134 PHYSICAL GEOGRAPHY. 



and that they increase with marvelous rapidity, a single pair being 

 capable by the end of the season of producing millions. The con- 

 ditions of their great increase during some seasons and their de- 

 crease during others are not well understood. During this season 

 they were abundant not only on the milkweeds, amorphas, and 

 some few sun flowers, but were specially abundant on oak trees, on 

 the willows, elms and cottonwoods, though I am not advised as to 

 any particular damage that they have done. It is claimed by many 

 that a moderate increase of plant-lice is an advantage where apiaries 

 are kept, because of the heavy honey dew that some species produce. 

 This is questionable, but it is one of those compensations of which 

 nature is so full. Something at least is gained, if when the vigor 

 of vegetation is impaired by the sucking of wood-lice, the bees pro- 

 duce double their ordinary stores. For a few years, in many por- 

 tions of the State, there has been an alarming increase of the 



COTTONWOOD LEAF BEETLE, 



or, as it is known to science, the Plogiodera scripta. Nowhere has 

 it done more injury than in Lancaster County, though it has been 

 sent to me to identify from many other places. Some of the groves 

 beyond the Antelope, and many of the cottonwoods on the State 

 Agricultural Farm, were despoiled of their leaves by this insect. 

 It prevailed as far north as Dakota and Dixon counties. I saw 

 trees stripped of their foliage by it in Burt and Washington coun- 

 ties. It has done more or less damage in at least tw r enty counties 

 of the State. During this season, however, it has greatly declined 

 in numbers, and in the damage it has been doing for several past 

 years. What has caused all this decrease I am unable to say, but 

 one element of the process has been the work of predatory insects. 

 I have found ichneumons and chalcis flies at work on them. Rainy 

 seasons also seem to be injurious to them. This, however, has been 

 denied. The fears, however, that many began to entertain that this 

 insect was going to place an embargo on the cultivation of the cot- 

 tonwood, is proved to be not well founded. Prof. Culbertson I 

 think has somewhere given an account of its life history, and the 

 best methods of counteracting its work, and that, therefore, I need 

 not here repeat. 



During this season, also, the various species of borers have not, so 

 far as I am advised, made any special inroads on the trees of th e 

 State. I have no doubt the increase of our insectiverous birds has had 

 much to do with lessening the number of many of our insect enemies . 



