Poleward increase in feeding efficiency of leafminer Stigmella lapponica(Lepidoptera:Nepticulidae)in a latitudinal gradient crossing a boreal forest zone

Damage to plant communities imposed by insect herbivores generally decreases from low to high latitudes.This decrease is routinely attributed to declines in herbivore abundance and/or diversity,whereas latitudinal changes in per capita food consumption remain virtually unknown.Here,we tested the hypothesis that the lifetime food consumption by a herbivore individual decreases from low to high latitudes due to a temperature-driven decrease in metabolic expenses.From 2016 to 2019,we explored latitudinal changes in multiple characteristics of linear(gallery)mines made by larvae of the pygmy moth,Stigmella lapponica,in leaves of downy birch,Betula pubescens.The mined leaves were larger than intact leaves at the southern end of our latitudinal gradient(at 60°N)but smaller than intact leaves at its northern end(at 69°N),suggesting that female oviposition preference changes with latitude.No latitudinal changes were observed in larval size,mine length or area,and in per capita food consumption,but the larval feeding efficiency(quantified as the ratio between larval size and mine size)increased with latitude.Consequently,S.lapponica larvae consumed less foliar biomass at higher latitudes than at lower latitudes to reach the same size.Based on space-for-time substitution,we suggest that climate warming will increase metabolic expenses of insect herbivores with uncertain consequences for plant-herbivore interactions.

Climate shapes the spatiotemporal variation in color morph diversity and composition across the distribution range of Chrysomela lapponica leaf beetle

Color polymorphism offers rich opportunities for studying the eco-evolutionary mechanisms that drive the adaptations of local populations to heterogeneous and changing environments.We explored the color morph diversity and composition in a Chrysomela lapponica leaf beetle across its entire distribution range to test the hypothesis that environmental and climatic variables shape spatiotemporal variation in the phenotypic structure of a polymorphic species.We obtained information on 13617 specimens of this beetle from museums,private collections,and websites.These specimens(collected from 1830-2020)originated from 959 localities spanning 33°latitude,178°longitude,and 4200 m altitude.We classified the beetles into five color morphs and searched for environmental factors that could explain the variation in the level of polymorphism(quantified by the Shannon diversity index)and in the relative frequencies of individual color morphs.The highest level of polymorphism was found at high latitudes and altitudes.The color morphs differed in their climatic requirements;composition of colour morphs was independent of the geographic distance that separated populations but changed with collection year,longitude,mean July temperature and betweenyear temperature fluctuations.The proportion of melanic beetles,in line with the thermal melanism hypothesis,increased with increasing latitude and altitude and decreased with increasing climate seasonality.Melanic morph frequencies also declined during the past century,but only at high latitudes and altitudes where recent climate warming was especially strong.The observed patterns suggest that color polymorphism is especially advantageous for populations inhabiting unpredictable environments,presumably due to the different climatic requirements of coexisting color morphs.

Decline of Eulia ministrana(Lepidoptera:Tortricidae)in polluted habitats is not accompanied by phenotypic stress responses

Env ironmental pollution is currently identified as one of the major drivers of rapid decline of insect populations,and this finding has revitalized interest in insect responses to pollution.We tested the hypothesis that the pollution-induced decline of insect populations can be predicted from phenotypic stress responses expressed as morphological differences between populations inhabiting polluted and unpolluted sites.We explored populations of the brassy tortrix Eulia ministrana in subarctic forests along an environmental disturbance gradient created by long-lasting severe impacts of aerial emissions of the copper-nickel smelter in Monchegorsk,northwestern Russia.We used pheromone traps to measure the population densities of this leafrolling moth and to collect specimens for assessment of three morphological stress indices:size,forewing melanization,and fluctuating asymmetry in wing venation.Wing length of E.ministrana increased by 10%,and neither forewing melanization nor fluctuating asymmetry changed from the unpolluted forest to the heavily polluted industrial barren.However,the population density of E.ministrana decreased 5 to 10 fold in the same pollution gradient.Thus,none of the studied potential morphological stress indicators signaled vulnerability of E.ministrana to environmental pollution and/or to pollution-induced environmental disturbance.We conclude that insect populations can decline without any visible signs of stress.The use of morphological proxies of insect fitness to predict the consequences of human impact on insect populations is therefore risky until causal relationships between these proxies and insect abundance are deciphered.