100 TRUCK-FARMING AT THE SOUTH. 



(Pieris rapce), the parent of the cabbage-worm, was un- 

 known in this country. It was at that time introduced 

 into Canada. Finding in the cabbage fields near Quebec 

 an abundance of food, and meeting no checks, it im- 

 proved its opportunities and propagated its species to 

 such an extent, as to cut short the cabbage crop of 

 the vicinity in one season to the extent of forty thousand 

 dollars. 



Suddenly its own especial enemy, the little Chalcid 

 fly (Pteromalus puparum) made its appearance, presum- 

 ably direct from Europe; and in turn, finding its ap- 

 propriate food in abundance, propagated its species so 

 rapidly, that, now in sections where the cabbage-worm 

 was most plentiful, neither the one nor the other is often 

 seen; thus showing the beautiful working of checks and 

 counter-checks in the general plan of nature. 



THE MIGRATION OF INSECTS. 



The number of injurious insects is on the increase all 

 over the world. The interchange between different 

 sections, different countries, and even different hemis- 

 pheres, of noxious insects, indigenous to each, is con- 

 stantly occurring, as shown by the case of the just-named 

 Pieris rapce. The Colorado potato-beetle once gained 

 a foothold in Germany; but through the paternal care of 

 the government, the large potato field, where he was ob- 

 served, was covered with inflammable material, and that 

 country was promptly made too hot for him. 



The Colorado potato-beetle has marched eastward to 

 the coast, a curse and ravager of every farmer on its 

 route, while the harlequin-bug (Strachia liistnonica), 

 coming north from its home in Mexico, will cross the 

 line of the other, unless it reaches a climatic limit to its 

 onward progress. An abundance of food has recruited 

 the ranks of noxious insects, and is still exerting the 

 same influence. Before the introduction of the cab- 



