Life history changes in Trogoderma variabile and T. inclusum due to mating delay with implications for mating disruption as a management tactic

Authors: Gerken, Alison; Campbell, James - Jim

Submitted to: Ecology and Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/2/2018
Publication Date: 3/1/2018
Citation: Gerken, A.R., Campbell, J.F. 2018. Life history changes in Trogoderma variabile and T. inclusum due to mating delay with implications for mating disruption as a management tactic. Ecology and Evolution. 8(5):2428-2439. https://doi.org/10.1002/ece3.3865.
DOI: https://doi.org/10.1002/ece3.3865

Interpretive Summary: The pest management technique of mating disruption is used to interfere with the ability of male insects to find females, thus reducing the number of progeny produced and population growth rate. Use of mating disruption for stored product moth management has been increasing in the food industry, but this tactic also has potential to be developed for other stored product species. The warehouse beetle (Trogoderma variabile) is a damaging pest that appears to be a good target for development of mating disruption as a management tactic. Mating disruption can still be effective even if complete shutdown is not achieved since delaying the time until mating can lead to a reduction in the number of eggs laid and their viability. As part of developing a new mating disruption program it is important to assess the vulnerability to mating delay since this determines the window of time mating disruption needs to be effective. We found that with delay in mating there was a decrease in the number of eggs laid and the number of progeny to survive to adulthood for warehouse beetle, and a closely related species the larger cabinet beetle (Trodogerma inclusum), although there was little decrease until after five or more days of delay. The larger cabinet beetle lived longer than the warehouse beetle and laid more eggs for all days mating was delayed. These two species did lay enough eggs to continue the population to further generations even with significant decreases in egg laying as female age at mating increased. However, survival of adults under laboratory conditions is likely to be much longer than under real world conditions and with increased mortality may drive population sizes even lower. Using simulated populations with different percentages of the population that are mated or unmated, we found that even when 80% of the population is not mating, the population size may decrease but the population will still persist to future generations. These results highlight that mating disruption techniques that lead to delays in mating can lead to partial control of the population which could aid in pest management. These results also stress the importance of species specific considerations when employing pest management tactics as well as the consideration of natural population variation in mated and unmated individuals.

Technical Abstract: Controlling postharvest pest species is a costly process with insecticide resistance and species specific control requiring multiple tactics. Mating disruption can be used to both decrease a female’s access to males and delay timing of mating and decreases overall mating success in a population and population growth rate. Development of new commercially available mating disruption products requires an understanding of life history parameters associated with mating delay. These can provide information for targeting proportions of reproducing individuals using mating disruption. After delaying mating for females of two closely related beetle species, Trogoderma variabile and T. inclusum, we surveyed survivorship, number of eggs laid, and number of progeny emerged. With increases in mating age, total number of eggs laid and total number of progeny emerged significantly declined over time. T. inclusum typically had greater numbers of eggs laid and progeny emerged compared to T. variabile as female age at mating increased, suggesting that T. inclusum may be more resistant to long-term delays in mating. Total lifespan showed an increase as mating age increased but lifespan significantly decreased almost immediately following mating. Simulations depicting multiple distributions of mating within a population suggest that in a closed population, high levels of mating delay significantly reduced reproductive growth rates. Although reproductive growth rates were decreased with increased mating age, they are still large enough to maintain populations. This study highlights the differences in life history between two closely related species, suggesting that T. inclusum outperforms T. variabile over the course of a lifespan, but T. variabile has better reproductive capabilities early in life. Mating disruption may also be a viable component of a pest management system for these two species as it significantly decreased overall reproductive output and population growth.