Page:The American Cyclopædia (1879) Volume XIII.djvu/495

 PHYLLOXEEA 479 rooted native varieties, are mainly owing to this insect. He also showed that some of our native varieties enjoy relative immunity from its attacks. In 1873 Prof. J. E. Planchon was commissioned by the French government to visit America to study the phylloxera. His investigations corrob- orated Prof. Kiley's conclusions as to the identity of the Amer- ican and European insects, and the rel- ative immunity of some of the American vines. His official reports of this visit have done much to dispel some of the prejudice existing among his countrymen in regard to American vines, and still more to create a large demand for such American vines as resist the insect, to be used as stocks on which to graft the French vines. The grape phylloxera is in- FIG. 2. Upper and Under Wings of Phylloxera. -Type Eadicicola. a, 6. Wingless mother lice, back and side views, c. Gran- ulations of shin. d. Tubercle, e. Transverse folds at border of joints. /. Simple eyes. Natural size indicated at side. digenous to the North American continent east of the Rocky mountains, and is found from Canada to Florida on the wild vines of the woods, and on the cultivated vines in most and probably all of the states. It presents itself in two different types. That which makes galls on the leaves is called gallicola; it is smooth and very prolific, and exists only as an agamous wingless fe- male. It is quite tran- sient, abundant one year and unseen the next, and seems to be unes- sential to the perpetu- ation of the species ; an abnormal deviation from the root-inhabit- ing type, rendered pos- sible under certain con- ditions. The root in- sect, distinguished as n*n/Jt*ifnln fhrmr/h rrA radwicola, though pre- cisely like the gall-ma- king type when first hatched, subsequently acquires tubercles. The grape phylloxera hi- bernates mostly as a young larva torpidly at- tached to the roots, and so deepened in color Fio. 4. Male Phylloxera, ventral view. Natural size indicated by dot in circle, FIG. 5. Type Gallicola. i. Egg. 6. Section of gall c. Swelling of tendril. as generally to be of a dull, brassy brown, and therefore with difficulty perceived, as the roots are often of the same color. With the re- newal of vine growth in the spring this larva moults, rapidly increases in size, and soon com- mences laying eggs. These eggs in due time give birth to young, which soon become vir- ginal, egg-laying moth- ers, like the first, and like them always remain wingless. Five or six generations of these par- thenogenetic, egg-bear- ing, apterous mothers follow each other, and then, about the middle of July in the latitude of St. Louis, some of the individuals begin to acquire wings. These are all females, and like the wingless moth- ers they are parthenogenetic. Having issued from the ground while in the pupa state, they rise in the air, and spread to new vineyards, where they deliver themselves of their issue in the form of eggs or egg-like bodies, usually two or three in number, and not exceeding eight, and then perish. It is not yet posi- tively known where these winged females pre- fer to lay their eggs ; but experiment indi- cates that while the eggs may be pushed into the tomentose buds, they are most probably laid as a rule in the minute crevices on the surface of the ground, near the base of the vine. These eggs are of two sizes, the larger about 0*02 of an inch long and the smaller about three fifths of that length. In the course of a fortnight they produce the sexual individuals, the larger ones giving birth to females, the smaller to males. These sexual individuals are born for no other purpose than the reproduc- tion of their kind, and are without means of flight or of taking food or excreting. They are quite active, and couple readily. The ab- domen of the female, after impregnation, en- larges somewhat, and she is soon delivered of a solitary egg, which differs from the ordina- ry eggs of the parthenogenetic mothers only in becoming some- what darker. This impregna- ted egg gives birth to a young louse, which be- comes a virgin- al, egg-bearing, wingless moth- er, and thus re- commences the cycle of the species' evolution. But a very im- portant discovery made by Balbiani is that du- ring the latter part of the season many of the wingless, hypogean mothers perform the very same function as the winged ones ; i. e., they lay FIG. 6. Type Gallicola. &. Newly hatched larva, ventral and dorsal view. Natural sizes in circles at sides.