**Pulse Beetles** is a general term primarily referring to the **Pea Weevil** (*Bruchus pisorum*) and various species of **Seed Beetles** or **Cowpea Weevils** (*Callosobruchus* spp.)—all members of the family Chrysomelidae, subfamily Bruchinae. These beetles are highly damaging pests of **pulses** (legumes) such as peas, beans, chickpeas, and lentils, both in the field and in storage. The larvae develop entirely inside the seeds, causing significant weight loss, loss of viability (germination), and rendering the seeds unfit for consumption or sale.
Taxonomy and Classification
Pulse Beetles belong to the family Chrysomelidae (leaf beetles). The subfamily Bruchinae is highly specialized for attacking the seeds of legumes. They undergo complete metamorphosis. Unlike weevils (Curculionidae), they do not possess an elongated snout, though they are commonly referred to as weevils.
Physical Description
Adult Pulse Beetles are small, stout, oval-shaped beetles, typically $1/8$ to $1/4$ inch long, often brown, gray, or mottled.
- **Larvae:** Creamy white, legless, fleshy grubs that live entirely within the seed, where they consume the cotyledon (food source).
- **Damage Sign:** The most characteristic sign of infestation is the circular **exit hole** chewed through the seed coat when the adult beetle emerges, leaving the seed hollowed out.
- **Eggs:** The eggs are small, whitish, and firmly glued to the outside of the developing seed pods in the field or on dry, stored seeds.
Distribution and Habitat
Pulse Beetles are cosmopolitan pests, found globally wherever pulses are grown and stored. Their habitat is the seed pod (in the field) and the stored seed (in granaries, silos, and pantries). Infestation often begins in the field, but the most severe damage occurs during the storage phase.
Behavior and Damage
The life cycle varies by species, but a key distinction is made between field-infesting species (*Bruchus*) which attack only in the field and store-infesting species (*Callosobruchus*) which can continue to reproduce generation after generation in the stored grain.
Damage is caused entirely by the larvae:
- **Loss of Viability:** Larval feeding consumes the embryo and cotyledon, destroying the seed’s ability to germinate.
- **Contamination:** Heavily damaged seeds are useless for food and can be rejected by processors.
- **Weight Loss:** Severe infestations cause significant loss of stored product weight and quality.
Management and Prevention
Control requires management in both the field and storage.
- **Field Control:** Applying insecticides to the crop when the pods are developing, targeting the adult beetles before they lay eggs, is necessary for high-value crops.
- **Storage Control (Most Important):**
- **Sanitation:** Thoroughly clean storage bins and facilities before harvest.
- **Fumigation:** Infested stored seeds are often treated with a powerful fumigant (e.g., phosphine) to eliminate internal larval populations, though this is tightly regulated.
- **Heat/Cold Treatment:** Small batches can be heated ($130^{\circ}\text{F}$ for 4–5 hours) or frozen ($0^{\circ}\text{F}$ for 7 days) to kill the internal larvae.
- **Hermetic Storage:** Storing seeds in sealed, oxygen-deprived containers can suppress population growth by suffocating the insects.
Conservation and Research
Pulse Beetles are managed as significant storage pests impacting global food security. Research focuses on breeding pulse varieties with genetically enhanced seed coat resistance and optimizing the use of highly specific parasitic wasps (biological controls) that attack the beetle’s eggs.