Effects of carbon dioxide and nitrogen enrichment on a plant–insect interaction: the quality of Calluna vulgaris as a host for Operophtera brumata

Abstract

Calluna vulgaris L. (Hull) is not one of the usual hosts of the winter moth, Operophtera brumata L., but outbreaks have caused extensive damage to heather moorland in Scotland in recent years. This study investigated the potential role of environmental change in such outbreaks by rearing O. brumata larvae on C. vulgaris plants grown in open‐top chambers for 20 months with enriched CO2 (600 ppm) and nitrogen supply (average 52·5 kg N ha−1 yr−1) in factorial combination. This prolonged exposure to elevated CO2 caused no change in shoot growth, photosynthesis or foliar C∶N ratio of C. vulgaris, even with increased N supply, indicating that the absence of response was not due to N limitation. Increased N supply itself resulted in increased shoot growth and a decrease in tissue C∶N ratio. Phenolic content did not change in response to either CO2 or N enrichment, contrary to the predictions of the carbon/nutrient balance hypothesis. In line with the absence of plant response, there was no effect of CO2 on the development of Operophtera brumata on C. vulgaris, and so continued increase in atmospheric CO2 concentration is unlikely to affect directly O. brumata outbreaks on heather moorland. Operophtera brumata showed increased larval development, growth rate and pupal weight on N‐treated plants, correlated both to the decrease in foliar C∶N ratio, and to the increase in shoot extension which was predictive of survivorship. Thus, increased atmospheric N deposition, or increased rates of mineralization in a warmer environment, might increase the severity of O. brumata outbreaks on C. vulgaris. Since the combination of high N availability and disturbance of heather canopy by herbivory is known to result in increased dominance of grasses, it is suggested that this could lead to further degradation of moorland in upland Britain.

The effect of nutrient supply and light intensity on tannins and mycorrhizal colonisation in Dutch heathland ecosystems

“…It is well established that nitrogen addition increases nitrogen concentrations in heather, C. vulgaris (Berdowski and Siepel 1988;Duncan et al 1994;Hartley et al 1995;Carrol et al 1999;Gordon et al 1999) and other ericaceous plants (Mallik 1996;Prescott et al 1993;Nordin et al 1998). However, the expected decrease in total phenolics or condensed tannin levels due to solely nitrogen additions has not yet been empirically shown either in the greenhouse or in the field (Iason and Hester 1993;Hartley et al 1995;Kerslake et al 1998;Bradley et al 2000;Alonso et al 2001;Hansen et al 2006). In contrast, Hansen et al (2006) recently showed that a combination of nitrogen addition with increased air temperature seems to induce a positive response of condensed tannins in one year old leaves of Vaccinium vitis-ideae (L.) and Cassiope tetragona (L.) D. Don.…”

Effects of climate warming on host–parasitoid interactions

“…Increased nitrogen deposition resulting from nitrogenous pollution and increased mineralisation rates in warmer climates can result in plant nitrogen enrichment, which in turn can positively affect insect herbivore development rates and body mass at pupation (Kerslake et al ., 1998) and ultimate insect herbivore densities (Stiling & Moon, 2005). Parasitism rates of galling insects can also be lowered under nitrogen enrichment because of increases in gall size and wall thickness, imposing mechanical challenges to parasitoids attacking these concealed hosts (Weis et al ., 1985;Stiling & Moon, 2005).…”

Potential Approaches to Developing Lichen-Based Critical Loads and Levels for Nitrogen, Sulfur and Metal-Containing Atmospheric Pollutants in North America

“…The increase in nitrogen content of C. vulgaris with nitrogen deposition has also been clearly demonstrated in experimental studies with a range of nitrogen treatments (Leith et al, 2001;Carroll et al, 1999). Increases in shoot nitrogen content have been linked in other studies to increased performance of winter moth (Operophtera brumata), outbreaks of which have led to extensive damage to heather moorland in Scotland over the last decade (Kerslake et al, 1998).…”

“…In addition, the growth of heather beetles instars was also significantly stimulated on C. vulgaris from UK heaths after ammonia fumigation, with relatively high concentrations, probably caused by the enhanced nitrogen concentrations in the plant material (Uren, 1992). It has also been demonstrated that increased nitrogen deposition to upland C. vulgaris stands stimulated larval development and growth rate of winter moth (Operophtera brumata) (Kerslake et al, 1998). It is thus likely that the frequency and the intensity of insect outbreaks can be stimulated by increased atmospheric nitrogen loads.…”