Bad Bugs: Insects That Can Cause Health Problems


If there is an insect that is truly a voracious feeder and a potential health hazard to humans and young animals, the warehouse beetle falls into that category because of the long list of foods that it attacks. Next to the dreaded quarantine pest, the Khapra beetle, it is the most serious stored product insect pest.

Imagine an insect that can live for three years without food or water. Imagine an insect that can live in a freezer for five days. Imagine an insect that can hide in cracks only to emerge to cause havoc with a museum collection or a complaining customer. That is the nature of the Warehouse beetle.

Let’s take a close look at this common stored product insect:

The Warehouse beetle prefers feeding on animal protein. This could be anything from road kill to dog food to powdered cheese and milk. The beetle will feed on plant material but a dead insect or mouse would be its preferred food source. You will often find Trogoderma spp. feeding in insect light traps on dead insects. It is important to empty these lights on a regular basis.

The larva (see figure) of the Warehouse beetle is approximately 1/4 inch long and prefers to breed in dark places. such as packed food cartons. Larval color varies from yellowish white to dark brown as the larvae mature. Warehouse beetle larvae have two different tones of hairs on the posterior end. These guard hairs protect them against attack from the rear. The warehouse beetle has about 1,706 hastisetae hairs and about 2,196 spicisetae hairs according to a publication by George Okumura. Since a larva sheds its hairs during each molt, the damage of this pest insect comes from the 1000’s of these pointed hairs that escape and enter a finished food product as an insect fragment. These insect fragments then can be swallowed by humans, young horses or pets and get lodged in their throats.

Health Hazard
Okumura (1967) mentioned two medical reports:

Case #1: “The establishment of a case of canthariasis in an infant in Indiana was based upon the following information: Two larval specimens of Trogoderma were submitted to me for identification. The specimens were collected in the stool of a four-month-old baby boy who was ill. Live larval Trogoderma were submitted later from packages from the same lot of high-protein baby cereal which had been fed to the child.”

Later a consulting doctor further explained: “As far as I know the symptoms in the Indiana infant with ulcerative colitis were attributed to the beetle larvae of Trogoderma glabrum (closely related to Warehouse beetle).”

Case #2: “The case of a four-month old baby boy in California was similar to the Indiana case. Here the baby was fed a high-protein baby cereal in which the larvae of Trogoderma onatum was later found. (One live, one dead, and two cast skins) were taken from the original package of the baby cereal. According to the mother, the baby became ill two or three days after eating the cereal. The baby did not vomit, but had mild diarrhea. The interviewed mother stated: ‘the baby showed signs of varying degrees of digestive distress, culminating in a severe outbreak of screaming and crying and absolute refusal to eat. Anytime it was offered food it became rigid and red, and arching his body and screaming, evidently in pain).’”

The doctor did not administer medication and after a couple of days the baby recovered.

There are 16 species of Trogoderma. The female adults are twice the size as the male beetles. They are members of the Demestidae family that also includes Black carpet beetles. However, they are not a carpet beetle. When inspecting it is often easy to spot the cast skins. This is much like a snake that sheds its skin. The adults are about 1/8 inch
and dark in color with yellowing mottling on the wing covers (elytra). This mottling can take on various shapes even within the same species.

The larvae is the damaging stage and can over winter in wasp nests and mud-dapper nests feeding on old insect carcasses and guano. During the spring months when plants are flowering, if is common to see Trogoderma adults on plants collecting pollen and looking for a mate.

Small white flowing bushes like spirea are very attractive to Dermestids. The adults have distinct antennae that other beetles lack.

For a positive identification of this or any stored product insect, Insects Limited, Inc. can provide this laboratory service.

The pheromone for the Warehouse beetle and other Trogoderma species is very effective in monitoring for the presence or absence of this pest insect. The pheromone lure lasts for
2-3 months and should be placed at least 50 feet from an open door or vent. Traps should be placed outdoors to detect pressure from the surrounding area. It is not uncommon to capture 1000 Trogoderma adult males in one trap in the summer months. By examining the hairs (setae) on these captures beetles one can often detect hitchhiking food particles
like cheese, milk powder, fish meal or pollen. This will give an indication where this pest
insect was crawling last.

Pheromone traps should be placed at eye level on vertical support beams. A date when the pheromone was last replaced should be written on the trap. Each trap should be examined every week on the same day and captured insects should be removed and recorded. An important pest management tip for Trogoderma pheromones is that the male beetle emerges 5-7 days before the female beetle. The pheromone trap captures only males. This allows an advanced warning to when a new generation of Warehouse beetles is emerging from the pupa stage. The other important tip is that the Warehouse beetle adults don’t fly until the temperature is about 73° F. (23° C). So you may have Warehouse beetles and still not be capturing them in traps until the temperature is warm.


The Macabre
“An early German report entitled ‘Fauna of the Grave’ refers to small flies, many species which are ‘interested more in dead men than living’ and which breed in human corpses and feces in ‘countless million.’ More than 70% of survey respondents collected Phorids from human cadavers.”

By the way, Phorid flies are a major pest of wet food processing areas in food facilities.

Just the Facts
W. Robinson states: “Eggs are laid in groups of 20-40 over a 12-hour period with hatching occurring after about 24 hours. This accounts for the common observation by pest
managers: ‘I fogged that area last night and today we see these little black flies back again.’ This fly has the habit of running on tables, walls, and windows.” One key characteristic is that the Phorid hovers unlike the housefly and fruit fly that can hover in the air almost suspended until you reach for it and it rushes away.

Some call this the Humpback Fly because of the way the back of the adult is humped over. The adults are very small 1/8 inch (like a fruit fly).

The larvae can be found in dark, secretive, damp and moldy places. They hide in drains and tiny places where they feed on highly nitrogenous organic matter that has begun to rot. Stale beer and fruit juices in bars are difficult places to control this tiny fly. Many Phorid larvae live as scavengers in the nests of ants, bees, wasps, and termites.

Health Effects
Phorids have been found to infest fruit that gets swallowed and digested. It has been proven that these flies have lived and mated in human intestines. Now do you need to ask if Phorid fly larvae can live in drains? This is an example of the extreme tolerance of these flies at all stages to asphyxiation and to chemical action. Larvae will also infest wounds and will live in preserved materials of all kinds, even specimens preserved in formalin.

The only really long-term solution to controlling Phorid flies is to remove the food source. This means cracks, drains, internal hiding places and more. Prevention and monitoring are the two keys to a pest management strategy. Control tools like pyrethrin fogs are only temporary.

Many times the problem may be under a floor. For example a garbage disposal line broke and liquid garbage soaked in to the ground under a kitchen floor. By drilling the floor with 1/4 inch holes every 3 feet in the suspected area and placing a paper cup over the holes, detection of where to start tearing the floor up was decided. In one case in Kentucky, over ten 55-gallon drums of waste were removed from under the broken garbage disposal line. Many times the solution to a Phorid fly problem is complex and costly.

Start with the insect first by proper identification. Controlling fruit flies is much different than controlling Phorids. Do not attempt to bluff the customer if you are unfamiliar with the pest causing the problem. Work with your customer to locate the source of the problem by conducting interviews with those close to the infestation (housekeeping, kitchen staff, etc.). Finally, develop a control program that utilizes the appropriate control measures and solves the problem on a permanent basis.


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