Asked by Alto saxaphone
Mosquitoes can carry and transmit many diseases to humans. The insecticide DDT was heavily used to reduce mosquito populations. However, mosquito populations developed a resistance to DDT. This made DDT less effective
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What happened is a straightforward example of evolution by natural selection.
- Before widespread DDT use, mosquito populations included genetic variation. A few individuals carried mutations (or other heritable differences) that made them less affected by DDT.
- When DDT was applied widely, susceptible mosquitoes were killed at much higher rates than those few resistant individuals.
- The resistant survivors reproduced and passed their resistance traits to their offspring, so the frequency of resistance alleles in the population rose. Over successive generations the population became dominated by resistant mosquitoes, and DDT’s effectiveness dropped.
Common biological mechanisms that confer DDT resistance in mosquitoes
- Target-site mutations: changes in the voltage-gated sodium channel (so-called “kdr” mutations, e.g. L1014F/S) reduce DDT’s ability to affect nerve function.
- Metabolic detoxification: higher activity or expression of enzymes (cytochrome P450s, glutathione S‑transferases, esterases) that break down or sequester the insecticide.
- Reduced penetration: thicker or altered cuticle slows insecticide uptake.
- Behavioral resistance: mosquitoes change behavior (e.g., avoiding sprayed surfaces) to reduce exposure.
Consequences and management
- Resistance makes single-insecticide strategies unreliable and can cause disease control failures.
- Resistance to DDT can cause cross-resistance to other insecticides with similar targets (for example some pyrethroids).
- Effective response uses insecticide-resistance management and integrated vector management: rotate or mosaic different insecticide classes, use mixtures with different modes of action, combine chemical with nonchemical measures (source reduction, larval control, bed nets, biological control), monitor resistance regularly, and deploy new tools (e.g., nets with dual actives, Wolbachia, sterile-male releases) when appropriate.
In short: heavy DDT use selected for resistant mosquitoes, so resistant alleles became common and the insecticide lost effectiveness.
- Before widespread DDT use, mosquito populations included genetic variation. A few individuals carried mutations (or other heritable differences) that made them less affected by DDT.
- When DDT was applied widely, susceptible mosquitoes were killed at much higher rates than those few resistant individuals.
- The resistant survivors reproduced and passed their resistance traits to their offspring, so the frequency of resistance alleles in the population rose. Over successive generations the population became dominated by resistant mosquitoes, and DDT’s effectiveness dropped.
Common biological mechanisms that confer DDT resistance in mosquitoes
- Target-site mutations: changes in the voltage-gated sodium channel (so-called “kdr” mutations, e.g. L1014F/S) reduce DDT’s ability to affect nerve function.
- Metabolic detoxification: higher activity or expression of enzymes (cytochrome P450s, glutathione S‑transferases, esterases) that break down or sequester the insecticide.
- Reduced penetration: thicker or altered cuticle slows insecticide uptake.
- Behavioral resistance: mosquitoes change behavior (e.g., avoiding sprayed surfaces) to reduce exposure.
Consequences and management
- Resistance makes single-insecticide strategies unreliable and can cause disease control failures.
- Resistance to DDT can cause cross-resistance to other insecticides with similar targets (for example some pyrethroids).
- Effective response uses insecticide-resistance management and integrated vector management: rotate or mosaic different insecticide classes, use mixtures with different modes of action, combine chemical with nonchemical measures (source reduction, larval control, bed nets, biological control), monitor resistance regularly, and deploy new tools (e.g., nets with dual actives, Wolbachia, sterile-male releases) when appropriate.
In short: heavy DDT use selected for resistant mosquitoes, so resistant alleles became common and the insecticide lost effectiveness.
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