The American Garden. 



Vol. XI. 



MARCH, 1890. 



No. 3. 



REINFORCEMENTS FOR THE ENEMY. 



NSECTS and fungi appear to be 

 increasing. In fact, tliey are in- 

 creasing, if increase is measured 

 by the experience of the horticul- 

 turist. We can scarcely suppose 

 that, taking nature altogether, 

 species are actually increasing, to any appreciable 

 extent at least. But the cultivator finds new 

 enemies every year, and in general he finds greater 

 numbers. 



This augmentation is partly apparent, partly 

 actual. Nowadays we are looking for the enemy, 

 while in other days he looked for us. Our vision 

 is sharpened and we discover plagues which were 

 overlooked but a few years since. This does not 

 imply that the plagues may not be grievous : we 

 may have known the results from childhood, but 

 now we separate and diagnose, and we often find 

 two or three things where we supposed there was 

 but one. The man who chanced to write about 

 blight fifty years ago probably covered the effects of 

 a score of causes. We not only analyze more 

 closely, but we publish more extensively. New 

 plagues are quickly known, and our minds are in 

 condition to receive an indelible impression of them. 

 Scourges are no longer merely local in interest ; 

 we carry the burdens of the entire country. It is 

 apparent, therefore, that pests appear to increase 

 in part because we know more than we did last 

 year. 



But after all, the pests are actually increasing, 

 yet less rapidly than we are apt to think. There 

 are two methods of reinforcement. 



First, insects and fungi, in common with all liv- 

 ing objects, may change their habits. Insects are 

 particularly adaptative to conditions. An insect 

 fed upon wild plants in Colorado, occupying a 



limited area which was largely determined by the 

 distribution of the food plants. A cultivated plant 

 closely allied to the wild plants was carried west- 

 ward to Colorado. The insects attacked it, liked 

 it, and spread. The plant was the potato, and the 

 insect became from that time the potato beetle. A 

 maggot lived in wild thorns. But it chanced to find 

 better and more abundant food in the cultivated 

 apple. It spread, and became the apple maggot. 

 A grub bored in oaks and other forest trees. The 

 forest trees were lessened, and fruit trees were in- 

 creased. The insect attacked the fruit trees and 

 became known as the flat-headed apple-tree borer. 

 An insect in Europe lived upon flowers of the fig- 

 wort, occasionally attacking furs and clothes. It 

 came to this country and attacked carpets, a habit 

 which it does not possess in its native country. In 

 America it is the carpet beetle. Instances of 

 change of habit are abundant. In fact, such 

 change is to be expected when insects find them 

 selves under new or changing conditions. And to 

 a lesser extent, the same is true of fungi. Culti- 

 vated plants are often infected from wild ones. 



Second, pests migrate, and are transferred. We 

 are carrying on a commerce of insects, fungi and 

 weeds. Many of our worst insects came from 

 Europe, and more are coming. But transfers have 

 been mutual. If Europe has given us the codlin 

 moth, currant worm, and scores of other pests, both 

 insect and fungous, so we have returned with phyl- 

 loxera and the grape mildew. Certain species of 

 animals and plants appear to be cosmopolitan. 

 They follow in the wake of settlement and trade. 

 And it often happens that introduced species are the 

 worst. There are certain definite reasons for this, 

 which cannot be detailed here. It simply means 

 that change of habit often follows change of place. 



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