Script 28.6

Notes to broadcasters

Content:  You can protect beans from weevils by mixing dry ashes, chillies, or vegetable oil in with stored beans.

Appendix: Identification and Life Cycle of Bean Weevil:

Eggs:  Eggs of the Acanthoscelides obtectus are like tiny grains of rice, so small you can hardly see them.  The females lay the eggs inside the pod of the bean when the beans are drying in the field; it also lays eggs between stored beans.  Eggs of the Zabrotes subfsciatus can be found stuck to stored beans in places where there is a warm climate.

Larvae:   This larva hatches and penetrates the top of the seed through a hole so tiny that it can only be seen through a microscope.  The larva has no legs.  It is white in colour with a brown head, and passes through four stages of development, feeding itself inside the seed.

Pupae: The bean weevil pupates inside the seed, leaving a circular, covered exit hole at the top; the adult will leave the seed through this “window.”  The pupa is white in colour.

Adults:   The adults leave the seed, mate, and then the females begin to lay eggs; in general they do not feed.  The adults of the Acanthosecelides obtectus measure 2 to 3 millimetres in length, are grey-brown with pale and dark stripes.  The females lay about sixty eggs.  This insect prefers to live in temperate zones (24o Centigrade) and more than 600 metres above sea level.  The adults of the Zabrtoes subfsciatus are a little smaller, brown, and lay about 35 eggs stuck to the beans.  They live and grow well in warm climates (32o Centigrade).


Today we are going to talk about a couple of ways you can prevent bean weevils from damaging stored beans. We will talk about adding ashes or vegetable oil to the beans in storage.

The very first step is to determine whether or not it is even necessary to use pest control. In other words, you need to decide whether or not there are enough weevils in the stored beans to make it worth your while to control them. To find out, separate several handfuls of beans from the rest of the beans. From this batch of one pound, count out 100 beans. Look for tiny, round holes about 2 millimetres across made by the weevil larvae. Repeat this process several times. If 4 out of every 100 beans that you count have these little holes in them, you will have to use some kind of control. Less damage than this, that is, less than 4% damage, will not cause a significant reduction in germination, food quality, or market price.

Once you decide there is enough damage so that you need to control the weevils, here is what you can do.

Between beans there are spaces where the weevils move around. If you fill these spaces with fine, dry ashes (the finer the better) it will be more difficult for the weevils to survive. Mix 1 part ashes for every 5 parts of grain. In other words, if you are storing 5 kilograms of grain, then you add one kilogram of ashes. Insects trying to move between the beans will scrape or cut their bodies on the ashes. Through the cuts they will lose moisture, get dehydrated, and die.

Some people in Guatemala also use dried ground chillies. They add one per cent chillies to the stored grain. In other words, they add 10 grams of dried ground chillies to 1 kilogram of grain. This works well if chillies are easy and inexpensive for you to get. Remember that the materials you use, ashes or chillies, should be very fine and very dry.

Vegetable oil can also be used to protect stored beans from weevils. The oil blocks the insects’ breathing pores so they cannot breathe. Then they die.

Add 50 millilitres of vegetable oil to 11 kilograms of dried beans. Mix well and store in a cool place. If you do not have much oil, you can use half water and half oil. If you are going to use this method with beans for planting, you must be very careful not to use more than 50 millilitres for every 11 kilograms of beans. Otherwise the oil can also damage the pores of the beans and they will not be good for seed.


The information in this script is from ALTERTEC.  ALTERTEC is a non-profit, non-governmental organization which works with farmers to promote integrated ecological agriculture systems.

Information Sources

Identification and Life Cycle of Bean Weevil (Acanthoscelides obtectus and zabrotes subfsciatus) (from Manejo integrado de plagas insectiles (1992, 95 pages), published by ALTERTEC, 2a Calle 10-14, Zona 1, Ciudad de Guatemala, GUATEMALA)

Interview with Hermogenes Castillo, P. Agronomo, Researcher, ALTERTEC, 2a Calle 10-14, Zona 1, Ciudad de Guatemala, GUATEMALA.

Manejo integrado de plagas insectiles (1992, 95 pages), published by ALTERTEC, 2a Calle 10-14, Zona 1, Ciudad de Guatemala, GUATEMALA.