1048 WALTER H. WELLHOUSE 



They furnish food for nearly all of the insects studied. A few excep- 

 tions, such as the snowy tree cricket (Oecanthus niveus) and th^ damsel 

 fly Lestes viridis, procure their food elsewhere and use the hawthorn 

 branches merely to shelter their eggs from the weather and their enemies. 

 Every part of the tree furnishes food for some species of insect, as may be 

 seen from the following outline: 



Trunk and branches 40 species 



A. External feeders (scales, aphids, and ethers), 10 



B. hiternal feeders (borers), 21 



Roots (aphids) 1 



Thorns (weevils) 1 



Leaves : 292 



A. External feeders (miscellaneous), 235 



B. Miners (tineids, weevils, sawflies), 37 



C. Gall makers (aphids, mites, cecidomyiids), 20 



Flowers (thrips, maggots, caterpillars, beetles, and others) 12 



Fruit (caterpillars, bugs, maggots, grubs) 30 



The other basic need of insects which a host plant may supply is 

 shelter. Most of the insects included in this paper are sheltered to some 

 extent by the hawthorn, although the completeness of the shelter varies 

 with the habits of each species of insect. Some are protected, only by their 

 position on the surface of the tree. Others are partially sheltered in rolled 

 leaves, bark crevices, and the like. Still others are securely housed within 

 the plant tissues. The degree of shelter secured by those species living 

 externally on the surface of the plant varies so greatly and so gradually 

 that no distinct lines of division can be drawn in so general a statement as 

 this. The more distinct groups of internal feeders (borers, leaf miners, 

 and gall makers) are indicated above and are distinguished from the 

 external feeders, which receive less complete shelter. 



The fact that so many species of insects feed at the expense of the haw- 

 thorns suggests the idea that these trees are in danger of extinction. Such 

 is not the case, however, for the hawthorns when not weakened by drought 

 or flood are very hardy, long-lived trees. Some indications as to why they so 

 successfully withstand the feeding of the insects may be seen from a study of 

 the following data, which are based on statistics given in the last sections of 

 this paper: 



APPROXIMATE FEEDING PERIOD OF HAWTHORV INSECTS 



Species Species 



March 11 August .117 



April 54 September 124 



May 190 October. . '. 80 



June 232 November 23 



July 131 Time of feeding unknown 58 



FOOD PLANTS OF HAWTHORN INSECTS 



Food plants restricted to Crataegus : 57 species 



Food plants including other related or associated groups 325 species 



