3.3 Stored Product Pests and Fabric Pests

Stored Product Pests and Fabric Pests

Stored product pests and fabric pests are economically destructive insect groups that fall under Branch 2 General Pest control. They damage food supplies, ruin clothing, carpets, and museum specimens, and can trigger allergies in humans. Proper identification is critical for developing targeted treatment strategies, particularly when differentiating food-infesting insects from fabric-damaging ones.

Stored Product Pests

Stored product pests (often called pantry pests) are divided into primary (internal) feeders and secondary (external) feeders.

1. Sawtoothed Grain Beetle (Oryzaephilus surinamensis)

• Identification: A small, slender, flattened beetle (about 2.5-3 mm) that is dark brown. The defining physical feature is the thorax, which has six saw-like projection teeth on each side. They are wingless in practice (they cannot fly).
• Habits (External Feeder): The sawtoothed grain beetle is an external feeder. It cannot penetrate sound, whole grain kernels. Instead, it feeds on processed cereals, flour, cornstarch, macaroni, dried fruits, nuts, and pet foods. Because of its flat body, it easily slips into cardboard packaging.

2. Indianmeal Moth (Plodia interpunctella)

• Identification: The adult moth has a wingspan of about 16-20 mm. The wings are copper-colored on the outer two-thirds and light gray or tan on the inner third.
• Damage (Webbing): Only the larval stage feeds on products. As they feed on grains, cereal, nuts, chocolate, and dried fruit, the larvae spin dense silken webbing over the food surface. This webbing accumulates fecal pellets and larval cast skins, ruining the product.
• Behavior: The larvae often crawl away from the food source to pupate in cracks, crevices, or high up on walls and ceilings. Adults fly in an irregular, zigzag pattern and are attracted to light, unlike fabric moths.

3. Rice Weevil (Sitophilus oryzae)

• Identification: A small beetle (2-3.5 mm) easily identified by its head, which is prolonged into a distinct snout (rostrum) with biting mouthparts at the tip. It is reddish-brown with four light reddish-yellow spots on its wing covers (elytra). Unlike the granary weevil, the rice weevil can fly.
• Habits (Internal Feeder): The rice weevil is an internal feeder. The female bores a hole into a sound, whole grain kernel (such as rice, wheat, corn, or barley), deposits an egg, and seals the opening with a gelatinous secretion. The larva hatches, feeds, and pupates entirely inside the kernel, emerging as an adult.

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Fabric Pests

Fabric pests feed on keratin, a tough, fibrous protein found in animal-based materials. They do not feed on synthetic fibers or clean cotton unless blended with wool or soiled with sweat or oils.

1. Webbing Clothes Moth (Tineola bisselliella)

• Identification: Small, golden-buff moths (6-8 mm long) with a tuft of reddish-gold hairs on the top of the head.
• Behavior (Shuns Light): Unlike pantry moths, webbing clothes moths are weak fliers and shun light. They are found in dark, undisturbed areas like closets, drawers, attics, and trunks.
• Damage: The larvae spin silk tubes or webbing over wool, silk, fur, feathers, and leather as they feed. The adult moths do not feed at all; their sole purpose is reproduction.

2. Varied Carpet Beetle (Anthrenus verbasci)

• Identification:
  • Adults: Small, round, beetle (2-3 mm) with a mottled pattern of white, yellow, and brown scales on their backs. Outdoors, they feed on pollen and nectar.
  • Larvae: Teardrop-shaped, brownish, and covered in dense, bristly hairs. They have specialized tufts of arrow-shaped hairs (hastisetae) at the rear of their abdomen.
• Damage and Health Risks (Dermatitis): The larvae feed on animal-based materials (wool carpets, feathers, hair, lint, dead insects, animal nests). As they grow, they shed their bristly skins. These shed skins (exuviae) accumulate in carpets and baseboards. The hairs can cause allergic skin reactions (contact dermatitis) in humans, which clients often mistake for bed bug bites.

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Comparison of Stored Product and Fabric Pests

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SPCB Exam Traps

1. Internal vs. External Feeders: The exam will ask which pests can attack whole, undamaged grains. Weevils (Rice and Granary weevils) are internal feeders because they lay eggs inside the kernel. Sawtoothed grain beetles and Indianmeal moths are external feeders and require cracked or processed grains.
2. Moth Behavior (Light vs. Dark): If the exam describes a moth flying around a light in the kitchen, it is an Indianmeal moth (pantry pest). If it describes a moth running and hiding in a dark closet, it is a Webbing clothes moth (fabric pest).
3. The Carpet Beetle Bite Trap: A customer complains of 'bites' on their legs, but an inspection reveals no bed bugs or fleas. Instead, the technician finds carpet beetle larvae in the wool rug. The 'bites' are actually carpet beetle dermatitis caused by contact with the larvae's bristly shed hairs.

Real-World Scenario

A technician inspects a home where the owner reports itchy red welts on their arms. The technician inspects the bed and bedroom perimeter thoroughly but finds no signs of bed bugs or fleas. However, when inspecting the closet, they find a wool coat covered in small holes, silken threads, and small, bristly, crawling larvae. The technician identifies the pests as carpet beetle larvae and explains to the homeowner that the welts are likely a reaction to the shed larval skins in the closet.