398 INSECTS AFFECTING VEGETATION 



within the piles to be raised to a uniform high temperature. The 

 building should be closed tightly and the temperature raised to 120 

 F., remaining at this point for at least 6 hours. A longer time is 

 advisable, as the penetration is thereby increased. Bags of shelled 

 stock are with difficulty heated to the center without a long expo- 

 sure, and although the larvae work near the outside of the bags they 

 may crawl to the center to escape the great heat, which tends to 

 make them much more active. 



The temperature should not be raised above 125 F. in the case 

 of peanuts, as experiments have shown that a slight degree of 

 blanching, or slipping of the skin, takes place in shelled Spanish 

 nuts exposed to such a heat. Virginia peanuts, being much less 

 oily, are not affected, while no injury whatever takes place in the 

 case of unshelled nuts. Germination is likewise unaffected, peanuts 

 exposed 6 hours to a temperature of 140 germinating better and 

 more quickly than those unheated. A temperature of 116 is fatal 

 to insect life in a short time, larvae, pupae, and adults of the Indian- 

 meal moth dying in less than one-half hour, when exposed. 



SUBSTANCES THAT REPEL. 



There are a number of substances that are more or less useful 

 for the purpose of driving insects away from places where they 

 would do harm if unmolested. I give below a few of the most 

 important. 



Napthaline, Gum-camphor, and Moth Balls. Napthalinei 

 crystals are much used in insect boxes and in boxes or trunks where 

 furs, feathers or woolen goods are kept, for the purpose of keeping 

 out insects that feed on these animal products. It is probably the 

 best single chemical that can be used for this purpose. Gum-cam- 

 phor is also much used for the same purpose and moth-balls are a 

 combination of these two volatile substances. These materials can- 

 not be used to kill insects, but only to repel them. 



Tobacco. Tobacco, in the form of dust, or otherwise, is often 

 used for the same purpose as the preceding, but to be effectual must 

 be used quite freely. 



Ashes. Ashes, particularly from wood, are frequently used to 

 dust upon plants after a rain or while the dew is on and often result 

 in the insects disappearing. Particularly is this true in case of flea- 

 beetles and the cucumber beetle when feeding upon leaves. Ashes 

 do not kill the insects, but they make the food distasteful, so the 

 insects are driven to other plants. 



Lime, Plaster, and Road Dust. These substances are also used 

 like ashes as repellents, but are of little or no use for the destruction 

 of insects. (Bui. 71, Col. Agr. Exp. Sta.) 



Phosphorus. Proprietary preparations containing this sub- 

 stance as their active ingredient are to be bought of most druggists, 

 and are effective against roaches and. some other vermin infesting 

 dwellings. They contain only a small percentage (about 1.50) of 

 phosphorus, the rest consisting ordinarily of sugar, sirup and 

 starch. 



