We learn from the passage that ______. A: the bacteria are only effective against three species of beetles B: Fields' technique is less effective in winter C: Fields' technique may kill nearly all the beetles at -10℃ D: Insects may develop resistance against the bacteria

Which of the following is not a natural enemy insect? A: Mantis B: Coccinella C: dewtail beetles D: Trichogramma

The following cases belong to polymorphosis（ ）. A: In the same season, there are two types of viviparous female aphids: wingless and winged. B: Long wing and short wing of brown planthopper C: Workers and soldiers in ant population. D: Females and males of stag beetles