PROCEEDINGS OF TWENTY-SIXTH FRUTT-GROWERS' CONVENTION. 159 



where the insects are excessively abundant, when the whole surface 

 may become blackened by an alteration of the contents of the leaf cells. 

 This blackening is, in addition to the blackened appearance of the 

 leaves, due to the accumulation of dust, or the growth of smut fungus on 

 the surface of the leaf like that which occurs on a plant affected by the 

 black scale. These poisoning effects, of course, are scarcely to be noticed, 

 except when the insects become excessively numerous. 



Its Life History. — The life history of but few of the species of 

 Aleurodidse has been made out. Many of them produce but one brood 

 a year, passing the winter as a nearly full-grown insect, which trans- 

 forms quite early in the spring into the winged adult condition. Some 

 that pass the winter in this way have a number of broods during the 

 summer. Others in California are active and breeding all winter as 

 well as summer, and this is true of those living on greenhouse plants. 



A large number of the species in the colder climates, which live on 

 deciduous trees and on annual herbs, have never been studied in the 

 winter, and their winter history is entirely unknown. It is probable, 

 however, that in most cases they had become fully fed before the leaves 

 fall in autumn, but do not transform until the next spring, remaining 

 merely attached to the fallen leaves during the winter.* The Aleurodes 

 of the vine do not have this history, but possess the habit, hitherto 

 unknown in this group, of transferring their attention, on the approach 

 of winter, to an entirely different plant, the evergreen Rhamnus califor- 

 nicus, and returning to the vine the next spring. The insect is two- 

 brooded; the adults that are produced on the grape leaves flying to the 

 Rhamnus before laying their eggs, and those developing on the leaves 

 of the Rhamnus likewise being impelled by instinct to seek a home for 

 their young on the grapevine. This remarkable habit is similar to 

 that possessed by a number of species of plant-lice and by some other 

 insects, and may possibly be found true of a number of other Aleurodidse. 



Remedies. — The remedies for white- fly will ordinarily be the spraying 

 of the plants in the same way as for plant-lice or scale insects. The 

 flies are not difficult to kill, but are often hard to reach with a spray, 

 because of their preference for the underside of the leaves. 



In the case of the species attacking the vine the peculiar habits of 

 the insect, described above, give the key to the most available method 

 of control. If it is desired to kill the insect by spraying, the winter 

 food-plant affords the best place to attack it, since while the shape of 

 the leaf makes it very difficult to spray a grapevine satisfactorily, the 



* Since writing the above I learn that my brother, Mr. H. O. Woodworth, has been 

 able to confirm this supposition for a number of species found on deciduous trees in 

 Illinois. 



