THE KEY TO PROTECTION

S. A. ROHWER.

Until research developed information on pests of our forests and devised means of combating them, there was little of immediate practical value that could be gained from knowing where the pests occurred. Fortunately we now know procedures which can be used to control many of the more common and most destructive pests. By using these methods we can prevent the development of outbreaks that would cause destruction and losses over wide areas.

The key to any effort to protect our forests from these or any of the numerous insects and diseases that attack them is a knowledge of where the pest occurs and how abundant and aggressive it is. This is fundamental. It is comparable with criminal and military intelligence. All types of programs to combat common enemies employ the principle of knowledge of its whereabouts and strength. To combat successfully the forest pests we must know where they occur. Thus detection surveys are the first step in any effort to protect forests by controlling destructive insects and diseases.

The initial procedure in protecting the forest from pests is basically the same as that used to prevent destruction from fire. In many respects, however, pest control differs from fire control. It is well established that occurrence of infestation or infection on a few trees does not necessarily mean that important destructive loss will follow unless control measures are applied. It is important that this be recognized as it has a significant relation to any program of forest-pest control and survey designed to provide a basis for action. It emphasizes the essential role of the entomologist and pathologist in the survey program. Facts assembled on the occurrence of forest pests must be appraised on the basis of knowledge of their behavior and development.

ESTIMATES OF TOTAL VOLUME OF TIMBER KILLED BY PINE BARK BEETLES DURING VARYING PERIODS UP TO 1946 (IN THOUSAND FEET BOARD MEASURE)

Such appraisal is the second essential step in any program to combat injurious forest insects and diseases. It provides the basis for any decision to combat the pest. It has an important bearing on the type of data the survey should develop.

DETECTION AND APPRAISAL METHODS differ with the pests. The wide differences in habits and appearance of the numerous kinds of insects and diseases destructive to forests make it impossible to use any single or simple procedure in carrying out inspections to detect their presence and determine the significance of their occurrence. Methods used in making surveys will also differ in various sections of the country. Practices will necessarily differ with the objective sought.

To PROTECT WHITE PINE from the destructive introduced disease white pine blister rust the detection of the disease organism is secondary to the location of the currant and gooseberry bushes on which the disease must spend part of its life. The spores of the disease produced on white pine are hardy and remain viable much longer, even when carried long distances. Protecting white pines from the disease is largely a matter of detecting and destroying currant and gooseberry bushes that grow among or adjacent to the pine trees. Hence, surveys for currants and gooseberries are a part of white pine blister rust control.

IN THE CASE of another introduced pest the gypsy moth where its eradication in designated areas is the objective and the basis of preventing natural spread to new sections, inspections for the insect pest must be detailed and provide complete coverage. Research has developed ways to do this effectively and without undue cost. An important feature of such surveys includes application of knowledge that the winged free-flying males are attracted to extracts made from the tip of the abdomen of the wingless female.

It is thus possible to trap the males and determine with reasonable accuracy whether the insect is present in any area. With this knowledge, intensive search for egg clusters provides data on where and how abundant the pest is.

WITH THE MORE DESTRUCTIVE NATIVE insect pests such intensive inspections are not needed. Here the objective is to keep informed as to the areas where the pest is developing in numbers sufficient to cause important loss. The fact that intensive inspections to locate all infestations are not required does not mean, however, that the task is simple. Restricting surveys to the forest pests of known importance still requires many observations and the use of much technical knowledge.

THERE ARE MANY DIFFERENT KINDS of important pests, and the habits and method of attack of these are widely varied. The habits of the various tree-killing bark beetles, although similar as to general pattern, cause different symptoms. The fading, browning, and reddening of the foliage of injured trees provide a valuable index of the presence of many forms, such as the deadly western pine beetle. Attacks of the equally destructive Engelmann spruce beetle, however, are not followed by the browning and reddening of foliage. A group of red-top trees killed by the mountain pine beetle in a lodgepole forest is often the sign of the beginning of an outbreak. Grouped red-top trees killed by the western pine beetle in a ponderosa pine forest in Colorado may indicate the subsidence of an outbreak. Only the trained, experienced entomologist can distinguish the potential difference between groups of like superficial appearance.

Many species of insects defoliate trees and here the significance of an infestation may depend on the kind Of insect and the type of forest. Where more than one species of insect is present, and this frequently occurs, the proportion of each in the mixture may have an important bearing on the potential damage of the infestation.