Using hybrid and backcross larvae of Papilio canadensis and Papilio glaucus to detect induced phytochemical resistance in hybrid poplar trees experimentally defoliated by gypsy moths

Abstract

Sub-plots of hybrid poplars were experimentally defoliated using 10 million gypsy moth larvae. Half of the defoliated (and undefoliated control) plots were fertilized to see if this would ameliorate the predicted induction of carbon-based phenolic defenses in the regrowth leaves. In order to bioassay the leaves of the four different treatments, we employed a continuum of genotypes (different hybrids and backcrosses of two different species of tiger swallowtail butterflies) with different abilities to detoxify these allelochemicals. Based on our previous studies with phytochemicals from the Salicaceae plant family, Papilio canadensis was likely to consume and process all Populus spp treatments, whereas P. glaucus predicted to either not consume or else quickly die on all Populus treatment leaves. Hybrid and backcross larvae of these two butterfly species are known to have intermediate levels of esterase detoxication enzymes and would therefore be likely to provide a continuum or at least varying degrees of sensitivity in bioassays for even the most subtle induction responses in the regrowth leaves. This presumption was supported in the feeding and growth studies conducted at different times post-defoliation during the 1997 growing season in Michigan.

Impacts of climate warming on hybrid zone movement: Geographically diffuse and biologically porous “species borders”

“…These co‐adapted radiations may carry over to the parasites (enemies) of the herbivores (Abrahamson & Blair, 2008; Forbes et al , 2009). It may be that if parental species with differential adaptations to pathogens exist (as seen in detoxification differences, Scriber et al , 1989, 1999), then “hybrid vigor” (as seen in lab crosses, Scriber et al , 2003) may be partly due to higher pathogen resistance in hybrids relative to parental species (see also Moulia, 1999; Moulia et al , 1995). This possibility could be addressed using known hybrids and backcrosses challenged with various pathogens (e.g., viral, fungal, bacterial, etc.…”

“…Both preference and performance traits can be readily passed to new recombinant genotypes (or potential homoploid hybrid species; Scriber & Ording, 2005). The evolution of an “ash‐feeding host race” inside the hybrid zone (that lacks tulip tree and hop tree favorites) suggests local specialization arising from generalist parental species, but at the same time these recombinant hybrids of the late flight and P. appalachiensis also reflect wider host potential because larval hybrids have both the Salicaceae and Magnoliaceae host detoxification enzymes (Scriber et al , 1989, 1999; Scriber & Ording, 2005). The derivation of the polyphagous P. glaucus and P. canadensis from the oligophagous Rutaceae‐feeding P. multicaudatus was due to a few mutations in the cytochrome P‐450 enzymes, which allowed host range broadening without loss of ancestral detoxification abilities (Li et al , 2002, 2004; Mao et al , 2007).…”

Integrating ancient patterns and current dynamics of insect–plant interactions: Taxonomic and geographic variation in herbivore specialization

“…The unadapted P. glaucus that all died on these plants were also not useful in detection of chemical defense induction. However, experimental creation of interspecific hybrids with intermediate genotypes and a “gradient in detoxification abilities and enzymes” (by hybridizing and backcrossing these two Papilio species; Scriber et al , 1989) permitted us to detect the differential defoliation‐induced resistance (probably due to the phenolic glycosides) among the four field treatments (defoliated/undefoliated and nitrogen fertized/unfertilized; Scriber et al , 1999).…”

NOTEGypsy moth defoliation and N fertilization affect hybrid poplar regeneration following coppicing

“…In this study, we examined the effects of an experimentally created gypsy moth outbreak in a hybrid poplar plantation on tree mortality and regeneration after harvest. The broader study for which these large-scale plots were created (Scriber et al 1999;Parry 2000;Kosola et al 2001) included a fertilization treatment, factorially crossed with defoliation. We were thus able to examine interactive effects of fertilization and defoliation on poplar survival and productivity following harvest and regeneration.…”