Cabbage damaged by diamondback moth. Photo by IITA

African cabbage farms ravaged by the Diamondback moth (DBM), Plutella xylostella, are set to recover with the help of a biopesticide (Beauveria bassiana) developed by IITA scientists to kill the pest.

Resource-poor farmers, who have tried the fungal pesticide, said the biocontrol method has proved effective in controlling the insect pest that has devastated both smallholder and large-scale cabbage farms in Africa. DBM had earlier forced thousands of farmers in West Africa to abandon cabbage production for other crops.

“We now have the hope of promising results obtained using B. bassiana,” says Raymond Ahinon, who heads the Crop Department at the Songhai Center. Songhai is a commercial farm center in Porto Novo, Republic of Bénin. “The product is effective, and has helped in eradicating DBM on our cabbage farms.”

Cabbages are among the most important vegetables in Africa in general and particularly in Bénin, especially for lower income groups. It serves as an income source among groups most affected by poverty, including small farmers, youths, and most especially women who play an important role in agricultural production.

Eaten daily, either raw in salads, steamed, boiled or fried, cabbages and their cousin, kale, serve as important cash-generating crops.

Why biological control
In recent years, chemical control of DBM is proving ineffective, according to farmer Louis, who has been cultivating the crop since 1986 in his farm in Porto Novo.

Ignace Godonou, IITA entomologist based in Cotonou, Republic of Bénin, says the pest has developed resistance to a wide range of insecticides, including Bacillus thuringiensis, a biological agent used against the pest. The situation is made worse by the high costs of inorganic or chemical pesticides.

“The most common chemical pesticides used by farmers are bifenthrin and deltamethrin,” says Godonou.

“These chemicals need to be applied about 19 times within three months of the crop’s growth prior to harvest. Also, acquiring these chemicals comes with a cost that is sometimes prohibitive.”

Diamondback moth, Plutella xylostella Lindsey, Wikimedia commons

On a global scale, chemical control is estimated to cost about US$1 billion annually. The accompanying package of health and environmental risks include pollution, destruction/death of nontarget but sometimes useful insects, and the reduction of biodiversity.

But there is good news. Biological options in an integrated pest management approach could offer a solution to sustainable control of DBM, according to Godonou.

So far resource-poor farmers use botanical pesticides, mostly aqueous seed extracts of the neem tree, against DBM and a wide range of other arthropod pests. The success of this approach, however, has been limited.

B. bassiana to the rescue
In search of sustainable biological agents to control the pest, Godonou says eight isolates of the entomopathogenic fungi B. bassiana and Metarhizium anisopliae indigenous to Bénin were screened for virulence against larvae of the insect. Two isolates showed promise.

Beauveria bassiana-covered pupa of DBM. Photo by IITA

One, Bba5653, caused 94% mortality of DBM larvae, and mortality was significantly higher than that caused by any other isolate. Cabbage yield was approximately three-fold higher than the yield in plots treated with the insecticide bifenthrin or in untreated plots.

In a study published in the journal Crop Protection in 2008, Godonou and his colleagues said that fungi, such as B. bassiana and M. anisopliae, are ubiquitous in nature and are specific to target pests. They persist in the environment and are easy to mass produce.

Co-author C. Atcha-Ahowe says field trials of the B. bassiana biopesticide have sparked demand for the commodity.

“The majority of farmers who abandoned cabbage cultivation for other crops are now requesting the biopesticide so they can go back to growing the crop, but not enough of the product is available,” he says.

When compared to the production of other vegetable crops, such as carrots and lettuce, cabbage cultivation results in higher returns, say resource-poor farmers. The gap is exacerbated by the increasing demand and the dwindling supply of cabbage.

An opportunity for the private sector
Like the highly successful Green Muscle®, which was picked up by the private sector, Godonou says the B. bassiana technology is another opportunity waiting for the private sector.

He says farmers are willing to patronize the product to control the cabbage enemy and increase farm yield, but there should be enough supply to meet the demand.

“With the ability to remain active on the field for several months after initial application, B. bassiana will end the rigor of repetitions and costs associated with the application of synthetic chemical pesticides,” he adds.