113 



has been practised. An unprecedented outbreak of the green clover 

 worm [Plathypena scabra] over the Eastern States has caused the 

 defoHation of all varieties of beans, but arsenicals were found to be an 

 effective remedy. For the striped cucumber beetle [Diabrotica 

 vittata] Bordeaux-lead arsenate mixture combined with other measures 

 has proved an effective check. Work on the sugar-beet leaf hopper 

 [Eutettix tenella] is being continued. It has been found that an 

 alternation of food-plants, involving at least two wild species, occurs 

 between the production of the disease of curly-top on beets and 

 reinoculation. Studies are being made of 350 types of resistant beets. 



It is estimated that the damage by insects to forest and shade trees 

 and their products amounts to more than £20,000,000 annually. 

 There has been no conspicuous increase in the more destructive insects, 

 except that of the spruce budworm [Tortrix fumiferand] in northern 

 New England, which has been a menace to the paper industry, and 

 a defoliating caterpillar on Texas pines. An outbreak of the southern 

 pine heei\e[Dendroctonus frontalis] was threatened. The western pine 

 beetle [Detidroclonns brevicuinis] was studied in Oregon. Figures are 

 given proving the value of remedial measures. Some 130,000 acres in 

 California were treated in 1920, and this will be continued over a period 

 of five years. The application of the Craighead solar heat principle of 

 control [R.A.E., A, viii, 365] against the western pine beetle has shown 

 that a maximum daily tempearture as low as 75° F. during a few 

 clear days will kill the beetles in infested bark removed from the trees 

 and exposed to the direct rays of the sun. Experiment has shown 

 that if mesquite, in southern Arizona, is cut for cordwood, posts, 

 etc., between 15th October and 15th January, and piled in open ricks, 

 little or no damage will be done by insects. If cut in the spring and 

 summer, as is usual, the wood is often reduced to dust before the end 

 of summer. The solar heat system was used with success ; the 

 posts, when cut, were put out in the sun and turned occasionally 

 until the bark was thoroughly dried. This kills the insects already 

 in the wood, and the dry bark is not attacked by insects destructive 

 to the wood. This makes it practicable to cufthe trees at any time 

 during the summer. The optimum times for cutting various trees 

 to avoid insect attack have been worked out. Recent studies have 

 shown that Hopkins' bioclimatic law [R.A.E., A, viii, 87] applies 

 to the continental areas of the northern and southern hemispheres, 

 and much attention has been given to applying this law to agricul- 

 tural research and economic practice. 



The increase in the area infested with gipsy moth [Porthelria dispar] 

 during the year amounts to 4,569 square miles ; these were added to 

 the previous quarantine area, which now covers 25,316 square miles. 

 In many old sites the pest seems to have been exterminated. The 

 area under quarantine for brown-tail moth [Nygmia phaeorr/ioea] 

 has been reduced by 10,677 square miles. Spraying and banding 

 operations for these pests are described. Parasitism by the enemies 

 discussed in the previous report has steadily increased in the case 

 of P. dispar, but those of A^. phaeorrhoea were less numerous, largely 

 owing to the occurrence of a fungous disease. New areas of infesta- 

 tion by P. dispar in New Jersey and New York threaten a further 

 wide distribution, unless prompt measures are taken and adequate 

 funds arc made available. 



With regard to southern crop pests, the use of calcium arsenate 

 against the cotton boll- weevil [Anthonomus grandis] has been greatly 



(1912) K 



