Since the advent of San Jose scale into the eastern United States, scale insects of all kinds have attracted world-wide attention. They are all small insects, and derive their name from the fact that their tender bodies are protected by hard, scale-like coverings secreted by the insects. Thus protected, they are difficult insects to kill, and as they are easily transported on nursery stock, buds or cions, and also multiply rapidly, the scale insects are justly to be considered as among the most dangerous and destructive of injurious insects. A single female San Jose scale may rear a brood of from 100 to 600 young, and there may be four or five generations a year; and more than 2,000 eggs have been laid by a single Lecanium scale. The scale insects, the dreaded San Jose species included, can be controlled successfully by judicious, intelligent and timely work with sprays of lime-sulfur, crude petroleum, or hydrocyanic acid gas, which should be used in the case of nursery stock. Since 1889 fumigation with hydrocyanic acid gas has been extensively practised in the citrus orchards of California, and now Florida and South African fruit-growers are also using it in their orchards. Large gas-tight tents or boxes are placed over the trees and the gas then generated within.

Much nursery stock is now treated with the gas in tight boxes or houses; this is required by law in many states, and it should be practised in other regions. Recently greenhouses, railway coaches, rooms in private houses, and whole flouring mills have been effectively fumigated with this gas.

Insects are preserved in collections by securing them in tight cases by means of a pin inserted through the thorax, or through the right wing if the subject is a beetle. Moths and butterflies are pinned in position on a spreading-board until thoroughly dried. See Figs. 1318-1322. Every horticulturist should make a collection of injurious insects.

A spreading board for drying soft winged insects.

Fig. 1321. A spreading board for drying soft-winged insects.