Insects are important to humans and ecosystems for a variety of reasons. In agriculture, aside from the pest species, the other species are beneficial as they play roles such as pollination, nutrient cycling, soil aeration, improving soil fertility, decomposition of organic matter and natural control of pests.
They are also an essential part of the food chain in nature, being a source of food for some animals like amphibians, reptiles, birds and other arthropods.
Most importantly, they play a role in preserving biodiversity by pollinating 85 per cent of flowering plants, both cultivated and wild species. Without the pollination services of insects, most of these plants could become extinct. Pollination is an ecosystem service key to food security as it has been directly linked to increased quantity and quality of produce from flowering plants.
Insect pollinators include bees, wasps, butterflies, moths, beetles and flies. Studies in Kenya indicate that the honey bee is the most important pollinator, pollinating many crops and wild plants. In Africa, most insect pollinators are wild, meaning they offer their services for free and in most cases, they go unnoticed by farmers.
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However, insects also have a negative impact. They spread major tropical human and animal health diseases, which include malaria, Rift Valley fever, yellow fever and trypanasomiasis. Additionally, they can cause significant damage to crops, leading to huge losses both in the field and during storage of dried cereals and legumes if left uncontrolled.
In as much as a few insect species threaten agriculture, some farming practices also pose major threats to beneficial insects through habitat modification and heavy pesticide use. Monoculture and heavy use of herbicides modify the habitat by reducing plant diversity, hence reducing choices of food sources for insects that depend on plants.
The loss of plant diversity has been shown to reduce availability of natural enemies of pest species. For pest species, monoculture provides them with unlimited supply of food, thus the continued increase in population.
Consequently, farmers are forced to apply pesticides to control the pest species. In some cases, the pesticides kill both the pests and the beneficial insects.
In fact, studies have shown that beneficials are more susceptible to pesticides than the target pest species. The loss of these non-target beneficials means that the target pest developing insecticide resistance, (a phenomenon common with insects) pest resurgence may occur. This will then lead to more pesticide use, which will be costly to the farmer and environment at large.
Various reports indicate that 33 per cent of the 862 registered insecticides in Kenya are toxic to bees. Reduction of bees and other pollinators will negatively impact pollination of many flowering crops and wild plant species. Reduced pollination will definitely reduce crop productivity, leading to food insecurity.
Belgian entomologist Maurice Maeterlinck said, and I quote “If the bee disappeared off the surface of the globe, then man would only have four years of life left. No more bees, no more pollination, no more plants, no more animals, no more man”. If humans were to do what pollinators do by hand, crop production would be a very costly affair.
Therefore, it is imperative that beneficial insects are protected by ensuring sustainable agricultural practices that include habitat conservation and friendly pest control methods. Mixed cropping and agroforestry are some of the ways to ensure presence of some plants, shrubs or hedgerows where insects can find refuge when crops have been removed from the field.
When controlling pest species, integrated pest management methods like push-pull strategy, natural enemies, natural products from plants, and good agricultural practices can be used. In cases where pesticide application is inevitable, it should be used in a targeted manner.
To conserve beneficial insects, safer selective pesticides with green labels should be recommended. Agrochemical dealers should categorise pesticides according to label classes and come up with green lists (safe pesticides) to be recommended to farmers.
Farmer advisory services on choice of pesticides and general safe pesticide use should be strengthened and finally, gradual phasing out of highly toxic pesticides will ensure agricultural and environmental sustainability for centuries to come.