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Go preventive rather than defensive

Thursday January 23 2020

desert locusts

Spraying of pesticide is used to combat desert locusts at Kipsing, which borders Isiolo and Laikipia counties, on January 13, 2020. This method is harmful in the long run. PHOTO | FILE | NATION MEDIA GROUP 

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Last November, the Food and Agriculture Organisation (FAO) of the United Nations warned on the possibility of a desert locust invasion of Kenya from Ethiopia — ostensibly to trigger preventive measures by the authorities.

But nothing happened until swarms of locusts entered through the northeastern region. The counties initially affected were Mandera, Wajir, Marsabit, Garissa, Isiolo, Samburu, Laikipia and Meru, with the risk of economic losses as they spread.

The government has resorted to aerial spraying of chemical insecticides in the affected areas.

The use of pesticides has been in the mainstay to combat pests of agricultural and health importance for centuries due to factors such as low cost, application simplicity, easy availability and stability.

But this is immensely associated with negative impacts as pesticides have adverse off-target effects on human health and the environment.

Some pesticides persist in the soil for a long time with their physical and chemical properties intact. The poisonous “residual chemicals” may spread to other land areas and water sources, adversely affecting non-target organisms such as humans and plants that they get in contact with.



One of the most documented aspects with respect to pesticide usage is the ability of pests to evolve resistance to almost all classes of chemicals being used to control them.

Prior to exposure to a chemical, pests already harbour genes that naturally predispose them to develop resistance under favourable conditions.

It could be disastrous to the control efforts if a small population of the swarm already has the ability to develop insensitivity to chemicals.

With increased frequency of pesticide applications, these genes are continuously selected and passed on to later generations within the locust population, increasing insecticide resistance and, hence, seriously hampering the mitigation efforts.

Unusual changes in weather patterns in the affected region may have provided a favourable breeding ground for the locusts.

With proper monitoring and forecasting, however, these changes would have been noticed and the invasion handled effectively in a preventive and strategic, rather than defensive, manner.


Reversion in the weather conditions to normal, but alien to the pests, would play a critical role in ensuring the reduction in the number of the swarms to levels that can then be adequately managed using biological control and chemical pesticides.

One of the most effective means to prevent the spread of locusts — or any other agricultural pest for that matter — is to employ biological-control strategies.

This constitutes the use of living organisms such as predators, parasitoids, nematodes and microbial agents, collectively known as “natural enemies”, to suppress pest populations.

Unlike chemical control, the biological method is highly advantageous. First, it is harmless to human beings and other beneficial organisms, environmental friendly, pest-specific - where only a pest is targeted - and has minimal chances of resistance development. In addition, it is comparatively cheaper to establish.

Top on the list of the suitable control methods would have been, as informed by forecasting, to deploy a large number of insecticide-resistant parasitoids at an early stage, preventing outbreaks.


Parasitoids are insects whose immature stages develop in or on insect pests.

Parasitoids are distinguished by their ability to attack pests at their immature life stages, before they can hatch into destructive stages that devour green vegetation.

They may kill, and thereby eliminate the developing pests. Or they could suppress their normal physiological functions, especially the reproductive and immune systems, leaving them paralysed and inefficient.

Since parasitoids are host-specific, accurate identification of the insect pest and parasitoid species is vital in their use for biological control.

This would then require the parasitoids to be mass-reared in a laboratory on artificial diet to produce large quantities, timing their field release with the migration of the pests.


However, the efficiency of parasitoids could be compromised by the application of insecticides, which remains the most important pest control agent.

Encouragingly, recent advances in pest control studies have developed strains of parasitoids that can withstand pesticide pressure.

This enables them to be used along with pesticides and other suitable control measures to contain pests, in what is referred to as Integrated Pest Management (IPM).

Dr Kerima is a molecular entomologist at Moi University. [email protected]