARIA - University Of Thessaly; GOURGOUTA, MARINA - University Of Thessaly; Morrison Iii, William; MONINGUE, MICHAEL - Animal And Plant Health Inspection Service (APHIS); ATHANASSIOU, CHRISTOS - University Of Thessaly

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/7/2025
Publication Date: 10/21/2025
Citation: Sakka, M.K., Gourgouta, M., Morrison III, W.R., Moningue, M.J., Athanassiou, C.G. 2025. The effect of the presence of dead adults with different susceptibility to phosphine in pitfall traps with four different stored product insect species. Journal of Economic Entomology. Volume 199, January 2026, 107439. https://doi.org/10.1016/j.cropro.2025.107439.
DOI: https://doi.org/10.1016/j.cropro.2025.107439

Interpretive Summary: The fumigant phosphine is widely used by the food industry for stored product insect pest management, but resistance to phosphine is an increasing problem among food facilities around the world. Many food facilities monitor for insect activity using commercial pitfall traps with an oil-based food attractant. As insects are captured, they may decay and release odors, altering the attractiveness of the trap to subsequent individuals and impacting the efficacy of the trap. It is also unclear if phosphine susceptibility or resistance of individuals captured in the trap impacts the efficacy of the trap. To address these knowledge gaps, we baited commercial pitfall traps with rice weevil, cigarette beetle, saw-toothed grain beetle, or red flour beetle adults that were either resistant or susceptible to phosphine and measured captures of individuals in trap. We also tested red flour beetle larvae because they are highly mobile and can be found in traps. Red flour beetle adults responded similarly to all the treatments, which included A) in an oil-based food attractant with 5 dead phosphine-resistant individuals; B) oil with 5 dead phosphine-susceptible individuals; C) oil only; D) 5 dead phosphine-resistant individuals; E) 5 dead phosphine-susceptible individuals. Rice weevil, cigarette beetle, and saw-toothed grain beetle responded most strongly to the oil-based food attractant, but presence of dead individuals did not impact trap catches regardless of phosphine susceptibility. However, red flour beetle larvae showed preference for traps containing oil and susceptible individuals. The current work illustrates that previous captures of resistant or susceptible individuals did not significantly influence the number of captured adults in ongoing monitoring programs but red flour beetle might exhibit some differences in responses that warrants further evaluation and could potentially impact interpretation of monitoring programs.

Technical Abstract: The impact on trapping of prior captures involving individuals that were resistant or susceptible to phosphine was evaluated in commercially available pitfall traps (e.g. Dome® traps) for Sitophilus oryzae (L.), Lasioderma serricorne (F.), Oryzaephilus surinamensis (L.), and Tribolium castaneum (Herbst). Adults were used for all the species above, except for T. castaneum in which larvae were also tested. A single trap was placed in a plastic container and used as an arena. Insects were separately released in the arena and different combinations were evaluated with individuals that were placed prior inside the traps as follows: A) in an oil-based kairomone food attractant with 5 dead phosphine-resistant individuals; B) oil with 5 dead phosphine-susceptible individuals; C) oil only; D) 5 dead phosphine-resistant individuals; E) 5 dead phosphine-susceptible individuals. After 7 days the adult or larval capture was recorded. The presence of the oil increased trap captures for S. oryzae, L. serricorne, and O. surinamensis compared to the traps that contained insects only. In general, T. castaneum adults showed a strong response to all five stimuli with prior captures of either phosphine susceptible or resistant individuals impacting trap captures. However, T. castaneum larvae responded most strongly to traps baited with oil and phosphine-susceptible individuals. Furthermore, among the traps baited with insects only, capture of T. castaneum larvae was highest in the traps baited with phosphine-susceptible individuals. The current work illustrates that previous captures of resistant or susceptible individuals may influence the number of captured individuals.