Resistance to the Birch Leafminer <I>Fenusa pusilla</I> (Hymenoptera: Tenthredinidae) within the Genus <I>Betula</I>

Abstract

Thirteen Betula species were tested for resistance to the birch leafminer, Femusa pusilla (Lepeletier), using no-choice assays. Birch leafminers were able to oviposit into expanding leaves of all Betula individuals tested. Larvae did not survive within any of the tested individuals of three species, B. alleghaniensis (Britt.), B. grossa (S. & Z.), and B. lenta (L.). Leafminer eggs deposited into the leaves of these species hatched, and larvae fed for a short period before dying. These three species were classified as highly resistant to birch leafminer, based on very low percent of mines (0.6-3.1%) with a diameter >3 mm. Eight species, B. papyrifera (Marsh), B. pendula (Roth), B. turkestanica (Litvin), B. glandulifira (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 mm diameter of 87-94%. Two species, B. costata (Trautv.) and B. davurica (Pall.), displayed intermediate and variable resistance. B. davurica exhibited a mechanism of resistance not observed in the other species, Eggs oviposited into the leaves of resistant B. davurica individuals became surrounded by an area of discolored and necrotic tissue, and died. This response resembles the programmed cell death associated with a hypersensitive response.

Using classification tree analysis to reveal causes of mortality in an insect population

“…This leafminer causes significant aesthetic damage to trees and repeated infestations may also contribute to reduced tree vigour or premature tree mortality (Drouin & Wong, 1984; Correspondence: Chris J. K. MacQuarrie. Tel: +780 435 7362; fax: +780 435 7359; e-mail: cjkmacquarrie@gmail.com Hoch et al ., 2000). Although P. thomsoni has become geographically widespread and abundant in North America (Snyder et al ., 2007;Digweed et al ., 2009), the species has only been studied for brief periods in New York, Ontario and Alberta (Martin, 1960;Pezzolesi & Hagar, 1994;Digweed, 2006).…”

Effectiveness of Interspecific Hybridization for Incorporating Birch Leafminer (Fenusa pusilla) Resistance into White-barked Betula

“…Parental species used in breeding were selected based on their potential to contribute either white bark or leafminer resistance. Previous work (Hoch et al, 2000) detailed the resistance/susceptibility of the parental species. The leafminer susceptible white-barked species used for breeding were B. ermanii Cham.…”

“…LEAFMINER RESISTANCE ASSAYS. Leafminers used in this study were reared in the laboratory and used in resistance assays as described by Hoch et al (2000). Leafminer resistance assays were first performed on each hybrid while individually potted.…”

“…This second method graded the diameter of larval mines into five categories based on the final diameter of mines in the leaves: ≤1 mm, >1 to ≤2 mm, >2 to ≤3 mm, >3 to ≤4 mm, and >4 mm. Use of the mine diameter categories identified a threshold at 3 mm mine diameter that provided a clear separation between individuals that are susceptible (majority of mines >3 mm diameter) and resistant (majority of mines <3 mm diameter) (Hoch et al, 2000). Data presented for the B. turkestanica x B. alleghaniensis hybrids are taken from a population resulting from a single cross between two individuals.…”

“…Although birch species resistant to F. pusilla have been identified (Hoch et al, 2000), it is apparent that no appreciable resistance exists in any species possessing bright-white bark. The use of interspecific hybridization could potentially incorporate leafminer resistance into the desirable white-barked phenotypes.…”