Steven Richardson and Qian "Karen" Sun
There are various insects that can invade homes and businesses. Most can be found around pantries and areas where food is stored. Some of these pests, known as stored product pests, can appear as infestations that, seemingly, occurred overnight. However, they were already an existing problem brought into the home inside an infested product with the new owner being unaware of what they placed on their shelf. Several pests can be referred to as stored product pests which are predominantly beetles and moths. Home and business owners typically discover them in congregations along isolated regions of a shelf or along part of a building. If these pest harborages are not identified and removed, they could spread to neighboring products.
Any product that is plant or animal based could have the potential for stored product pest issues. The most common are food items from plant and animal material but fabrics and other materials are also susceptible. Common dry, edible pantry items targeted by pests include but are not limited to rice, dried corn products (from popcorn to deer feed), flour, cereal, crackers, cake mix, protein powder, other wheat products (pasta and spaghetti noodles), spices, peppers, herbs, legumes, other dried vegetables, fruits, candy, nuts, and dried meats (jerky). Pet items can also be targeted, such as pet food, dog bones, bird seed, dried lizard and fish food, and various animal treats. In addition to edible items, non-edible items made from plant or animal matter can also be targeted, including tobacco products and decorative holiday items (reeds, flowers, mistletoe, acorns, etc.).
Stored product pests can be located anywhere dried or semi-dried organic based items are found. This could be on grocery store shelves, warehouses, cupboards, pantries and anywhere in the home or business stored products have been taken. However, adults and, depending on the species, the pupae can be distant from targeted food sources that their larvae are found on. This is dependent on how mobile the larvae are but also how mobile the adults are and if they have the ability to fly. Highly mobile larvae that feed externally on the food source, rather than being encapsulated in it, will move away from the other larvae to pupate undisturbed. The distance traveled could be a few centimeters away from their food source or a completely different room. Non-encapsulated larvae can also be found wedging themselves into small cracks and spaces all around the shelve, in corners, behind door seams, in decorative items, or on products that have not yet been damaged by pests.
Factors that make stored product pests a serious problem are their small size, large reproductive potentials, overlapping of generations, and their lack of dependency on food water content. Because the eggs and larvae of most stored product pests are inside the product, it could be difficult to spot. And even when inspecting an infested package, it could still be difficult to identify to the untrained eye due to their small size as larvae and eggs. Most adults of these species are also small and inconspicuous, making them easy to ignore until a breakout, or emergence, of multiple adults takes place. Most have biological capabilities that prevent eggs and pupae from emerging under unfavorable conditions. And they have high reproductive potentials, where one female can produce up to 500 eggs in her lifetime, dependent on the species. Most of these pests can complete development in a few weeks with adults living for several years in some species. Because of this, there is also the potential for overlapping generations where hatching, pupation, and mating occur simultaneously. Lastly, the reason they are so effective in exploiting stored products is they need little to no dietary water for survival. Through digestion, they can metabolize their food to create water rather than drinking it. Stored product pest larvae can complete their lifecycle without needing any additional water added to their dry food. However, if water were present, they would utilize it. Most of these insects are also efficient in preventing desiccation through their exoskeleton because it is less permeable to water compared to other insects, allowing for better water retention.
Primary pests of stored product attack undamaged, whole grains. The larvae feed and develop inside the grain and chew their way out. Some of the primary pests include the Angoumois grain moth, rice weevil, and lesser grain borer. In contrast, secondary pests feed externally, and attack broken, damaged grain and powdered products. They may infest stored food following the primary pests. These pests include the Indian meal moth and a variety of beetle species, such as the sawtoothed grain beetle, cigarette beetle, drugstore beetle, the red flour and confused flour beetles.
The best control strategy is to find the damaged products or goods and dispose of it. This can be done by searching through the pantry or storage area looking for any exposed products, open packaging, torn packaging, or damp areas that could have compromised packaging. Following this, the shelf itself needs to be inspected to determine if there is any possibility of pests moving to neighboring shelves. In the case for most grocery stores where shelving is not touching a wall, that shelf, the shelves below it, and any connecting shelving need to be inspected for pupae, larvae, and adults of the pest. In the case of shelves touching or being connected to a wall, such as along the side of the store or in a pantry, all neighboring shelves need to be inspected and products removed. Pantry doors, door seams, ceiling corners and edges, and the floor all need to be inspected as well.
The most effective means of monitoring is with sticky traps. Various species-specific pheromone sticky traps are available for detection of stored product pests. However, these traps are not to be used as control measures because they will do nothing to control larvae from spreading to open or damaged goods. Pheromone traps generally use a sex pheromone to attract adults. The problem is this will only attract males which would negate their effectiveness. Alternatively, there are chemical attractants that mimic the target food source of the pest. These would attract both male and female adults, assuming they feed as adults, and are a good option if the desire is not to target any one specific pest. There are also general sticky traps that do not include a pheromone attractant. They will also be infective in mitigating large numbers of adults and will not keep them from mating and infesting other exposed products. Additionally, the more insects there are stuck to the trap, the less effective the trap will become in catching adults.
When infested products are found, they should be frozen (below -18°C overnight) or heat treated (over 60°C for 15-30 min). It is recommended that, when a pest infestation is found, all products need to be removed from that shelf and inspected for pests. Upon removal of products and inspection, the shelves and connecting structures need to be cleaned (e.g., vacuumed, washed, or heat treated) thoroughly. This includes repairing or sealing any small cracks on the surface or underneath the shelves where pupae could be hiding. The surrounding area of shelves need to be inspected and cleaned as well to make sure all pupae, larvae, and adults have been removed.
Once all damaged, opened, unsealed, or infested products have been thrown out, the remaining products need to be properly sealed. It is recommended that all food items, even those that are in paper and cardboard containers, should be sealed individually by product in plastic tupperware, sealable containers, or storage bags. This will ensure that if any infested products were missed during inspection, infestation would not take place outside of that container and the product can easily be thrown away. There still may be some stragglers that manage to avoid detection from the original infestation and emerge as adults. But, if all products are properly sealed, they will be unable to infest any other products.
There are various control methods available for stored product pests. And various insecticides are labeled for mitigation or control ranging from fumigation to insect growth regulators (IGRs). Fumigation is the more expensive rout and would require that the entire pantry or region of the house be quarantined and sealed off in order to treat that area with fumigants. IGRs could also be used to interfere with infestations. But IGRs have mixed efficacy in research, negating them as an effective control strategy. Additionally, residual chemicals should be avoided considering the area being treated contains products used for human consumption.
If homeowners are experiencing stored product pest infestations, it is recommended that they contact a local pest management professional for advice and an inspection as locating infested products or the extent of the infestation can be difficult. Additionally, it does not matter how effective the control effort is from the pest control technician if proper education to the customer on preventing future pest problems has not been provided. It is important to inform homeowners that all stored products need to be properly sealed and stored in containers that cannot be chewed through by pests. This includes hard plastic or glass containers with sealable lids as well as thick zip shut bags. And if there is water damage or other conducive conditions causing the pest issue that cannot be resolved by the technician, the homeowner needs to be made aware that the issue may not be permanently resolved until those conditions are mitigated.
Steven Richardson is a graduate student, and Qian "Karen" Sun is an assistant professor in the Department of Entomology.