THE INSECT FAUNA OF THE GENUS CRATAEGUS 1047 



Among the popular names by which the genus is known most commonly 

 are the following: hawthorn, thorn apple, red haw, white thorn, and thorn, 

 in America; hawthorn and may, in England; aubepine, in France (snellier, 

 by French Canadians); Weissdorn, in Germany; spinalba, in Italy. As 

 the name hawthorn seems to be the one most commonly used by English- 

 speaking peoples, the writer has used it in this paper to represent all 

 species of Crataegus. 



The genus is placed by many botanists in the family Rosaceae. Other 

 botanists have divided the Rosaceae group and formed an apple family, 

 Malaceae, in which Crataegus is included along with Malus, Pyrus, 

 Cydonia, Mespilus, Sorbus, Amelanchier, Aronia, and Eriobotrya. 



The determination of species of Crataegus is as great a taxonomic 

 problem to botanists as the determination of the parasitic Hymenoptera 

 is to entomologists. During the first ten years of this century about 

 one thousand species of Crataegus were described in North America. 

 Many of them are now regarded as hybrids and varieties, and a still 

 further reduction of species is in progress. This taxonomic uncertainty 

 makes it impossible in many cases to recognize specific hosts for the 

 insects that feed on the hawthorns. 



Crataegus is distributed over most of the temperate parts of the North- 

 ern Hemisphere. The genus is not indigenous in the Southern Hemis- 

 phere except in America, where it follows the unbroken mountain chain 

 through the Tropics and grows in the Andes Mountains. It is found as 

 far north as Newfoundland, Norway, and Sweden, and extends south- 

 ward to the Mediterranean borders of Africa and Asia Minor. The 

 European species have been introduced into Australia and other European 

 colonies in the Southern Hemisphere for cultivation. 



Most species of hawthorns seem to thrive in any well-drained soil 

 which is not acid and where rainfall is sufficient for the growth of 

 forest trees, while a few species thrive in acid soils also. They are usu- 

 ally long-lived trees, and individuals one hundred years old are not 

 uncommon. 



Distribution is effected largely by means of birds and mammals, which 

 eat the ripe fruits and carry the seeds in their digestive tracts to other 

 communities. Within the same community, thickets are commonly 

 formed from the new stems which grow from the roots of a single tree. 

 Wherever the roots become exposed to light, as by washing on hillsides, 

 a new stem may grow and a tree be formed from it. 



ECOLOGICAL SUMMARY 



The ecological relations of the hawthorns to their insect fauna may be 

 summarized in a general way very briefly. The two basic needs of an 

 insect which it is possible for a host plant to supply are food and shelter. 

 The hawthorns furnish both food and shelter. 



