What is pesticide resistance ? Differentiate between simple and multiple resistance in insect pests with examples. Prescribe measures to overcome pesticide resistance problems.

What is Pesticide Resistance?

Pesticide resistance occurs when a population of pests becomes less susceptible to a pesticide over time, requiring higher doses or alternative pesticides for effective control. This is a natural evolutionary process; within any pest population, there exists genetic variation. When a pesticide is applied, most susceptible individuals are killed, but those with genetic traits conferring some degree of resistance survive and reproduce, passing on these resistance genes. Repeated selection pressure leads to an increase in the proportion of resistant individuals within the population.

Simple Resistance vs. Multiple Resistance

Resistance can manifest in different forms. Here’s a differentiation with examples:

Simple Resistance

Simple resistance involves a pest population developing resistance to a single pesticide or a class of pesticides with a similar mode of action. This typically arises from a single genetic mutation.

Example: The diamondback moth (Plutella xylostella) has developed resistance to synthetic pyrethroid insecticides in many cotton-growing regions worldwide. Initially susceptible to pyrethroids, repeated use has led to the selection of moths with mutations in the sodium channel gene, reducing the effectiveness of these insecticides.

Multiple Resistance

Multiple resistance, also known as cross-resistance, occurs when a pest population develops resistance to multiple pesticides with different modes of action due to a single genetic mechanism or linked genes. This is a more complex and concerning form of resistance.

Example: The fall armyworm (Spodoptera frugiperda), a devastating pest affecting maize and other crops, has exhibited multiple resistance to insecticides in several countries including India. Resistance to pyrethroids, organophosphates, and neonicotinoids has been observed, often linked to mutations in the GABA receptor gene, rendering the pest less susceptible to a wide range of insecticide classes.

Feature	Simple Resistance	Multiple Resistance
Resistance to	Single pesticide or class	Multiple pesticides with different modes of action
Genetic Mechanism	Often single gene mutation	Often linked genes or a single mutation affecting multiple targets
Complexity	Less complex	More complex and difficult to manage
Example	Diamondback moth resistance to pyrethroids	Fall armyworm resistance to pyrethroids, organophosphates, and neonicotinoids

Measures to Overcome Pesticide Resistance Problems

Addressing pesticide resistance requires a multifaceted approach, integrating preventative and remedial strategies. These can be broadly categorized as:

Preventative Measures (Proactive Strategies)

• Crop Rotation: Rotating crops disrupts pest life cycles and reduces selection pressure for resistance.
• Use of Resistant Varieties: Planting crop varieties with inherent resistance to specific pests minimizes the need for pesticides.
• Integrated Pest Management (IPM): This is the cornerstone of resistance management. IPM emphasizes a holistic approach, combining biological control, cultural practices, physical controls, and judicious use of pesticides only when necessary. The National IPM Policy in India (2014) promotes this.
• Refugia: Maintaining areas of untreated crops (refugia) allows susceptible pests to survive and breed, diluting the resistant gene pool.
• Monitoring Pest Populations: Regular monitoring helps detect resistance early and adjust pest management strategies accordingly.
• Proper Pesticide Application: Following label instructions regarding dosage and timing minimizes selection pressure.

Remedial Measures (Reactive Strategies)

• Rotation of Pesticide Modes of Action: Alternating pesticides with different modes of action prevents the selection of resistance to any single compound.
• Mixtures of Pesticides: Using mixtures of pesticides with different modes of action can provide broader control and delay resistance development. However, this strategy needs careful consideration due to potential synergistic or antagonistic effects.
• Introduction of New Pesticides: Developing and introducing new pesticides with novel modes of action is crucial, but resistance to these new compounds is inevitable if not managed properly.
• Biopesticides: Utilizing biopesticides (e.g., Bacillus thuringiensis - Bt) offers a more targeted and environmentally friendly alternative, reducing selection pressure for resistance to conventional insecticides.
• Gene Editing Technologies: CRISPR and other gene-editing technologies offer potential for developing pest-resistant crops with greater precision and reduced reliance on pesticides, although regulatory hurdles remain.