Abstract
Almost all previous work on host-plant selection by insect herbivores has focused on adult behaviour; however, immature life stages can also play an active role in host discrimination. The important forest pest Lymantria dispar (gypsy moth) has three recognised subspecies: the European, Asian, and Japanese gypsy moth. Unlike the other two subspecies, the European subspecies is characterised by a loss of female flight ability, which might impose a selective pressure on larvae to actively engage in host-plant selection. We therefore explored the interactions of early-instar larvae from laboratory colonies of each subspecies with four potential hosts of differing quality: oak, beech, maple, and pine—measuring larval survival and performance, feeding preferences, responses to host-derived odour cues, and the propensity to disperse from hosts via ballooning. Compared to larvae from the Asian and Japanese subspecies, larvae from the (American-originated) European gypsy moth colony exhibited (i) significantly lower survival on the poorest quality host (pine), (ii) an ability to discriminate among hosts via olfactory cues; and (iii) higher propensity to disperse from sub-optimal hosts. These results are consistent with the hypothesis that larvae from flightless female European Gypsy moth subspecies play a more active role in host-plant selection.
Highlights
The behavioural and sensory mechanisms by which insect herbivores locate and select among potential host plants have been extensively documented[1,2,3,4,5,6]
Survival was lowest on pine (P. sylvestris), yet both Asian gypsy moth (AGM) and Japanese gypsy moth (JGM) had significantly higher survival on pine than European gypsy moth (EGM) (Fig. 1)
Our findings reveal differences in the survival and performance of lab-reared gypsy moth larvae belonging to three different subspecies (EGM, AGM and JGM) on four potential host trees
Summary
The behavioural and sensory mechanisms by which insect herbivores locate and select among potential host plants have been extensively documented[1,2,3,4,5,6]. In addition to having relevance for the ecology and evolution of plant-herbivore interactions, improved understanding of the role of immature insects in host selection may inform efforts to control damaging insect pests, in the case of biological invaders and species with broad geographic ranges. The European gypsy moth (EGM) is distributed across most of temperate Europe, from Portugal to the Ural Mountains, and in the late 19th century was introduced into North America, where it soon became a major forest pest[11,12,13]. Differences among subspecies, in the mechanisms by which they select host trees, may have important ecological implications, including their ability to colonize and spread within new geographic areas. We compared the host selection behaviour of the three recognised subspecies using lab colonies originating from different geographical locations
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