Phenological variation as protection against defoliating insects: the case of Quercus robur and Operophtera brumata

Abstract

Phenological synchrony between budburst and emergence of larvae is critical for the fitness of many spring-feeding insect herbivores. Therefore, large intraspecific variation in timing of budburst of the host may have a negative effect on the herbivore. We studied how asynchrony between emergence of larvae and budburst affects the fitness of Operophtera brumata (Lepidoptera: Geometridae), a major defoliator of Quercus robur, which can adapt to the phenology of a single tree. It is known that, in maturing leaves of Q. robur, accumulation of condensed tannins has a negative effect on growth of O. brumata. However, there is no information about the effect of hydrolysable tannins and other phenolics that are potential antifeedants. In this study, we also analysed changes in secondary chemistry of the foliage of Q. robur and how different compounds are correlated with growth and survival of O. brumata. The effect of asynchrony on O. brumata was studied in rearing experiments. The neonate larvae were incubated without food for different periods of time. The decline in nutritional quality of foliage was estimated by rearing cohorts of larvae with manipulated hatching times on the leaves of ten individual Q. robur trees. For the chemical analysis, the foliage of these trees was sampled at regular intervals. In the absence of foliage, mortality of neonate larvae started to increase exponentially soon after the larvae emerged. If the larvae missed budburst, the decline in nutritional quality of the foliage led to increased mortality and lower body mass (= fecundity). Hydrolysable tannins were not significantly correlated with performance of the larvae. Only condensed tannins were found to correlate negatively with the growth and survival of O. brumata. Certain individual trees were unsuitable hosts for O. brumata because the decline in quality of the foliage was very rapid. Based on regression equations for increasing rate of mortality and decreasing fecundity, we calculated that a relatively small mismatch of +/-30 degree days between budburst and hatching of larvae leads to a 50% decrease in the fitness of O. brumata. Thus, large phenological variation within a Q. robur stand can limit the colonisation of neighbouring trees by dispersing larvae. Furthermore, the hybridisation of moths adapted to phenologically different trees may lead to maladapted phenology of their offspring.

Assessment of ecological risks in weed biocontrol: Input from retrospective ecological analyses

“…To evaluate the risk quantitatively, we combined host specificity tests and garden rearing data with the evaluation of ecological field data on relative phenology, suggested as important by the retrospective studies summarized above, to prospectively evaluate the likelihood and magnitude of the potential interaction of R. conicus with C. pitcheri . While phenology is recognized as important in insect-plant interactions (e.g., Russell and Louda, 2004;Tikkanen and Julkunen-Tiitto, 2003), we found no prior studies that quantified the degree of likely phenological synchrony between a biocontrol agent and a potential secondary host plant species prior to contact.…”

Comparison of Quantitative Trait Loci for Adaptive Traits Between Oak and Chestnut Based on an Expressed Sequence Tag Consensus Map

“…Our results suggested that these selection pressures were acting on the same genomic regions through mechanisms able to maintain diversity over long evolutionary times (balancing, disruptive, or frequency-dependent selection). At least in oaks, it has been shown that coevolution of defoliating insects and oaks may be responsible for wide within-population variation of bud burst (Tikkanen and Tiitto 2003). Maintenance of a high level of heterozygote loci would fit well with the hypothesis of a phenotypic plasticity mainly based on allelic sensitivity.…”

Effects of drought and heat on forest insect populations in relation to the 2003 drought in Western Europe

“…For many defoliators of temperate forests synchrony in phenology between budburst and larval development is determinant to growth and survival of these defoliators [83,91,92]. A good synchronization between hatching and budburst allows larvae to feed on soft and young foliage, with high food quality [5,30,36]; see also indirect effects).…”

“…For geometrids, generalist defoliators of broadleaf trees such as O. brumata, larvae feeding on ageing foliage show declining growth rates and increasing dispersal with a dramatic increase in mortality since this dispersal is passive [19,82,83]. Consequently, a differential effect of warmer temperatures on budburst and larval phenology would have marked effects on the abundance of this species in extreme years such as 2003.…”