63 



been long known in regard to plant growth and theoretically of insects, 

 that sadden changes in the winter temperature, such as "freezes" or 

 severe and protracted cold "snaps" which sometimes follow unseasonably 

 warm spells, are more inimical to insect life here (and particularly when 

 these occur after warm, sunny days in early spring or late winter when 

 many species are tempted to issue prematurely from their winter quar- 

 ters) than are hot spells in summer or autumn and periods of long 

 drought. 1 In Kansas and other States of the middle West, and especially 

 southward in the arid region of the Upper and Lower Austral (Sonoran) 

 areas, the contrary, according to Mr. Marlatt, is true owing to the greater 

 frequency and length of droughts in that region. 



During the entire season of 1899 not a single instance came under 

 notice of an insect which was lessened in numbers to any appreciable 

 extent by atmospheric conditions existent during the summer. During 

 the season of 1896, on the other hand, it was noticed of two species, 

 the Colorado potato beetle and the common asparagus beetle, 2 whose 

 larvae feed freely exposed upon their host plants, that the intense heat 

 of that summer had the effect of killing them off in a very marked 

 degree. 



It also appears to me what has been observed by Mr. Marlatt in the 

 case of scale insects (Bui. ISTo. 20, n. s., p. 73), is true in general, viz, 

 that favorable or unfavorable climatic conditions are of greater impor- 

 tance in determining the abundance or scarcity of insects as a whole 

 than are other natural checks such as parasitic and other enemies, or 

 even fungous or bacterial diseases. 



The year that has just passed, with its blizzards and low temperatures, 

 was an exceptional one, and for that very reason had so striking an 

 effect as to have called forth general remark on the part of the botan- 

 ist, fruit grower, and in fact all others interested in plant life as well 

 as the entomologist, and it is in just such years that we are best able 

 to observe the effect of the weather and to draw conclusions as to 

 the particular factors which conduce toward the preservation of the 

 balance of nature. 



1 This subject is treated more fully by Dr. Howard iu his article, entitled (i Tem- 

 perature experiments as affecting received ideas on the hibernation of injurious 

 insects/' and in the discussion which followed the presentation of that paper before 

 the meeting of the Association of Economic Entomologists in 1897 (Bui. No. 9, n. s., 

 pp. 18, 19). It was conclusively shown by Dr. Howard, through an experiment con- 

 ducted by Dr. A. M. Read, with larva? of Tineela bisellieUa and Attagenus piceus, that 

 a consistent temperature of 18° F. would not destroy these insects, but that an 

 alternation of a low temperature with a comparatively high one invariably resulted 

 in the death of both. 



2 The latter species affords an excellent example of the effect of temperature in 

 limiting the distribution of an introduced insect northward and southward, the cold 

 11 snaps" killing off the hibernating beetles in the northern limits of the species and 

 the hot dry spells of summer effecting a similar result in respect to the larva? in its 

 southern limit (see writer's remarks in Yearbook Dept. Agr. for 1896, p. 374). 



