379 



end of August till the beginning of September. The larvae may thus 

 be carried for miles, and though countless numbers perish, others give 

 rise to the sudden heavy infestations of plantations previously free 

 from them. Before beginning to feed the young larvae spin their sill^y 

 bags, and these become entangled on the feet of birds and may be 

 carried long distances to new situations. The larvae damage trees 

 by completely defoliating them, beginning at the top and working 

 downwards, so that by December the majority of the trees are bare 

 and reddish brown in colour. The greatest enemy of the larvae is 

 moisture, which quickly proves fatal to them, either by collecting 

 in the bags and inducing fungus disease, or by causing a digestive 

 disorder due to eating wet food. Four species of Hymenopterous 

 parasites and the same number of Tachinidae have been bred from 

 the caterpillar of this bagworm, but under the most favourable con- 

 ditions only 24 per cent, are killed by them. Predaceous enemies, 

 such as the yellow weaver bird and two species of rats, destroy large 

 numbers, as also does a deadly fungus disease due to Isaria pstjchidae. 

 This however does not afford an effective control owing to the difficulty 

 of distributing the spores so as to reach the tops of the trees where 

 the young larvae are feeding, the result being that only 22*5 per cent, 

 are destroyed by it. 



Swingle (D. B.) & Morris (H. E.). Arsenical Injury through the 

 Bark of Fruit Trees. — Jl. Agric. Research, Washington, D.C., viii, 

 no. 8, 19th February 1917, 35 pp., 11 tables, 6 plates. [Received 

 26th June 1917.] 



Extensive experiments undertaken to determine whether trees are 

 injured at the crowns by arsenical spray mixtures are here described. 

 The tests were made almost entirely upon apple trees, the solutions 

 being applied to the trunk, branches or larger roots by means of an 

 absorbent cotton bandage protected with medical gauze and moistened 

 ■\\itli distilled water, and in some cases covered with dental rubber. 

 In the case of the crown, the treatment was effected by removing 

 some inches of soil and pouring the solution round the tree, afterwards 

 lightly replacing the soil, thus giving, as nearly as possible, the condi- 

 tions which obtain after spraying. In trees with smooth bark 

 it was found that injury began round the lenticel as a small indefinite 

 zone of a darker colour. For a week or two this became darker in 

 colour, and increased slightly in size. It soon ceased to grow, became 

 nearly black in colour and very sunken, so that a crack appeared 

 between the injured and healthy tissues. Absorption through a 

 wound caused a long narrow streak running upwards and downwards 

 through the wood. The leaves also showed signs of injury, becoming 

 first dull and of a lighter green, either over the whole surface or in 

 spots or patches, which later became dry, brown and crisp. Of all 

 the arsenical insecticides, calcium arsenite and arsenic trioxide are 

 the most injurious when they reach the inner-bark. This happens 

 on old trees and those with rough bark by way of the cracks in the 

 bark and through wounds, the injury being much worse on wounded 

 limbs. Both washed and unwashed chemicals of the purest brands 

 caused severe injuries, the addition of lime apparently making no 

 difference. The variety of apple had no influence on the extent of 



