Observations on Insects affecting the Turnip Crops. 75 



with aphides'^ and the growth of the plants and the roots is re- 

 tarded. 



168 aphides were seen upon one small turnip-leaf in July. 



It is by thrusting their beaks, called the rostrum^ into the plants, /, 

 and imbibing the sap, that they injure our crops. 



The females are both oviparous and viviparous : they are 

 winged and apterous. 



In autumn they lay e^^s , w hich hatgh th e fo llowing spring -. /^ 



The eggs are laid! upon the~l eaves, undertlie buds, and other 



secure places. 



The females bring forth young, without sexual intercourse, for 

 many generations. ^ 



Their increase is prodigious : it is calculated that one female 

 might be the progenitor of upwards of 5900 millions of de- 

 scendants in one year. ^ 



The eggs hatch about the period ^f north and north-east 

 winds, in M arch and A pril. 



Their increase is accelerated by damp sidtry weather as the 

 season advances, i-^ 



Electricity probably often causes their simultaneous appearance. 



The aphides can wcdk about as soon as they are born^ and are 

 able to do so until their lives are terminated. 



Abundant in August, September, and October, and even at the 

 end of November, secreted beneath the diseased leaves. ^ 



It is doubtful if these species deposit the saccharine matter 

 called honey-deiv. 



Cutting off the infested leaves and destroying them on the 

 spot, or carrying them away in sacks to be burnt, is the best 

 remedy. 

 ^ To bacco and Um e_ water will kill the aphides^. Lime-dust, if 



strewed in cTry weather, is an effective cure^ . "^ 



i^ They often d p not suffer from heavy rains. 



Insectivorous birds, and various i7isects, our best friends in 

 checking their increase. 

 y_. The lady-birds and their larvw are particularly useful in de- 

 stroying the aphides. 



Immense swarms of the lady-birds sometimes appear on our 

 shores. 



A little fly called Aphidius lays its eggs in the aphides, and 

 when they hatch the maggot destroys the aphis. 



These again become the victims of other small flies, called 

 Ceraphron Carpenteri, Cyrtogaster vulgaris, and Colax aphidii. 



Some of the Cynipsidce, or gcdl-flies, are also parasites, which 

 live in the aphides as maggots. 



Four other wasp-like flies collect the aphides as food for their 

 young. 



