Local adaptations and phenotypic plasticity may render gypsy moth and nun moth future pests in northern European boreal forests

Abstract

<p>Phenotypic plasticity and local adaptations are important factors in predicting range expansions and shifts of pest insects in a changing climate. We reared two lepidopteran forest pests, <i>Lymantria monacha</i> (Linnaeus) and <i>Lymantria dispar</i> (Linnaeus), at three climatically different field sites from central Germany to northern Finland to investigate differences among populations in plasticity in the timing of pupation and adult emergence (measured as cumulative temperature sums, degree-days >5 °C), pupal mass, and duration of the pupal period. We also compared the phenologies of continental and boreal <i>L. monacha</i> populations feeding on Scots pine (<i>Pinus sylvestris</i> L.) to reveal possible local adaptations. <i>Lymantria dispar</i> was reared on different host plants, <i>Quercus robur</i> L., <i>Betula pendula</i> Roth, and <i>Betula pubescens</i> ssp. <i>czerepanovii</i> (Orl.) Hämet-Ahti, to evaluate the possibilities of a range expansion northwards. There was stronger indication of adaptive phenotypic plasticity, which enables species to cope with changing environmental conditions, in continental <i>L. dispar</i> and boreal <i>L. monacha</i> populations than in the continental <i>L. monacha</i> population. Differences between boreal and continental <i>L. monacha</i> populations may denote adaptation to local conditions. All three host plants used for <i>L. dispar</i> proved suitable for the species, revealing that host plant availability would not limit its range expansion in northern Europe.<br /></p>