The behavioral response to the putative necromones from dead Tribolium castaneum (Coleoptera: Tenebrionidae) in traps by conspecifics as a function of density and time since capture

Long-term trapping programs of stored product pests provide information for timely and accurate pest management. Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) is a highly successful external-infesting grain pest and is frequently monitored using a commercial pitfall trap that combines pheromonal and kairomonal stimuli. However, an often overlooked component of lure-based traps is the potential for the volatile plume to change over time as individuals are captured. These now-dead insects may then release necromones altering the captures of conspecifics. In this study, we evaluated changes in (i) the behavior of T. castaneum and (ii) the relative change in volatiles over time since dead insects were added and among different densities of dead conspecifics in a commercially available kairomone oil. We used multiple behavior assays, including wind tunnel, release-recapture, and 2-way olfactometer, and performed chemical analyses via headspace collection and gas chromatography coupled with mass spectrometry. Tribolium castaneum response to the kairomone lure was not consistent among assays of density of conspecifics between 4 and 40 adults after 24 or 96 h, or time of seeding over 1-96 h or 8-11 days prior. Tested strains collected in 2012 and 2019 ruled out strain-specific differences. Oil batch effects were also ruled out as a factor contributing to the response of T. castaneum. The relative volatile composition was generally stable among the treatments despite using different seeding densities and seeding times. Given that attraction and relative volatile composition were generally unaffected by prior captures, long-term monitoring programs may be robust in their interpretability over time. Graphical Abstract