A、They are rare species. B、They protect the environment. C、They pollinate crops and wild plants. D、They protect crops and wild p

A new study says a widely-used insecticide is damaging wild bee populations.(3)Wild bees are important, because they pollinate(授粉)crops and wild plants. Environmentalists in the United States and Europe say this insecticide is causing a drop in the number of bees.
    These insecticides are among the most commonly-used worldwide. Farmers often use seeds treated with the insecticides. The chemicals target insects that eat crops, and they do not spread beyond the field. But they do get into pollen(花粉)and nectar(花蜜), which is where the bees come into contact with them. Researchers studied bees in fields. They say there were about half as many wild bees per square meter in treated fields as in untreated ones. Using the chemicals too much may be hurting bees.(4)They suggest that the chemicals should be used more sensibly, or. in other words, only when necessary.
3. Why are wild bees important?
4. What do researchers suggest when using chemicals?