1. Genetic Mutations:
- Point Mutations: Random changes in the DNA sequence can lead to alterations in proteins, such as those involved in the metabolism or binding of DDT. These mutations can reduce the effectiveness of DDT by altering its target sites or reducing its toxicity.
- Gene Duplication: Duplication of genes that encode proteins responsible for DDT metabolism can result in increased production of these proteins. This can enhance the mosquito's ability to detoxify and eliminate DDT, making it less susceptible to the insecticide.
2. Increased Metabolic Detoxification:
- Enhanced Enzyme Activity: Mutations in genes that control the production of detoxification enzymes can lead to increased activity of these enzymes. This enables mosquitoes to break down DDT more efficiently and reduce its toxic effects. Enzymes like glutathione S-transferases and cytochrome P450 monooxygenases are commonly involved in DDT detoxification.
- Altered Enzyme Production: Changes in the expression or regulation of detoxification genes can result in increased production of enzymes that metabolize DDT. This increased enzyme production enhances the mosquito's capacity to detoxify and eliminate DDT.
3. Reduced Target Site Sensitivity:
- Target Site Mutations: Mutations in the genes encoding proteins that are targeted by DDT can reduce the binding affinity of DDT to these sites. This decreased sensitivity makes DDT less effective in disrupting the normal function of these proteins, rendering the mosquitoes more tolerant of DDT.
4. Behavioral Adaptations:
- Reduced Contact: Some mosquito populations may evolve behavioral changes that reduce their contact with DDT-treated surfaces. For example, they may avoid resting on or feeding near treated areas, minimizing their exposure to DDT.
- Altered Feeding Patterns: Mosquitoes may modify their feeding habits to avoid consuming DDT-contaminated blood. This can reduce the uptake of DDT and decrease its toxic impact on the mosquito population.
The evolution of resistance to DDT is a complex process influenced by genetic variation, selection pressure from DDT usage, and environmental factors. Over time, continued exposure to DDT can select for resistant individuals within mosquito populations, leading to decreased effectiveness of DDT as an insecticide.