1907.] 



White-grubs and May-beetles. 



451 



in the first appearance of the different species of Lachnosterna in 

 spring. Inversa, fusca, rugosa, hirticula, and tristis have all been 

 taken by us in the later days of March, and gibbosa on April 6 

 Imphcita and ilicis have made their first appearances about a month 

 later than the average, but, although implicita is sometimes excess- 

 ively abundant, these two species have been much less frequently 

 taken by us than the others, and the record might have been differ- 

 ent if the collections made had been equally numerous. The dates 

 of last occurrence are also nearly the same for these species, and 

 their periods of greatest abundance do not vary greatly. 



Pusca, however, commonly appears in large numbers at electric 

 lights about a week earlier than the other species, and gibbosa is 

 about as much later than the others— a fortnight later than fusca. 

 Our records of egg-laying are substantially the same for all the 

 seven species covered by them. So far, consequently, as the mere 

 period of adult activity is concerned, these insects are virtually one 

 species, and we must look to other facts and conditions for any spe- 

 cific distinctions of habit or agricultural relation. 



I find that the data of the relative abundance and dates of emer- 

 gence of the various species derived from electric-light collections 

 disagree widely with the data of collections made from the food 

 plants of the beetles at the same time. Apparently some of the 

 species are more strongly attracted to lights than others. In 1891, 

 and again in 1906, collections were made at Urbana from trees and 

 from lights during the greater part of the active period of the May- 

 beetles, with the results shown in the following table . 



