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

For the first time, 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. • The addition of kairomone oil increased trap catches in most species tested. • Resistance status alone had limited effect on trap response. • Greater trap response was observed in T. castaneum larvae than adults. • Prior captures may influence trap performance, particularly after fumigation.