Cotton stem weevil

The cotton stem weevil, scientifically known as Eutinobothrus gossypii, belongs to the Curculionidae family. It is a specialized pest that exclusively targets cotton plants, causing significant economic losses.

Adult weevils are small, measuring approximately 3-4 mm in length. They typically possess a dark brown or black coloration, often covered with fine hairs that help them blend into the plant tissue.

The larvae are apodous (legless), creamy white, and curved in shape. They spend their entire developmental phase feeding inside the stem of the cotton plant.

Pupation occurs within small galleries constructed by the larvae inside the host stem. This protected environment shields the pupae from both external predators and climatic changes.

Identification of the insect is challenging for the average observer, as its life cycle is almost entirely completed within the internal vascular tissues of the host plant.

The pest primarily causes damage to the genus Gossypium. The larvae bore into the stem, feeding on the inner layers, which disrupts the normal flow of nutrients and water.

Young plants are particularly vulnerable and may succumb to the attack quickly, leading to stand reduction. In older plants, the internal damage weakens the stem's structural integrity.

Affected plants often display reduced growth rates and poor fiber development. The weakening of the stem makes the crop prone to lodging during adverse weather conditions like heavy wind.

If the stem is severely hollowed out by larval activity, the plant may wilt or die entirely due to the inability to support its canopy or transport water efficiently.

Additionally, the entry and exit holes created by the weevils serve as entry points for secondary bacterial and fungal pathogens, further exacerbating the damage to the cotton crop.

The most prominent sign of infestation is the appearance of galls or swellings on the stem, typically near the soil level or the lower portion of the plant.

Visible exit holes in the bark of the lower stem indicate that adult weevils have emerged. These holes are a clear sign that the pest population is established in the field.

Plants suffering from infestation often exhibit yellowing foliage and general chlorosis. The plant may look stunted compared to neighboring healthy cotton bushes.

Upon inspecting the stem, one can find internal tunnels packed with frass and decaying wood tissue, which confirms the presence of larval feeding activity.

• Swollen or gall-like growths on the base of the stem.
• Premature wilting of the leaves during the hottest part of the day.
• Small, circular exit holes on the lower stem.
• Reduced overall biomass and height of the cotton plants.

Cultural control is the most effective approach to managing this pest. Implementing a strict crop rotation cycle prevents the buildup of weevil populations in the soil.

Post-harvest sanitation is critical. Removing all cotton stalks and burning them helps destroy the larvae that are still residing inside the stem tissue.

Deep plowing after the harvest season disrupts the soil environment, which can kill or expose the overwintering stages of the weevil to environmental stress.

Chemical control is difficult because the larvae are hidden inside the plant. Applications should be timed precisely to coincide with the emergence of adult beetles.

Field monitoring and the use of pheromone or light traps can help determine the exact timing for insecticide applications, ensuring that treatments are effective and targeted.