Microrhopala xerene (Newman, 1838)

Eiseman, Charles S., 2015, Notes on Leaf-Mining Chrysomelidae (Coleoptera) in New England, The Coleopterists Bulletin 69 (3), pp. 453-458 : 455

Microrhopala xerene (Newman, 1838)

On 2 September in Ashfield, Massachusetts (42.548407° N, 72.868125° W), I collected three leaf mines on an aster ( Symphyotrichum Nees , Asteraceae ), from which all three adults emerged on 19 September. My observations are in general agreement with the account given by Chittenden (1902) for M. xerene , but one detail is worthy of elaboration. He states that “[t]he mine, at the point where the pupal cell is formed, puffs up to form a hard blister, more or less rounded oval in shape, usually a little over an eighth of an inch wide, which sometimes becomes as thick through, its dimensions being dependent upon the number of individuals which inhabit it.” In the young mine, the area that will become this blister is evident as a dark, more or less circular spot on the upper leaf surface, which is to some extent also visible on the lower surface ( Fig. 3 ). In each mine I examined, there was a single egg attached to the lower leaf surface at the edge of the dark spot, largely covered by an excrement-like coating. My dissection of a mature mine revealed that within the dark spot, the ceiling and floor are thickly plastered with long strips of frass ( Fig. 4 ), which are otherwise fairly sparsely scattered through the mine. Based on my previous unpublished observations, this dark spot will distinguish M. xerene mines from those of Microrhopala vittata (F.) on Solidago L. ( Asteraceae ), the only host known to be used by both beetles ( Staines 2012).

The blister I dissected measured 9 mm by 7.5 mm, substantially larger than suggested by Chittenden’ s description. My observations of the adult feeding habits also differ from Chittenden’ s statement that “[t]he beetles eat out little elliptical holes in the leaves of their food plants”. The adults I reared fed in elongate channels on the upper leaf surface, 0.5–0.8 mm wide and 3–6 mm long, leaving the lower epidermis and some mesophyll intact. In the field, I have seen adults feeding similarly on foliage of Symphyotrichum puniceum (L.) Á. Löve and D. Löve.

On 6 August in Plainfield, Massachusetts (42.540991° N, 72.914145° W), I collected a single mine on Doellingeria umbellata (Mill.) Nees (Asteraceae) that was identical to those from which I reared M. xerene . Within four days, the larva emerged. Having no fresh D. umbellata leaves available, I offered it leaves of Symphyotrichum lateriflorum (L.) Á. Löve and D. Löve. It mined into one of these for a few days, then on 16 August entered a leaf of Symphyotrichum laeve (L.) Á. Löve and D. Löve. Each new mine immediately developed the same dark central patch. Unfortunately no adult ever emerged, but I consider it highly likely that the larva was another M. xerene . The only hispine previously recorded from D. umbellata is Microrhopala excavata excavata (Olivier) ( Staines 2012) , and this evidently is not a rearing record. It appears to have originated with Clark (1983), who stated only that this species “feeds on” D. umbellata . According to Ford and Cavey (1985), the larval host of M. excavata excavata is unknown.

Figures

Figs. 1–8. 1) Egg of Chalepus bicolor, lateral view); 2) Egg of Chalepus walshii, dorsal view; 3) Larva and leaf mine of Microrhopala xerene; 4) Abandoned mine of M. xerene, with pupal blister torn open; 5) Mine of Sumitrosis inaequalis in Symphyotrichum cordifolium; 6) Mine of Dibolia chelones, showing two frass types; 7) Mature larva of D. chelones; 8) Five young larvae of D. chelones in a single leaf.