Latin: Acanthoscelides obtectus
There are many different species within the bean beetle genus, which include Bruchus, Callosobruchus and Acanthoscelides. Common to them all is that they are serious pests. Especially in the warmer areas around the globe where they can ruin the harvest for the local farmers.
The bean beetle originates from the tropical regions and is native to South America. But it is not unheard of for it to be shipped to other countries where it is transported through imported goods.
Appearance
Although the bean beetle can do great damage, it has a fairly modest size. An adult bean beetle grows between 3 and 4 millimeters long. The beetle has a greyish brown color, while its coverts, which do not cover the hind body, are characterized by light markings and dark stripes. Its legs and antennae are reddish.
Newly hatched larvae are straight with legs, older larvae are c-shaped and have no legs. The larvae grow up to 4mm.
Biology and behavior
The bean beetle belongs to the family of leaf beetles (Chrysomelidae) under the family of seed beetles (Bruchinae). The bean beetle feeds on dried goods, which is why it likes to attack foods such as dried beans, dried peas, lentils, and soybeans. It is also among these foods that the female lays her eggs. The female can lay up to 85 eggs.
When the larvae hatch from the eggs, they go out into the world for food. This means that they gnaw their way into beans or peas, for instance. Here they go through their next three larval stages, which eventually results in the larvae pupating. Once the larvae have gone through the process, they gnaw their way back out of the shell of the bean. The development from egg to adult takes four weeks at 30 degrees. At 20 degrees it takes 2.5 to 3 months.
The process from larva to adult bean beetle takes place exclusively inside the bean, where they can even hollow it out completely. The highest documented number of larvae in one bean is recorded at 28 pieces.
The given temperatures also play a significant role in the reproduction and development of the bean beetles. If the temperature is 27 to 31 ° C, it is in the bean beetle’s favor, and then they can increase their number no less than 25 times in just a single month. But less can do it too. However, the larvae stop their development if the temperature falls below 12 ° C. The beetle cannot overwinter outdoors in Denmark.
Damage
The bean beetles are feared because they can quickly destroy large areas of pea-flowering plants, which are their target. The beetles attack the seeds of the plants while they are in the field. But their possible ravages do not stop here. The bean beetles can be taken to the seed warehouses and thus continue their destruction in peas and dried beans, where they can lay their eggs.
They are therefore considered one of the worst pests on bean and pea stocks.
Prevention and pest control
The control of the bean beetle can be made more difficult by the fact that the beetle is a quite good aviator, just as it is also known for crawling around lively. It therefore has no problem leaving its place of origin.
If the bean beetle is found in the home, it has often been transported inside through an infested food in which the larvae have developed. Most often a bag of dried beans or peas. It is therefore important to find the food in question and discard it, just as a thorough vacuuming should be done.
If you do not want to discard the food, they can be frozen for a minimum of 2 days, which any larvae would not be able to survive. After this, you should also always store these foods in containers with tight-fitting lids.
If a store with seeds or food has been attacked, the entire area should be thoroughly inspected. Again, suspicious items must be discarded or frozen for a minimum of 2 days at -18 ° C. It is even possible to perform a heat treatment of an infested item, which will kill the bean beetle. Depending on the size of the lot, it must be heat-treated between 2 to 24 hours at a temperature of between 55 and 60 ° C. In particularly severe cases, it may be necessary to control the bean beetle with phosphorus hydrogen. Please note, however, that this type of control may only be carried out by persons with proper authorization for this purpose.
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