CHECKS TO INCREASE OP APHIDES. 183 



the evil is spread over a large area; the immediate 

 destructive agents are legion, and their economy 

 is often obscure. 



Some years ago Mr. F. Walker, after noticing the 

 destruction of the water-lilies on the Thames near 

 Hampton Court, suggested the artificial introduction, 

 or transplanting, as it were, of diseased individuals of 

 Rhopalosiphum nymphcece ; these Aphides being very 

 commonly infested by the larvas of small Ichneumonida3 

 and Ohalcidise. 



These parasites would, after becoming winged, 

 deposit their eggs in myriads of healthy Aphidian 

 larvse, and thus check their evil influence. 



There can be no doubt that our corn harvest is 

 repeatedly saved by the presence of the little black 

 Ephedrus plagiator, which oviposits in the larvas of 

 Siphonophora granaria. The brown, globular, ichneu- 

 moned bodies of the rose Aphis is also familiar to most 

 horticulturists. The common rape Aphis, Rhopa- 

 losiphum dia?ithi,&nd the cabbage Aphis, Aphis brassicce, 

 are so much attacked by parasites, that scarcely one 

 individual in a hundred escapes and passes into the 

 winged state. 



The hop-grower knows the value of the " lady-bird," 

 and will not allow them to be wantonly destroyed ; and 

 equal protection should be given to the Aphis-eating 

 " golden-eye." 



Some Aphides undergo a sugary degeneration ; the 

 internal organs apparently at first become abnormally 

 charged with oily globules, which afterwards crystal- 

 lise like grape sugar, and finally the insect is destroyed. 

 The Aphides of the swede-turnip are often thus affected, 

 and their bodies then turn to a foxy-yellow colour. 



Rhopalosiphum lactucce and many other species are 

 often covered by a yellowish fur-like coat, which 

 under the microscope has much the appearance of a 

 fungus, not unlike the Empusa of the house-fly. The 

 entire body of the insect becomes clothed with trans- 

 parent ovoid bladders, interlaced with what appears to 



