6 



CIRCULAR 3 4 6, U. S. DEPARTMENT OF AGRICULTURE 



insects. At the time of pupation the larvae of this and some other 

 species of scale feeders have the habit of congregating in large 

 colonies on favored twigs or on the branches or trunk of a tree 

 (fig. 3). These colonies may contain several hundred individuals 

 and are often conspicuous. 



CONTROL OF APHIDS. 



SCALE INSECTS, AND MEALYBUGS BY THE LIBERATION OF 

 LADYBIRD BEETLES 



The fact that a number of serious insect pests have been fully 

 controlled by the liberation of ladybird beetles has led to the belief 



Figure 2. — The vedalia beetle (Rodolia cardinalis), an effective enemy of the cottony- 

 cushion scale on citrus trees: A, Larvae feeding upon an egg mass; B, pupa; C, adult 

 beetle ; D, an infested twig showing eggs, larvae, and beetles among the scales. A, B, 

 and C, X about 10; D, X 2. 



among growers that many other farm, garden, and greenhouse pests 

 can be controlled in the same way. This belief does not take into 

 consideration the limitations of the different species as regards food 

 habits, the conditions necessary for maximum increase, and other 

 influences that control their effectiveness. The vedalia beetle, for 

 instance, is effective only against the cottony-cushion scale, and its 

 liberation in the hope of checking other pests cannot possibly be of 

 any value. Likewise no control can be hoped for by the liberation 

 of the convergent lady beetle upon trees infested with scale insects 

 or mealybugs. 



