INJURIOUS INSECTS. 133 



MEETING FOR DISCUSSION. 



Notes on Some Injurious Insects. 



By John G. Jack, Arnold Arboretum, Jamaica Plain. 



The subject of injurious insects is so broad and many sided, 

 that it is not easy to select particular points for a short review, 

 without seeming to neglect others equally important ; because 

 every person naturally regards those insects which attack his 

 particular plants or crops as deserving of the most attention. 



The ravages of some species of insects appeal to, and directly 

 or indirectly affect, almost everybody over a wide area ; as in the 

 cases of the Potato Beetle {Doi-yphora decem-Uneata) , and the Tent 

 Caterpillar {Clisiocampa Americana and C. si/lvatica) . The 

 different species of insects which derive their sustenance from 

 plants may be numbered by tens of thousands in North America 

 and Europe ; but very few of them are likely to attract the atten- 

 tion of people who are not entomologists. In the United States, 

 for instance, there are recorded more than five hundred kinds of 

 insects which feed upon the oaks, and there are undoubtedly 

 hundreds of others which have not been studied. 



While we have many kinds of insects which may be called 

 standard pests, or which are pretty constantly abundant and 

 injurious to certain plants, we can never be sure fr()m what 

 quarter a new depredator may appear, or what hitherto healthy 

 plant may be afflicted with an enemy not recognized as previously 

 affecting, or seriously' injuring it. 



It sometimes happens that au insect, once considered rare, 

 suddenly becomes conspicuously abundant and destructive for a 

 season, or longer, and then it may almost entirely disappear from 

 notice for an indefinite time. An insect hitherto regarded as 

 common, may become a great rarity, or even extinct. 



The commonly injurious iusects may, in the course of nature, 

 be much lessened for a time, by various agencies. The Clisio- 

 campa Americana or Tent Caterpillars of early summer, for in- 

 stance, hatch from the eggs very early in the spring, and the young 

 larvae may be largely destroyed by late frosts, or a period of cold, 

 wet weather. An almost complete cessation of injuries by a species 

 of borer, which was destroying immense numbers of conifers in 

 the forests of West Virginia a year or two ago, is only accounted 



