﻿28 BULLETIN 1117, I . S. I 'KPARTMENT OF AGRICULTURE. 



be tested was prepared. A temporary preservative was added to 

 the mash. The poisoned mash was so prepared that each pint had 

 an arsenic content of 1.0S per cent. The grasshoppers were fed daily. 

 Parasitism was common, causing a high daily mortality among the 

 controls. The temporary preservative in the control food seems to 

 have increased the mortality about 4 per cent. 



Horieybees. — To obtain bees of practically the same age for insec- 

 ticidal purposes, the brood chamber of a hive was moved 30 feet from 

 the old stand. On the following day all the old bees had returned 

 to the old stand, leaving only young workers (nurse bees and wax 

 generators), the brood, and the queen in the brood chamber. Fifty 

 of these young workers were placed in each of many screen-wire 

 experimental cases and were fed the spray mixtures, diluted twenty 

 times, in the following manner: One cubic centimeter of a diluted 

 mixture was thoroughly mixed with 4 cubic centimeters of honey in 

 a small feeder which was so covered with wire that the bees could not 

 waste the food. The 50 bees were given 0.038 milligram of arsenic or 

 arsenious oxid. If all consumed equal quantities, each one ate 0.0005 

 milligram of metallic arsenic when the arsenic oxid form was used, 

 or 0.00057 milligram when the arsenious oxid form was employed. 

 After the bees had eaten the poisoned honey they were given queen 

 cage candy. The number found dead was recorded daily. Great 

 care was taken to see that the bees always had plenty of food. 



STATEMENT OF RESULTS. 



Amount of food consumed. — Not having had time to calculate accu- 

 rately the amount of food consumed during all of these tests, an effort 

 was made to estimate it, but this was found possible only with the 

 food eaten by the webworms and tent caterpillars. The amount 

 consumed of the foliage placed daily in each jar of larva3 was estimated 

 in tenths and fractional parts of tenths, if necessary. On the twen- 

 tieth day the experiments were ended and the total amount of food 

 eaten during this period was used in calculating the amount consumed 

 per larva, counting one-hundredth of each daily feeding as a unit. 



Criteria of toxicity. — In order to judge the value of these methods, 

 so that the results obtained by using them can be properly inter- 

 preted, the following uncontrollable factors should De mentioned: 

 (a) The insects always varied more or less in age and size. (6) The 

 immature insects molted irregularly, causing an irregularity in feed- 

 ing, as insects do not eat during the molting period, which may last 

 from one to three days, (c) Disease and parasitism were often dis- 

 covered several days after the experiments had been started. 



(d) The temperature often varied, causing the caterpillars, which are 

 chiefly night "feeders," to eat less on cool nights than on warm nights. 



(e) Some insects die soon after eating a dose of poison, while others 

 lie "sick " for several days before dying, which causes a great variation 

 in their mortality record, (f) The sensitiveness of insects to poisons 

 varies, (g) In applving the spray mixtures it was impossible to 

 spray two bunches oi" foliage in such a manner that equal amounts of 

 arsenicals adhered to all the leaves. Moreover, the metallic arsenic 

 in the arsenites and arsenates varied slightly. No two arsenicals ad- 

 here equally well to leaves, and all of them have a tendency to collect 

 in drops, causing an unequal distribution of the poison. Neverthe- 



