Indicator Species in Food Environments

Departments - Tech Talk

Nothing operates independently. It’s as true in pest management as it is in the rest of the world. We are clear about this in our documentation and communication with our clients. Every organism has basic needs that must be met to sustain life. For pests to successfully infest a structure, those basic needs must be supplied by that environment. If not, they will either relocate or die.

During inspections we are looking for the presence of conditions — poor sanitation, door gaps, pooled water, etc. — that could support pests even if the pests themselves aren’t present. You can think of this relationship in reverse, too. If you find a German cockroach infestation, that means there must be conducive conditions allowing them to thrive.

In some situations, the pests themselves are a “conducive condition” and their presence alone is attracting other organisms and keeping them nearby. I call these “indicator species” in that the presence of this secondary pest is an indicator that the primary pest must be present. Usually you will be aware of the primary pest before the secondary one, but in complex environments it’s possible that the indicator species will be your first clue that you have two (or more) problems. Your ability to identify and understand why an obscure organism is appearing in an account may save you countless callbacks and help keep your clients happy.


Indicator organism: Dermestid beetle
What its presence may suggest: Live rodents, dead animals

Let’s start with one of the most well-known indicator organisms: carpet beetles and several other dermestid beetles. If you’re finding any dermestid beetle inside, you need to locate the source. While materials containing natural fibers may be the source, the beetles may be consuming dead insects or other animals in voids instead. Carpet beetles, cabinet beetles and hide beetles are voracious consumers of carcasses, as anyone with an insect collection can attest to.

The presence of dermestid beetles also can signal a current or bygone rodent infestation. House mice, and, to a lesser extent, commensal rats, maintain food caches to get them through lean times. Food cached by rodents, like dry dog food, is also not a bad food source for dermestid beetles, Indianmeal moths and some other stored product pests.

Dermestid beetles can be difficult to source since they exploit resources in, around and far from structures.


Indicator organism: Ensign wasp
What its presence suggests: Blattid cockroaches

If ensign wasps are found, particularly Evania appendigaster, there are cockroach oothecae nearby. If there is a cockroach ootheca nearby, the female that deposited it probably isn’t far off. Though American cockroaches are usually identified as the primary victim, other Blattid species like Oriental, brown and Australian cockroach oothecae also are used by ensign wasps as larval development sites. Sometimes referred to as parasitoids, ensign wasp larvae may better be described as predators since they eat cockroach eggs rather than develop on or in them. If you spot an ensign wasp, but have not identified the presence of cockroaches yet, adjust your inspection focus and put out additional monitors where cockroaches are likely to be. I have experienced this firsthand and fortunately recognized this distinctive wasp during a routine inspection.


Indicator organism: Predatory bug
What its presence suggests: Stored product insects and mites

These insects are predators of other insects and mites and there are two main groups that you may encounter in a food-processing or food-storage environment — flower bugs (Anthocoridae) and assassin bugs (Reduviidae). They do not feed on grains themselves, just associated pests. Both possess piercing sucking mouthparts that they use to feed (primarily) on soft-bodied life stages of stored product beetles and moths. Flower bugs are very small, less than 0.2 inches long, and assassin bugs are only slightly larger.

These can be tricky because they both have many similar-looking relatives, are infrequently encountered and are often mistakenly assumed to be occasional invaders. If there is only one or two of them present, perhaps it is an occasional invader situation. However, if there are significant numbers, or you are finding them on a consistent basis, there is a strong chance that they are in the facility to feed on a stored product pest or other entrenched pest. It’s important to consider where you are finding them in a facility, too. Predatory bugs on or near stored grain products are a very strong indicator of their prey.

Familiarize yourself with the notable flower bugs: the stack bug, or larger pirate bug, Lyctocoris campestris; and cereal bugs, Xylocoris spp., including the warehouse pirate bug, Xylocoris flavipes; and with two prominent assassin bugs — Amphibolus venator and Peregrinator biannulipes.


Indicator organism: Straw itch mite
What its presence suggests: Stored product caterpillars

The straw itch mite, Pyemotes tritici, is seldom discussed in any context within structural pest management, but if it is, it’s because of its public health implications. People that handle mite-infested straw or grains can develop symptoms like those caused by scabies, Sarcoptes scabei, another parasitic mite. Reports of a client’s employees complaining of rashes with intense itching could be your first indication that there is a pest problem and during your investigation of the complaints, you may uncover there is more to the situation. Female straw itch mites are parasitic, and their source of sustenance is not limited to humans. (In fact, humans are likely pretty far from ideal in terms of their preferences.)

Presence of the mites is probably an indication that there are larvae of Indianmeal moths, Angoumois grain moths or stored product beetles infesting something else that straw itch mites are feeding on. One of the most common places these mites show up as stored product larval parasites is in bagged dog food that is being stored in an area with high humidity.

If you are pressed by a client when the presence of an unknown “biting insect” is suspected, you must confirm an identification before any recommendation or treatment is made. In the case of straw itch mites, we wouldn’t provide relief to those affected but may be able to fix the underlying source of the mites and their food source.


Indicator organism: Parasitic and parasitoid wasps
What its presence suggests: Stored product pests

There are a host of parasitic wasps and parasitoid wasps that attack the eggs or larvae of stored product beetles and moths. At least five families of wasps rely on their unwilling hosts for development, including Indianmeal moths, Mediterranean flour moths, rice weevils, drugstore beetles, foreign grain beetles, flour beetles and more. These wasps are beneficial in that they can suppress stored product pest populations, but in a food environment, their presence is unacceptable in most cases.

These wasps are quite numerous and differ greatly in their appearance and life history, so the best advice is to collect any suspicious wasps that you find indoors in food-processing and storage facilities and have them identified. This identification process can be difficult, and you may need to have them checked out by a university extension entomologist or other trained expert.

The author is director of technical support and regulatory compliance, Copesan Services, Menomonee Falls, Wis.


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