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Today we have not only intensive cultivation and lowered disease-resistance of most plants, but many other factors contributing to a lessening of what might be termed biological control of diseases. The balance of nature is being disturbed. There is less smoke from factories than in former years, but buildings of greater height and in greater numbers-particularly blocks of flats-have brought more shade and draughts. Man and his domestic cat have reduced the garden-dwelling birds by killing and fright. The use of E605, DDT, and the gamma isomer of BHC (Lindane) as sprays kills all sorts of insects, whether they are pests or not. But we have developed a bad habit of regarding all
insects and grubs as pests. Many of them are priceless friends, for they feed on
destructive creatures. Without them we would be quite powerless in controlling
diseases, despite all our sprays and dusts. It is highly important that we learn
to know our friends from our foes, even in the garden. These friends fall into
two main groups-insects and birds.
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