M07.] White-grubs and May-beetles. 



453 



cent.), the only other species represented being gibbosa (2 per cent.). 

 In 1906, on the other hand, the dominant species was implicita (72 

 per cent.), the remaining species, mentioned in the order of their 

 abundance, being ilicis ( 10 per cent.), hirficula (7 per cent.), rugosa 

 (6 per cent.), gibbosa (3 per cent.), and fusca and tristis (each i 

 per cent.). This latter comparison is vitiated, however, by the fact 

 that the collections were made from different kinds of trees, those of 

 1891 mainly from butternuts and hickories, and those of 1906 from 

 poplars, willows, elms, and oaks,— another example of the fragmen- 

 tary and disjointed character of the data now available for a study 

 of this subject. 



It so happens that extensive collections of May-beetles were 

 made in 1888 both in Cook county. 111., by Westcott, and in the Dis- 

 trict of Columbia by J. B. Smith,* and a comparison of the relative 

 numbers of the dominant species in these two widely separate locali- 

 ties would be possible by their means if it were not for the fact that 

 Westcott's specimens were all taken at lights and Smith's were ob- 

 tained from trees and shrubs. As already shown, collections are 

 not comparable when made in these different ways. 



Much more nearly equivalent collections were made in 1906 by 

 two assistants of my office, one working at Urbana, in Champaign 

 county, between May 26 and June 23, and the other at Elliott, in 

 Ford county, between May 23 and June 5, the first collecting at 

 lights scattered through fields of grass a total of 142 specimens in 

 ten nights, and the second obtaining at a single light in a large corn 

 field 389 specimens in six nights. At Urbana the dominant species 

 was inversa (54 per cent.).; at Elliott it was gibbosa (71 per cent.). 

 At Urbana gibbosa was- not taken in these light-collections, and at 

 Elliott inversa made but 20 per cent, of all obtained. 



A further profitable comparison may be made of data contrib- 

 uted by Prof. M. V. Slingerland from the product of light-traps 

 kept in continuous operation at Ithaca, N. Y., during the seasons of 

 1889 ^"^d 1892.1 Four hundred and thirty-eight specimens of 

 Lachnosterna were taken during the first of these years, and 273 

 during the second. Fusca was much the most abundant species in 

 both years, making 76 per cent, of the product of the traps in 1889, 

 and 90 per cent, in 1892. Dubia'was next to fusca in 1889 (15 per 

 cent.) ; and this species and ilicis, each 4 per cent., were likewise 

 next to fusca in 1892. The similarity of the records for these two 

 years is possibly due to a three-year period of the dominant species, 



*"Proc. U. S. National Museum, 1888, Vol. II., p. 488. 

 fCanadian Entomoloffist, March, 1893, Vol. XXV., p 81. 



