Divergence in behaviour between the European corn borer,Ostrinia nubilalis, and its sibling speciesOstrinia scapulalis: adaptation to human harvesting?

Abstract

Divergent adaptation to host plant species may be the major mechanism driving speciation and adaptive radiations in phytophagous insects. Host plants can differ intrinsically in a number of attributes, but the role of natural enemies in host plant specialization is often underappreciated. Here, we report behavioural divergence between the European corn borer (ECB, Ostrinia nubilalis) and its sibling species Ostrinia scapulalis, in relation to a major enemy: humans. Harvesting maize imposes selective mortality on Ostrinia larvae: those located above the cut-off line of the stalk face almost certain death. We show that ECB larvae diapause closer to the ground than those of O. scapulalis, which is sympatric but feeds mainly on weeds. The difference in diapause height results from genetically determined differences in geotactic behaviour. ECB larvae descend towards the ground specifically at harvest time, increasing their chances of surviving harvesting by about 50 per cent over O. scapulalis larvae. Natural enemies appear as a major driver of hostplant specialization in this example, stressing the need to consider 'tri-trophic' ecological niches to understand insect diversification. Our results also strongly suggest that geotaxis evolved as a singular instance of behavioural resistance in a major agricultural pest.

Influence of host plant, geography and pheromone strain on genomic differentiation in sympatric populations of Ostrinia nubilalis

“…Strong associations were demonstrated among moths using the Z‐pheromone communication system for maize (C4) and the E‐system moths for C3 host plants (Bontemps et al, ; Bourguet et al, ) which were accompanied by significant levels of genetic differentiation (Bethenod et al, ; Malausa et al, ). However, subsequent studies concluded that Ostrinia using the E‐pheromone system in France were O. scapulalis , and a different species compared to sympatric Z‐strain O. nubilalis (Calcagno, Bonhomme, Thomas, Singer, & Bourguet, ; Frolov, Bourguet, & Ponsard, ; Malausa et al, ). Thus, results of these European studies are not directly transferrable to E‐ and Z‐strain O. nubilalis in North America which show significant, but less pronounced and spatially‐dependent associations with C3 and C4 host plants, respectively (O'Rourke et al, ).…”

Cryptic diversity in Brevipalpus mites (Tenuipalpidae)

“…These cryptic species might differ in physiological, behavioural and ecological traits (Pfenninger & Schwenk ; Calcagno et al . ; Henry & Wells ). With the application of molecular techniques during the last two decades, cryptic diversity has been detected in almost all taxonomic groups (e.g.…”

Parallel evolution of behaviour during independent host‐shifts following maize introduction into Asia and Europe

“…This is a slight simplification of Calcagno et al. 's () protocol, our stacks containing seven instead of 11 vials, allowing to monitor more populations while maintaining a similar number of replicates per population.…”

“…Comparing the vertical movements of ECB and European ABB, Calcagno et al. () found that ECB exhibited positive geotaxis (locomotion towards the ground; Toma, White, Hirsch, & Greenspan, ; Bourguet, Gair, Mattice, & Whitlock, ) in late instars, whereas ABB larvae showed no such behaviour. This behavioural difference translated into contrasted vertical distributions of larvae in the field at the time of harvest.…”