LEAF HOPPERS INJURIOUS TO CEREAL AND FORAGE CROPS ( 



NATURAL ENEMIES 



That leaf hoppers maintain a fairly average abundance from year 

 to year, for the most part causing no perceptible devastation, is due 

 to the fact that there are so many different natural agencies tending 

 to reduce their numbers or to keep them in check. Of these natural 

 enemies, birds, spiders, and predacious and parasitic insects would 

 appear to be the most important and to require careful consideration. 

 It seems improbable that leaf hoppers are affected to any extent by 

 mammals, except as eggs may be swallowed by forage-eating spe- 

 cies — cattle, sheep, etc. The only forms which would seem likely to 

 feed upon them are the moles, and these confine their work so largely 

 beneath the surface of the ground that it is doubtful whether they 

 would secure many of the leaf hoppers. 



There are records in the Bureau of Biological Survey of leaf- 

 hopper remains in the stomachs of a bat (Myotis), the common mole, 

 a grasshopper mouse, the skunk, and the domestic cat. The bat must 

 have taken the leaf hoppers on the occasion of a nocturnal flight and 

 not from their host plants, and the other cases would appear to be 

 accidental rather than a regular habit of feeding. 



BIRDS 



Birds would undoubtedly be thought of as an important factor in 

 the natural control of leaf hoppers, and it would seem that they 

 might feed very commonly upon these insects. The most complete 

 records in this line are those accumulated by the Bureau of Biological 

 Survey of the Department of Agriculture, which has for many years 

 been making a record of the contents of birds' stomachs. Besides the 

 published data concerning certain species of birds, that bureau has 

 an immense collection of unpublished records, and these have been 

 very kindly put at the writer's disposal for the purpose of this study. 

 Practically all of the data here presented on this point were derived 

 from this material. Although these records do not, in most cases, 

 give the particular kinds of leaf hoppers which are fed upon by cer- 

 tain species of birds, there should be represented, of course, the kinds 

 of leaf hoppers which were abundant at the time and place indicated. 

 The birds, of course, make no discrimination between species, except 

 as these might appear in greater numbers or prove an easier prey. 



While at first thought birds might be considered as a most impor- 

 tant element in control of these insects, a closer study reveals many 

 reasons why they must depend upon them but little as a food supply. 

 Even with this more conservative view in mind, however, the actual 

 condition as represented by the records of the Biological Survey is 

 rather disappointing, since they show that for practically all of our 

 common birds the leaf hoppers constitute so small a portion of the 

 food supply that birds may be considered as almost negligible in any 

 consideration of the natural agencies of leaf-hopper control. It is, 

 however, important, both as a matter of record and for the benefit of 

 future workers, that the actual condition as indicated by these records 

 should be made available in brief form. 



Early records (19) showed that there were 119 different species of 

 birds whose stomachs contained remains of leaf hoppers in various 



