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Thanks to the Protein Aid Scheme, the production of faba beans in Ireland has increased threefold since 2015. This strategy assists Europe in reducing its dependence on imported protein crops, in particular soya beans.
However, the increase in pulse crops can promote the development of legume pests.
This is the case for the bruchid beetle (Bruchus rufimanus).
This beetle is considered to be a major pest of beans in Europe.
Very common in Mediterranean countries, it was identified by Teagasc in Irish grown beans in 2016.
Life cycle of the bruchid beetle
The adult bruchid beetle emerges between April and May when daily mean temperatures reach 9°C (48°F).
Initially, adults feed from the pollen of different flowers available in their habitat.
They fly into flowering bean crops when the temperature reaches 15°C to 20°C (59°F to 68°F). When bean crops start to flower, bruchid beetles are attracted by the odours of the faba bean flower.
The consumption of the bean pollen induces the mating of adults, and once pods appear, mated females become more attracted to pod odours, laying eggs on the pod skin.
After one to six weeks, the larvae hatch and dig a hole through the pod and enter a seed, consuming the seed during their larval development.
Larvae utilise two strategies to survive during winter. Some of the larvae display fast development and emerge as adults between the end of the summer and the start of autumn, overwintering in wooded places.
High-quality seeds (less than 3% infested) are used for human consumption
The remainder of the larvae develop slowly and emerge as adults from the seed in the following spring.
It is only larvae that damage seeds and impact yield. At the end of their development, emerging adults leave a characteristic round hole in the seed.
Impact on the market
The European market categorises seeds based on the percentage of bruchid beetle infestation.
High-quality seeds (less than 3% infested) are used for human consumption, while poor-quality seeds (between 3% and 10% infested) are used for animal feeding.
If the proportion of damaged seed is too high, it may be necessary to grade out the infested seeds.
Some Mediterranean countries, like France, have ceased selling high-quality beans because of the high proportion of bruchid beetle damage.
Levels found in Ireland
Since 2018, Teagasc assessed the incidence of bruchid beetle on different farms in Ireland.
This first study on the bruchid beetle’s prevalence indicated a low infestation across the country, with only a few hotspots showing higher damage to beans.
However, an increase in the bruchid beetle population is likely as the area sown to beans increases and also as temperature increases. Levels of bruchid beetle damage in bean crops must be managed if we are to access high-quality seed markets.
A new project aims to assess the population of bruchid beetles in Ireland and the levels of associated damage on a field scale over three years.
For this study, two methods will be adopted in association with farmers.
1 Pest monitoring: farmers will put two traps on the edge of their bean field during the flowering stage of the crop. The beetles caught in the traps must be collected each week and sent to Teagasc. Traps will emit a specific lure, imitating the odours of bean flowers, so as to attract only the bruchid beetle. Pollinators and other helpful insects are not attracted or harmed by these traps.
2 Damage assessment: bean-seed samples sent by farmers will be analysed. A sample of 500 seeds (300g) from the bean crop will be visually assessed by Teagasc to estimate the percentage of seeds damaged by bruchid beetles.
If you grow beans and are interested in participating by placing traps in your field and/or sending a seed sample after harvest, please send an e-mail to antoine.pichon@teagasc.ie.
All traps, lures and shipping will be provided by Teagasc. Traps will be sampled and lures refilled weekly by growers.
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