When we think of insect pests that threaten our food, it’s typically easy to rattle off the usual suspects: cockroaches, flies and ants. Lesser known are the Stored Product Pests (SPPs), which are economic threats to stored products during the entire chain of food custody. Cocoa, nuts, baking mixes, cereals, rice and products which utilize these ingredients are favorite foods of this lesser known group of pests. However, this group threatens our food supply at all stages of food processing: from whole kernels in grain silos and processed grains in a flour mill to food production, storage and distribution — even in our homes and at restaurants. They rarely gain the notoriety of the more infamous food pests because the food safety risk is low, although the economic risk is high.
There are many species of SPPs that food manufacturers can encounter. To understand what to look for, it is important to know that these pests are all quite small (typically about an eighth of an inch) and at least one of their life stages (typically the larvae) live in food, making it very difficult to see them until the population grows. As a group, SSPs pose risks to commodities at all stages of the food chain of custody, but each species tends to have preferences based on feeding requirements. There are four types of SPPs:
- Internal feeders: Internal feeders such as weevils and borers, which develop inside a kernel are pests of whole kernels of grain and hard uncooked pastas.
- Scavengers: Scavengers, who prefer processed foods and particulates, such as flour beetles, are common pests of processed grains like cereal or flour.
- Secondary feeders: Secondary feeders are those SPPs which prefer a little mold with their grain, so we find them in moist grain environments.
- External feeders: External feeders, which do not have strong preferences the way the other three groups do. We call them cosmopolitan pests, and they are successful at many stages of food processing. Indianmeal moths, cigarette beetles and warehouse beetles are three of our more common external feeders.
Monitoring pest populations and controlling these populations are very different concepts. When we monitor, we are in an information-gathering stage. We are trying to discover who is in the facility, in what quantity and in what area. We then take that information and focus our inspection to find the source of the population and determine a control technique. Successful control is hard and often impossible without monitoring. These tasks are not interchangeable, so we cannot employ monitoring tools and expect them to control a population. This is particularly true for SPPs as these pests undergo complete metamorphosis, resulting in different harborage and behavior between the juvenile and adult stages.
Due to their small size and the fact that they typically live in the food they’re eating, finding SPPs based on inspection alone can be challenging. Instead, pest management professionals employ several tools to monitor for SPPs. The results of the monitoring, along with knowledge of the food preferences of the species help to focus facility inspections. The most common monitoring tools for SSPs are:
- Pheromone Traps: Pheromones are species-specific semiochemicals that insects use to communicate. Pest management professionals can use synthetic versions of the SPPs’ pheromones and place them in traps to draw adult SPPs out of their harborage.
- Kairomone Traps: Kairomone traps use a food odor in a pitfall trap to catch crawling SPPs that do not have commercially available pheromones. Kairomones are less attractive than pheromones because our SPPs are already in the food and less likely to respond to a food smell. However, they can have an important place in pheromone programs where we have limited monitoring options and minimal food competition.
- Insect Light Traps (ILT): Many of our SPPs both fly and are attracted to light, with some very strongly attracted. While we often install ILTs to monitor fly and night flyer populations, this tool also has an important place in SPPs monitoring.
- Sticky Glue Traps (Glue Boards): Though more commonly used to monitor for cockroaches or occasional invaders, glue boards can yield information on SPPs populations, particularly those species which crawl away from the food source.
All of these tools can have a role in SPPs monitoring, depending on the SPPs of interest. If we’re interested in monitoring for Indianmeal Moths, we’ll have both ILTs and pheromone traps available to us. If we’re interested in Sawtoothed Grain beetles, we’ll use glue boards and kairomone traps on the floor. If we are monitoring for flour beetles, we can use kairomone and pheromone traps. The options are dependent on the species and what their behavior is (flying vs. crawling) and whether pheromones have been commercially synthesized for them.
Of the tools available for SPPs monitoring, pheromone monitoring is unique to SPPs. Two types of pheromones are synthesized and available for use in monitoring:
Typically released by a female, and detected by males, sex pheromones let those who detect it know that the sender is ready to mate. Sex pheromones are strongly attractive and typically associated with those adult SPPs that have short adult lifespans as they need to ensure they find a mate before they die. A sex pheromone helps the male and female find each other and mate. Though a very effective pheromone, only a handful of species have strong sex pheromones that are synthetically available:
- Indianmeal Moth (Plodia interpunctella)
- Mediterranean Flour Moth (Ephestia kuehniella)
- Raisin Moth (Cadra figulilella)
- Tobacco Moth (Ephestia elutella)
- Almond Moth (Cadra cautella)
- Angoumois Grain Moth (Sitotroga cerealella)
- European Grain Moth (Nemapogon granellus)
- Warehouse Beetle (Trogoderma variabile)
- Khapra Beetle (Trogoderma granarium)
- Cigarette Beetle (Lasioderma serricorne)
- Webbing Clothes Moth (Tineola bisselliella)
Aggregate pheromones may be released by either males or females, depending on the species, but both males and females can detect them, unlike sex pheromones which are sex-dependent. These pheromones are saying “come here” because of a food or shelter source. Unfortunately, aggregate pheromones tend to be less effective than sex pheromones because SPPs are typically in the food they live in, so they will not leave to respond to a pheromone that’s saying “I found food and shelter.” However, aggregate pheromones do have a place in pheromone programs when there is not a lot of food competition. There are commercially available aggregate pheromone lures synthesized for:
- Casemaking Clothes Moth (Tinea pellionella)
- Confused Flour Beetle (Tribolium confusum)
- Red Flour Beetle (Tribolium castaneum)
- Lesser Grain Borer (Rhyzopertha dominica)
- Larger Grain Borer (Prostephanus truncates)
- Rice Weevil (Sitophilus oryzae)
How to Trap SPPs with Pheromones
The pheromone lure, whether sex or aggregate, is placed in a trap that catches the SPPs. Most SPPs pheromone traps are:
- Tent: Also known as diamond traps, these are glueboards that hang in a tent or diamond shape. The pheromone is placed inside the trap, catching any members of the species that respond to the pheromone. Because they hang, these traps are designed to catch SPPs that fly.
- Pit-fall: Pit-fall traps are floor traps that have the pheromone inside, a cover to protect the pheromone and any insects caught, and a small space in between where crawling SPPs can climb through. Once they climb into the trap they fall in a pit and are unable to crawl out. These traps are often used in conjunction with a kairomone oil which helps to keep the captured SPPs in the trap.
The placement of pheromone traps is key. Pest management professionals are using these traps to monitor, not to control, so where the traps are placed will help determine where we need to focus our inspection. The distance between traps is determined by the target species (always refer to the manufacturer’s label directions) and the obstacles to placement. When possible, a grid pattern is preferred as it helps narrow down the areas to inspect. Pest management professionals can spend more time inspecting areas with high counts, and less time in areas with low counts. We can even plot this data to create a heat map.
SPPs are tough to find without proper monitoring tools. Pheromone monitoring traps assist in narrowing down and focusing the inspection to specific areas. Through pheromone monitoring, we can be alerted to and find a SPPs population before they are able to cause significant product damage and, in turn, brand damage.
Anna Berry, BCE, is Training Manager/Entomologist at McCloud Services.