258 INSECTS 



by means of hopper-dozers on one part only. This part 

 supported exactly twice the number of cattle during 

 the season that could be maintained where the hoppers 

 were left undisturbed. 



It is comparatively easy for the farmer to estimate 

 his loss when the green-fly drains his wheat so that 

 instead of the expected twenty bushels he harvests 

 only ten or none at all. The drain upon all sorts of 

 crops by the myriad of specimens constantly sucking 

 plant juices and reducing the yield to a less obvious 

 extent, is rarely capable of estimation, but varies from 

 ten to fifty per cent, almost every year on most of our 

 staple crops. This sounds like an exaggeration, but 

 every person who has ever studied the problem at all 

 carefully will agree in the estimate, I think. 



And then come the host of species that feed directly 

 upon leaf tissue. They come from many orders: grass- 

 hoppers, locusts, crickets and their allies of many 

 kinds; slugs and grubs as well as adult beetles in great 

 variety; caterpillars of the most diverse appearance 

 but always great devourers; saw-fly larvae from the 

 Hymenoptera and a few maggots from the Diptera or 

 fly tribe. Perhaps no kinds of insects do more obvious 

 injury than those that feed openly on the foliage and 

 yet the real harm that they cause is not always in 

 proportion to their feeding, because many plants and 

 trees will support the destruction of a great percentage 

 of leafage without material impairment of crops. This 

 does not apply where the crop consists of the leaves 

 themselves as in cabbage, spinach and other vege- 

 tables, all of which have their own particular insect 

 friends. 



Unfortunately some of these foliage feeders modify 

 their habits somewhat, on occasion, and attack more 

 important parts of the plant, e.g., when the rose-chafer 



