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INTRODUCED TREE DISEASES AND INSECTS 



G. F. GRAVATT, D. E. PARKER 



Many people now are asking: Are 

 there more insects and diseases than 

 before? How does it happen that in a 

 few years we have suffered scourges of 

 gypsy moths and Japanese beetles and 

 many others that were not here before? 



The answer is that we are plagued 

 by more insects and diseases and more 

 destructive ones than our grandfathers 

 were. The reason is easy to find. 



Some of our present-day kinds of 

 trees (as indicated by fossil remains) 

 flourished in North America millions 

 of years ago; trees and their parasites 

 must have fluctuated in abundance 

 long before the coming of the white 

 man. Then, as now, periodic epidemics 

 must have caused extensive losses but 

 when the trees were attacked they usu- 

 ally could maintain themselves against 

 borer and beetle. 



This natural balance was upset by a 

 new factor: The early settlers, who 

 brought in new diseases and new in- 

 sects along with their new plants. Some 

 tree pests now considered native no 

 doubt originated in foreign countries. 

 Many serious diseases and insects are 

 known to have come from abroad dur- 

 ing the past 60 years, the entire span of 

 any real study of the diseases and in- 

 sects of tree species in North America. 

 The end of such invasions is not in 

 sight. All over the world disease-pro- 

 ducing organisms and insects are lurk- 

 ing, ready to hitchhike to this country 

 and pounce on our important forest 

 and shade trees. 



Before the enactment of our plant- 

 quarantine laws, the gypsy moth, chest- 

 nut blight, and white pine blister rust 

 were introduced. Since the enactment 

 of the laws, the so-called Dutch elm 

 disease has sneaked in. Other less well- 

 known foreign diseases and insects also 

 have been introduced and are attack- 

 ing various kinds of trees. 



In their native homes, many insects 

 are kept under partial control by their 



parasites and other natural enemies, 

 but when they are introduced into 

 some other area they usually leave these 

 enemies behind. For example, when 

 the Japanese beetle and the gypsy moth 

 reached this country, they multiplied 

 rapidly, partly because of a lack of nat- 

 ural enemies. Insect, fungus, bacterial 

 and virus parasites of these introduced 

 insects now are being imported, but the 

 parasites are valuable only when the 

 environment favors their development. 

 Unlike insects, the organisms causing 

 our introduced diseases do not have 

 any important parasites that directly 

 affect them, although parasites may be 

 used to reduce the populations of the 

 insects that transmit certain of those 

 diseases. 



THE GYPSY MOTH illustrates the 

 serious consequences of the introduc- 

 tion of a forest insect from Europe. In 

 1869 a number of egg clusters of the 

 gypsy moth were brought from France 

 to Medford, Mass., by a French mathe- 

 matician and astronomer who hoped 

 to develop a hardy silk-producing in- 

 sect by crossing gypsy moths with silk- 

 worm moths. During his experiments 

 some of the insects escaped. Some 20 

 years later the population of the gypsy 

 moth had increased to a point where 

 the damage was severe enough to 

 attract general notice. At that time 

 about 360 square miles was found to be 

 infested. Within another 5 years, the 

 infested area had increased to 2,200 

 square miles. Now the gypsy moth, 

 which defoliates both deciduous and 

 evergreen trees, is prevalent in New 

 England, in an extensive area in east- 

 ern New York, and in an isolated area 

 in Pennsylvania. 



At least 65 million dollars have been 

 spent by the Federal Government and 

 various States, chiefly during the past 

 40 years, in fighting the gypsy moth. 

 The main objective of the Federal 



