The Biology of The Alder Flea-Beetle. 253 



THE LIFE HISTORY OF THE INDIVIDUAL. 



Summary of the Life History. 



The adult Altica bimarginata is a dark shiny steel blue flea- 

 beetle, which can be distinguished from all other species in our 

 fauna by the longitudinal plica or fold on the side of the elytra. 

 Like the greater number of other chrysomelids, these beetles 

 hibernate as adults ; in Maine they seek winter quarters in late 

 September, and emerge in the spring as soon as the alder leaves, 

 on which they feed voraciously, are well expanded. Pairs may 

 be taken in copulation from the first of June until early July. 

 From mid-June until late July the females deposit clusters of 

 yellow eggs on the foliage which hatch in a few days into grubs 

 or larvae which skeletonize the leaves. The larval life extends 

 over a period of about 25 days, during which they molt twice ; 

 there are, therefore, 3 larval instars. When the grubs are full 

 grown, they enter the ground and construct a rude cell, in which 

 they pass about 6 days as prepupae and 10 days as pupae. At 

 the end of that time the adults appear. Before they seek hiber- 

 nating quarters, the beetles feed freely on the leaves of the alder, 

 which is the preferred food-plant of this species. There is but 

 one generation each year. 



Seasonal History and Biological Data, 

 duration of the egg stage. 



A record which, was kept of 476 eggs deposited between 

 June 16 and July 20, inclusive, may be tabulated as follows : 

 87 hatched in 7 days ; 207, in 8 days ; 157, in 9 days ; 25, in 10 days ; 

 average 8.3 days. 



LENGTH OF THE FIRST LARVAL INSTAR. 



A record which was kept of 425 larvae which hatched 

 between July 13 and July 28 inclusive, may be tabulated as fol- 

 lows : 



182 molted to the second instar in 5 days; 115, in 6 days; 31, in 7 

 days ; 18, in 8 days ; 73, in 9 days ; 6, in 10 days ; average 6.3 days. 



