202 ENTOMOLOGY. 



luxuriant plants; severe rains destroy them, as do late cold 

 rains, while frequent summer rains favor their development, 

 and hot, dry weather is destructive to them. 



The. natural enemies of the cotton-worm are numerous; 

 birds, toads, lizards, and certain kinds of ants prey on them, 

 besides ground-beetles, bags, and a number of species of 

 ichneumons, including an egg-parasite (Trichogramma). 



REMEDIES. While many moths can be destroyed by lights, the 

 universal remedies by which great numbers of the worms are destroyed 

 are Paris green, petroleum emulsions, and Persian insect-powder; 

 and among devices for applying the liquid insecticides the centrifugal 

 or cyclone spraying-nozzle is the most efficacious. 



The dry preparation is one pound of the green to from 20 to 35 

 pounds of cheap flour, or, instead of flour, land plaster (gypsum) or 

 cotton-seed meal. The best preparation of Paris green consists of 1 

 pound to 40 gallons of water. London purple may be applied dry, 

 using 2 pounds to 18 of flour, etc. ; or wet, one half a pound to 50 or 

 55 gallons of water. 



A fine spray of kerosene oil applied to the leaves will kill all the 

 worms in a remarkably short time; but as petroleum in any form 

 injures the plant, the oil must be so diluted as to injure only the worm 

 and not affect the plant. Prof. Barnard suggested the use of milk as 

 a diluent, and finally an emulsion was perfected by Mr. Hubbard for 

 orange insects, which is now in general use. Cotton-seed emulsions 

 are less efficacious than those made with petroleum. 



Another important insecticide for field use against the cotton- worm 

 is pyrethrtim or Persian insect-powder, applied by a bellows, or in 

 water solution, the powder being simply stirred up in water (200 

 grains to 2 gallons of water), applied by means of a fountain-pump 

 or an atomizer. The inventions for applying insecticides, both dry 

 and wet, are very fully described and illustrated in Riley's report on 

 the cotton-worm, forming the fourth report of the U. S. Ento- 

 mological Commission. 



Injuring the Potato. 



The Colorado Potato-beetle (Leptinotarsa W-lineata Say). 

 Devouring the leaves, a large, thick-bodied, reddish- 

 orange grub, with black spots on the sides, changing usually 

 under ground into a large hemispherical yellow beetle, 

 about half an inch long, with ten wide black stripes on the 

 back; three broods of the grub appearing in one season. 

 Originally an inhabitant of Colorado, this destructive beetle 

 is a constant plague all over the Northern and Middle 



