28 



as the next most abundant species (implicit a) , and in southern Illinois 

 it was surpassed in numbers only by forbesi, for which we made so 

 special a search in midsummer that our recorded numbers of it are 

 probably disproportionate. This predominance of the species in cen- 

 tral Illinois is not due to excessive numbers in any one year, but is 

 well marked in four of the six years during which our field work was 

 done. While the central Illinois ratios of Mrticula for 1907 and 1909 

 are only 9.1 and 12.8 percent respectively, those for the four remain- 

 ing years range from 56.9 to 70 percent, with an average of 64.7 

 percent. 



I do not find in these general data any clue to the life history 

 of the species, but this must be found, if anywhere, in the May-beetle 

 population of smaller areas than one of the principal divisions of the 

 state. Such an examination of our more local data shows us that 

 Mrticula was not abundant at Urbana in 1906 ; that it was nowhere 

 dominant in 1907 ; that it was immensely dominant in central Illinois 

 generally in 1908, and possibly at Carbondale, in southern Illinois 

 also, where 349 of the 1242 of our specimens of Phyllophaga were of 

 this species ; that it was perhaps subdominant in McLean county in 

 1909 ; that it was strongly dominant in 1910 at Galesburg and dis- 

 tinctly so (with inversa) at Urbana (Mrticula, 871; inversa, 715). 

 and also at Carbondale, at which latter place, however, its numbers 

 were approached by micans and veJiemens (Mrticula, 1813 ; micans. 

 1379 ; veliemens, 1267) ; and that at Urbana it was strongly dominant 

 in 1911, comprising nearly two thirds of the 10,203 specimens col- 

 lected there, but followed at some distance by inversa (2107 inversa 

 to 6501 of Mrticula). As only 102 May-beetles were collected in cen- 

 tral Illinois in 1913, the fact that 58 of these belonged to Mrticula 

 probably has little importance. Its prevalence in central Ilinois in 

 1908 and again in 1911 is consistent with the supposition that it has 

 a three-year life cycle ; but as this apparent periodicity in seasons of 

 unusual abundance might well be due to other causes, we are thrown 

 back upon breeding experiments for this detail of the life history. 



Our earliest open-air collections of Mrticula have been made 

 from April 28 to May 10' in different years in central Illinois and 

 from April 4 to 18 in southern Illinois, and our latest collections from 

 June 30 to July 21 for the central section and from June 17 to 23 

 for the southern. The periods of the greatest abundance of the species 

 have extended from about the middle of May to the middle of June 

 for central Illinois, and from the last of April to the last of May 

 for the southern part of the state. 



By following the plow in central Illinois, my field assistants have 

 obtained from the ground 822 specimens of Mrticula in many fields 

 at twenty-six dates between April 6 and June 16, as well as 15 more 

 specimens on the 16th of July. The April-June series were probably 



