2OO 



Nature-Study Agriculture 



Carbon 

 bisulfid 



Fumigating 

 the soil 

 and clean- 

 ing nursery 

 stock 



Killing 



grain 



weevils 



Caution 



Predacious 

 insects 



Another fumigating material used for killing certain 

 insects is carbon bisulfid. This is a liquid which evap- 

 orates even more rapidly than gasoline. Worms that 

 burrow in the ground and attack the roots can be de- 

 stroyed in loose, sandy soil by pouring the carbon bisulfid 

 into holes made with sharp sticks. Care must be taken 

 to punch the holes at safe distances from the roots of 

 plants. The holes are closed so that the gas will per- 

 meate the soil. Carbon bisulfid is also used to fumigate 

 nursery stock that can be placed in an air-tight box or 

 room. A dish containing sufficient liquid to fill the in- 

 closed space with gas is set in the upper part of the 

 box or room. As the liquid evaporates, the gas, which 

 is very heavy, sinks and floods the inclosure. 



Beans and peas and grain in storehouses are often 

 infested with weevils, which gnaw their way into the 

 seed and eat the inside, leaving nothing but the hull 

 (Fig. 153). These weevils are easily killed in a store- 

 house or in a tight box by fumigating with carbon bisul- 

 fid. Grain elevators and mills are regularly fumigated 

 with cyanide gas. Moths in a trunk or tight closet 

 can be got rid of by fumigating with carbon bisulfid. 

 This gas, though suffocating, is not so poisonous as 

 cyanide, though it may cause headaches ; and the liquid, 

 like gasoline, is dangerous near a fire. The gas from it 

 is explosive. 



Natural destroyers of insects. In spite of all that we 

 can do to destroy harmful insects, we still need the assist- 

 ance of their natural enemies. Every form of animal 

 life has its enemies that hold it in check, and the most 

 effective enemies of many harmful insects are other 



