REMEDIES AGAINST FOREST INSECTS. 31 



poultry have access to it ; or, if still partly adhering, it may be ripped from the wood 

 by barking tools and bnrnt; bnt it is a tangible and serious cause of injury, and if 

 our landed proprietors were fully aware of the mischief thus caused to their own trees 

 and those of the neighborhood they would quickly get rid of it. 



INSECTICIDES AND MEANS OF APPLYING THEM TO SHADE AND FOREST 



TREES.* 



This subject may be divided into two parts, viz, (1) a discussion of 

 insecticides and (2) a discussion of insecticide apparatus. 



(1) INSECTICIDES. — Remedial measures against forest-tree insects 

 are not different from those employed against the insect enemies of fruit- 

 trees or farm and garden crops. The same species are frequently the 

 culprits in both cases; and, in general, insects of the same orders and 

 families, having similar habits and requiring similar treatment, attack 

 wild-growing, woody plants and the cultivated sorts. 



For convenience of treatment, the first part may be considered under 

 the following heads : Insecticides which act through the food ; insecti- 

 cides which act by contact; fumigants and gases. 



Insecticides which act through the food. — These insecticides 

 are available against all mandibulate insects that feed externally on the 

 leaves, such as the larvse of Lepidoptera, larvae and adults of leaf- 

 feeding beetles, and saw-fly larvae. Gall-insects, leaf-miners, and in- 

 sects which burrow beneath the bark or in the wood cannot be con- 

 trolled by these means. 



It would be possible to enumerate under this heading a large number 

 of substances depending for their effects on arsenic, strychnine, or other 

 poisons, but I prefer to limit the discussion to the consideration of two 

 substances which are now commonly used to the exclusion of nearly all 

 others. 



Paris green and London purple. — The arsenites of copper and cal- 

 cium, Paris green and London purple, are so well known as not to 

 need particular description here. The safety and efficiency with which 

 they can be used and their slight cost fully satisfy all the demands 

 of practical work. 



As containing records of a general nature, together with full in- 

 structions for the use of these poisons, I cannot do better than quote 

 from Bulletin No. 10 of the division of entomology,t the conclusions 

 being based on experiments under my direction, especially by the late 

 Dr. W. S. Barnard. 



The quotation refers particularly to work against the imported Elm 

 leaf- beetle (Galeruca xanthomelcena) and deals with the treatment of 

 elm trees only, but the results obtained may apply to other insects 

 infesting various shade and forest trees. The recommendation given 



'Prepared, at the author's request, by Professor Riley. 



t Our Shade Trees and Their Insect Defoliators, by C. V. Riley, Entomologist, 

 Washington, 1887. Second revised edition, 1888. 



