[Stored Product Pests] Bait and Switch Strategy

Features - Problems & Solutions

Exploiting the “personality” traits typical of warehouse beetles will help you devise more effective control strategies.

November 21, 2011
David Mueller
Magnified hastisetae, or spear-headed hairs, found on the end of a warehouse beetle larvae. Hastisetae are used for protection but can get lodged in a person’s or pet’s throat and cause health issues.

Consider the warehouse beetle, Trogoderma variabile, a serious stored product pest, which has its own particular habits and customs. The adult is an active indoor and outdoor flier that is easily attracted by odors. Stash a pheromone lure in your pocket and it will come to you like a puppy dog.

Then there's its larva, which has a proclivity for dark hiding spots. It's often found hiding in false ceilings, slowly munching on dead cluster flies. The pupa is too lazy even to spin its own cocoon, so it sleeps in a cast beetle larva skin like a Boy Scout in a sleeping bag.

Being aware of facts and habits like these can be deciding factors in allowing you to manage a stored product pest population to an acceptable level. In fact, to solve any customer complaint, you need to understand the difference between insect personalities so you can design a customized strategy to eliminate them.

A Serious Pest. Most insects cause customer complaints by their mere presence. However, warehouse beetle larva can cause ill health effects. There have been reported medical cases where the hairs from the warehouse beetle larvae are found in the throats of small animals and children. The hairs cause the throat to become inflamed and the breathing passage becomes constricted.

The warehouse beetle (Trogoderma variabile) larval cast skin and adult.

The warehouse beetle goes through five or six molts in the larva stage and releases more than 15,000 hairs from its cast skins per individual during this time. There are three different types of hairs found on the warehouse beetle larva: 1) smooth hairs, 2) slender hairs and 3) spear-headed hairs (hastisetae).

The warehouse beetle also has a unique personality. The larvae can survive three years without food or water when placed in an empty glass container. They will survive by eating their cast skins and slowing down their respiration. They are very hard to kill because the larva is negative phototropic, which means they prefer dark places. Therefore, they will hide behind hard-to-clean equipment and in isolated areas that are hard to inspect. This insect has been found thriving inside electrical boxes, conduit and attics. They like undisturbed locations such as food product that has been forgotten. In a home, they will eat dead insects like cluster flies or Asian lady bugs, and abandoned mud dauber tubes.

Trapping Tips. The warehouse beetle and several related species of the Trogoderma (TROG-a-derma) genus are found outdoors feeding on dead animals and plant protein. Male beetles are often attracted to a pheromone trap placed inside a structure. These males recognize the scent of the pheromone lure and fly indoors to be captured by these sensitive monitoring tools. The correct interpretation of the traps is important by the pest manager. Placing traps outdoors will allow you to gauge the outdoor stresses from warehouse beetles in the warm months. These traps also should be used indoors but not near openings like truck doors, roof vents or other obvious openings. They work well as spot-checks of certain areas. A trap and lure can be placed in an area for a few days to develop a better understanding of a suspect product that may need more inspection by the pest manager.

Insects are a symptom of a condition. Their strong ability to fly and smell odors from long distances has made this beetle particularly troublesome for the food industry. Warehouse beetles can detect many different odors with its antennae. The female often migrates to the product with the strongest odors to feed and lay her eggs.

Why is it important to understand one insect's personality from another? As you can see, the warehouse beetle is very different from a red flour beetle and even more so from an Indian meal moth. Each has its own habits and personality.

The pressures from these stored product insects can change from region to region and season to season. No two locations are the same and each one has conditions that can allow a particular pest to survive and thrive. The warehouse beetles and related species have their own particular environment and preferred food source. It is our job to understand what this serious insect pest likes and dislikes. Then we can offer it what it dislikes and it will leave or die.


Photos are courtesy of David Mueller.

The author is a stored product entomologist and author of the book "Reducing Customer Complaints in Stored Products." He is the president and founder of Insects Limited in Indianapolis, Ind. He can be reached at dmueller@giemedia.com.