Hello,
The observation that the pesticide was effective in killing insects in week 1 but became ineffective by week 3 is likely due to the development of resistance in the insect population.
When a pesticide is introduced, it may be very effective in killing a large proportion of the target insects. However, some insects may have genetic variations that allow them to survive exposure to the pesticide. These insects then go on to reproduce, passing on the genes that allowed them to survive to their offspring. Over time, the proportion of insects in the population with these resistant genes increases, making the population as a whole less susceptible to the pesticide. This is known as pesticide resistance.
Insects can develop resistance to pesticides through a variety of mechanisms, including mutations that make them less susceptible to the toxic effects of the pesticide, increased detoxification of the pesticide by enzymes in their bodies, or changes in their behavior that allow them to avoid exposure to the pesticide.
To combat pesticide resistance, farmers may need to use different pesticides or alternative methods of pest control. They may also need to use pesticides in a targeted and judicious manner, rotating different types of pesticides to avoid overuse of any one type and minimize the selection pressure for resistance.