j6 Mr. CTniTis*'s OBfervations on Aphtdeu 



alfo attach themfelves to the bark of trees, like the Aphis faficls^ 

 which being oae of our very largeft fpecies, and hence poflefling 

 foperior ftrength, is enabled to penetrate a fubftance harder than the 

 leaves themfelves. 



As among cr.terpillars we find fome that are confl:autly and un- 

 alterably attached to one or more particular fpecies of plants, and 

 others that feed indifcriminately on moft forts of herbage ; fo it is 

 preciiely with the Aphides: fome of them are particular, others more 

 general feeders. 



As they refemble other infedls in the above refpe<S, fo do they 

 alfo in being infinitely more abundant fome years than others; and 

 though, with regard to certain infefts, this variation (fometimes 

 wonderful in the extreme, as in the brown-tail moth which ravaged 

 the quickfet hedges in 1782) is not eafily accounted for, it is folved 

 without much difficulty as to the Aphis, as will be fhown in the 

 fequel. In the year 1793 they were the chief, and in 1798 the fole, 

 caufe of the failure of the crop of hops. In 1794* a feafon almofl 

 unparalleled for drought, the hop was perfedtly free from them, 

 while peas and beans, efpecially the former, fuffered' very much 

 from their depredations. Beans were in 1798 almofl: wholly cut 

 off by them; indeed they fuffer more or lefs every year by a black, 

 fpecies of -^A/f, particularly the latter crops. To potatoes^ and even 

 to corn,, we have known them fome years prove highly detri-- 

 mental, and no lefs fo to melons. To plants in (loves, green- 

 houfes and frames, where, from the warmth and fhelter afforded 

 them, a preternatural multiplication takes place, they prove ex- 

 tremely injurious, and many a rare and valuable plant alfo in 

 the open ground of our botanic gardens falls a vi£tim to thefe 

 general depredators. Seeing, therefore, that our neceffaries as well as 

 luxuries of life are (o materially afiecled by the infe6ls of this genus,, 

 »n attempt to afcertain fome of the curious and important fads- 

 9, relative. 



