325 



Pupation is completed by June of the second year following oviposition. 

 The only possible remedial measure on large shade-trees would 

 be to prune all small dead branches and burn them, but the cost of 

 labour of such a measure is practically prohibitive. It is possible 

 that spraying the trees with Bordeaux mixture or lime-sulphur might 

 act as a preventive. A Hymenopterous parasite, a new species of 

 Tetrastichus, has been reared from larvae and pupae taken in the 

 burrows of this twig-girdler. 



Graham (S A.). Potato Spraying in Minnesota. — 17th Rept. Minnesota 

 S'ate Entomologist, Agric. Expt. Sia., Univ. Farm, St., Paul, 1st 

 December 1918, pp. 21-31, 1 fig. [Received 21st May 1919.] 



Experiments to test the value of various insecticides for spraying 

 potatoes were made during the spring of 1918 on a modified co-operative 

 scheme, all the spraying, mixing of materials and taking of observations 

 being done by the Experiment Station, and a standard type of spraying 

 machine being used on land owned by a single person. The pests 

 present were Leptinofarsa decemlineata. Say (Colorado potato beetle), 

 Epitrix cucumeris, Harr. (potato flea-beetle), and Empoasca mali, 

 Le B. (leaf-hopper). In addition to these Lygus pratensis, L. (tarnished 

 plant-bug) and several other bugs were common. 



The stomach poisons tested were lead arsenate, zinc arsenite, 

 calcium arsenate and Paris green, each of these being applied with and 

 without Bordeaux mixture. The arsenical sprays were applied to 

 the early and late potatoes on 13th and 14th June when the plants 

 were 8 and 6 inches high respectively and infested with L. decemlineata 

 and E. cucumeris. All four of the poisons tested were equally effective 

 under ideal conditions against L. decemlineata, the quantities used 

 being 2 lb. to the acre, or 4 lb. to each 100 U.S. gals, of liquid, except 

 in the case of Paris green, which was 1 lb. to the acre or 2 lb. to each 

 100 U.S. gals, of liquid, and each was applied with and without 4-4-50 

 Bordeaux mixture. All of them, however, appeared ineffective as a 

 poison or deterrent for the adult flea-beetles. A second spray applied 

 about 1st July with similar dilutions gave almost perfect control 

 in each case, the plants then presenting a large unpoisoned surface, 

 but the beetles being present in only small numbers. On another 

 block spraying was deferred till 29th June, Paris green, lead arsenate 

 and zinc arsenite being used at the above dilution. The treatment 

 was repeated on 23rd July when the infestation was so slight that it 

 was not commercially profitable. A heavy dose of 2 lb. lead arsenate 

 and 1 lb. Pans green per acre was used, the beetles being thereby 

 almost entirely exterminated. 



From these experiments it is evident that all four poisons are equally 

 effective against L. decemlineata imder favourable conditions, and 

 that the choice of one of them must depend upon its cost and adhesive 

 power. To determine the latter point a series of experiments with 

 glass slides and geranium leaves was undertaken, and it was found 

 that Paris green was the least, and calcium arsenate the most adherent, 

 zinc arsenite and lead arsenate being intermediate. In computing 

 the cost of an arsenical the proportion of arsenic present must be 

 considered, and thus Paris green and lead arsenate cost about the 

 same, for though the price of the former is double that of the latter. 



