Outcome of direct competition between Trogoderma granarium and Trogoderma inclusum over varying commodities, temperatures and experimental duration

Authors: DOMINGUE, MICHAEL - Animal And Plant Health Inspection Service (APHIS); WU, YUNKE - Animal And Plant Health Inspection Service (APHIS); VIEIRA, KENDRA - Animal And Plant Health Inspection Service (APHIS); MCGRAW, ALANA - Animal And Plant Health Inspection Service (APHIS); FURTADO, MANDY - Animal And Plant Health Inspection Service (APHIS); ATHANASSIOU, CHRISTOS - University Of Thessaly; Morrison, William - Rob; MYERS, SCOTT - Animal And Plant Health Inspection Service (APHIS)

Submitted to: Journal of Pest Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/27/2023
Publication Date: 3/4/2023
Citation: Domingue, M.J., Wu, Y., Vieira, K.A., McGraw, A.R., Furtado, M., Athanassiou, C.G., Morrison III, W.R., Myers, S.W. 2023. Outcome of direct competition between Trogoderma granarium and Trogoderma inclusum over varying commodities, temperatures and experimental duration. Journal of Pest Science. 13. Article 3656. https://doi.org/10.1038/s41598-023-30618-8.
DOI: https://doi.org/10.1038/s41598-023-30618-8

Interpretive Summary: Khapra beetle is an invasive, quarantined stored product dermestid species in the US which would have large negative effects on US export markets if it were to become established. It is closely related to other native beetles already present in the US such as larger cabinet beetle that are not quarantined or invasive. It is unknown if khapra beetle invades the US whether it would outcompete native dermestids at food facilities. In this study, we examined the potential of khapra beetle to displace larger cabinet beetle on wheat and rice in direct competition experiments at two temperatures for nine weeks, and on one commodity (wheat) for 25 weeks. Because larvae of closely related dermestids are extremely difficult to identify morphologically, including these two species, we used a molecular approach to confidently distinguish between each. It was determined that commodity type significantly affected the speed of larval development. The progeny production by khapra beetle was best on wheat at 32°C, while rice was optimal for larger cabinet beetle. However, larger cabinet beetle was more prolific than Khapra beetle on all commodities. Khapra beetle generally did better at warmer than cooler temperatures. When adults were used at the start of the 25-week competition, larger cabinet beetle maintained an advantage at both temperatures. However, if larvae were used to initiate the competition, both species coexisted well at the cooler temperature, but khapra beetle nearly excluded larger cabinet beetle at the warmer temperature. Overall, the results suggest larger cabinet beetle is more resistant to displacement than previously thought, but there may be circumstances in which khapra beetle may successfully invade.

Technical Abstract: The establishment of an exotic pest may require displacing local competitors. Here, we examined the potential of Trogoderma granarium to displace Trogoderma inclusum in a stored product setting. We performed direct competition experiments on three commodities at two temperatures for nine weeks, and on one commodity (wheat) for 25 weeks. Because larvae of different species of the genus Trogoderma are extremely difficult to identify morphologically, we used a molecular approach to confidently distinguish between T. granarium and T. inclusum. We determined that commodity type significantly affected the speed of larval development. The nine-week production of T. granarium was best on wheat at 32°C, while rice was optimal for T. inclusum. However, T. inclusum outproduced T. granarium on all commodities. In all commodities, the percentage of T. granarium progeny was greater at 32°C compared to 25°C. In direct competition experiments, it was particularly noted that T. granarium performed better than expected on rice at 32°C, while T. inclusum was worse than expected on wheat at 32°C, but better at 25°C. On wheat after 25 weeks, when adults were used at the start of competition, T. inclusum maintained an advantage in population number at either temperature. However, if larvae were used to initiate the competition the species coexisted well at 25°C, but T. granarium nearly excluded T. inclusum at 32°C. The results are discussed with respect to the known ability of T. granarium to enter facultative diapause in conjunction with its capacity for population growth and importance as a quarantine species.