[Pest Management] Stick 'em at the Point of Entry

In a previous issue of AIB quarterly (Fall 2005), we focused on implementation and interpretation of insect monitoring programs for a highly mobile and widespread pest, the Indianmeal moth, and showed how immigration from the outdoors can contribute to indoor populations, thereby requiring consideration in pest management programs. One response to this problem is to identify where insects are getting into a facility and work at closing these routes of entry. The important questions are: (1) where are these entry points, (2) what is the relative importance of different potential entry points, and (3) what impact do different methods of sealing have on immigration rate and degree of infestation inside a particular facility?

Here, we expand on these questions and provide some practical advice on detecting and reducing immigration. The results reported in this article were collected at two Foundation- certified seed storage facilities located in the Midwest. These locations do not have the same level of sanitation and pest management as would be present in a food processing facility or warehouse, but illustrate characteristic patterns found at many food facilities. The data was collected as part of a larger collaborative project between the USDA-ARS Grain Marketing and Production Research Center and the Department of Entomology at Kansas State University that was funded by US-EPA Region VII and USDA/CSREES/RAMP competitive grant programs. By adopting our techniques, savvy pest managers will learn to further exploit pest biology to formulate more effective approaches to pest management.

PEST PREVENTION. A key tenant of a proactive pest management program is that it is better to prevent problems from developing than having to respond to an infestation. It is also widely understood that sealing openings in the exterior of a building is an important part of any program. This can include dealing with obvious large openings such as doors, windows, and vents by keeping doors closed or screening windows and vents. Structures also have many other potential routes of entry that could be exploited by small and highly mobile stored product insects. Examples of these routes include gaps around doors and windows, cracks and seams in the building, and openings around pipes. While all of these openings are potential routes of entry, it is unclear whether they are equally used by insects. Rather than taking a shotgun approach to this complex problem, identifying the most important routes of entry can enable management efforts to be focused where they will have the most benefit. Follow-up evaluation of insect activity at that entry point can then enable pest managers to determine the effectiveness of their intervention and what further actions may be necessary. For instance, if you found a gap around a door and installed a gasket, did this solve the problem? Are insects no longer able to enter through that gap?

To investigate routes of insect immigration into warehouses, we positioned simple and inexpensive unbaited rodent glue traps (also known as glue boards) in areas where we hypothesized insects were entering the facilities. Glue traps, the same type that are commonly used inside mechanical mouse traps, are comprised of a single layer of cardboard covered by a layer of sticky glue that will entangle any animal that blunders into the glue. Traps were attached with duct tape on and around two loose fitting windows, positioned on the floor against the wall beside two pedestrian doors, and on the floor and interior walls adjacent to a pair of overhead loading doors. Along both sides of the overhead doors, traps were placed to a height of 6 feet above the floor with four additional traps on top of the doors. Traps were checked weekly from May through October and replaced every month or sooner when they became excessively dirty.

At the facilities where we conducted this research, stored product insects were captured in each location where we placed traps. In the traps around the windows we observed captures of Indianmeal moths, hairy fungus beetles, rusty grain beetles, and houseflies, but these captures may also represent attraction of the insects to bright light coming through the windows. On the floor around pedestrian doors we primarily captured incidental species like ground beetles and rove beetles. This does indicate that there is a potential route into the facility that needs to be dealt with, but these insect species do not infest cereal products. Species diversity including red flour beetles, warehouse beetles, rice weevils, lesser grain borers, foreign grain beetles, rusty grain beetles, and hairy fungus beetles, as well as numerous Indianmeal moths, was greatest on the traps located on the floor adjacent to overhead doors (Fig. 1). This evidence strongly suggests that these stored grain pests were moving from outdoors to inside the facilities through the small (1/8 to 3/16 inch) gaps detectable between the doorframe and overhead doors.

It should be noted that it can be difficult to determine if the insect source is outdoor or indoor using glue traps, since we cannot determine where they originated or which direction they were traveling before being captured. Insects could also be attracted to these openings from inside due to light or air movement. Placing glue traps facing outward in gaps, placing glue traps in areas without openings to the outdoors to serve as control traps (compare capture rates around doors to captures on these control traps), or placing traps both inside and outdoors around doors can help with interpretation of these trap captures. While both movement into and out of structures can occur, pest levels are often greater outdoors and food odors will be leaving the building so the net direction of insect movement is likely inward.

One approach to eliminating the small gaps around a door is to install exterior weather stripping (vinyl gaskets) between the overhead door and the doorframe. These gaskets have a flexible vinyl leaf that floats against the face of the overhead door and are designed to keep wind and rain out. One of the two warehouses in our study had similar weather stripping already installed on the overhead doors. To test the importance of these gaskets for insect pest management, we installed gaskets on only one side of each overhead door at the warehouse that did not have these gaskets. Results showed that installation of the weather stripping reduced the number of beetles captured immediately inside the doors by more than 50% compared to the opposite side of the same door without the gasket. At the warehouse with gaskets already installed, insect captures on traps placed on the floor adjacent to each side of the door accounted for approximately 75% of all captures (Fig. 2). Insect captures decreased with increasing trap height along the sides of the doors and no beetles were ever captured on traps placed above the overhead doors. Indianmeal moths, in comparison with beetles, were captured in traps from floor to the top of the door (Fig. 3). Moths often land and rest on vertical surfaces and this behavior may explain the different pattern of capture between beetles and moths.

These results show that gaskets placed around doors reduced insect immigration and tended to focus beetles primarily at the floor level where presumably they could still gain entry. This illustrates how follow-up monitoring can show the impact of the management tactic and reveal where additional attention needs to be focused. In this case, some potential options to alleviate the ingress routes under the door include install/replace the gasket or door sweep at the bottom of the door to make a better seal, address problems with uneven floor surfaces, or target pesticide applications to this area thereby treating much less surface area than spraying the entire perimeter.

SEASONAL FACTORS. The time of year is an important factor influencing immigration into structures through these different routes of entry. This needs to be taken into account to resolve when a building will be most vulnerable to insect entry and to determine when to evaluate the effectiveness of sealing since checking when insects are less active will not be very informative. Different insect species can have different seasonal patterns of immigration that may also need to be taken into account.

At the warehouses where we conducted this study, seasonal changes in the number of insects captured on the glue traps around overhead doors varied by insect species (Fig. 1). With the exception of lesser grain borers, insect captures in glue traps around doors were minimal in the early spring (May through June). Lesser grain borers can have a spring flight peak and at this location were captured in very large numbers in early May and then captures greatly decreased until late fall. Total insect captures tended to increase from June until the onset of cool weather in the fall: at this location peaking between September and November with very few insects of any species being captured after the second week of November.

Alternative activity patterns are likely to be observed in other parts of the world, but seasonal patterns for a given location can be determined and used to help target pest management using techniques described here. This information could be used by managers to make sure exclusion methods and residual insecticide applications are updated during the key times of year for the target pests of their particular facility.

Food processing facilities, retail stores, warehouses, and other storage structures each have unique construction and building features, but all have potential routes of entry for insects. Reducing the ability of insects to enter a facility is a critical component of a pest management program because it focuses on preventing pest infestation problems from occurring in the first place.

While it is widely known that immigration and identification and sealing of potential routes of entry are important, determining how to evaluate the impacts of sealing is not as well understood. Insect monitoring is more labor intensive than blind insecticide applications, but the fruits of such a program are better management and the ability to detect and respond to situations before they become a problem. Prevention of pest problems requires a better understanding of pest populations and behavior and is a continuous learning process that requires good information. Fortunately, relatively simple tools such as visual inspection, pheromone trapping, and glue traps can provide the necessary information. The key is to use them effectively. For more information on this topic, including reprints of related articles and poster presentations, please visit our Web site at www.ars.usda.gov/npa/gmprc/bru. AIB

M.D. Toews and J.F. Campbell are with the United States Department of Agriculture, Agricultural Research Service, Grain Marketing and Production Resource Center.