172 Bugs, Cicadas, Aphids, and Scale-insects 



plump-bodied, pale-green insects, some with two pairs of long, delicate, 

 transparent wings, some without wings, common on flowers in conserva- 

 tories and gardens and known as "green fly." Other often-noticed kinds 

 are the cockscomb gall-louse of the elm and the "blights" of various foliage 



trees, as alder-blight, beech-blight, elm- 

 blight, etc., these "blight" aphids all 

 secreting conspicuous white woolly masses 

 of wax and most of them also excreting 

 honey-dew, which is conspicuous on the 

 leaves and on the sidewalks under the 

 trees. 



Of more economic importance are 

 so of those plant-lice which infest 



migrant. (After Pergande; much crop-plants, the extraordinarily ruinous 

 enlarged.) grape-phylloxera, for example, the apple- 



tree root-louse, and the woolly apple-aphis, the cherry-, plum-, and 

 peach-aphids, the corn-root louse, the hop-louse, and the cabbage-aphis, 

 turnip-louse, and other aphid pests of garden vegetables. All of these 

 insects are minute soft-bodied defenceless creatures, which effect their great 

 injuries to their host-plants by virtue 

 of great numbers. Fitch, New York's 

 first state entomologist, estimated the 

 number of cherry-aphids that were 

 living at one time on a small young 

 cherry-tree to be 12,000,000. Although 

 uncounted millions of the toothsome 

 juicy little aphid bodies are being con- 

 .stantly eaten in spring and summer by 

 eager predaceous insects, such as lady- 

 bird beetles, certain syrphid-fly larvae 

 and aphis-lions (larvae of lace-wing and hemerobius flies), just as constantly 

 are new millions being produced by the fecund aphis mothers, most of the 

 young being born alive and requiring but a few days to complete their 

 growth and development, and to be ready to take up the production of 

 young themselves. 



Professor Forbes has made an estimate of the rate of increase of the corn- 

 xoot louse that shows this great fecundity. A single stem-mother of the 

 corn-root aphis produces twelve to fifteen young that mature in a fortnight. 

 "'Supposing that all the plant-lice descending from a single female hatched 

 from the egg in spring were to live and reproduce throughout the year, we 

 should have coming from the egg the following spring nine and a half tril- 

 lion young. As each plant-louse measures about 1.4 mm. in length and .93 



FIG. 245. The southern grain-louse, 

 Toxoptera gramineum, wingless. A, 

 female; B, young nymph; C, older 

 nymph. (After Pergande; much en- 

 larged.) 



