TISSUE PREFERENCE AND DAMAGE BYFENUSA PUSILLAANDMESSA NANA(HYMENOPTERA: TENTHREDINIDAE), LEAF-MINING SAWFLIES ON WHITE BIRCH (BETULA PAPYRIFERA)

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Abstract
Fenusa pusilla(Lepeletier) andMessa nanaKlug 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-generationF. pusillaoviposit in unfolding leaves arising from currently expanding shoots situated distally on the branch, whereasM. nanaoviposits in fully expanded leaves arising from older shoots situated proximally on the branch. Leaf tissues damaged by oviposition and larval feeding were examined. Larvae ofF. pusillaconsume both palisade and spongy mesophyll, whereas larvae ofM. nanaconsume only palisade. It is suggested thatF. pusilladevelops faster thanM. nanabecause it feeds on leaves of greater nutritional value and digests more cellular components.