1923 



ENTOMOLOGICAL SOCIETY. 



19 



observed to be eating the borers in cages, and from one series alone had taken 

 1,200 borers, but no observations were made at the time on their methods of 

 attack. It is possible that these ants may have some slight effect in springtime, 

 in reducing the numbers of borers in any field where they might occur. The 

 Tachinid fly, Exorista nigripalpis Towns, which was found in 1921 to be a para- 

 site on from four to eight per cent, of larvae in one field, was practically absent 

 in 1922, and a very small and practically negligible number of larvae were des- 

 troyed by it. 



It will be seen that we have found very few natural enemies of the borer 

 in Canada so far, and that the attacks of these parasites have very little effect 

 in reducing the number of larvae. Consequently it was found this spring that 

 there were enough borers in the areas under observation to practically ensure 

 a heavy infestation of the 1922 crop. 



Pupation 



Pupation began this year about two days later than last year, but the pupal 

 periods showed certain differences, as tabulated below: 



1921 



1922 



1. Length of pupal period, in days: 



Males only, average 



Females only, average 



Both sexes, average 



2. Shortest pupal period, either sex 



Longest pupal period, males only 



3. Season of shortest pupal periods 



Average temperature for these periods 



4. Relative numbers of each sex. — 



Males only 



Females only 



12 



10.19 



11.7 



8 

 16 

 June 24 to Tuly 

 86°-87'° F. 



14 



15.72 

 14.63 

 15.29 

 11 

 21 

 July 7 to 12 

 75° F. 



56.38% 

 43.62% 





51.08% 

 48.92% 



Rates of Pupation under Various Conditions 



Experiments conducted over both years, showed that the rates of pupation 

 of the corn borer larvae varied under different conditions. 



1. Extreme Dryness. In the autumn of 1921, thirty-nine larvae were placed in 

 a corrugated roll of paper in which they had spun up, in a dry can with a ventilated 

 lid, and were kept indoors in a dry place all winter. They were examined from 

 time to time all during the summer of 1922. By August 17 twenty-nine had 

 dried up; by September 30, one only showed very slight movement and was 

 very shrivelled. The rest were dead. 



2. Exposed to Outside Conditions. As opposed to the experiment above, 

 nearly one hundred larvae were placed in a can with a perforated lid in precisely 

 the same way as above, but the can was left outside on a window sill all winter, 

 exposed to all conditions of weather, By the end of the emergence season in 

 1922, less than a dozen larvae had failed to come through as moths and had 

 died. 



3. In Piled Stalks. In the case of stalks which had been in stooks in the 

 field all winter, as opposed to stalks which had been lying loose on the ground 

 during the same period, it was found that the moths emerged sooner from the 

 loose-lying and damper stalks, than from the former drier material. 



4. Debris Gathered from the Field. From debris and stubble picked in early 

 spring from a cornfield and heaped in a pile under the shade of an apple tree, 



