452 



Bulletin No. 116. [August, 



' In 1891, when 1,874 specimens were'taken from lights and 836 

 from trees, the dominant species at Hghts was inversa (76 per cent.), 

 hirticula, tristis, and fusca following with ratios of 10 per cent., 7 

 per cent., and 5 per cent, respectively. The dominant species from 

 trees, on the other hand, were hirticula (42 per cent.), inversa (32 

 per cent), and fusca (23 per cent.), the only other species being 

 gibbosa (2 per cent.). The results for 1906, when 142 specimens 

 were taken at lights and 3,484 at trees, were equally discordant. 

 The leading species at lights this year was inversa (54 per cent), 

 rugosa and implicita following with 24 per cent, and 15 per cent, 

 respectively; while the leading species in trees was implicita (72 

 per cent.), followed by ilicis and rugosa, 10 per cent, and 6 per cent, 

 respectively. 



Variation of Numbers in Different Localities and Years. — The 

 numbers of the several species vary greatly from year to year in the 

 same locality, and in different localities during the same season. It 

 consequently happens that the dominant species in a locality may be 

 different in successive years, and that the dominant species in one 

 locality may be different from that in another, within the same year. 

 Collections have not been made on a large enough scale or in suf- 

 ficiently continuous series to enable us to exhibit these differences in 

 any detail, but the following may serve as illustrations : — 



Collections made at a street-lamp in Maywood, near Chicago, by 

 O. S. Westcott,* on seventeen nights from May 9 to June 14, 1887, 

 contained 798 specimens of fusca and 313 of gibbosa — fusca pre- 

 dominating in a ratio of more than 2 J4 to i ; and collections made 

 the following year at the same place by the same person, on seven- 

 teen nights between June 2 and July 2, gave ,73 specimens of fusca 

 and 1,836 of gibbosa — gibbosa now predominating in a ratio of 

 25 to I. The difference in the collection period of the two years 

 was due to the difference in the weather of the spring, which was 

 backward and stormy in 1888. If we compare the collections of the 

 sarne periods for these two years — ^June 9 to 14 in 1887, ^^^ ]vLr\t 9 

 to 13 in 1888 — we have 96 specimens of fusca to 82 of gibbosa in 

 1887, and 29 of fusca to 1,020 of gibbosa in 1888. 



A similar comparison may be made between the contents of fre- 

 quent collections from trees made at Urbana through the whole 

 period of activity of the May-beetles in 1891 and again in 1906 — 836 

 specimens in the former year and 3,484 in the latter. (See table 

 on p. 451.) In the collections of 1891 the dominant species were 

 hirticula (42 per cent.), inversa (32 per cent.), and ftisca (23 per 



♦"Entomolopica Aijiericana, Nov., 1888, Vol. IV-, p. 155. 



