Using long-term capture data to predict Trogoderma variabile Ballion and Plodia interpunctella (Hübner) population patterns

Authors: Gerken, Alison; Campbell, James - Jim

Submitted to: Insects
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/28/2019
Publication Date: 4/1/2019
Citation: Gerken, A.R., Campbell, J.F. 2019. Using long-term capture data to predict Trogoderma variabile Ballion and Plodia interpunctella (Hübner) population patterns. Insects. 10(4):93. https://doi.org/10.3390/insects10040093.
DOI: https://doi.org/10.3390/insects10040093

Interpretive Summary: Monitoring of pest insects in facilities that process post-harvest commodities such as flour mills provides important information to guide pest management programs. Understanding the factors that contribute to insect abundance are helpful in refining monitoring programs and targeting pest management, but the high level of variation in insect captures at different trap locations make drawing conclusions difficult. Long term monitoring data could be used to help deal with this variation and be useful in detecting patterns, but this information is rarely available. Here we used 10-years of insect trapping data collected at a flour mill to assess populations of Indianmeal moth, Plodia interpunctella, and warehouse beetle, Trogoderma variabile, two common and important stored product insect pests. We find that Indianmeal moths had a more predictable long-term pattern of activity within the facility compared to warehouse beetles. Outdoor temperature was an important factor in predicting captures of these two species and specific threshold temperatures were identified above which captures were more likely to have large changes in number captured between sampling periods. Warehouse beetles were less influenced by outdoor temperature than Indianmeal moths but captures of both insects increased around the same time of year (April/May). Specific trap locations could be identified that more frequently had high or low insect captures, and typically locations with high captures of the one species had low captures of the other. Use of fumigation to manage insects inside the facility occurred frequently, and analysis of the trends in capture of these pest species suggests that season had a major impact on rebound in insect captures following the fumigation. Species activity inside the mill before and after the fumigation appeared closely tied to outside flight activity, although results suggest warehouse beetles may have a small resident population inside as well. Results show how managers could potentially save time and effort in monitoring by using fewer but more targeted traps and adjusting monitoring efforts during critical periods of time with flight activity is high.

Technical Abstract: Insects can infest facilities that house and process post-harvest grains and grain-based products. Integrated pest management tactics rely on tracking insect populations and using this information to select and target management tactics. Our ability to predict when and where to best focus treatment relies on an understanding of long-term trends, but often any available monitoring data is limited in its duration. Here we present data collected over a 10-year period at a flour mill in the central part of the United States. Using traps placed both inside and outside a flour mill and baited with pheromone-lures for Plodia interpunctella (Hübner), Indianmeal moth, and Trogoderma variabile Ballion, warehouse beetle, we examine environmental and spatial variability in insect captures. We find that both species, inside and outside the mill, are highly influenced by seasonal patterns, with peaks of insect captures during the warm season (April through September). There is also consistency across time and space in trap capture for P. interpunctella with traps in an open location consistently capturing high numbers of insects. In contrast, T. variabile lacked consistency in trap capture but were most often not found in the same trap locations as P. interpunctella. Fumigations conducted within the facility appeared to have little impact on insect captures inside, with dynamics appearing to be driven more by broader seasonal patterns in activity. These data and analyses suggest that there is a larger population of these insects that are readily moving in and out of the structures, while fumigation treatments are only impacting a small portion of the overall population and tactics targeting immigration may be an important addition to the pest management program.