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Scientists find wasps that eliminate deadly fall armyworm

Saturday March 23 2019

Dr Tadele Tefera, a principal investigator at Icipe, observes specimen collected from a field at Icipe in Nairobi, using a microscope.

Dr Tadele Tefera, a principal investigator at Icipe, observes specimen collected from a field at Icipe in Nairobi, using a microscope. With him is Dr Malik Ba. Scientists at the institution have identified two local varieties of wasps, Trichogramma and Telenomous, which they release in affected maize plantations to search for and lay their eggs on armyworm eggs thus killing them before they reach the larvae stage. PHOTO | COURTESY 

CAROLINE WAMBUI
By CAROLINE WAMBUI
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As farmers ready for a new maize planting season, many of them are hoping that fall armyworms (FAW) will not attack their crops this time round.

The pests have ravaged acres of crops in the last two years, heaping losses on farmers, some who are finding pesticides ineffective.

This season, however, things are looking up for farmers when it comes to controlling pests as the International Centre of Insect Physiology and Ecology (Icipe) and its partners work on insect-controlled method to curb the pests.

Scientists at Icipe have identified two local varieties of wasps, Trichogramma and Telenomous, which they release in affected maize plantations to search for and lay their eggs on armyworm eggs thus killing them before they reach the larvae stage where they are most destructive to crops.

The two wasps act as natural enemies to most caterpillars that harm a wide array of crops, not just maize.

In the field, the armyworm eggs are spherical, green or cream white in colour, turning dark brown before hatching.

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The eggs that are usually laid in masses of approximately 150-200 are found in two to four layers deep on the surface of the leaf and are covered with a protective layer that takes three to four days to mature depending on the temperature. Up to 2,500 eggs may be laid by each female.

Within a few days, the larvae emerge and starts to feed on the different crops creating pinholes on leaves and easily make its way to the next crop, county or country.

“The developing larvae eats different parts of the host plant creating gaps on the leaf and a moist sawdust like tress near the funnel of the upper leaves. If the larva attacks early in the season, the feeding can kill the growing plant,” explains Dr Tadele Tefera, a principal investigator at Icipe, noting that their experiment on Zakayo Kamiti’s farm in Nyangati location in Mwea, Kirinyaga County is showing success.

In the last few years, control has been through use of synthetic pesticides. However, the method is proving ineffective as during the day, the young larvae is relatively inactive as it hides in the funnel shielding from sprays and predators and only emerges at night to feed on the leaves. At night, the adult moths also emerge and travel great distances.

CONSIDERED FRIENDS TO FARMERS

Most farmers do their spraying during the day making the control method ineffective as the pest becomes resistant.

“Application of synthetic pesticides in agriculture has expanded in the last five years in Africa, and continued use causes soil, underground water pollution and a health hazard to both the farmers and consumers,” says Dr Tefera.

According to her, farmers need to understand that repeated chemical applications to mitigate the spread of pests could force the FAW to develop resistance.

Using the natural method, Icipe does not introduce foreign insects but instead goes to the farms, collects the insects which are readily available and multiplies them in the laboratory then releases them back to the farm at no cost.

“Introduction of the two insects is neither hazardous to farmers nor to the crop. These two wasps are considered friends to farmers as they don’t feed on crops but rather on the eggs of the FAW,” explains Dr Tefera.

Icipe in partnership with Kalro and University of Nairobi, are working on the mass production of the wasps.

Dr Malik Ba, the principal entomologist at International Crops Research Institute for the Semi-Arid Tropics (Icrisat) in Niger, where a similar fall armyworm eradication method is being used, notes that the pest is polyphagous, meaning it feeds on various crops.

“In Niger, we have identified promising indigenous natural enemies, which develop on eggs of the FAW attacking sorghum in the field. In the laboratory, the natural enemies can cause up to 70 per cent mortality of eggs of the FAW. We have mastered the mass culture of the natural enemies and are now in the process of on-farm testing.”

The scientists are using the same approach to control other cereal insect pests and are confident of the effectiveness of the technology.

“As a component of integrated pest management, biological control of FAW with indigenous natural enemies has an important role to play in the control of the pest for the benefit of smallholder farmers,” Dr Ba notes.