30 



78.8 percent (4541 implicita out of 5758 of all species) ; in 1910, 5.5 

 percent; and in 1911, .8 of 1 percent (88 of implicita in a total of 

 10,203). The recurrence of a strongly marked implicita year in east- 

 central Illinois in 1909, after the great preponderance of the species 

 at Urbana in 1906, is consistent with a three-year life cycle for the 

 species. In southern Illinois our ratios were: 1907, 3.8 percent; 

 1908, 4.4 percent; 1909, 22.2 percent; and 1910, .6 of 1 percent. A 

 notable feature of the southern Illinois record is the dominance in 

 the south of implicita in 1909, when it was overwhelmingly dominant 

 in central Illinois also. 



Our earliest dates for implicita in northern Illinois vary from 

 May 20 to 28 in the different years, and our latest, from June 6 to 

 25, the period of greatest abundance coming from the last two or 

 three days of May to about the 10th or, in one case, to the 21st of 

 June. Our central Illinois dates of earliest appearance range finm 

 April 27 to May 15, and those of latest occurrence, from June 5 to 

 July 1. The time of its greatest abundance commonly fell between the 

 last days of May and the middle of June or a little beyond, but in 

 the relatively early season of 1906, it came between May 17 and June 

 4. In southern Illinois we have found the beetles out as early as April 

 21 and as late as July 1, with the month from May 20 and June 21 

 as the time when our collections of the species were largest. 



Implicita is unusually definite in its choice of food, being rather 

 closely limited to apple, poplar, and willow. Of our 15,724 specimens 

 of this species collected from food-plants within our six-year period, 

 5107 were from poplar-trees, 4335 from willows, and 4279 from the 

 apple — 92.5 percent of the whole number from these three kinds of 

 trees. The remaining 8.5 percent were divided in only insignificant 

 numbers over twenty-four other kinds of trees and shrubs, the largest 

 ratios being from oak and elm, 1.5 percent for each. In 1906, when 

 2517 specimens of this species were obtained in collections regularly 

 made from only four kinds of trees, 2311 of them were from poplars 

 and willows, and 206 from oaks and elms. 



The contrast in food habits between this species and liirticula, 

 both widespread thru out the state and extraordinarily abundant es- 

 pecially in central Illinois, is interesting and suggestive. In the table 

 on p. 60. the relative importance to the species of each food-plant is 

 shown by the ratio which the number of specimens taken from the 

 plant bears to the total number of the species collected from food- 

 plants of all descriptions. Since the main features of the food are 

 the only ones of any significance in this comparison, ratios of less than 

 1 percent are indicated only by a check. From this table it will be 

 seen that 30,213 specimens of liirticula and 15,724 of implicita were 

 the numbers obtained from food-plants during our six years' collec- 

 tions; that oak and hickory are represented in the food of liirticula 

 by 43.6 percent and 18.8 percent respectively, blackberry giving the 



