THE FARMER'S MAGAZINE. 



329 



THE INSECT PESTS. 



An interesting subject presents itself to our notice ; 

 and, with a view to its elucidation, we proceed to state a 

 few facts connected with it. 



We now especially allude to the prevalence of insects 

 at particular seasons. In many, we are altogether 

 exempt from them, 'n others we are subjected to their 

 ravages to an extraordinary extent. 



The year 1856 was remarkable for the myriads of 

 the turnip-beetle (Altica nemorwn) that prevailed 

 throughout this country. The year 1857 has been 

 equally remarkable for its absence, and in some districts 

 as altogether so (of course we are now speaking more 

 especially of a single locality, as exemplifying others). 

 Undoubtedly there are exceptions to the rule ; but, 

 upon a broad basis, the result in one year has been 

 reversed in the next. 



The pest next to the turnip-beetle, in point of de- 

 structiveness to our turnip crops, is produced by the 

 black caterpillar, the larvae of the Athalia spinarum, 

 which last season devastated whole districts, and is 

 again this season showing itself to an almost equal 

 extent. We have just witnessed, in several large fields 

 of the common turnip, that they had already attack- 

 ed nearly evei-y plant, and that to all appearance 

 the crop would be destroyed. Still, as many pieces last 

 year entirely recovered the scourge to which they had 

 been subjected, we are not without hope that a similar 

 result may follow in the present autumn. 



Again, the aphis tribe, infesting our beans, peas, 

 hops, and vegetables, prevail in certain seasons to a 

 very great extent — upon some plants in particular ; 

 whilst upon others their attacks are scarcely visible. 

 This is more especially the case with the aphis infesting 

 the hop; and they are also attacking the pea and bean. 

 It has long been observed by country people that a 

 good hop and pea crop rarely occur in the same years, 

 and we have observed on various occasions it has been 

 verified. Upon the China roses of last year these in- 

 sects were exceedingly prevalent; this year but few 

 have been observed. 



We adduce these examples only as affecting the 

 general prevalence of any particular insect for one or 

 for many years together, and then, on the other hand, 

 its disappearance almost entirely for many years after- 

 wards. This shows that such occurrences are not en- 

 tirely dependent upon seasons, but rather are influenced 

 by mysterious causes which we are unable to fathom. 



The prevalence or no.n-prevalence of the turnip- 

 beetle has ever been notorious. In some seasons the 

 crops are devastated by its ravages ; in other seasons 

 it scarcely appears, and they escape altogether. 

 This probably may be dependent upon the intensity of 

 cold of the preceding winter, as the insect does not 

 appear to take any extraordinary precaution towards 

 its own safety. This has been verified by many of 

 our correspondents, who state they have found 



them in considerable numbers in a torpid state during 

 the winter months, only partially protected by the 

 covering obtained in old decayed stubs of thorns in 

 hedge-rows, and in similar situations. 



As regards the black caterpillar secondly adverted 

 to, it is the larvtE of a peculiar description of fly, the 

 females of which are of a dirty yellow colour, the 

 males much larger, and of a dusky grey. These, 

 doubtless, remain in the chrysalis state during winter, 

 and most probably at such a depth in the soil as to 

 render them secure from the severity of the weathei*. 

 The dryness of the two preceding winters may have 

 been conducive to their preservation, and thus it may 

 be that they are this year equally prevalent with that 

 of the preceding one. An observation, however, that 

 we are about to make tends rather against this suppo- 

 sition. We have for many years been connected with 

 a considerable occupation, and until the year 1856 had 

 never experienced any attack from this pest. Last 

 year, however, a large breadth of the common turnip 

 was apparently destroyed by them, the ribs of the 

 leaves alone remaining to tell the tale of the work of 

 destruction that had been going on. This year a repe- 

 tition of the attack has taken place, and probably will 

 become as extensive as in that of the preceding season. 

 This we are not much surprised at ; but what does 

 rather puzzle us is that for 30 years preceding, upon 

 the same farm, we have no recollection of their hav- 

 ing ever appeared. 



The tribe of insects next adverted to is that denomi- 

 nated the aphis, and is known to everyone from its 

 destructive effects upon the pea, bean, hop, and many 

 plants of the brassica tribe, especially of the Swedish 

 turnip and cattle cabbage, whilst the common or white 

 turnip is rarely, if ever, affected. Mangold wurzel 

 is also exempted, not only from its attacks, but 

 also from the attacks of insects altogether, to a greater 

 extent than any other vegetable whatever; and this 

 circumstance alone points to it as a vegetable de- 

 serving our best attention and cultivation. It has the 

 property also of resisting the effects of drought better 

 than any other cultivated root, and is capable of being 

 grown upon a greater variety of soil than the turnip. 



All insects of the aphis tribe appear more 

 dependent upon atmospheric agency than any others 

 with which we are at present acquainted. A dry north- 

 east or north-easterly wind appears to very much favour 

 their production, arising from their peculiar habits 

 and modes of procreation, being at some periods 

 oviparous and others viviparous, or both together. 

 A single impregnation of the male suffices 

 throughout several generations, and tends to their 

 increase in a most marvellous and astonishing manner. 

 These insects have been this season less prevalent upon 

 our roses than usual, but the pea and bean crops have 

 suffered considerably from their attacks. 



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