February, '17] 



AIlSiSLEE: CRAMBID MOTHS 



117 



The peak of the female hne is reached at 7.30, that of the male line not 

 until 12.45. Fifty per cent of the females have appeared at 9,15 and 

 75 per cent at 11.45, while of the males 50 per cent have not come till 

 12.15 and 75 per cent until 1.45. The peak representing the male 

 flight is much broader than that of the female flight and attention is 

 called to the fact that the female peak should be even more constricted 

 than it is for no correction has been made for the error caused by the 

 earlier setting of the sun later in the season. As will be seen from 

 Chart A, the time for the collection of the first moth moved back from 

 8.15 p. m. on June 3 to 7.00 p. m. in late September and October. If 



Chart A. Seasonal Records Arranged by Date op Collection 



the time of the female flight be counted from sunset instead of by the 

 clock, the maximum flight will be found to come on the average 30 

 minutes after it becomes dark enough for the light to attract, while in 

 the chart it is spread over an interval of an hour and a quarter, from 

 7.15 to 8.30. 



As a practical application of these facts it can be seen that a trap 

 lantern run from dusk until say 10.00 p. m., an average of three hours, 

 will capture over 60 per cent of the female moths that would be taken 

 in the entire night at an expense for fuel or current of about one-third 

 what it would cost to run the lights throughout the night. These 

 observations also explain the apparent discrepancy between the state- 

 ments of observers as to the sex of moths coming to light, for it is clear 



