(1) Darwin called the process of survival of the fittest and elimination of the unsuitable in the competition for survival natural selection. Genetic variation is the basis of biological evolution. First of all, the resistance of pests varies. Some are strong, some are weak. When using pesticides, killing pests with weak drug resistance is called eliminating the unsuitable. Pests with strong drug resistance survive, which is called survival of the fittest. Surviving pests with strong drug resistance, some with strong drug resistance and some with weak drug resistance. When using pesticides, mosquitoes with weak drug resistance are killed and mosquitoes with strong drug resistance survive. In this way, after several generations of repeated selection, most of the mosquitoes that survived were resistant to drugs. When using the same dosage of pesticides, it can't play a good role in killing insects. As a result, the mosquito killing effect of pesticides is getting worse and worse. Therefore, the resistance of pests is getting stronger and stronger because pesticides play a selective role in pests. In this process, individuals who can survive generally have some slight variation, that is, drug resistance. It can be seen from this that both natural selection and biological evolution are directional.

(2) It can be seen from the curve in the figure that in the sixth year after using pesticide 1, the pests adapted to the environment with pesticides, and this adaptation was the result of natural selection. When pesticide 2 was used in the seventh year, a large number of pests died because they did not adapt to the changed environment. After re-accumulation, new favorable mutations adapted to the environment again.

(3) In dealing with potato beetles, besides using pesticides, biological control methods can also be used, that is, biological control of pests. It can be roughly divided into three categories: insect control, bird control and fungal control. It is a method to reduce the population density of pests such as weeds and pests. It takes advantage of the relationship between biological species and uses one organism to suppress another. Its biggest advantage is no environmental pollution and low cost.

So the answer is:

(1) How to choose the mutation direction of drug resistance? (2) Natural selection (3) Biological control (bird control, insect control, bacterial control, etc. )