200 



On the Imeds affecting the Turnip CroiJ. 



by the strong and projecting ribs that support tlie leaf from 

 any injury that might occur from the lea-\'es being ruffled by the 

 wind or other casualties ; and the inferior skin being the most 

 dehcate, is best adapted for the entry of the infant and tender 

 maggots into the substance of the leaf^ It is not^ therefore^ at 

 this stage that much could be done in destroying them. 



The maggots, it is evident, live upon the rough leaf, and do 

 little or no mischief to the growth of th# plants ; they dwell per- 

 fectly secure between the two cuticles, unless it be when they 

 leave the burrows they had first conimenced, probably not of 

 common occurrence, to form new ones at a remote part of the 

 same or upon another leaf. At this period they are most pro- 

 bably affected by parasitic enemies. 



The chrysalis is buried only just beneath the surface of the 

 earth, but it is probably protected in a slight web, forming a 

 cradle for it to lie in free from pressure. I think some efforts 

 might be successfully made for its destruction at this time. 



It is, however, in its last and perfect state that the mischief is 

 done. It is the beetle which destroys the two first smooth leaves, 

 called the cotyledons, and the heart of the plant between them, by 

 piercing them like a sieve, destroying the cellular tissue and 

 stopping the growth of the plant. They also feed upon the 

 rough leaves, drilling them full of round holes (fig. d), which are 

 larger on the upper than the under side of the leaf ; and if the 

 appetite of the beetle be not satisfied, he enlarges the aperture, 

 and thus gives it an irregular form, which dilates with the 

 growth of the leaf: hence the large holes we see at a later period. 

 After all, it is at this stage of their existence, I am inclined to 

 believe, that we can attack them with the best prospect of success, 

 if they cannot be kept off by other means. 



In collecting the turnip- beetles by sweeping and various me- 

 thods, large numbers of small carnivorous beetles, belonging to 

 the Carahidce and Staphylinidcc,^ are found with them : these pro- 

 bably feed upon the larvse ; but, from the very recent discovery of 

 the early stages of the turnip-beetle, we are yet ignorant of the 

 parasites, of which it may be presumed there are more than one 

 species, that prey upon the maggots and chrysalides ; for it is a 

 wise dispensation of Providence to keep every animal in check by 

 some other that is either more powerful or more sagacious than 

 itself, and this counteracting effect is produced in a degree equal, 

 or eventually superior to the noxious animal, so that in a greater 

 or less space of time the destructive power may be rendered no 

 longer formidable, or be absolutely annihilated by the attacks 

 of its parasites. This natural process, though never failing, is 



* Curtis's British Entomology, folios 446, 758, &c. 



