Insect Enemies and Allies 



199 



their way into the fruit. If the tree is sprayed with 

 lead arsenate after the petals fall and before the calyx 

 cup closes (Fig. 151), the larvae are killed. But if 

 the spraying is not done before the calyx closes, as it 

 does very soon, the poison does" no good. In the case 

 of scale we have another example showing how necessary 

 it is to choose the right time for spraying. Scale insects 

 are soft-bodied. They crawl about for a few days when 

 first hatched and then settle down in one spot, where 

 the female insects cover themselves with a scaly coat- 

 ing which protects them. The time to spray for scale 

 is evidently when a new brood hatches. 



Fumigation. A method of killing insects that is more 

 certain than spraying is fumigation. This consists in 

 producing a poisonous gas (usually cyanide gas) under 

 a tree and letting it rise among the branches. To keep 

 the gas from escaping, a tent is placed over the tree, 

 and the gas is generated under it. The gas is held in 

 for about an hour (Fig. 152). Cyanide and its gas are 

 very deadly. Extreme care must be taken to avoid 

 inhaling any of the gas. 



When to 

 spray for 

 codling 

 moth; 

 scale 



Using 



cyanide 



gas 



Caution 



u. s. D. A. 



FIG. 152 A tent properly adjusted over a tree that is to be fumigated. 



