Bean Weevil Control Guide: Prevention, Monitoring, and Sustainable Management Strategies

The bean weevil is one of the most serious insect pests of legumes of all countries. While many growers may think of infestation when they think of storage, infestations are often present in the field prior to the beans being brought in for storage. After establishment populations may continue to develop during storage resulting in serious declines in seed quality, marketability, germination rates, and economic losses.

Since it may be very difficult to notice the presence of infestation in the seed, proactive monitoring and intervention are important. Recent trends in bean weevil control programs focus on prevention, monitoring, and integrated pest management in preference to treating the problem after a serious bean weevil infestation has been encountered.

Why are bean weevils important to be identified?

The word bean weevil is applied to a group of beetles (family Chrysomelidae) which attack legumes and grains in storage. Beans are attacked by two common species, A. obtectus and C. maculatus which can be serious economic pests under favorable conditions.

The bean weevil scientific name aids growers and storage managers in choosing the most effective management strategy because there can be some slight differences in host preference, environmental needs and behavior among the various species. Proper identification also helps to optimize monitoring programs and help predict the development of pests based on the bean weevil life cycle.

A knowledge of the Bean Weevil Life Cycle

The first step in successful pest management is to know the biology of the pest. The bean weevil life cycle has several separate phases: egg laying, larval development, pupation and emergence of the adults.

Unfinished pods were used in the field as a breeding ground for beetles to lay their eggs or directly on the stored beans. Upon hatching bean weevil larvae bore into the seed and continue to feed on internal seed tissues while being protected within the seed. Pupation will take place in the seed after development is complete and adults emerge through distinct exit holes.

Since larvae develop inside the bean for large periods of time, correct timing is critical to the successful bean weevil control. Efforts aimed at the most susceptible life stages of a species tend to be more effective than programs after the population of adults has been large enough.

The damage caused by Bean Weevil Larvae

Larval feeding is its most detrimental phase of infestation. After bean weevil larvae enter the bean the inside tissues of the bean (cotyledon and embryo) are eaten by the larvae and this affects the quality and germinability of the beans.

The quality of the beans decreases and weight losses increase as feeding goes on. Heavy infestation of bean weevil damage can cause grain to be unfit for use, processing or seed planting. Seed production systems can have a significant impact on germination and seed vigor.

When severe bean weevil infestations are present, infestation may be present for a large portion of the development of the larva before symptoms are visible.

Identifying early infestation is the best approach to controlling the problem

One of the best ways to effectively manage a pest is to detect it early. There are a number of factors that may be considered some of the symptoms of an emerging bean weevil damage.

Some of the most telltale signs include small round exit holes on the surfaces of seeds. Growers also might notice the presence of hollow, unfilled seed, powder inside storage containers, broken seed coats, lower seed weight and lower germination rates.

Often the only signs are seen once some serious feeding has taken place in the interior of the plant. Therefore, regular monitoring becomes imperative to reduce bean weevil infestation and prevent the spread of bean weevils in storage areas and production systems.

Integrated pest management (IPM) is the best way to control bean weevils

How to get rid of bean weevil? Integrated pest management (IPM) strategies are growing in popularity among growers looking for bean weevil control methods to use, as well as a means for prevention.

Effective programs usually start with sanitation measures that remove crop stubbles and those from previous infestations. Crop rotation can help prevent the development of pests in field production systems and resistant varieties can help limit pest establishment in some cases.

Monitoring is also crucial for early detection, before damage occurs, and is an important part of the programs. Biological control methods are becoming more and more popular and are effective in reducing the quantity of pesticides employed and contributing to maintaining a healthy environment in today's bean weevil control program.

Why is Metarhizium anisopliae relevant for sustainable pest management?

It is the fungus which is effective against susceptible insects. Spores are deposited on the cuticle of the insect, germinate and enter the insect through the cuticle leading to internal infection. The infected insect eventually dies and the new spores are formed and continue to control the insect.

This distinctive mechanism of action from biological control makes Metarhizium anisopliae a significant part of the sustainable bean weevil control. Biological management also helps integrated management systems and decreases the environmental side effects of reapplication with chemicals.

Microbial technologies are playing a more critical role in managing future bean weevil infestation risks for growers as they seek sustainable solutions to the question of how to get rid of bean weevil.

Novobac Met Zone provides biological bean weevil management that is both simple and effective

Novobac is an R&D company specializing in biological technologies for crop protection that are relevant to sustainable agriculture and integrated pest management.

Novobac Met Zone is a biological insect management product that uses naturally occurring microbial processes to help suppress soil associated insects, and contains Metarhizium anisopliae. Because of the product's efficacy and insecticidal activity, it is designed to be used in conjunction with integrated pest management programs, and it will not require frequent chemical sprayings.

Biological solutions have become more common in the pest management programs of growers in Canada, the United States, Mexico, Europe, India and many other regions of the world where agriculture makes up the bulk of the economy.

In these programs products like Met Zone are contributing to better bean weevil control, to manage a potential bean weevil infestation and to minimize long-term bean weevil damage in the bean production system.

The development of a Long-Term Prevention Strategy

How to preserve beans from weevils? It takes prevention, not reaction, to be successful in the long term. Good management practices include field sanitation, storage hygiene, environmental monitoring, biological interventions and regular inspections, all of which are part of a sustainable management strategy.

To diminish favorable conditions for pest growth, storage areas should be kept clean, dry and well ventilated. Monitoring systems can help detect issues early on, and preemptively before economic losses result.

Growers are becoming aware that it is better to bean weevil control rather than trying to manage an infestation once it becomes a major problem. The manner in which beans are stored is also a key element in how to keep beans from being damaged by weevils for long periods.

The integrated management programs, which integrate prevention, monitoring and biological tools, provide growers with more consistent solutions on how to get rid of bean weevil and enable sustainable agricultural production systems for the future.

Reference:

• Verkleij, F. N., PAM van Amelsvoort, and P. H. Smits. "Control of the pea weevil (Sitona lineatus L.)(Col., Curculionidae) by the entomopathogenic fungus Metarhizium anisopliae in field beans." Journal of applied Entomology 113.1‐5 (1992): 183-193.
• Lak, Fatemeh, et al. "Synergic effects of some plant-derived essential oils and Iranian isolates of entomopathogenic fungus Metarhizium anisopliae Sorokin to control Acanthoscelides obtectus (Say)(Coleoptera: Chrysomelidae)." Frontiers in Plant Science 13 (2022): 1075761.