Comparison of insect, fungal, and mechanically induced defoliation of larch: effects on plant productivity and subsequent host susceptibility

Abstract

Larch sawfly, Pristiphora erichsonii Hartig, and larch needlecast fungus, Mycosphaerella laricinia (R. Hartig) Neg., are early season defoliators restricted only to Larix host trees. Larch defoliation (100%) by either the fungus or insect, but not mechanical removal, induced systemic responses that reduced sawfly consumption and digestion rates one year later. In a feeding behavior assay, larvae quickly abandoned seedlings previously defoliated by M. laricinia. Adult female oviposition choice and egg deposition were unaffected. Seedling growth was not affected during the year of defoliation by M. laricinia, but was significantly reduced one year later. Defoliation by M. laricinia reduced stem volume, radial growth, root biomass and new shoot production. The latter tissue is the only oviposition resource for larch sawfly, and, in contrast, is not influenced by sawfly feeding. We hypothesize that M. laricinia infection may limit larch sawfly populations where both species coexist. However, this reduction is at a substantial net cost to larch productivity.

Induced Response of the Siebold's Beech (Fagus crenataBlume) to Manual Defoliation

“…The possibility remains that defoliation by insects or pathogens might elicit a stronger delayed induced resistance than manual defoliation (Haukioja and Neuvonen, 1985;Krause and Raffa, 1992). However, in this paper, even one year of manual defoliation caused an apparent response, and two successive years of manual defoliation, which is more similar to actual outbreak dynamics, reduced insect performance even more.…”

Defoliation causes parallel temporal responses in a host tree and its fungal symbionts

“…Generally, the growth of forest trees is decreased after insect herbivory, browsing by mammals or artiWcial defoliation (Krause and RaVa 1992;Reich et al 1993;Kolb et al 1999), the response to damage often being proportional to the amount of foliage lost (e.g., May and Carlyle 2003). Although aboveground responses of trees to herbivory are now rather well studied, eVects on soil microbes are largely unclear (but see Ayres et al 2004;Carline and Bardgett 2005).…”

Fungal diversity and plant disease in mangrove forests: salt excretion as a possible defense mechanism

“…Little, however, is known of the factors governing the distribution, incidence, or effects of fungi that infect leaves of mangrove species (McMillan 1964;García López et al 1989;Suryanarayanan et al 1998). Foliar diseases have been shown to have significant effects on plant survival, growth, and fitness in natural ecosystems (Alexander and Burdon 1984;Krause and Raffa 1992;Lively et al 1995). Our observation that Rhizophora suffers greater pressure from foliar diseases than do Laguncularia and Avicennia is supported by the fungal host index of Farr et al (1989), who list ten known foliar diseases of Rhizophora, but only three for Laguncularia and one for Avicennia.…”