The main study systems of my team are the polymorphic leaf beetle, Chrysomela lapponica, and its host plants (willows and poplar), and several leaf-mining and leaf-rolling species of moths that feed on birches. We demonstrated that industrial pollution favours some plant-feeding insects via changes in host-plant architecture and by decreases in the predation or parasitism rates, and that minor local damage to plant leaves can cause their premature abscission and trigger delayed local responses. The most recent findings concern the evolution of chemical defences in herbivorous insects and the impacts of the engineering activity of moth larvae on litter decomposition rates.
We are presently analysing the outcomes of a long-term, large-scale defoliation experiment aimed at exploring the impacts of climate on responses of boreal trees to background insect herbivory. We are also collecting published data to analyse the geographical patterns of the losses of root biomass to insects and the patterns of predation and parasitism rates of leaf-feeding insects across the globe. An ongoing field experiment addresses the impacts of leaf engineering activity (tying or rolling) of moth larvae on damage to leaves by externally feeding defoliators.
Zvereva, E. L. & Kozlov, M. V. (2016) The costs and effectiveness of chemical defenses in herbivorous insects: a meta-analysis. Ecological Monographs, 86, 107-124 (doi: 10.1890/15-0911.1).
We tested several hypotheses about the evolution of chemical defenses in plant-feeding insects using a meta-analysis of the effectiveness and costs of chemical defenses in various prey–predator systems (140 herbivore species and 124 enemy species). These defenses, on average, were effective against generalist predators, but increased the risk of parasitism. We found no physiological costs of the production of chemical defenses. We conclude that the cost–benefit trade-offs are affected by ecological costs (i.e., increased susceptibility to parasitoids) more than by costs in terms of resources.
Zvereva, E. L., Kozlov, M. V. & Rank, N. E. (2016) Does leaf beetle specialization on toxic host plants protect them from ants? Biological Journal of the Linnean Society, 119, 201–212 (doi: 10.1111/bij.12801).
We tested the hypothesis that predators may favour specialization of herbivores on host plants containing toxic chemicals. We found that ants were more strongly repelled by leaf beetle larvae with host plant-derived, salicylaldehyde-containing secretions than by larvae with various autogenous secretions, but collectively foraging of ants in the vicinity of their nests ultimately overcame any type of chemical defence. We conclude that evolutionary shifts from autogenous production of secretion to sequestration of plant allelochemicals in leaf beetles may be favoured mostly at low ant densities on the periphery of ant foraging areas.
Kozlov, M. V., Zverev, V. & Zvereva, E. L. (2016) Shelters of leaf-tying herbivores decompose faster than untied leaves damaged by free-living insects. Science of the Total Environment (published online; doi: 10.1016/j.scitotenv.2016.04.121).
We hypothesized that the decomposition rate is faster for shelters of leaf-tying larvae than for leaves damaged by free-living insects, in particular due to the accumulation of larval frass within shelters. We found that while leaf damage by insects per se reduces litter quality and its decomposition rate, structuring of litter by leaf-tying insects counterbalances these negative effects. We conclude that leaf-tying larvae, in contrast to free-living defoliators, do not impose negative effects on nutrient turnover rate even at their high densities, which are frequently observed in heavily polluted sites.
Kozlov, M. V., Lanta, V., Zverev, V. E. & Zvereva, E. L. (2012) Delayed local responses of downy birch to damage by leafminers and leafrollers. Oikos, 121, 428-434 (DOI: 10.1111/j.1600-0706.2011.19625.x).
We demonstrated delayed local compensatory growth and increased antiherbivore defence in downy birch shoots following local injuries by several leafmining and leafrolling insects. We suggest that this pattern reflects evolutionary adaptations of plants to permanently acting minor, dispersed and spatially unpredictable damage imposed by endemic herbivory. Local responses are less costly and represent a more sustainable strategy to maintain plant fitness under low levels of herbivory than constitutive resistance or systemic responses.
N. E. Rank