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

Alternative evolutionary strategies and tactics used by polyphagous insect to inhabit agricultural environment: Ostrinia nubialis as a case

Substantial differentiation was found between Ostrinia populations, adapted to feed on dicotyledonous and monocotyledonous host plants, which results not only in oviposition and larval survival differences but also in formation of ethological premating sex isolation mechanisms. Two strategies are surmised in warmer and colder areas, correspondingly: wide range of host plant species in combination with strict developmental stages of the plant, and alternatively, few host plant are infested during almost all the stages of their development, Inside these strategies, tactics are plastic. They are activated by the sensory stimuli, such as temperature, humidity and odorants. The tactic of dispersal flight before mating could be beneficial when the host plant is abundant, but mating before the flight is a better choice under the situation of sparse cornfields. There are still multiple questions to address for clear understanding of Ostrinia behavior and evolution.

De novo genome and transcriptome resources of the Adzuki bean borer Ostrinia scapulalis (Lepidoptera: Crambidae)

We present a draft genome assembly with a de novo prediction and automated functional annotation of coding genes, and a reference transcriptome of the Adzuki bean borer, Ostrinia scapulalis, based on RNA sequencing of various tissues and developmental stages. The genome assembly spans 419 Mb, has a GC content of 37.4% and includes 26,120 predicted coding genes. The reference transcriptome holds 33,080 unigenes and contains a high proportion of a set of genes conserved in eukaryotes and arthropods, used as quality assessment of the reconstructed transcripts. The new genomic and transcriptomic data presented here significantly enrich the public sequence databases for the Crambidae and Lepidoptera, and represent useful resources for future researches related to the evolution and the adaptation of phytophagous moths. The genome and transcriptome assemblies have been deposited and made accessible via a NCBI BioProject (id PRJNA390510) and the LepidoDB database (http://bipaa.genouest.org/sp/ostrinia_scapulalis/).

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

Maize was introduced into opposite sides of Eurasia 500 years ago, in Western Europe and in Asia. This caused two host-shifts in the phytophagous genus Ostrinia; O. nubilalis (the European corn borer; ECB) and O. furnacalis (the Asian corn borer; ACB) are now major pests of maize worldwide. They originated independently from Dicot-feeding ancestors, similar to O. scapulalis (the Adzuki bean borer; ABB). Unlike other host-plants, maize is yearly harvested, and harvesting practices impose severe mortality on larvae found above the cut-off line. Positive geotaxis in the ECB has been proposed as a behavioural adaptation to harvesting practices, allowing larvae to move below the cut-off line and thus escape harvest mortality. Here, we test whether the same behavioural adaptation evolved independently in Europe and in Asia. We sampled eight genetically differentiated ECB, ACB and ABB populations in France and China and monitored geotaxis through the entire larval development in artificial stacks mimicking maize stems. We find that all ECB and ACB populations show a similar tendency to move down during the latest larval stages, a behaviour not observed in any European or Asian ABB population. The behaviour is robustly expressed regardless of larval density, development mode or environmental conditions. Our results indicate that maize introduction triggered parallel behavioural adaptations in Europe and Asia, harvest selection presumably being the main driver.