220 INSECT PESTS OF FARM, GARDEN AND ORCHARD 



It is recommended that arsenate of lead be used against the 



tobacco horn worms and that it be applied as a dust or powder. 

 The dosage of arsenate of lead in powdered form varies from 



3J pounds to 5 pounds per acre. If applied as a spray, use from 



3 to 4 pounds in 100 gallons of water. 



To apply arsenate of lead in powdered form, without a carrier, 



use a dust gun having 

 a fan diameter of at 

 least 10 inches and a 

 special device for pre- 

 venting clogging of the 

 delivery pipe. If a gun 

 with such a device is 

 not used, it will be 

 necessary to mix the 

 arsenate of lead thor- 

 oughlywith equal 

 parts of dry wood 

 ashes. 



Apply arsenate of 



lead when there is no breeze and when dew is on the plants. 



Use only such brands of arsenate of lead as are guaranteed to 



contain at least 30 per cent of arsenic oxid, of which not more than 



1 per cent is free, or water-soluble" 



Natural Enemies. Very frequently worms are found covered 



with what seem to be small, white eggs. These are not eggs, how- 

 ever, but are the small silken cocoons 



of a little wasp-like parasite (Apan- 



teles congregatus) whose larvae feed 



internally upon the juices of the 



worm and thus ultimately kill it 



before it transforms to a pupa. Such 



parasitized worms should never be FlG . 135. Southern tobacco-worm 



destroyed, as the parasites are of with cocoons of parasite. 



more value than the damage the 



worm might do. Very frequently the caterpillars are attacked by 



a bacterial disease which causes them to turn dark and become 



shrunken and flaccid. 



FIG. 184. Southern tobacco-worm killed by 

 fungus. (After Carman.) 



