REPORT OF THE DIVISION OF ENTOMOLOGY AND BOTANY 49 



SESSIONAL PAPER No. 16 



March 16. — The bahince of the larva3 in these two nests were fumigated a fifth 

 time. The strength was the same as on March 12, but the exposure was lengthened to 

 three hours. The larva) were active in the jar before the fumigation. Result: 32 

 larva3 were found the following day to be dead, but the larger number were still alive. 



March 18. — Two new nests on pear were fumigated at a strength of 3| ounces of 

 cyanide of potassium, 3^- ounces of sulphuric acid and 11^ ounces of water to the 

 128 cubic feet of space. This is three times the strength used in the federal fumiga- 

 'ticn houses for the destruction of the San Jose Scale on stock imported into Canada 

 under the San Jose Scale Act. These two nests had been kept in cold storage until 

 the day previous, and on bringing them into a warm office the larvae soon began to 

 leave the nests, and by the time the fumigation took place, by far the larger number 

 of the caterpillars had emerged. The fumigation lasted for one hour. Result : only 

 18 larvaj dead. 



On March 19 it was discovered that the chamber was leaking somewhat. It was 

 at once tightened with new felt. 



March 22. — The larvae from the two nests fumigated on March 18 were again 

 submitted to ths same strength, but the exposure was lengthened to two hours. Result : 

 about 30 larva) killed, the balance active. 



March 29.— Other larva), not previously fumigated, but many of which had been 

 out of the nests for a considerable time, were exposed to the same strength of gas, 

 and length of time, as those fumigated on March 22. In this jar there were 55 living 

 larvce. At first it was thought that 50 of these had been killed, but a later examina- 

 tion showed that only 37 were dead and that the rest were reviving. 



The above experiments, although not very extensive, go to show that fumigation 

 with hydrocyanic acid gas evidently cannot be relied upon as a practical remedy for 

 this insect when in its winter condition. At the above strengths, even when the 

 fumigation chamber was tightened, only a very small percentage of larvae which had 

 left the nests were killed. It would certainly require considerably greater strength 

 and much longer exposure to kill the larvse when within the nests, and, owing to the 

 tough, closely-woven nature of these nests, the outcome would be very doubtful. 



The following notes on some of the more important injurious insects of the past 

 year have been compiled by Mr. Arthur Gibson, Chief Assistant, mainly from memo- 

 randa gathered by the Division of Entomology and Botany prior to the decease of the 

 late head of the Division, Dr. James Fletcher. 



THE CHIEF INJURIOUS INSECTS OF 1908. 



INSECTS INJURIOUS TO CEREAL AND OTHER FIELD CROPS. 



(By Arthur Gibson, Chief Assistant.) 



During the season of 1908 very few of the well-known insect enemies of gram 

 crops were injuriously abundant. 



The Hessian Fly, Mayetiola destructor. Say. — From Manitob<.c a single report 

 came to the Division of injury by this insect. The only occurrence in Ontario which 

 came under our notice was of a rather important outbreak which occurred in some 

 wheat fields near Ottawa. Plants were noticed to be infested about the end of May, 

 and in some places the attack was quite serious. In fields where the soil was poor and 

 where the unfavourable weather conditions had weakened the plants, probably as many 

 as fifty per cent were infested by the Hessian Fly. In other fields where the soil was 

 better, the plants were stronger and better able to withstand the unfavourable condi- 

 tions of the season, and in these fields the loss from Hessian Fly would amount to 

 about five per cent. From collected material, both sexes of the flies emerged on June 



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