INSECT PARASITES AND PKEDATORS~OF INSECT PESTS 



11 



or more aphids makes possible an exceedingly rapid increase under 

 favorable conditions. 



In many sections the destructive woolly aphid (Eriosoma lanigerum 

 Hausm.) of the apple is quite effectively controlled by Aphelinus mali 

 Hald. Usually the parasites occur normally in the field where the 

 aphid host is found, and climatic conditions largely determine the ; ; 

 extent to which they are able to increase. i 



Practically all species of scale insects and mealybugs are attacked 

 by minute wasps which develop within the body. Individual scale 



Figure 7. — Grain aphids parasitized by the wasp Lysiphlebus testaceipes: A, An aphid 

 showing the parasite larva within the body ; B, a dead, mummified aphid ; C, a parasite 

 emerging from an aphid, and two aphid bodies showing the typical emergence holes. 

 A and B, X 12. 



insects can normally be recognized as parasitized only after the, adult 

 parasite has emerged, leaving its exit hole, for when the wasp reaches 

 maturity it chews a small circular hole through the upper side of the 

 scale sufficiently large to permit its escape. In heavy infestations of 

 the soft brown scale {Coccus hesperiditm L.) and the black scale 

 (Saissetia oleae Bern.) on citrus, the San Jose scale on apple, and 

 various others, a very large proportion of the scales may be found dead 

 because of parasite attack and showing these characteristic holes in 

 the body wall. 



