24 



OBJECTIONS ANSWERED. 



wliich transpires a white cottony secretion. Some of the pro- 

 prietors of orchards about Evesham, observing an insect which 

 secreted a similar substance upon the poplar, imagined that 

 from this tree the creature which they had found so noxious 

 was generated ; and in consequence of this mistaken notion 

 cut down all their poplars. ^ The same indistinct ideas might 

 have induced them to fell all their larches and beeches, since 

 they also are infested by Aphides which transpire a similar 

 substance. Had these persons possessed any entomological 

 knowledge, they would have examined and compared the 

 insects before they had formed their opinions, and being 

 convinced that the poplar and apple Aphis are distinct spe- 

 cies, would have saved their trees. 



But could an entomological observer even ascertain the 

 species of any noxious insect, still in many cases, without 

 further information, he may fall short of his purpose of pre- 

 vention. Thus we are told that in Germany the gardeners 

 and country people, with great industry, gather whole baskets 

 full of the caterpillar of the destructive cabbage moth (^Ma- 

 mestra Brassicce), and then bury them, which, as Roesel well 

 observes^, is just as if we should endeavour to kill a crab by 

 covering it with water ; for, many of them being full grown 

 and ready to pass into their next state, which they do under- 

 ground, instead of destroying them by this manoeuvre, their 

 appearing again the following year in greater numbers is ac- 

 tually facilitated. Yet this plan applied to our common 

 cabbage caterpillar, which does not go underground, would 

 succeed. So that some knowledge of the manners of an in- 

 sect is often requisite to enable us to check its ravages effec- 

 tually. With respect to noxious caterpillars in general, agri- 

 culturists and gardeners are not usually aware that the best 

 mode of preventing their attacks is to destroy the female fly 

 before she has laid her eggs, to do which the moth proceeding 

 from each must be first ascertained. But if their research 

 were carried still further, so as to enable them to distinguish 

 the pupa and discover its haunts, and it would not be at all 

 difficult to detect that of the greatest pest of our gardens, the 



1 Collet, in Munih. Mag. xxxii. 320. 



2 Roesel, T. iv, 170. 



