THE PAST twenty years have been very fertile with practical results in the warfare against insects. Not only does this period include a remarkable advance in our knowledge of the life-histories of pests, but it is distinguished by the discovery of far-reaching remedies and the true beginning of national investigations. Many obstacles have been overcome, and the economic entomologist is to-day prepared by this work to offer fairly satisfactory remedies for a great majority of our most prominent insect pests. Many problems yet remain unsolved, however, and work upon these will engage the best energies of our workers in this branch of agricultural science for many years to come. They include, among other things, the improvement of remedies already known, and of insecticide appliances, together with the investigation of the new insect enemies to agriculture, which are, in our comparatively new country, constantly making their appearance, either from change of habit or of food-plant of some hitherto innocuous species, or from the importation of species from other countries.

All late advances in the study, and all probable advances in the immediate future, come under three chief categories:

1. The ascertaining of every detail in the life history of species at present injurious or likely to become injurious.

2. Thorough and careful experiment with insecticide substances.

3. The invention and improvement of apparatus for the application of insecticides.

(1) The first of these three categories is fully as important as the last two, since upon the careful performance of the work indicated depends the question of prevention and of ridding ourselves of our enemies by natural means. It even influences, in a potent degree, the proper application of insecticides, thus underlying and forming the basis for work in the second and third categories.

Take the case of the codlin moth, for example. Had we not learned by careful examination that the larvae, leaving wind-falls, crawl back to the trunk of the tree in order to find proper places for spinning their cocoons, and leaving apples before they have fallen, crawl down the limbs to seek the rougher bark of the trunk, the admirable bandage remedy, our principal means against this pest before the use of arsenical sprays had proved safe and satisfactory, would never have come into use. The discovery of the applicability of the sprays themselves was to a certain extent empirical; yet a knowledge of the egg-laying method and of the habits of the newly-hatched larvae at once explains its applicability and proves to the cautious man its theoretical efficacy.

Take another and perhaps even more striking example : From 1874 to 1878 the thick-thighed walking-stick, an insect which had previously been considered harmless, did a great deal of damage to shrubbery and forest trees in Yates county, N. Y., completely defoliating the hickory and oak timber. So many acres were infested by the insects in large numbers that the application of arsenical poisons was practically out of the question; but a study of the life-history of the insect disclosed a safe and comparatively inexpensive remedy. Visiting the woods in the latter part of autumn, a constant dropping, like falling rain, was to be heard, and this was considered to be due to the dropping of their excrements by the thousands of these leaf-destroyers. Close examination, however, showed that the particles thus constantly dropped from the trees were eggs which fell loosely upon the leaf-covered ground, and so abundantly that they could be scraped up in places in great quantities. Thus, by recommending the burning of the leaves during winter, I was able, by a very simple means, to give those who suffered complete protection for the future.

No fact, however seemingly insignificant, should be overlooked, and not only must the round of the insect's life, as it appears at the time and point of actual damage be studied, but every fact in reference to the species - its original home, its spread, its natural enemies - wherever it exists, must be ascertained and recorded. The significance of such information as this is shown with striking force in the case of the fluted scale (Icerya Pur-chasi), an insect coming from Australia, and which has been extremely destructive to citrus fruits in California. In this case the investigation as to the original home of the species, which required some years and a trip to Europe, resulted in the discovery of a natural enemy in its native country which not only kept it in perfect subjection there, but which, with the cooperation of the State Department and through one of my assistants, Mr. A. Koebele, I was enabled to introduce and colonize in California. The result was almost magical, for within a single year the icerya has been practically swept away, bringing about an immense money-saving to the citrus-growers of that state with the expenditure of a very insignificant sum on the part of the government.

Investigations of this kind are often attended with extreme difficulty in the accurate ascertaining of every possible point connected with the life of the insect, and occasionally such knowledge makes the question of remedies seem only more complicated. An instance of this kind is afforded by the buffalo-gnats of the south-west. It was known from the beginning of the investigation, which I undertook in 1886, that the early stages of this fly are aquatic; but, nevertheless, the problem was attacked with the belief that, however hopeless a case may at first seem, a careful study of all the facts may show some vulnerable point and give man the advantage. The work of the first year resulted in discovering the breeding-places, the eggs, the larvae and the pupae, in ascertaining the life periods and in bringing together much other information; but now, after four years of more or less consecutive investigation, we can suggest no direct remedies other than slight improvements upon the re-pellants already in use against the adult insects before we took the subject up. Even this rather difficult and discouraging investigation, however, has not been entirely without its practical result.