252 MAINE AGRICULTURAL EXPERIMENT STATION. 1917. 



far from favorable, yet this can hardly be postulated as the 

 cause of their disappearance, as it seemed to have little if any 

 effect on the abundance of other species of Altica. The sum- 

 mer of 1915 was a favorable one for the growth of fungi, and 

 many larvae and some adults were killed in this fashion, but the 

 alder flea-beetle is not more suspectible to fungous attacks than 

 other members of the genus whose numbers remained undimin- 

 ished. However this species was much more abundant than 

 any of the others, and on that account fungus could work much 

 more effectively. Undoubtedly the fungus played a large role 

 in checking the outbreak. 



There is one peculiar circumstance which should be noted 

 in this regard, as it seems to be correlated with the disappearance 

 of A. bimarginata. As is pointed out under another heading, 

 most of the eggs of these flea-beetles are deposited within the 

 leaf-rolls of an alder caterpillar,^ crobasis rubrifasciella Pack- 

 ard. So far as the writer has observed, the abundance of this 

 larva on the alder almost parallels that of the alder flea-beetle. 

 It was abundant in 1912 and 1913, and very abundant in 1914; 

 it was somewhat less common in 1915, and scarce in 1916. What- 

 ever may have been the complex of conditions acting as deter- 

 minative factors, the same conditions which acted as a check 

 on the abundance of Altica bimarginata Say apparently acted 

 also as a check on Acrobasis rubrifasciella Packard, and the 

 abundance of the two species was evidently closely correlated. 



Fortunately these beetles are not yet of great economic 

 importance. The alder is not used commercially, and so long 

 as the depredations are confined to it, the beetles cause no great 

 injury, except where the alders have been used for ornamental 

 planting in landscape gardening. But as is pointed out later, 

 they can live on willow and probably on balsam poplar; and 

 whenever this species is abundant, there is always the possibility 

 that it may become a serious pest, should the beetles transfer 

 their ravages either to the willow or to the poplar, both of which 

 are of commercial importance. 



