The period between the discovery of the insecticidal properties of Dichlorodiphenyltrichloroethane (DDT) by Paul Muller and the publication of Silent spring by Rachel Carson played a significant role in establishing chemical agriculture in the global food production system. The use of synthetic (artificial) pesticides and the so-called green revolution rooted the flow of synthetic chemicals into the food chain. Spraying chemical insecticides has become the most popular approach to reducing insect pest populations, currently due to their easy availability, immediate results and cheaper products. The Stockholm Convention has banned persistent organic pollutants (POPs), and several countries have restricted different pesticides. However, the use and abuse remained relatively high, and the permitted pesticides are also not in harmony with the agro-ecological balance. Long-term degradation of the environment, increase in cultivation expenses and adverse effects on soil, water, air and plant biomass that increase every year are certain and inevitable.
The use of synthetic inputs can be discouraged by organic pest management techniques. Insect pest management in organic systems involves the adoption of scientific and ecologically sound techniques specified by national and international standards. The standards prohibit synthetic insecticides and genetically modified organisms (GMOs) and rely on various cultural practices, habitat manipulation, deployment of biocontrol agents and approved insecticides. The methods and tools allowed in organic production systems are not yet well defined by law, and therefore regional variations exist.
Microbial pest control
There is a long history of complex interactions between insects and microorganisms. In the natural ecosystem, the insect pest population is continuously suppressed without human intervention. They are attacked by soil-dwelling microbes that live near the insect population, such as entomopathogens. Entomopathogens are infectious microorganisms that invade one insect and multiply and spread to infect other insects, covering non-cellular (viruses), prokaryotes (bacteria) and eukaryotes (fungi and protists) to multicellular nematodes. The purposeful utilization of such organisms by humans for pest control mechanisms is at the heart of microbial pest control. Microbial control strategies aim to suppress a pest population below the economic injury level (EIL). The objective is achieved by increasing the incidence of disease in a target population.
Fungi are one of the most commonly seen pathogens causing disease on insects in nature. Already in 1835, Agostino Bassi showed that a microorganism (fungus), Beauveria bassiana, was the causative agent of the white muscardine disease of the silkworm and that this disease could be transmitted from one insect to another. Bassi therefore assumed that these microorganisms could be used to control pests on cultivated crops. In the late 18th century, Elie Metchnikoff in Russia, while working to develop the control measure of corn cockroach, discovered a fungus that attacks this pest, which he called the “green muscardine” and described the remedy as Entomophthora anisopliae. The fungus is now called Metarhizium anisopliae. The disease caused by the fungus on insects is commonly called “green muscardine disease”.
Beauveria bassiana and Metarhizium anisopliae can be found in soils of all continents, including the climatic extremes, except Antarctica. The group is best known for its ability to kill a wide spectrum of insects and infect hundreds of host species from most insect orders. It can also survive for a long period of time in a saprotrophic environment in the soil. As a rule, a fungus with a wider host range is often facultative, meaning that it can obtain nutrients from non-host sources, for survival. This is a great advantage that humans can take from these fungi because they can be extracted from their natural habitat, ie soil, and multiplied in vitro conditions, providing suitable, artificially prepared media for storage and future use. In addition, it is non-toxic to mammals, including humans, and is selective against the target insects and safe for most non-target species. It protects pollinators, parasitoids, predators and other industrial insects such as honeybees. The diversity of beneficial insects is thus protected, ultimately improving the ecological balance.
Applying an ultra-low volume to the plant surface or insect environment is a good approach to introduce a fungal inoculum with a high concentration of inoculum, and spraying is also very similar to conventional pesticide spraying. Compared to synthetic insecticides, this procedure is time-consuming and has a slow mortality rate. However, it is not always necessary to completely kill the host to stop damage; slight inactivation in the insect’s physiology can also hinder its feeding performance and fecundity, ultimately helping to lower the level of damage. In addition, when conditions are favorable, fungal infections can cause dramatic epizootic diseases that wipe out populations of specific insects.
Challenges and way forward
The growth of organic pest management in Nepal is still in its infancy. Our organic soil is the most important reservoir of insecticides, but we are behind in exploration, awareness, research and development. Farmers are unaware of laboratory facilities and emerging technologies for organic pest management. Limited producers produce some mushroom products, but their effectiveness is not good. Therefore, the local strains must be sought and produced from our own soil to obtain maximum efficiency. The field of epizoetiology needs to be developed by highlighting and integrating it into graduate and undergraduate curricula.
Silent spring inspired a modern environmental movement, but the human and environmental health issues depend on how democracies and liberal economies function. Despite the extensive exploration and utilization possibilities of various microorganisms such as e.g Beauveria and Metarhizium, the dominance of for-profit commercial farms and corporate agriculture overshadows organic, agroecological and biodynamic pest management, which not only exploits nature, but also kills subsistence producers, peasants and consumers on a global scale. Pest control techniques must be incorporated into a more comprehensive pest management approach. The emphasis should be on pest control interventions that can deliver pest control benefits across a wide range of pests suitable for diverse crops and cropping systems.