BULLETIN 192. 



INSECTS INJURIOUS TO THE VINE. 



101 



normal root form and show slight protuberances on the sides, which 

 finally develop into wings. These are the winged or colonizing insects, 

 which emerge from the soil, and, though possessing very weak powers 

 of flight, are capable of sailing a short distance, and if a wind is 

 blowing may be taken many rods, or even miles. Those which reach 

 a vine crawl to the under side of a leaf and deposit from three to six 

 eggs. These eggs are of two sizes, the smaller of Avhich produce males 

 and the larger females. The females arising from these eggs, after 

 fertilization, migrate to 

 the rough bark of the 

 two-year-old wood, where 

 each deposits a single 

 egg, called the winter 

 egg, which remains upon 

 the vine until the fol- 

 lowing spring. The in- 

 sect which hatches from 

 this egg in the spring 

 goes either to the young 

 leaves and becomes a 

 gall-maker, or descends 

 to the roots and gives 

 rise to a new generation 

 of egg-laying root-feed- 

 ers. 



The normal and com- 

 plete life cycle of the 

 phylloxera appears then 

 to be as follows: Male 

 and female insects (one 



generation in autumn) ; FIG - 2 .Root'Form of Phylloxera, a, healthy root; 6, root 



on which the lice are working, representing the knots and 

 swellings caused by their punctures ; c, root deserted by 

 lice and beginning to decay ; d, d, d, show how the lice 

 appear on the larger roots ; e, the nymph ; g, winged female. 

 After Riley. 



gall insects (one to five 

 generations while the 

 vines are in leaf) ; root 

 insects (an unknown number of generations throughout the year) ; 

 nymphs, which become winged insects (one generation in midsummer). 

 The gall stage may be omitted, as it generally is in California, and the 

 insects which hatch from the fertilized eggs laid by the female go 

 directly to the root and produce offspring, which are indistinguishable 

 from the root form produced in the normal cycle. For how many 

 generations the root form can exist and reproduce without invigoratioh 

 supposed to come from the production of the sexual form is not known, 

 but certainly for four years and probably more. The gall form on 



