TISSUE PREFERENCE AND DAMAGE BY FENUSA PUSILLA AND MESSA NANA (HYMENOPTERA: TENTHREDINIDAE), LEAF-MINING SAWFLIES ON WHITE BIRCH (BETULA PAPYRIFERA)
AbstractFenusa pusilla (Lepeletier) and Messa nana Klug coexist on white birch near Sudbury, ON. Both species often oviposit simultaneously, but their mines are spatially separated because of differences in ovipositional behavior. Most first-generation F. pusilla oviposit in unfolding leaves arising from currently expanding shoots situated distally on the branch, whereas M. nana oviposits in fully expanded leaves arising from older shoots situated proximally on the branch. Leaf tissues damaged by oviposition and larval feeding were examined. Larvae of F. pusilla consume both palisade and spongy mesophyll, whereas larvae of M. nana consume only palisade. It is suggested that F. pusilla develops faster than M. nana because it feeds on leaves of greater nutritional value and digests more cellular components.