By: Don Foster, A.C.E.

One important aspect of servicing commercial clients is understanding their operations. This statement alone can have several meanings to different people. However, frontline professionals need to be very perceptive and understand how standard operating procedures can impact routine inspections.

As an industry, we stress the importance of addressing conducive conditions that can negatively impact our clients’ operations. Food-processing facilities, particularly those that handle fruits and vegetables, are faced with several challenges regarding the introduction of pests when these commodities are harvested and delivered directly to the plant. Most product is delivered in 40-foot trailers and parked in a receiving yard.

Depending on the raw material, the trailer is emptied into a hopper, sampled for grading and either stored in bins or entered directly into production lines. Fruits and vegetables that enter production lines may be washed several times or blanched, then checked for pests. Those that are sent to storage bins may not be used for several days.

Fruits and vegetables stored in bulk bins can create some challenges, especially with rodents. When the trailers are emptied, it is no longer a conducive condition but a source of activity. In these types of environments, measures have been taken to monitor for activity with the use of rodent bait stations, exterior rodent traps, snap traps, etc.

Historically, we have been trained to locate the source of activity by inspecting for evidence such as droppings, rub marks, urine stains, gnawing, paw prints, tail drags, etc. If none of the obvious signs of activity are present and the data from our strategically positioned devices does not reveal the presence of rodents, then zero evidence equals zero activity, right? Wrong. This is a huge fallacy. Failing to understand your client’s operation can place your pest management firm at a huge disadvantage when it comes to controlling rodents (or any target pest).

Bulk Storage Study

Bulk storage bins are used seasonally and, in most cases, may only be used for one type of fruit or vegetable. During the off-season, teams begin cleaning and repairing these bins for the next harvest, unless the bins are used for different incoming product due to season. The bulk bins may be constructed out of wood with a tin roof or steel with expanded metal walls (see figures 1 and 2). Start thinking about the types of pests you may encounter in these two setups.  

Fig. 1. Steel bulk storage bin.

Fig. 2. Wooden bulk storage bin

In the citrus industry, bulk bins are used in the degreening process dependent upon the end use. Bins can tower higher than a three-story building, have back-to-back compartments and multiple void spaces and contain multiple gaps throughout the structures. The design plays a major part for citrus products. Citrus must have airflow to prevent gas buildup emitted by the rind and condensation. The interior of the bins must have baffles to prevent injury to the fruit due to the weight of the product.

Steel vs. Wood

Differences between steel construction and wooden construction can impact control measures. Metals are known to be great thermal conductors but poor insulators. Research has shown us that as much as 25 percent of the total heat production in a rat can be lost through the tail, leading to hypothermia. A bulk storage bin constructed out of steel, designed to reduce condensation, increase airflow and prevent injury to the citrus product, also can be a benefit when addressing rodent issues.

The wooden bulk storage bin is a structure similar to the appearance of several pallets stacked vertically end-to-end with a wood floor (see figure 3), towering over three stories with multiple bins side-by-side to hold between 20-30 trailer loads of citrus on each side. These bins may be used for lemons, limes, oranges, grapefruit, etc. The load is graded and assigned a specific bin number so that the grower can be identified if a risk is identified prior to processing.

Fig. 3. Wood flooring underneath bins.

Pest Detection

This particular example demonstrates how a rodent population in bulk storage bins can occur undetected for multiple seasons. In this case, multiple rodent bait stations were strategically placed around the perimeter and underneath several bulk storage bins for routine maintenance. Standard operating procedures required employees assigned to the area to conduct multiple washdowns during each shift year-round, regardless of the season. The bins did not contain any fresh citrus. Evidence suggested minimal activity was present in the area, and it was considered normal due to how the citrus was offloaded from the trailers during season. One day, four juvenile roof rats were noted under the bulk storage bins near a drain trough. Cleaning operations were paused to perform an inspection. Multiple droppings were found underneath several bins. One juvenile rat was observed and followed. The rodent climbed up the support leg for the bins and entered a hole on the front of the bin.

A team of professionals placed several traps on the interior and exterior of the bulk bins. A few adult and juvenile rats were captured. The team also noted the presence of cockroaches inside of the bins and conducted a ULV application to the empty bins. Multiple cockroaches exited the bins and expired on the conveyor belts. Afternoon weather produced rain that misted the conveyor belts. Shortly after the weather passed, several tail-drags and paw prints (see figure 4) were found on the belts where rodents came out to feed on the dead cockroaches.

Perceptive Inspections

Being very perceptive during your pest inspection can identify other food sources apart from the obvious ones that can support a rodent population. The wooden construction supported the cockroach activity, along with providing shelter for the rodents. The rodents would come down to acquire water from the washdowns and return into the bins. The washdowns were removing the evidence of the rodent activity. The result was capturing more than 150 rodents in the process.

Another factor to consider when dealing with a situation like this is that rodents are acutely aware of your presence. During the process, the team paused for several days, and the client was asked to cease all work activities to allow any remaining activity to become complacent and return to their normal activities. What we found was that the rodents were avoiding all trapping devices. Treating for the cockroaches reduced their food source, and heavy feeding occurred in the bait stations for the first time.

In situations like this, you cannot rely solely on inspections and data capture. Focus on what your client produces, how the supply chain operates and how incoming product is handled. Be perceptive during your inspections and investigate further when environmental factors are less than revealing. Zero evidence does not equate to zero activity.


All article photos courtesy of author Don Foster, A.C.E. Cover photo by Jon Moore on Unsplash.

Don Foster, A.C.E., is a 27-year veteran in the pest management industry and serves as a Technical Manager for Terminix International. Terminix Commercial is a sister brand of Copesan. He holds a bachelor’s degree in entomology from the University of Florida with an emphasis in urban pest management and a master’s degree in entomology and nematology. 

This Tech Talk article was originally published in the November 2021 edition of PCT magazine.