170 



THE AGRICULTURAL NEWS. 



May 21, 1904. 



On the otliei- band, corrosive sublimate apjieared to 

 exercise no .such injurious iuHueiice. 



The conclusion is, therefore, that the corrosive 

 sulilimate solution is the most useful agent, since it destroys 

 the eggs and does not affect the germinating power of the 

 cane. 



INSECT NOTES. 



Grenada Maribunta. 



The usefulness of the (Jrenada Maribunta {Polybia 

 occidentalis) is mentioned in the A(iyiculfnrnl A>/''s (Vol. I, 

 I>. 200). A mass of these insects hanging to a palm leaf was 

 recentlj- captured in the Botanic Gardens at Grenada. They 

 were probably swarming, as honey bees swarm when tliey 

 start to establish a new nest. A swarm, or colony, of 

 these insects contains three kinds of individuals — queens, 

 workers and males. The adults feed their young on insects, 

 generally caterpillars, which they partially masticate for them. 



Sugar-cane Leaf Hopper in Hawaii. 



In the last issue of the Aijvicultural News we published 

 a brief note on the occurrence of this pest in Hawaii. In the 

 Bulletin there referred to as having been issued by the 

 Hawaiian Commissioners of Agriculture and Forestry, 

 an interesting account is given, as an appendix, of the 

 chemical treatment of seed-canes containing eggs of the 

 leaf hopper, with a view to destroying these without injury 

 to the cane. The following is a brief summary of the 

 experiments which were carried out by Mr. C. F. Eckart, the 

 ])irector of the Experiment Station at Makiki : — 



The chemicals emjiloyed in these experiments were 

 hydrocyanic acid gas, corrosive sublimate, and carbolic acid, 

 and the relative resistance of the eggs of the leaf hopper to 

 these was clearly shown. Sections of cane, 8 inches long, 

 were cut from badly affected first-year canes, only such 

 portions being taken as bore evidence of hopper eggs having 

 been recently deposited. 



The canes were divided into eight lots and treated with 

 corrosive sublimate solution, in various strengths for varying 

 periods ; with carbolic acid, in various strengths for varying 

 periods : fumigated with hydrocyanic acid gas for twenty- 

 four hours ; finally one lot was left untreated. 



After this treatment the canes were placed in boxes 

 with tight-fitting glass toi)s, and the young hopi>ers which 

 hatched out were counted at intervals. 



The various solutions of carbolic acid were found 

 ineffective in destroying the eggs. The effect of the other 

 chemicals will be seen from the fact that, although after 

 nineteen days a total of 200 hoppers had hatched from the 

 untreated canes, only one had hatched from the canes treated 

 with corrosive sublimate and one from the lot fumigated 

 with hydrocyanic acid gas. 



A further series of tests was carried out to note the 

 effect of fumigating canes for varying lengths of time, and 

 of merely dipping canes in corrosive sublimate instead of 

 soaking. The gas was found to be very effective in destroying 

 the eggs when the canes were fumigated for periods of six 

 hours and over : treatment for three hours was insufficient. 

 The corrosive sublimate treatment appeared to be most 

 effective when a 2 per cent, solution was used. 



Further tests to note the effect of the different treat- 

 ments on the gerini)iating power of the canes showed, 

 however, that the length of time that the cane was in contact 

 with the gas had a marked effect on the vitality of the eye. 



Paris Green and London Purple. 



During the last cotton-growing season Paris green and 

 London purple were recouimended in the AgricuUural A'eirs 

 for use in combatiiig the cotton worm. It may be of interest 

 to our readers to have a comi>arison of these materials to 

 help in deciding which of them to use. 



London purple and Paris green are both arsenical 

 poisons ; that is to .saj', arsenic is the killing agent, and their 

 value as insecticides depends largely on the amount of this 

 element they contain. They are known as stomach poisons, 

 that is, they are effective onlj- when taken into the stomach 

 with food. 



Paris green is a chemical compound of arsenic, copper 

 and acetic acid, and the higher the percentage of total arsenic 

 and the lower the percentage of free or unconibined arsenic 

 or arsenious acid, the better the insecticide. This is because, 

 as already stated, the killing value of Paris green depends on 

 the jiroportion of arsenic compounds, and because unconibined 

 arsenic is almost certain to scald the leaves of the plants to 

 which it is applied. 



London purple is a chemical compound of calcium and 

 arsenic, and is much more variable in composition than Paris 

 green. It is also much more finely divided and much 

 lighter. It contains a lower percentage of total arsenic and, 

 generally, a considerably higher percentage of unconibined or 

 soluble arsenic, and this would have the same burning effect 

 as in the case of Paris green. 



The fact that London purple is much lighter than Paris 

 green and remains in susftension much longer is in favour of 

 London jiurple when used in spraying oiierations ; further, its 

 cost is slightly less. On account, however, of its lower 

 arsenic content, a larger amount will lie required to do a given 

 amount of work. 



In using either Paris green or London purjile as a spray, 

 ipiick lime should be added to the mixture, equal weights of 

 lime and ]>oison being used. The free arsenic combines with 

 the lime and is thereliy rendered harmless to the leaves, 

 while it retains its killing properties as a stomach poison. 

 When dusted on to the leaves in a dry state, mixed with 

 lime at the rate of one to six, neither of these poLsons is likely 

 to cause any serious injury to the plants. It is recommended 

 in spraying operations that the mixture be made up and 

 allowed to stand for from .six to ten days before being used, 

 and stirred every day : this gives time for the lime and 

 arsenic to combine. For the same reason it would prol)ably 

 be equally advantageous to mix the poison ami dry lime for 

 dusting a few days before using. 



Briefly stated, then, the characteristics of Paris green 

 and London purple are as follows : — • 



Paris green. Lomlon purjile. 



Rather heavy. Light in weight. 



Coarse. Finely ground. 



Settles quickly in water. Remains in suspension. 



High total arsenic content Low total arsenic content 



(.56 to 60 per cent.). (35 to 44 per cent.). 



Low free arsenic content Comparatively high free 



(usually about 6 percent.). arsenic content (up to 15 



per cent.). 



Uniform in composition. Variable in composition. 



