290 



THE AGRICULTURAL NEWS. 



September 14, 1912. 



■studies of ticks and biting insects which resulte<l in 

 giving a knowledge of the manner nf transmission of 

 malaria, yellow fever, sleeping sickness and filaria — 

 among the diseases of the human subject — and of 

 several tick- and insect-borne diseases of domestic 

 animals. This knowledge Has had the effect of causing 

 all biting and blood-sucking arthropods to be regarded 

 with grave suspicion as to the part that they may 

 play in the dissemination of disease. 



Further study of the tick led to a knovvledge of 

 its life-history and habits, from which it appeared that 

 the fully-gorged female ticks drop from the cattle in 

 order to deposit their eggs on the ground, and that 

 the young hatching from the eggs can live for only 

 a certain time without food. This led to the adoption 

 of a pasture rotation system, which consists of the prac- 

 tice of enclosing cattle on a certain area during the 

 time when the adult ticks are dropping, and removing 

 them to another, tick-free, area before the young are 

 hatched; cattle are prevented from entering the pasture 

 where the eggs are deposited, until the young should 

 all have died for want of food. This, in general, is the 

 practice by means of which large grazing areas have 

 been rendered tick-free in certain of the Southern 

 .States, and in consequence fever-free. In this manner 

 more than 100.000 square miles of territory formerly 

 included in the tick-infested area is now declared tick- 

 free, and the cattle industry of that region is thus 

 relieved from a tax, imposed by parasites and disease, 

 which was formerly very severe. 



The benefit derived from the employment of insec- 

 ticides in combating insect pests is incalculable. In 

 manv parts of the world certain crops are subject to 

 attack by insects of different sorts, and in order that 

 profitable returns may be obtained, it is necessary that 

 the effects of insecticides of various kinds should be 

 understood and the life-history of the insects known. 

 The proper insecticide can be used so as to produce the 

 ;ureatest killing effect on the in.sect and the least injur- 

 ious effect on the crop plant. 



Not many years have elapsed since the use of 

 insecticides was but little understood, and when there 

 were but few well-known substances available for the 

 purpose. At the present time there are several arsen- 

 ical and other stomach poisons, prussic acid from 

 potassium and sodium cyanides as a fumigant, and 

 a great variety of contact spray materials including 

 such substances as kerosene and other oils, soap, rosin, 

 salt, sulphur and lime, the use of which is understood 

 by planters and farmers in those localities where it is 

 necessary. 



The San .Jose scale has been a serious pest on 

 apple and other orchard crops in nearly all parts of the 

 Temperate Zone, and it is due largely to the resistance 

 of this insect to the ordinai-y spray washes that so 

 much improvement in contact insecticides has been 

 made in the past few years. 



The gypsy moth is a European insect which 

 during the past twenty-five years has been a mosli 

 serious pest to orchards and woodland in the Eastern 

 United States. When the attempt was made to control 

 this pest by means of Paris green and London purple 

 it was found that these insecticides were not effieieni;, 

 for the foliage of the trees was injured by the poison 

 even when used at strengths which were insufficient* 

 to kill the caterpillars of the moth. To meet the need 

 for a more satisfactory poison, lead arsenate was pre- 

 pared. This compound can be used in mixtures with 

 water at strengths sufficient to kill any leaf-eating 

 insect without injury to the foliage, and is thus one of 

 the most useful arsenical insecticides for spraying 

 plants, if not the most useful insecticide among these. 



Another result of great value that has come abouli 

 trom the stud}' of the gypsy moth problem is the 

 stimulus that has been given to the interest in control 

 by natural enemies; this method of control had been 

 used previously, notably in Hawaii, California, and 

 Australia, but probabl}' nowhere on the same large 

 scale. Parasitic and predatory insects from Europe 

 and Asia, where the gypsy moth occurs, are transported 

 in enormous ijuantitie.s to Eastern Massachusetts, 

 where they are carefully reared in the inseetary, and 

 colonized in the open. This work is still in an experi- 

 mental stage, although it is being carried out on 

 a large scale involving the expenditure of enormous 

 sums of money. 



The Mexican cotton boll weevil is one of the mosli 

 serious pests of an agricultural crop known. Less than 

 twenty years have elapsed since this insect spread from 

 Mexico into the cotton fields of Southern Texas. 

 During this period it has progressed steadily north and 

 eastward, until it now occupies a large part of the cotton 

 belt. No insecticides or remedial measures have 

 sufficed to stop its progress; native parasites do noti 

 sei'iously reduce its numbers, and wherever it becomes 

 established it greatly reduces the yield of cotton. As 

 a result of careful study and investigation over a long 

 series of years, it has been found that early planting of 

 early-maturing varieties greatly reduces the liability of 

 serious attack; while cultural methods such as wide 

 planting, which allows the sun to penetrate to tha 



