Thirteen Betula species were tested for resistanceto the birch leafminer, Fenusa pusilla (Lepeletier), usingno-choice assays. Birch leafminers were able to oviposit into expandingleaves of all Betula individuals tested. Larvae did notsurvive within any of the tested individuals of three species, B.alleghaniensis (Britt.), B. grossa (S. & Z.), andB. lenta (L.). Leafminer eggs deposited into the leaves ofthese species hatched, and larvae fed for a short period before dying.These three species were classified as highly resistant to birchleafminer, based on very low percent of mines (0.6-3.1%) with adiameter >3 mm. Eight species, B. papyrifera (Marsh),B. pendula (Roth), B. turkestanica (Litvin),B. glandulifera (Regal), B. ermanii (Cham.),B. platyphylla variety japonica [(Miq.) Hara],B. populifolia (Marsh) and B. maximowicziana(Regal) were classified as susceptible, with percent of mines >3 mmdiameter of 87-94%. Two species, B. costata (Trautv.) andB. davurica (Pall.), displayed intermediate and variableresistance. B. davurica exhibited a mechanism of resistancenot observed in the other species. Eggs oviposited into the leaves ofresistant B. davurica individuals became surrounded by anarea of discolored and necrotic tissue, and died. This responseresembles the programmed cell death associated with a hypersensitiveresponse.
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Vol. 93 • No. 6