How Insects Spread

The spread of insects is brought about by a great variety of agencies, some of which are within human control, while others are not. It is the purpose of this article to point out a few of the former as well as the latter, and to emphasize the value of taking precautions to prevent the spread of noxious species. With many serious pests an ounce of prevention is worth a good many pounds of cure.

Certainly the power of flight possessed by most insects is normally their principal means of dispersal to new feeding grounds. Unfortunately this is a matter usually beyond human control. Nevertheless there are barriers even to powers of flight, and some of our most injurious pests, which are capable also of sustained flight, would never have reached this country at all, or the section where they are now a menace, had it not been for other means of dispersal entirely within the control of man.

Strong winds, streams, ocean currents carrying debris or drift infested with insects, birds which are known occasionally to bear minute forms on their feet, all these are occasional means of the dispersal of insects and their introduction into new locations.

But if we were to count up the hundreds of pests that are working greatest havoc with our farms and orchards today, we should find that at least half of them, if not three fifths, had been introduced, directly or indirectly, through the agency of man himself.

There are many ways with which this comes about. When shrubs or trees are imported from foreign countries, they are likely to be infested with pests new to this continent. The insect thus imported is apt to get a foothold and to develop into a pest of large magnitude. It was in this way that the San Jose' scale was brought to the United States, and similar circumstances made possible the introduction of the brown tail moth.

Various substances used as packing for manufactured products imported from the far corners of the world may harbor threatening insects.

Fruits, fruit products, or other edibles imported for consumption in the United States may, and often do, introduce injurious species.

Undoubtedly the majority of the pests thus accidentally introduced fail to become established and never are heard from. But if only an occasional species gains a foothold and multiplies, the results are sufficiently disastrous.

Finally, it happens sometimes that living specimens are imported for experiment or study, and through accident are allowed to escape. The best known example of this found in the gypsy moth, which cost New England millions of dollars in attempted suppression or control.