37 6 Diseases of Truck Crops 



within its body (fig. 72 c-d). The egg of Lysiphlebus 

 hatches and soon begins to feed on the vital parts of 

 the Aphis. The latter gradually ceases activity and 

 finally dies and becomes mummified. When the 

 larva of Lysiphlebus reaches maturity and pupates, it 

 emerges through a circular lid cut on the back of the 

 dead Aphis. Lysiphlebus is not active at tempera- 

 tures below 56 degrees F. 



2. Of the parasites which feed externally on 

 Aphids may be mentioned the lady-bird beetle, of 

 which there are several species. These actually de- 

 vour great numbers of plant lice. Lady beetles 

 need no description, as they are well known to all 

 truckers. There are, of course, other important 

 beneficial insects such as the Syrphid and the lace- 

 winged flies. For a further description of these the 

 reader should consult Webster's original publication 

 already cited. 



(b) Beneficial Fungus Parasites. There are numer- 

 ous species of fungi which from an economic consider- 

 ation are very important. These live parasitically 

 on numerous insect pests and undoubtedly greatly 

 help in keeping them in check. Of these may be 

 mentioned species of Empusa, and of Acrostalagmus, 

 which live on Aphids or plant lice. Fungi which 

 belong to species of Aschersonia are parasitic on the 

 white fly. The fungus Botrytis rileyi is parasitic on 

 numerous caterpillars. The fungus Cordyceps (fig. 

 72 a-b) contains some important species which are 

 parasitic on the Harlequin bugs and other insect 

 pests. The green muscardine fungus Metarrhizium 



