Why we are failing to control only 1% of insect pests?
Muhammad Usman, Shahid Javed, Muneeb Akhter and M.Sajid Hussain
Department of Plant Pathology University of Agriculture, Faisalabad
Nature always wants to maintain a balance in biodiversity. This natural balance between populations of species can only be disturbed to a limited extent after which the organism may evolve into a more aggressive form. Any imbalance to the biodiversity may disturb the whole ecosystem and interspecies interaction which nature does not allow. We have to work more in harmony with nature’s checks and balances we will be able to enjoy sustainable and profitable pest management strategies, which are beneficial to all participants in the ecosystem, including humans.
According to an estimate there are 40 tons of insects on mass basis for a human being. There are about 99 % insects which are harmless to mankind and there is only 1 % insets compete with human being for food, feed and shelter. But we are failing to control these 1 % insect pests. The reason behind that is our reliance on therapeutic or chemical control of insect pests to prevent the crop from damaging but we did not take into account that although we got quick control and saves our crop from economic losses but we make these insect pest resistant to these therapeutic or pesticides in future. Pesticide resistance describes the decreased susceptibility of a pest population to a pesticide that was previously effective at controlling the pest. Pest species evolve pesticide resistance via natural selection: the most resistant specimens survive and pass on their genetic traits to their offspring.
The Insecticide Resistance Action Committee (IRAC) definition of insecticide resistance is a heritable change in the sensitivity of a pest population that is reflected in the repeated failure of a product to achieve the expected level of control when used according to the label recommendation for that pest species. Pesticide resistance is increasing. Farmers in the USA lost 7% of their crops to pests in the 1940s; over the 1980s and 1990s, the loss was 13%, even though more pesticides were being used. Over 500 species of pests have evolved a resistance to a pesticide. Other sources estimate the number to be around 1000 species since 1945.
Although the evolution of pesticide resistance is usually discussed as a result of pesticide use, it is important to keep in mind that pest populations can also adapt to non-chemical methods of control. For example, the northern corn rootworm (Diabrotica barberi) became adapted to a corn-soybean crop rotation by spending the year when field is planted to soybeans in a diapause.
Factors causing the failure of controlling Insect pests
- Large number of off springs:
Many pest species produce large broods. This increases the probability of mutations and ensures the rapid expansion of resistant populations. Pests with shorter generation times develop resistance more quickly than others.
- Resistance against natural toxins:
Pest species had been exposed to natural toxins long before agriculture began. For example, many plants produce phytotoxins to protect them from herbivores. As a result, coevolution of herbivores and their host plants required development of the physiological capability to detoxify or tolerate poisons. Humans often rely almost exclusively on pesticides for pest control. This increases selection pressure towards resistance. Pesticides that fail to break down quickly contribute to selection for resistant strains even after they are no longer being applied.
- Resistance due to over-doze of pesticides:
In response to resistance, managers may increase pesticide quantities/frequency, which increase the problem. In addition, some pesticides are toxic toward species that feed on or compete with pests. This can allow the pest population to expand, requiring more pesticides. This is sometimes referred to as pesticide trap, or a pesticide treadmill, since farmers progressively pay more for less benefit.
- Reduced populations of natural enemies:
Insect predators and parasites generally have smaller populations and are less likely to evolve resistance than are pesticides primary targets, such as mosquitoes and those that feed on plants. Weakening them allows the pests to flourish. Alternatively, resistant predators can be bred in laboratories.
- Resistance has evolved in multiple species:
Resistance to insecticides was first documented by A. L. Melander in 1914 when scale insects demonstrated resistance to an inorganic insecticide. Between 1914 and 1946, 11 additional cases were recorded. The development of organic insecticides, such as DDT, gave hope that insecticide resistance was a dead issue. However, by 1947 housefly resistance to DDT had evolved. With the introduction of every new insecticide class, cyclodienes, carbamates, formamidines, organophosphates, pyrethroids, even Bacillus thuringiensis cases of resistance surfaced within 2 to 20 years.
- Multiple and Cross resistance:
Multiple resistance pests are resistant to more than one class of pesticide, this can happen when pesticides are used in sequence, with a new class replacing one to which pests display resistance with another. Cross resistance, a related phenomenon, occurs when the genetic mutation that made the pest resistant to one pesticide also makes it resistant to others, often those with a similar mechanism of action.
Pests become resistant by evolving physiological changes that protect them from the chemical. One protection mechanism is to increase the number of copies of a gene, allowing the organism to produce more of a protective enzyme that breaks the pesticide into less toxic chemicals. Such enzymes include esterases, glutathione, transferases, and mixed microsomal oxidases. Alternatively, the number and/or sensitivity of biochemical receptors that bind to the pesticide may be reduced. Behavioral resistance has been described for some chemicals. For example, some Anopheles mosquitoes evolved a preference for resting outside that kept them away from pesticide sprayed on interior walls.
- In the US, studies have shown that fruit fliesthat infest orange groves were becoming resistant to malathion
- DDT is no longer effective in preventing malariain some places.
- The Colorado potato beetlehas evolved resistance to 52 different compounds belonging to all major insecticide classes.