HOMOPTERA 433 



generation, if, as stated, the pines are free from the pest during the 

 summer. 



Subfamily PHYLLOXERIN^ 



The Phylloxerids 



The distinguishing characters of this subfamily are given under 

 AA in the table on page 428 and need not be repeated here. It in- 

 cludes two genera, Phylloxera and Phylloxerina. 



The genus Phylloxerina is distinguished by the fact that the 

 wingless agamic females excrete a waxy powder, which gives them 

 the appearance of mealy-bugs. Species of this genus have been found 

 in this country on poplar, willow, and sour-gum. 



The genus Phylloxera is represented by the grape Phylloxera and 

 thirty or more described species that infest forest-trees — ^hickory, 

 oak, and cnestnut. Most of these are foimd on hickory. Those 

 on hickory cause the growth of galls either on the leaves or on the 

 tender twigs and petioles. Other species produce either pseudogalls 

 or white or yellowish circular spots on the infested leaves. The species 

 infesting forest -trees were monographed by Pergande ('04). 



Although in this subfamily there is a generation of winged mi- 

 grants in the life-cycle of each species, few if any of them have a 

 secondary host. The migrants fly to other parts of the infested plant 

 or to other plants of the same species. 



So far as is known, the life-cycle of the species infesting forest-trees 

 is a comparatively simple one. The stem-mother hatches in the 

 spring from an over-wintering, fertilized egg and causes the growth of 

 a gall; she develops within the gall and produces unfertilized eggs. 

 From these eggs hatch young that develop into winged agamic 

 females. These produce eggs of two sizes; from the smaller eggs 

 hatch males; and from the larger ones, females. The sexes pair and 

 each female lays a single fertilized egg. In some species these eggs 

 are laid in June and do not hatch till the following April. 



The grape Phylloxera, Phylloxera vastdtrix. — From an economic 

 standpoint this species is the most important member of the Phyl- 

 loxerince; millions of acres of vineyards have been destroyed by it.* 

 The most extensive ravages of this pest have occurred in France 

 and in California. This species is a native of the eastern United 

 States, where it infests various species of wild grapes. It does not 

 injure these seriously; but when it was introduced into France it 

 was found that the European grape, Vitis vinifera, is extremely sus- 

 ceptible to its attack. The great injury to the vineyards of California 

 is due to the fact that it is the European grape that is chiefly grown 

 there. 



The presence of this insect is manifested by the infested vines 

 in two ways: first, in the case of certain species of grapes, there 



*"The Phylloxera when at its worst had destroyed in France some 2,500,000 

 acres of vineyards, representing an annual loss in wine products of the value of 

 150,000,000." (Marlatt '98.) 



