Introduction
The European corn borer (ECB), Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae), is a major pest insect in maize. New cultivars and climate change have allowed range expansion of the ...crop northwards in Europe, and a similar range expansion of associated pests has been predicted. ECB exists as two distinct pheromone strains using different blends of (E)‐11‐tetradecenyl acetate and (Z)‐11‐tetradecenyl acetate for sexual communication; in addition, the Z‐strain feeds almost exclusively on maize. In Sweden, the maize cropping area has increased tenfold during the last two decades, increasing the potential for spread of the Z‐strain, which was recorded for the first time in the country in 2010.
Aim of the study/methods
In this study, we performed trapping experiments with strain‐specific lures in maize fields in southern Sweden during 2013–2022 to monitor the presence and relative abundance of the two ECB strains and evaluate the potential increase of the Z‐strain. Trapping was also performed at least 5 km away from maize fields. Molecular markers were used to verify the strain identity of trapped males and larvae that fed on maize.
Results
Catch data revealed that both pheromone strains were present in the major maize cultivation areas of Sweden, as predicted by recent modelling studies. Our data indicate that the flight period of ECB in southern Sweden lasts from the middle of June to late August, with peak flight in July. Catches of both strains were low at all trapping sites and throughout the study period and decreased further during the years following the dry summer of 2018. No Z‐strain males were trapped far away from maize fields.
Conclusion
Based on our results, and the low levels of ECB‐related damage observed in local maize fields, the Z‐strain is currently not imposing a threat to Swedish maize growers.
From 2005 to 2015, Ostrinia nubilalis were collected in the most important maize‐growing areas in Europe where MON 810 was cultivated. The susceptibility of these O. nubilalis collections to the ...Cry1Ab protein was determined using overlay bioassays and compared to that of reference (control) strains. Larvae that died or did not moult after 7 days were used to calculate a moulting inhibition concentration (MIC). Two different batches of Cry1Ab protein were used over the course of this study. Between 2005 and 2015, 145 collections of O. nubilalis from 14 areas were analysed. The Cry1Ab susceptibility of populations from different geographic regions differed only slightly across years. The greatest variability in the MIC50 for field samples collected from 2005 to 2011 and tested with batch 1 was 6.6‐fold in 2006. For field‐collected O. nubilalis, the difference between MIC50 values of the most susceptible and most tolerant samples was 13.1‐fold for this period. For samples collected in 2012–2015 and tested with batch 2, the greatest variability was 4.1‐fold in 2014. A diagnostic concentration (MIC99) was calculated for batch 1 (48 ng/cm2) using the results from all the collections in 2005–2012. Bridging experiments indicated that the diagnostic concentration for batch 2 was 28 ng/cm2. From 2006 onwards, no O. nubilalis reached the 2nd larval stage when the diagnostic concentration of either batch of Cry1Ab was used. Only one insect collected from Romania in 2012 and two insects collected as reference strain from Spain in 2015 survived exposure to a dosage of 20 ng/cm2, and none of these larvae survived on MON 810 maize. Our results indicate that there has been no significant change in susceptibility to Cry1Ab in European populations of O. nubilalis over the period 2005–2015.
Genetically modified (GM) Bt maize MON810 is promoted as being beneficial for farmers and the environment. The aim of this study was to compare particular claims of the benefits associated with this ...GM maize with Czech farmers' practice. Ten semi-structured interviews and 27 questionnaires obtained from Czech farmers who had grown Bt maize for at least one year in 2005–2016 were analysed qualitatively. The alleged benefits of MON810 cultivation regarding lower levels of fungal disease infestation, yield increase, reduction of insecticide usage, lowered costs, time saving and simple manipulation were enjoyed by a varying proportion of Czech GM farmers. In contrast, some farmers experienced the opposite of the claimed benefit regarding yield, costs, manipulation and time requirements. The exception was the 100% control of the European Corn Borer (ECB). The current and previous studies suggest that most of the benefits manifest themselves rather on farms under high ECB pressure. Seen from an economic viewpoint, the cultivation of Bt maize could be recommended in areas with persistent high corn borer pressure. However, the benefit to the environment is challenged and it is suggested that farmers should employ a complex of cultural control methods.
To protect themselves from herbivory, plants have evolved an arsenal of physical and chemical defences and release a variety of volatile organic compounds (VOCs). By releasing these VOCs, a ...signalling plant can both reduce herbivory, sometimes by more than 90%, and also warn neighbouring plants about an attack. The aim of this study was to assess the influence of herbivory and insect extract application on VOC release by damaged/treated and nearby undamaged/untreated maize plants. We confirmed that European corn borer (Ostrinia nubilalis) larvae attack or larvae extract application induced maize VOC release. Greater amounts of (Z)‐3‐hexenal, (E)‐2‐hexenal, (Z)‐3‐hexen‐1‐ol, (E)‐2‐hexen‐1‐ol, β‐myrcene, (Z)‐3‐hexen‐1‐yl acetate, 1‐hexyl acetate, (Z)‐ocimene, linalool, benzyl acetate, methyl salicylate, indole, methyl anthranilate, geranyl acetate, β‐caryophyllene, (E)‐β‐farnesene and (Z)‐3‐hexenal, (Z)‐3‐hexen‐1‐ol, (Z)‐3‐hexen‐1‐yl acetate, (Z)‐ocimene, linalool, indole, methyl anthranilate, geranyl acetate, β‐caryophyllene and (E)‐β‐farnesene were released as a result of biotic stress after insect attack or insect extract application. The amounts of each VOC released were qualitatively and quantitatively distinct and dependent on time after biotic stress exposure. However, for all biotic stresses, significantly lower VOC induction was measured when leaves were damaged/treated for three days, as compared to seven days. Our work also demonstrated that undamaged/untreated neighbouring plants also release significant amounts of VOCs. This suggests that VOC emission by a damaged/treated plant stimulates VOC induction in nearby undamaged/untreated plants. However, the concentrations of all VOCs released by neighbouring undamaged/untreated maize plants were lower than those from damaged/treated plants and were negatively correlated with distance from a damaged/treated plant. Still, significant VOC induction occurred in undamaged/untreated plants even at 3 m distance from a damaged/infected plant. Our work suggests that maize plant protective defence responses (VOC emission) can be induced via application of European corn borer extracts.
The European corn borer (ECB) Ostrinia nubilalis and Fusarium ear rot
Fusarium spp. pose a continuous threat to maize production worldwide. There
are several reports indicating that ECB damage to ...maize ears promotes
Fusarium ear rot infection. The aim of this study was to monitor the
influence of different insecticide treatments (a.i. chlorantraniliprole,
indoxacarb, and chlorantraniliprole+lambda-cyhalothrin) on the ECB and
fungal diversity on maize kernels in the field in a four-year trial
(2013-2016). A total of 16 different fungal genera were isolated from maize
kernels, and Fusarium species were confirmed to be the dominant pathogens,
present in all treatments, throughout the four years of experiments. The
incidence of Aspergillus spp. and Penicillium spp. was established to be
low. Apart from Fusarium species, the most frequent genera were: Aspergillus
spp., Mortierella spp., Mucor spp., Penicillium spp., Acremonium spp. and
Rhizopus spp. Treatments with chlorantraniliprole and
chlorantraniliprole+lambda-cyhalothrin showed higher efficacy, though not
statistically significant, compared to indoxacarb, in reducing the number of
ECB larvae and damage they cause. However, no direct effect on the number of
isolated fungal genera has been observed in any of the three insecticide
treatments.
Slow and consistent nutrient release by organic fertilizers can improve plant nutrient balance and defenses, leading to herbivore avoidance of organically managed crops in favor of conventional crops ...with weaker defenses. We propose that this relative attraction to conventional plants, coupled with the use of genetically modified, insecticidal crops (Bt), has created an unintentional attract-and-kill system. We sought to determine whether Bt and non-Bt corn Zea mays L. plants grown in soil collected from five paired organic and conventional fields differed in attractiveness to European corn borer Ostrinia nubilalis (Hübner) moths, by conducting ovipositional choice and flight tunnel assays. We then examined the mechanisms driving the observed differences in attraction by comparing soil nutrient profiles, soil microbial activity, plant nutrition, and plant volatile profiles. Finally, we assessed whether European corn borer abundance near corn fields differed based on soil management. European corn borer preferred plants grown in conventional soil but did not discriminate between Bt and non-Bt corn. Organic management and more alkaline soil were associated with an increased soil magnesium:potassium ratio, which increased plant magnesium, and were linked to reduced European corn borer oviposition. There was an inconsistent trend for higher European corn borer moth activity near conventional fields. Our results extend the mineral balance hypothesis describing conventional plant preference by showing that it can also improve attraction to plants with genetically inserted toxins. Unintentional attract (to conventional) and (Bt) kill is a plausible scenario for pest declines in response to Bt corn adoption, but this effect may be obscured by variation in other management practices and landscape characteristics. Graphical Abstract
Of 12 potential reproductive isolating barriers between closely related Z- and E-pheromone strains of the European corn borer moth (Ostrinia nubilalis), seven significantly reduced gene flow but none ...were complete, suggesting that speciation in this lineage is a gradual process in which multiple barriers of intermediate strength accumulate. Estimation of the cumulative effect of all barriers resulted in nearly complete isolation (>99%), but geographic variation in seasonal isolation allowed as much as ∼10% gene flow. With the strongest barriers arising from mate-selection behavior or ecologically relevant traits, sexual and natural selection are the most likely evolutionary processes driving population divergence. A recent multilocus genealogical study corroborates the roles of selection and gene flow (Dopman et al. 2005), because introgression is supported at all loci besides Tpi, a sex-linked gene. Tpi reveals strains as exclusive groups, possesses signatures of selection, and is tightly linked to a QTL that contributes to seasonal isolation. With more than 98% of total cumulative isolation consisting of prezygotic barriers, Z and E strains of ECB join a growing list of taxa in which species boundaries are primarily maintained by the prevention of hybridization, possibly because premating barriers evolve during early stages of population divergence.
Insect migratory flight differs fundamentally from most other kinds of flight behavior,in that it is non-appetitive.The adult is not searching for anything,and migratory flight is not terminated by ...encounters with potential resources.Many insect pests of agricultural crops are long-distance migrants,moving from lower latitudes where they overwinter to higher latitudes in the spring to exploit superabundant,but seasonally ephemeral,host crops.The migratory nature of these pests is somewhat easy to recognize because of their sudden appearance in areas where they had been absent only a day or two earlier.Many other serious pests survive hostile winter conditions by diapausing,and therefore do not require migration to move between overwintering and breeding ranges.Yet there is evidence of migratory behavior engaged in by several pest species that inhabit high latitudes year-round.In these cases,the consequences of migratory flight are not immediately noticeable at the population level,because migration takes place for the most part within their larger year-round distribution.Nevertheless,the potential population-level consequences can be quite important in the contexts of pest management and insect resistance management.As a case study,I review the evidence for migratory flight behavior by individual European corn borer adults,and discuss the importance of understanding it.The kind of migratory behavior posited for pest species inhabiting a permanent distribution may be more common than we realize.
Understanding adaptation involves establishing connections between selective agents and beneficial population responses. However, relatively little attention has been paid to seasonal adaptation, in ...part, because it requires complex and integrative knowledge about seasonally fluctuating environmental factors, the effects of variable phenology on exposure to those factors, and evidence for temporal specialization. In the European corn borer moth, Ostrinia nubilalis, sympatric pheromone strains exploit the same host plant (Zea mays) but may genetically differ in phenology and be reproductively "isolated by time." Z strain populations in eastern North America have been shown to have a prolonged larval diapause and produce one annual mating flight (July), whereas E strain populations complete an earlier (June) and a later (August) mating flight by shortening diapause duration. Here, we find evidence consistent with seasonal "adaptation by time" between these ecotypes.
We use 12 years of field observation of adult seasonal abundance to estimate phenology of ecotype life cycles and to quantify life-stage specific climatic conditions. We find that the observed reduction of diapause duration in the E strain leads their non-diapausing, active life stages to experience a ~ 4 °C colder environment compared to the equivalent life stages in the Z strain. For a representative pair of populations under controlled laboratory conditions, we compare life-stage specific cold tolerance and find non-diapausing, active life stages in the E strain have as much as a 60% greater capacity to survive rapid cold shock. Enhanced cold hardiness appears unrelated to life-stage specific changes in the temperature at which tissues freeze.
Our results suggest that isolation by time and adaptation by time may both contribute to population divergence, and they argue for expanded study in this species of allochronic populations in nature experiencing the full spectrum of seasonal environments. Cyclical selective pressures are inherent properties of seasonal habitats. Diverse fluctuating selective agents across each year (temperature, predation, competition, precipitation, etc.) may therefore be underappreciated drivers of biological diversity.
Industrial hemp cultivation restarted in Estonia in mid 2000s and the hemp cultivation area has increased very fast in recent years, but it is unknown to what extent hemp productivity can be curbed ...by widespread crop pests. Thus, the main aim of this study was to evaluate the presence and damage of hemp pests in northern field conditions. A field trial with the hemp cultivars ‘Finola’ (2021) and ‘Estica’ (2022) was established in Central Estonia (58° N, 26° E), and the plants were grown with different fertilizer types (complex fertilizer, ammonium nitrate), fertilization methods (at sowing/top dressing) and nitrogen rates (0–200 kg ha
−1
) and their effect on the European corn borer (ECB,
Ostrinia nubilalis
) damage was assessed. The
O. nubilalis
infestation increased with every observation date throughout the seasons until the harvest. The
O. nubilalis
damage was overall greater in 2022 than in 2021, and the seed yield reduction reached to 120 kg ha
−1
in 2022, indicating progressive increase in
O. nubilalis
damage. Fertilization rate strongly increased biomass and seed yields, but weakly reduced
O. nubilalis
infection. Estonia is one of the most important hemp-cultivation areas in Europe, and in northern conditions, the crop was previously considered to be relatively pest-free. The northward movement of crop infection by
O. nubilalis
implies that future hemp cultivation might need integrated
O. nubilalis
control practices adapted to site-specific agro-climatic conditions.
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