HANDBOOK ON INSECT ENEMIES OF FLOWERS AND SHRUBS 95 



the plants, and as the insects devour the 

 tissue they swallow the poison with it 

 and are killed. Certain species of chew- 

 ing insects, however, may also be killed 

 with contact insecticides. 



The sucking insects, which include 

 aphids, scale insects, mealybugs, leaf- 

 hoppers, and plant bugs, as well as plant- 

 feeding mites, are not affected by stom- 

 ach poisons because they draw their food 

 from within the plant. Therefore they 

 must be combated with insecticides 

 which, on coming in contact with the 

 body, will kill the insects by their burn- 

 ing action, by poisoning them through 

 the breathing apparatus, by suffocating 

 them, or by affecting their nervous sys- 

 tem. Among the more important con- 

 tact insecticides may be mentioned 

 pyrethrum, nicotine, sulfur, soap, cer- 

 tain organic thiocyanates, and oil emul- 

 sions. These are applied to the insect 

 and only incidentally to the plant, since 

 it is impossible to hit one and avoid the 

 other. It is essential, however, that 

 contact insecticides be applied in such a 

 manner that the material will come into 

 direct contact with the body of the pest. 



Root- or soil-infesting forms, on ac- 

 count of their underground habits, re- 

 quire a different treatment. Some may 

 be killed by working poisons such as 

 lead arsenate into the upper layer of 

 the soil or by fumigating the soil with 

 carbon disulfide, whereas others that 

 come to the surface to feed may be 

 combated with poisoned baits. 



Stem- and root-boring insects tunnel 

 through the pith, under the bark, or in 

 the fleshy roots or bulbs of plants. Since 

 these insects are difficult to reach and 

 kill with insecticides, other means must 

 therefore be used to control them. These 

 methods of control are usually given 

 under the discussion of the pest con- 

 cerned. 



Since the preparation of this publica- 

 tion, DDT has become an outstanding 

 insecticide. A brief discussion of the 

 preparation and possible uses of DDT 

 for the control of certain insects has 

 been included in an appendix (p. 110). 



There have been developed several 

 other new insecticides about which 

 there is not sufficient information avail- 

 able to warrant recommendations in 

 this publication. Some of the more 

 outstanding of these materials are 

 chlordane, benzene hexachloride, chlo- 

 rinated camphene, hexaethyl tetraphos- 

 phate, tetraethyl pyrophosphate and 

 parathion. These materials will be 

 available on the market and will some- 

 times be found in mixtures with insec- 

 ticides that are recommended. Re- 

 search work underway will provide 



information on the uses of these mate- 

 rials and of DDT, therefore you should 

 consult a local entomologist or count}* 

 agent before using the materials ou 

 ornamental plants and flowers. 



STOMACH POISONS 

 Lead Arsenate as a Spray 



Lead arsenate is widely used for the 

 control of chewing insects. Two forms 

 are available, acid lead arsenate and 

 basic lead arsenate. The former is by 

 far the more generally used and is the 

 one meant when the term "lead arse- 

 nate" is employed. The term is so used 

 throughout this publication. Lead arse- 

 nate is available commercially in pow- 

 dered form and is readily incorporated 

 in dusts or sprays and then applied to 

 the foliage on which the insect is feeding. 

 This poison may also be mixed with 

 other insecticides, such as nicotine or 

 oil emulsions, or with fungicides, such 

 as sulfur, lime-sulfur, or bordeaux mix- 

 ture. Sprays may be prepared accord- 

 ing to the following formulas: 



Use % ounce, or 3 level tablespoonfuls, 

 of lead arsenate to 1 gallon of water or 1 

 pound per 25 gallons for larger quanti- 

 ties. Make up a thin paste by adding 

 only a small quantity of water to the 

 powder. Then stir this paste thoroughly 

 into the full quantity of water. For 

 preparing larger quantities see table 1 

 on page 105. Since lead arsenate settles 

 slowly, it is necessary to shake the con- 

 tainer occasionally to maintain a uni- 

 form mixture. 



Spreaders and stickers are not usually 

 necessary. However, for plants having 

 glossy, waxy, or smooth leaves, the 

 stirring in of 2^ level teaspoonfuls of 

 powdered skim milk, or 6 level tea- 

 spoonfuls of wheat flour, or 2 teaspoon- 

 fuls of linseed oil or fish oil, or 4 tea- 

 spoonfuls of white-oil emulsion, to each 

 gallon, will aid materially in making the 

 insecticide spread and adhere better. 

 Commercial spreaders and stickers should 

 be used according to the manufacturer's 

 directions. 



The spray described above is usually 

 tolerated by most plants. It must be 

 remembered, however, that certain 

 delicate plants, and especially brightly 

 colored flowers and tender foliage, are 

 likely to be injured. For certain resist- 

 ant insects, such as the Japanese beetle 

 and the Asiatic garden beetle, the 

 strength must be increased to 1 ounce 

 (instead of % ounce) per gallon. 



A satisfactory spray combining the 

 properties of a stomach poison and a 

 contact insecticide may be made bv 



