igoS] Biological Notes on Potato Beetle 157 



THE EGG. 



I . Length of Lnstar. The duration of the egg instar has been 

 determined for over seven hundred cases at dif=ferent dates during 

 the breeding season and the records are tabulated in table I. 

 Each separate batch of eggs was confined immediately after 

 deposition in an ordinary pasteboard pill-box, and they were 

 thus in darkness. Moisture was supplied by the daily addition 

 of fresh foliage. The temperature was the most apparent 

 variable factor during development. 



The effective temperatures were not determined in five cases, 

 but enough are recorded to show that during the period covered 

 the instar is about inversely proportional to the variation m 

 temperature; that is to say, when the instar is long, the daily 

 average effective temperature is low, and conversely. These 

 records should have been made from a thermograph and calcu- 

 lated on the basis of hours; instead, I had to depend on maxima 

 and minima for daily averages, and hence fractions of days had 

 to be largely ignored. Undoubtedly, therefore, the records of 

 effective tempe'^.-atures in table I are more or less inaccurate. 

 Forty-three degrees Fahrenheit is here assumed to mark the point 

 of the inception of activity and reproduction, which as yet has 

 not been determined for decemlineata. Wheeler (1889, p. 355) 

 records the period of embryonic development as 6 days. 



2 . Number of Eggs Deposited. Our ignorance in regard to the 

 average reproductive capability of our most common insects is 

 profound, and this fact is weh illustrated in the case of the Colo- 

 rado Potato Beetle. I have simply to point out the fact that 

 up to within the past two or three years its maximum oviposition 

 was supposed to be in the neighborhood of 500 eggs, more probably 

 less than that number. My observations on this point in 1907 

 are of importance because they show that this estimate is 

 wrong, and also that with how slight an effort many of the facts 

 of this nature can be learned more or less definitely. It was 

 unfortunate that with the time at my disposal I was unable to 

 make a large series of observations, thus obtaining maxima, 

 minima, range, and average. William Lawrence Tower (1906) 

 was the first to record actual observations on this point; appar- 

 ently from a number of observations, on page 237, table 104, 

 he records a range in oviposition of from 190 to 600 eggs, with 

 an average of 450. The number of batches of eggs deposited 

 ranged from 4 to 18 with an average of 12. Later (July 23, 1907, 



