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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. [ABSTRACT FROM AUTHOR]

New agricultural pest species attacking introduced crops may evolve from pre-existing local herbivores by ecological speciation, thereby becoming a species by becoming a pest. We compare the evolutionary pathways by which two maize pests (the Asian and the European corn borers, ACB and ECB) in the genus Ostrinia (Lepidoptera, Crambidae) probably diverged from an ancestral species close to the current Adzuki bean borer ( ABB). We typed larval Ostrinia populations collected on maize and dicotyledons across China and eastern Siberia, at microsatellite and mitochondrial loci. We found only two clusters: one on maize (as expected) and a single one on dicotyledons despite differences in male mid-tibia morphology, suggesting that all individuals from dicotyledons belonged to the ABB. We found evidence for migrants and hybrids on both host plant types. Hybrids suggest that field reproductive isolation is incomplete between ACB and ABB. Interestingly, a few individuals with an ' ABB-like' microsatellite profile collected on dicotyledons had ' ACB' mtDNA rather than ' ABB-like' mt DNA, whereas the reverse was never found on maize. This suggests asymmetrical gene flow directed from the ACB towards the ABB. Hybrids and backcrosses in all directions were obtained in no-choice tests. In laboratory conditions, they survived as well as parental strain individuals. In Xinjiang, we found ACB and ECB in sympatry, but no hybrids. Altogether, our results suggest that reproductive isolation between ACB and ABB is incomplete and mostly prezygotic. This points to ecological speciation as a possible evolutionary scenario, as previously found for ECB and ABB in Europe. [ABSTRACT FROM AUTHOR]

Two cornborer species, Ostrinia furnacalis (Lepidoptera: Crambidae) and O. nubilalis, are major corn pests in Asia and Europe, respectively. In both continents, the larval endoparasitoid Macrocentrus cingulum (Hymenoptera: Braconidae) develops on another, closely related stemborer, O. scapulalis, which feeds on mugwort and other dicotyledons. M. cingulum also emerges from O. furnacalis in Asia and O. nubilalis in North America, but not from O. nubilalis in Europe. We assessed the ability of three populations of each of the three Ostrinia species to encapsulate foreign bodies of a size similar to that of a M. cingulum egg. We conclude that variations in encapsulation ability alone cannot account for the differences observed in the field between parasite emergence rates in these different host species and geographic areas. [ABSTRACT FROM AUTHOR]

Specifying species boundaries is often tricky, because advanced biomolecular analyses can reveal that morphologically similar individuals in fact belong to distinct species. This is frequently the case when populations previously considered as a single polyphagous taxon prove to consist of several genetically distinct taxa using different resources, e.g., among insect parasitoids. Macrocentrus cingulum Brischke ( Hymenoptera: Braconidae), a parasitoid of the genus Ostrinia ( Lepidoptera: Crambidae) feeding on various host plants across the world, is one of them. In Western Europe, M. cingulum has never been found in Ostrinia nubilalis ( Hübner) populations feeding on maize, although it heavily parasitizes sympatric Ostrinia scapulalis Walker populations feeding on mugwort. In contrast, it contributes to pest control of Ostrinia furnacalis Guenée feeding on maize in Asia and O. nubilalis feeding on maize in America, suggesting that European and Asian M. cingulum populations might form two distinct taxa. We tested this hypothesis by conducting phylogenetic and population genetic analyses based on two mitochondrial and two nuclear genes, on 97 M. cingulum individuals sampled in Asia, USA, and Europe. Our analyses not only suggest that all sampled M. cingulum probably belong to the same species, but also show a significant genetic differentiation between individuals originating from Europe on the one hand and Asia/ USA on the other, which correlates with infestation patterns. Moreover, they show that American specimens are closely related to Asian ones, consistent with historical records about M. cingulum introductions into the USA in the 1920s and 1930s to control expanding O. nubilalis populations. Combining these results with what is known about the evolutionary history within the genus Ostrinia, we offer a candidate evolutionary scenario that is amenable to future empirical testing. [ABSTRACT FROM AUTHOR]

1. Bacillus thuringiensis ( Bt) crops kill pest larvae but have led to resistance evolution in several target pests. The high dose-refuge (HDR) strategy aimed at delaying Bt resistance evolution depends on dispersal patterns of target pests. Examination of adult dispersal of the European corn borer Ostrinia nubilalis (ECB), the main target of Bt maize, can help to improve resistance management. 2. Estimated recapture rates over 20 mark–release–recapture sessions in herbaceous field borders, where ECB adults rest during the day and mate at night, were used to examine the influence of sex, release period and site on ECB dispersal. Data from an additional 30 sessions were used to test the influence of night temperature, humidity, dew index and wind speed. 3. Average recaptures within 50 m of release were lower 12 h after night (7·7%) than 12 h after day (34·5%) releases, did not differ between sexes, and decreased during nights with higher temperatures and lower wind speed. 4. Local habitat had a major influence on dispersal. The number of unmarked adults caught initially in a given section of field border was strongly correlated with those subsequently captured in the same section, suggesting that moths flying in from the surroundings consistently settle in the same preferred spots. Moreover, recapture rates of marked adults were positively correlated with the prior density of unmarked adults in the release section. 5. The spatial distribution of recaptured moths around the release point suggests that they moved on a very local scale, while those not recaptured probably left the area by a different, long-range type of dispersal. 6. Synthesis and applications. A proportion of European corn borer adults typically remained within a few metres of their initial location for at least 12 h. This should favour non-random mating early in the flight season when nights are cold, population mixture is low and most individuals are unmated. Non-random mating can accelerate the evolution of resistance, but this effect may be offset by non-random oviposition. Our findings suggest that the intensity and direction of dispersal could be manipulated by field border management. Our data on the range and prevalence of short-range dispersal and the factors influencing this process, support the view that resistance evolution is multifactorial. Our results can be used to parameterize multifactorial models from which specific management recommendations can be formulated. [ABSTRACT FROM AUTHOR]

Target pests may become resistant to Bacillus thuringiensis (Bt) toxins produced by trangenic maize ( Zea mays L.). Untreated refuge areas are set aside to conserve high frequencies of susceptibility alleles: a delay in resistance evolution is expected if susceptible individuals from refuges mate randomly with resistant individuals from Bt fields. In principle, refuges can be toxin-free maize or any other plant, provided it hosts sufficiently large pest populations mating randomly with populations from Bt-maize fields. Our aim was to examine the suitability of several cultivated or weedy plants [pepper ( Capsicum frutescens L.), sorghum ( Sorghum spec .), sunflower ( Helianthus annuus L.), cocklebur ( Xanthium spec .), cantaloupe ( Cucumis melo L.), and hop ( Humulus lupulus L.)] as refuges for Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae) and Sesamia nonagrioides Lefebvre (Lepidoptera: Noctuidae), two major maize pests in southern Europe. Larvae of both species were collected on these plants. Their genetic population structure was examined at several allozyme loci. We found little or no evidence for an influence of geographic distance, but detected a significant host-plant effect on the genetic differentiation for both species. Ostrinia nubilalis populations from sunflower, pepper, cocklebur, and sorghum appear to belong to the same genetic entity as populations collected on maize, but to differ from populations on hop. Accordingly, females from pepper and cocklebur produced exclusively the ‘Z’ type sexual pheromone, which, in France, characterizes populations developing on maize. Qualitatively, these plants (except hop) could thus serve as refuges for O. nubilalis; however, they may be of little use quantitatively as they were found much less infested than maize. Sesamia nonagrioides populations on maize and sorghum reached comparable densities, but a slight genetic differentiation was detected between both. The degree of assortative mating between populations feeding on both hosts must therefore be assessed before sorghum can be considered as a suitable refuge for this species. [ABSTRACT FROM AUTHOR]

The relative importance of top-down and bottom-up control in setting the equilibrium abundances within trophic levels is examined in a comparative study on the litter-based food chain of a temperate deciduous forest. During two consecutive years, we estimated the abundances of macroinvertebrate detritivores and their predators on a natural gradient of annual litterfall. Detritus-based food chains are thought to be classical examples of donor-controlled systems. Indeed, both trophic levels showed higher abundances on sites with higher annual litterfall. Therefore, they appear to be bottom-up controlled. Using the Errors-in-Variables regression technique, we quantitatively compared our data with the equilibrium predictions of a set of simple trophic chain models including bottom-up effects with different types of functional responses (Beddington-DeAngelis, Hassell-Varley, and ratio-dependent). The model with a Hassell-Varley type functional response yielded the best adjustment to the data, although with a very high value of the mutual interference parameter suggesting the existence of overcompensating density dependence. Several changes to the structure of this model were considered. Their adjustment to the data consistently yielded such high values of the interference parameter. [ABSTRACT FROM AUTHOR]

Measures stable isotope ratios omega 15N and omega 13C for the litter, soil, and macro-invertebrates of three temperate decidious forest sites in spring, summer, and autumn. Determination of the trophic structure of soil macro-invertebrates; Variance of the isotopic ratios of the detritivorous species.