Bean weevil: what is it? How to get rid of it?

Identifying

Correctly identifying the bean weevil in legumes is the first crucial step for effective control. This insect, belonging to the beetle family, is characterised by its small size, typically between 3 and 5 mm, and its colour ranging from brown to black. Adults have wings and can fly, while the larvae, whitish and wingless, develop inside the seeds.

Infestation signs are often subtle at first. Gardeners should watch for several indicators, mainly in stored seeds, but also in cultivation:

• Holes in seeds: a small round hole on a seed is an obvious sign of the bean weevil’s presence. This hole is created by the larva as it emerges from the seed.
• Damaged seeds: seeds infested by the larvae may show signs of deterioration, such as cracks or deformations.
• Presence of adult beetles: finding small beetles near legume plants is an infestation indicator.

It is important to note that bean weevils prefer certain species. The beans, broad beans and lentils are their favourite targets. Regular monitoring of these crops is therefore essential, especially during hot, dry periods that are conducive to their development.

Bean weevil damage includes, among other things, holes in seeds

What is it?

To effectively combat the bean weevil, it is essential to understand its life cycle and host preferences. This knowledge allows for more targeted control and prevention strategies.

Legume species most affected

• • Beans: Beans are particularly susceptible to the bean weevil. Stored dry varieties are often the most affected, but field crops can be as well. Moreover, the bean weevil can have several generations in a year.
  • Broad beans: Broad beans, with their large seeds, are a prime target for the bean weevil. Infestation can occur in both the kitchen garden and storage.
  • Lentils: Lentils, due to their small size, can be seriously damaged by the larvae of the bean weevil.

Life cycle

The bean weevil goes through several stages: egg, larva, pupa and adult. Females lay their eggs directly on the seeds. The larvae, once hatched, penetrate the seeds in which they feed and develop. After pupation, the adults emerge from the seeds, ready to reproduce. This cycle can vary in duration depending on environmental conditions, particularly temperature.

• Bean weevil: When temperatures reach 11 °C, the bean weevil adult, having spent the winter inside the seeds, begins to move into stores or fields. In dry, sunny conditions, and at a temperature of 21 °C, it can even fly. The female bean weevil can lay up to 40 eggs, which she deposits in groups of 2 to 20, either on the pods in the field or directly on the seeds in storage. The eggs hatch after an embryonic period of 3 to 15 days, and the larva then penetrates a seed. Its growth phase lasts approximately three weeks. Thereafter, it creates a circular opening in the seed to pupate. After 12 to 25 days, it emerges as an adult ready to reproduce.
• Bean and pea weevil: Adult bean and pea weevils spend the winter nestled in seeds or in various refugia. At the return of spring, they fly in search of their host plants. On these, they feed on pollen and consume a few flowers. The reproduction period then comes, during which they lay eggs on the pods. These weevils are characterised by high fecundity, capable of up to 400 eggs, but there is only one generation.

Bean weevil

Treating an active infestation

When the bean weevil is already present in your crops, it’s crucial to act quickly to limit damage. Here are the steps to follow to effectively treat an active infestation:

• Infestation assessment: Start by assessing the extent of the infestation. Carefully inspect your legume plants, particularly beans, broad beans and lentils, to identify signs of bean weevil presence.
• Removal of infested seeds: Remove and destroy, by destroying (do not compost) all infested seeds and plants. This prevents the propagation of larvae and reduces the adult bean weevil population.
• Thorough cleaning: Clean the growing area to remove plant residues and seeds that have fallen to the soil. A clean environment reduces hiding places and food sources for the bean weevil.
• Freezing treatment: Place your seeds in the freezer for 24 hours. The larvae do not withstand this intense cold.

Specifically in storage locations

• Two options are available to you to eliminate the bean weevils in your seed storage jars: add a few unpeeled garlic cloves to each jar. Or, light a cotton wool ball soaked in alcohol just before sealing the container. This action aims to consume the oxygen present in the jar and suffocate the bean weevils.

After treatment

After treatment, continue to monitor your crops regularly. Early detection of any new infestation is essential to prevent its spread.

Pea weevil

Preventing

Here are preventive strategies to integrate into your gardening practices:

• Crop rotation: Alternate legume crops with other types of plants from year to year. This practice disrupts weevils’ life cycle and reduces risk of infestation.
• Garden cleanliness: Keep your garden tidy. Remove harvest residues and weeds that can provide shelter for weevils.
• Proper seed storage: Store harvested seeds in dry, cool conditions. Use airtight containers to prevent access by weevils.