﻿ARSENICALS. 27 



(mostly Melanoplus femur-rubrum Do G.), oelonging to Orthoptera*; 

 and honeybees (Apis mellijica L.), belonging to Hymenoptera. An 

 atomizer was used in all the spraying experiments. 



Silkworms. — Silkworm larvae were fed leaves treated as follows: 

 Mulberry leaves were sprayed with the various mixtures, the con- 

 trol leaves being sprayed with tap water only. After having been 

 dried in the air the leaves were cut into small strips which, were then 

 placed in small wire-screen cages. An effort was made to put ap- 

 proximately the same quantity of food in each cage, so that a rough 

 comparative estimate of that consumed could be made. In 1919 

 about 50 normal silkworms in the second instar (varying in length 

 from 7 to 12 millimeters, with an average of 10 millimeters, and not 

 ready to molt) were put in each cage, but in 1920 silkworms in the 

 third instar (18 to 30 millimeters long, average 25 millimeters) were 

 employed. Counts were made daily except on Sundays, the cages 

 being cleaned and treated food being renewed at the same time. No 

 disease was noticed among these larvae. 



Webworms. — The webs were collected in the fields from a variety of 

 plants on Monday. At the laboratory these webs containing web- 

 worms were kept in large cages with a small amount of food until 

 Tuesday noon, when the larvae, which were then very hungry, were 

 well mixed according to size (all instars but first one). Tuesday 

 morning approximately the same quantity of mulberry foliage was 

 placed in each of several wide-mouthed bottles containing water. 

 It was then sprayed, and, when dry, a bottle with contents was placed 

 in a large battery j ar, 8 inches in diameter by 12 inches high. Tuesday 

 afternoon approximately the same number of webworms were placed 

 in each jar, and thereafter the sprayed food was renewed daily. 

 Thus by starting each set of experiments on the same day of the week, 

 the days (Sundays) on which no records were taken always fell on 

 the fifth, twelfth, and nineteenth days of the tests. Very little 

 disease or parasitism was noticed among these larvae. 



Tent caterpillars. — The tents, collected in the fields on wild cherry 

 trees, were handled in the same manner as the webs of webworms. 

 Sprayed wild cherry foliage was placed in the jars daily and counts 

 were made daily. Owing to the prevalence of the "wilt," or polyhe- 

 dral disease, it was necessary to test these larvae while in the earliest 

 instars. 



Potato-beetle larvse. — Collected on potato plants, these larvae were 

 placed in cheesecloth cages, 9 inches square by 12 inches high. They 

 were so well mixed before being placed in the cages that each cage 

 contained about the same number in the various instars. Spra} T ed 

 potato-plant foliage was given to them daily. Parasitism was com- 

 mon only in the last instar. 



Grasshoppers. — The fourth, fifth, and sixth (adults) instars caught 

 in the fields were tested in the cheesecloth cages. Having been 

 unable to use the foregoing spray mixtures, bran mash, mixed with 

 some of the same powdered arsenicals, served as food. Using Paris 

 green (sample 64, containing 55.09 per cent As 2 3 ) as a standard, 

 and the regular formula 8 as a basis, a modified formula was derived, 

 whereby a pint of poisoned bran mash containing each arsenical to 



8 Bran, 25 pounds; Paris green, 1 pound; lemons or oranges, 6; molasses, 2 quarts; and water, from 

 2 to 4 gallons. 



