Interactive effects of host resistance and drought stress on the performance of a gall-making aphid living on Norway spruce

Abstract

Four full-sib families of Norway spruce (Picea abies), of which two were resistant to a galling aphid (Adelges abietis) and two were susceptible, were exposed to drought stress for 2 years. The primary aim was to test the hypothesis that the various life stages of the aphid differ in their response to environmentally induced changes in the host plant. The drought treatment had a significant negative effect on tree growth. This was reflected in gall size which responded in a similar way to the drought stress, thus supporting the plant vigour hypothesis. Drought affected the survival of aphid stem-mothers negatively in susceptible trees but positively in resistant trees. This result was matched by the response of an individual phenolic compound which, contrary to the total phenolic concentration, tended to increase in susceptible trees exposed to drought and decrease in similarly exposed resistant trees. Thus it is possible that this single, as yet unidentified, phenolic compound could be used as a marker of resistance. The performance of surviving stem-mothers, evaluated by measuring the diameter of the wax cover they produced (a correlate of fecundity), was not significantly affected by drought, but aphids on susceptible trees produced more wax than those on resistant trees. The change in gall density over time (analysed separately for each treatment and phenotype) correlated best with patterns of stem-mother survival. This indicates that stem-mother survival, which is closely linked to host plant quality and resistance, may play a significant role in the population dynamics of this aphid. However, drought-stress-induced changes in host plant quality affected survival, and hence gall density, less than the genetically determined level of resistance. The results also support the hypothesis that an insect may respond differently to environmentally induced changes in the host plant at different stages in its development.

Herbivory among habitats on the Neotropical tree Cnidoscolus quercifolius Pohl. in a seasonally deciduous forest

“…Several studies have reported the susceptibility of free-feeding insects to the hygrothermal stress to explain the higher incidence on wetlands than in xeric habitats Price, 1988, 1992;Preszler and Price, 1988;Fernandes and Lara, 1993;Price et al, 1998;Blanche, 2000;Björkman, 2000;Blanche and Ludwig, 2001;Lara et al, 2002;Veldtman and Mcgeoch, 2003;Cuevas-Reyes et al, 2004). Our results support this hypothesis as the desiccating factors are more amenable in mesic and interior forest habitats, causing higher herbivory rates by chewing insects on C. quercifolius individuals.…”

Leaf traits, water stress, and insect herbivory: Is food selection a hierarchical process?

“…result is opposite to the increase in nitrogen concentration as a consequence of drought supposed by White (1984) when proposing the plant stress hypothesis. Indeed, several studies have reported decreased nitrogen concentration in water-stressed plants (e.g., Inbar et al 2001;Staley et al 2006), while others found no differences in nitrogen concentration between water-stressed and control plants (Björkman 2000;De Bruyn et al 2002). This discrepancy among studies was attributed to nonlinear effects of drought on plant chemistry (Scheirs and De Bruyn 2005;Staley et al 2006).…”

Adaptation to Climate Change in Swedish Forestry

“…If a new trait (such as resistance to a specific damaging agent) is to be included in the breeding program, it must be under strong genetic control, be efficiently measurable and clearly contribute to the overall breeding goal. Even though boreal forest trees show great genetic variation in resistance [99][100][101][102][103], the interactive effects of warmer temperatures and other factors, such as day length and food quality, and the potentially improved performance of natural enemies and pathogens, illustrate the possibility of complex outcomes arising in response to climate change [104][105][106]. Many climate scenarios predict that warming will accelerate insect development rate and facilitate range expansions of pests.…”