183 
Dr. Harris states that “lice multiply much faster, and are more in¬ 
jurious to plants in a dry than in a wet atmosphere.” That as a very 
general and almost universal rule, plants are more easily injured in dry 
weather than in moist, is undoubtedly true; but as to the other part 
of the statement, I think he is mistaken as a rule, for there is scarcely 
an individual, who has paid any attention to this matter, who is not 
aware that a warm, humid atmosphere is favorable to their increase. 
Yet it must be admitted that there are some species, especially those 
that infest trees, which appear to be more abundant in dry than in 
wet seasons. Curtis remarks that “their increase in damp sultry weath¬ 
er is equally surprising; and the universal diffusion of such myriads 
after a thunder storm, lias led, as with the black caterpillers, to the 
vulgar error of their falling from the clouds.” He thinks it probable 
that electricity also assists in their rapid and sudden development 
sometimes observed. On the other hand, Dickson in his Practical 
Agriculture , remarks that “In such summers as are dry, beans are 
liable to be much injured by the attacks of the Black Fly , or what 
is often termed the 'Dolphin , the whole field, in particular cases being 
in danger of being destroyed in the course of a few days.” Black- 
fly, Dolphin and Collier, are terms applied in England to a variety of 
the Bean Aphis. It is not stated here that it is the rapid increase 
of these insects in such weather that renders the beans more liable to 
destruction in dry than wet seasons; it is therefore more probable 
that the weakened vitality caused by the want of moisture, has much 
to do with it. 
As a rule, the remedies applicable to one species, are equally appli¬ 
cable to another of similar habits, where the one is as easy of access 
as the other. But the measures so far suggested, apply almost ex¬ 
clusively to species that operate on the surface, and not to those which 
enclose themselves in galls. For such species it is evident that topical 
applications will be of no effect, and the same thing is true of fumi¬ 
gations. The surest, and in fact, the only remedy which so far, has 
been suggested, is to pluck the leaves and twigs containing them, and 
consigning them to the flames. 
If it should hereafter be ascertained that it is a habit of many of 
the foliage species to deposit eggs on trunks of trees in the crevices 
of the bark, as is suggested by some entomologists, and thus pass the 
winter, rubbing the bark, in the spring, with soft soap, will doubtless 
aid in their destruction. As this practice is beneficial in other respects, 
I think it would be well at any rate, to practice it to a greater ex¬ 
tent than is now customary. It will be beneficial, at least, in destroy* 
ing the species that reside on the trunks, and the rains will carry it 
down to roots, and assist to some extent, in disturbing those that 
work around the base and on the roots. 
According to Boisduval ( Fntornologie Horticola) , M. Gehin, in an 
article on injurious insects, ( Bull. Soc. Hist. Nat. Moselle , 1862), ex¬ 
presses the opinion that the injury occasioned to the peach, supposed 
to be by the plant-louse that attacks the leaves, is not clue solely to 
these insects, but in consequence of some sudden atmospheric change, 
which effects the leaves and renders them more suitable for the sus¬ 
tenance of the lice, and thu^ causes their more rapid development, 
which augments the injury. He states that where the trees are per¬ 
fect and vigorous, they are seldom attacked by these insects. 
