INSECTS IN RELATION TO PLANTS 2IQ 



growing shoots. Other investigators have found that apple aphids, 

 leafhoppers, the tarnished plant bug (Lygus pratensis). and the shot-hole 

 borer (Scolytus rugulosus) are also responsible for the inoculation of 

 fruit trees with the bacilli of blight. 



Dr. E. F. Smith demonstrated that cucurbit wilt is spread, probably 

 exclusively, by insects, particularly the striped and the twelve-spotted 

 cucumber beetles (Diabrotica vittata and D. duodecimpunctata, respect- 

 ively), which introduce the bacilli of the disease into the plants as they 

 feed. Some of the beetles carry the bacillus over winter, in the alimen- 

 tary tract, and infect young plants with the wilt in spring. 



The spores of the fungous disease known as brown rot of peach and 

 plum are probably carried by bees, wasps and certain other insects, 

 and introduced into wounds in the fruits made by themselves or other 

 insects. The plum curculio almost certainly leaves these spores in 

 "punctures that it makes. 



Cankers of Leptosphceria on apple bark occur around the oviposition 

 wounds made by tree-crickets (CEcanthus) , and it has been shown experi- 

 mentally that these insects convey the spores of the disease both 

 externally and internally and inoculate them into the host plant. 

 Typical cankers on apple branches have been obtained artficially by 

 inoculation with feces of tree-crickets fed on spores of the disease. 



The mosaic diseases of cucumber, potato and tobacco are trans- 

 mitted by plant lice. The spores of bitter rot of apples are conveyed 

 from decaying apples to sound fruits by pomace flies (Drosophila). 



Insects in Relation to Flowers.-^-Among the most marvelous phe- 

 nomena known to the biologist are the innumerable and complex 

 adaptations by means of which flowers secure cross pollination through 

 the agency of insect visitors. Cross fertilization is actually a necessity 

 for the continued vigor and fertility of flowering plants, and while some 

 of them are adapted for cross pollination by wind or water, the majority 

 of flowering plants exhibit profound modifications of floral structure for 

 compelling insects (and a few other animals, as birds or snails) to carry 

 pollen from one flower to another. In general, the conspicuous colors 

 of flowers are for the purpose of attracting insects, as are also the odors 

 of flowers. Night-blooming flowers are often white or yellow and as a 

 rule strongly scented. Colors and odors, however, are simply indica- 

 tions to insects that edible nectar or pollen is at hand. Such is the 

 usual statement, and it is indeed probable that insects actually do asso- 

 ciate color and nectar, even though they will fly to bits of colored paper 

 almost as readily as they will to flowers of the same colors. It is not . 



