Scientists use swarms of wasps to fight pinworm

Friday November 13 2020

Recently, the International Centre of Insect Physiology and Ecology (Icipe) released the first swarm of parasitoid wasps to control pinworms, which devastate tomato crop. PHOTO | COURTESY | ICIPE


For the past decade and a half, the pinworm has devastated acres of tomato crop in the region.

The methods to fight this pest, currently in use in Africa, have almost exclusively involved use of chemicals. Now, researchers want science-based solutions to protect biodiversity, consumers and traders from indiscriminate use of broad-spectrum insecticides.

Recently, the International Centre of Insect Physiology and Ecology (Icipe) released the first swarm of parasitoid wasps to control tomato leaf miners in Mwea East, Kirinyaga County.

Kirinyaga County is the leading producer of tomatoes in Kenya.

The wasps have been used in South America to fight the pests, where the pinworms are thought to have originated. Kenya is the first to release the wasps to fight the pinworms outside of South America.

The wasps lay eggs inside the caterpillars. The wasp eggs develop slowly and eventually emerge as adults, killing the leaf miners.


Icipe co-ordinator of the Tuta Absoluta control project Shepard Ndlela said when released in large numbers, wasps spread rapidly, looking for infested plant material.

“These wasps do not affect plants, animals and humans in any way, they are specific to Tuta absoluta. Thus, they are generally referred to as the farmer’s friends,” he said.

The release is part of an integrated pest management (IPM) scheme that is being established and will involve other environmentally-friendly interventions.

Icipe, in conjunction with Biovision Foundation, is establishing demonstration learning sites that will also act as centres of technology and information dissemination in Kirinyaga, Kitui, Taita Taveta and in Uganda on the pest’s management, while also training agricultural extension officers and farmers.

The Icipe-Biovision Foundation partnership will also implement a systems approach project in Kenya and Uganda, dubbed “Combating the invasive tomato leafminer-Tuta absoluta through the implementation of eco-friendly IPM approach on tomato in East Africa.”

The scientists are also encouraging the adoption of economical methods that are friendly to both human beings and the environment.

The scheme will include pheromone traps, destroying infected plants, staking, organic pesticide and crushing larvae.

By maintaining cleanliness around the crop’s nursery, Dr Ndlela said farmers would be well equipped to fight the pests.

“In most cases, seedlings are transplanted into fields or greenhouses when already infested from the nursery. This results in tomato plants being attacked when they are still young and die before the fruiting stage. It is important that seedlings are raised in a pest free nursery to ensure that seedlings are healthy prior to transplanting,” said Dr Ndlela.

He suggests using different kinds of substances as lures, which emit pheromone (sex hormone) to attract male moths.

“The lures are available from suppliers and distributors of pest control products,” he added.

Dr Ndlela advises farmers to set up the lure units two weeks before establishing the nursery for monitoring purposes.

“If traps catch any moths, the farmer must proceed to lay out traps, the cheapest is water and detergent to drown the insects in the nursery so that moths are captured and removed from the system prior to establishing the nursery. Most farmers usually cry foul because they begin mass trapping when the pest is already established in the farm making it very difficult to manage,” said Dr Ndlela.


In mass trapping, more traps per unit area are deployed so that male moths are captured and killed. This deprives female moths of males to fertilise them and thus lay unfertilised eggs that do not hatch.

The lures should be replaced every six weeks as their effectiveness decreases the more they are exposed in the field.

“Mass trapping is very effective and can result in a more than 80 percent reduction in Tuta populations when started early and used consistently with other management measures,” he said.

For farmers with affected farms, Dr Ndlela advised they cut down and bury infested plants at least one-metre in the ground to ensure all maggots in the leaves and tomato fruits don’t develop further and die.

“When plants are not destroyed, the maggots develop into adult moths, which will lay eggs and start another destructive generation,” said Dr Ndlela.

Pesticides are the main method used by farmers to control the pest with 96.5 percent of farmers in Kenya using this method compared with 97.6 percent of farmers in Zambia. However, only 27.2 percent and 17.2 percent of farmers in Kenya and Zambia, respectively, indicated pesticide treatments as being successful.