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.
Plants turn on induced defenses upon insect herbivory. In the current study, we evaluated the role of European corn borer (ECB) elicitors (molecules secreted by herbivores) that either ...induce/suppress defenses in Solanum lycopersicum (tomato) and Zea mays (maize), two very important crop plants that are grown for food and/or fuel throughout the world.
We used a combination of molecular, biochemical, confocal and scanning electron microscopy, caterpillar spinneret ablation/cauterization, and conventional insect bioassay methods to determine the role of ECB elicitors in modulating defenses in both tomato and maize crop plants.
Our results clearly demonstrate that the components present in the ECB saliva induce defenserelated proteinase inhibitors in both tomato (PIN2) and maize (MPI). Presence of glucose oxidase in the ECB saliva induced defenses in tomato, but not in maize. However, ECB saliva induced genes present in the jasmonic acid biosynthesis pathway in both tomato and maize.
Although ECB saliva can induce defenses in both tomato and maize, our results suggest that host-specific salivary components are responsible for inducing host plant defenses. Proteomic analysis of ECB salivary elicitors and plant receptors/signaling mechanisms involved in recognizing different ECB elicitors remains to be determined.
High specificity for silencing target genes and single‐copy target genes that yield clear phenotypes are two important factors for the success of RNA interference (RNAi). The lethal giant larvae ...(Lgl) gene appears to be an ideal gene for RNAi because RNAi can effectively suppress its expression and results in molting defects and mortality in Tribolium castaneum. To investigate the suitability of this gene for RNAi in other insects, we identified and characterized DvLgl from the western corn rootworm, Diabrotica virgifera virgifera, a species exhibiting high RNAi efficiency. DvLgl was expressed in all developmental stages and tissues investigated. The deduced DvLgl protein showed high amino‐acid sequence identities and similar domain architecture to Lgls from other insect species. Despite many similarities among insect Lgls, RNAi‐mediated suppression of DvLgl failed to produce a phenotype in D. v. virgifera adults. The difference in developing phenotypes could be attributed greatly to the level of gene suppression and the insect developmental stages for RNAi. These results highlight the variability in RNAi response among insects and showcase the importance of screening multiple target genes when conducting RNAi studies. Our findings are expected to help the design of future RNAi studies and future investigations of Lgl in insects.
Investigation of the lethal giant larvae (Lgl) gene as an RNAi target.
Research Highlights
•
Lgl appeared to be an ideal target gene for RNAi. However, suppression in D. v. virgifera failed to produce a phenotype, indicating additional challenges in selecting effective target genes for use of RNAi in research and insect pest management.
Variable RNA interference (RNAi) efficiencies limit RNAi-based pest management strategies for many pests. Previous efforts to understand mechanisms contributing to low RNAi efficiency indicate that ...double-stranded RNA (dsRNA) is degraded in the European corn borer (ECB), Ostrinia nubilalis, due to nuclease activity. To investigate the contribution of dsRNA-degrading endonucleases (dsRNases) and lepidopteran-specific RNAi efficiency-related nucleases (REases) to dsRNA instability and low RNAi efficiency in ECB, five complementary DNAs putatively encoding four dsRNases (OndsRNase1, 2, 3, and 4) and one REase (OnREase) were sequenced. Characterization of these transcripts revealed that substrate specificity might vary among the four dsRNases due to different amino acid combinations in the substrate-binding sites. Gene expression analysis indicated that OndsRNase2 and OnREase were highly expressed in the larval gut, and OndsRNase1 showed the highest expression in hemolymph, especially in older developmental stages. Transcript level analysis after dsRNA exposure revealed that expression of OnREase rapidly increased upon dsRNA ingestion or injection, whereas OndsRNase4 expression only increased after long-term ingestion of dsRNA. While the biological function of these nucleases remains to be verified, our results suggest that OnREase and OndsRNase2, and OndsRNase1 and OndsRNase4 may be responsible for degradation of dsRNAs in the ECB gut and hemolymph, respectively, thereby contributing to low RNAi efficiency.
The European corn borer (ECB;
Ostrinia nubilalis
) is an economically damaging insect pest of maize (
Zea mays
L.), an important cereal crop widely grown globally. Among inbred lines, the maize ...genotype Mp708 has shown resistance to diverse herbivorous insects, although several aspects of the defense mechanisms of Mp708 plants are yet to be explored. Here, the changes in root physiology arising from short-term feeding by ECB on the shoot tissues of Mp708 plants was evaluated directly using transcriptomics, and indirectly by monitoring changes in growth of western corn rootworm (WCR;
Diabrotica virgifera virgifera
) larvae. Mp708 defense responses negatively impacted both ECB and WCR larval weights, providing evidence for changes in root physiology in response to ECB feeding on shoot tissues. There was a significant downregulation of genes in the root tissues following short-term ECB feeding, including genes needed for direct defense (e.g., proteinase inhibitors and chitinases). Our transcriptomic analysis also revealed specific regulation of the genes involved in hormonal and metabolite pathways in the roots of Mp708 plants subjected to ECB herbivory. These data provide support for the long-distance signaling-mediated defense in Mp708 plants and suggest that altered metabolite profiles of roots in response to ECB feeding of shoots likely negatively impacted WCR growth.
Between 2020 and 2021, we conducted research in eastern Romania to monitor the bioecology of the European corn borer (Ostrinia nubilalis Hbn.), an important pest of corn. The bioecology research ...established the pest stage duration (egg, larva, pupa, and moth), the flight curve, and the flight peak. The bioecological study occurred in the experimental corn field and a field cage. According to our findings, the insect has one generation per year. The European corn borer hibernates as a mature larva in corn residues and continues developing in the spring, when the weather warms. It pupates from May to July over 37 days. Analyzing the data recorded during the winters of 2020 and 2021, we observed that the warming trend favored the high survival of hibernating larvae (60.7%). Due to the large number of mature larvae that had favorable conditions during the winter, there is an intense flight, starting in June and ending in September. When the first moth was caught in the light trap, the ∑(tn-10) °C (sum of degree days) was 245.6 °C. In 2020, the flight was recorded for 94 days. In 2021, the European corn borer flight lasted 104 days. The initial egg masses were detected when the total of ∑(tn-10) °C reached 351.5 °C. Moths laid the eggs for 25 days, mostly during peak flight in late June and early July. The first larvae hatched when ∑(tn-10) °C totaled 438.4 °C, and stages III–V were recorded in the harvested crop. Understanding the bioecology of the European corn borer can offer valuable insights into managing population levels and identifying optimal timing for addressing infestations in corn crops.
We assessed the effectiveness of a biofortified maize line (4BtxHC) which accumulates high levels of antioxidant carotenoids that also expressed the insecticidal Cry1Ac Bacillus thuringiensis (Bt) ...gene against the European corn borer Ostrinia nubilalis. This line had been previously engineered to accumulate carotenoids specifically in the seed endosperm, whereas the Bt gene was expressed constitutively. The concentrations of Bt toxin (Cry 1Ac) in the leaves of the 4Bt and 4BtxHC lines were not significantly different at 47±6 μg/g of fresh weight (FW); neither were they in the kernels of both lines (35±3 μg/g FW). The kernels and leaves were toxic to the larvae of O. nubilalis. However, the insecticidal activity was substantially lower (ca. 20%) than that of lines that expressed only Bt in spite that the two lines showed a quantity of toxin not significantly different in kernels or in leaves. Although the reduced effectiveness of Cry1Ac in kernels may not be entirely surprising, the observation of the same phenomenon in vegetative tissues was unexpected. When semi-artificial diets containing kernels from 4Bt supplemented with different levels of β-carotene were used in insect bioassays, the β-carotene moderated the effectiveness of the Bt similarly to the plant material with carotenoid enrichment. To elucidate the biochemical basis of the reduced effectiveness of Bt toxin in the carotenoid-enriched plants, we measured the activity of three enzymes known to be implicated in the detoxification defence, namely, catalase, superoxide dismutase and glutathione S-transferase. Whereas Cry1Ac expression significantly increased SOD and CAT enzymatic activity in the absence of carotenoids, carotenoids, either in 4BtxHC or in artificial diets enriched with β-carotene, significantly lowered CAT activity. Carotenoids can therefore moderate the susceptibility of the maize borer O. nubilalis to Cry1Ac, and we hypothesize that their role as antioxidants could explain this phenomenon via their scavenging of reactive oxygen species produced during Cry1Ac detoxification in the larvae. The involvement of this mechanism in the decreased mortality caused by Cry1Ac when carotenoids are present in the diet is discussed.
The damage of the European corn borer, Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae), causes is mainly determined by the success of its overwintering. The aim of our study was to assess the ...consequences of the artificial cooling on the movement and survival ability of overwintering larvae of O. nubilalis by using computer‐assisted tomography. The in situ movement of the examined larvae in icy media of different thickness (5, 15, and 30 cm) and during freezing periods of 5, 10, 20, 40, and 60 min was determined in maize stalks using CT and the positioner‐laser of the CT apparatus. It has been found that the thickness of the ice had a significant effect on the displacement of the overwintering larvae, however, the impact of the duration of freezing on the moving of the larvae could not be proven statistically. Enhanced larvae activity due to thinner ice layers (5, 15 cm) were of exponential type, which was more pronounced just prior to the freezing point. In contrast, thicker ice covering (30 cm) caused complete immobility. According to our results, the diapausing larvae were still able to move and albeit it appeared to be capable of surviving the direct impact of extreme cold, it could even leave its overwintering place as a result of low temperature. Furthermore, the maize stalk tissue contributes to the survival‐success of the larvae as it seems to act as a temperature‐buffer moderating the severe impact that low temperature exerts on living tissue.
The thickness of the ice had a significant effect on the displacement of the overwintering larvae, however, the impact of the duration of freezing on the moving of the larvae could not be proven statistically. Enhanced larvae activity due to thinner ice layers (5, 15 cm) were of exponential type, which was more pronounced just prior to the freezing point.
The thicker ice covering (30 cm) caused complete immobility. The diapausing larvae were still able to move and albeit it appeared to be capable of surviving the direct impact of extreme cold, it could even leave its overwintering place as a result of low temperature.
The maize stalk tissue contributes to the survival‐success of the larvae as it seems to act as a temperature‐buffer moderating the severe impact that low temperature exerts on living tissue.
The insecticidal toxin encoded by the
cry1Ab gene from
Bacillus thuringiensis was released in root exudates from transgenic
Bt corn during 40 days of growth in soil amended to 0, 3, 6, 9, or 12% ...(v/v) with montmorillonite or kaolinite in a plant growth room and from plants grown to maturity in the field. The presence of the toxin in rhizosphere soil was determined by immunological and larvicidal assays. No toxin was detected in any soils from isogenic non-
Bt corn or without plants. Persistence of the toxin was apparently the result of its binding on surface-active particles in the soils, which reduced the biodegradation of the toxin. The release of the toxin could enhance the control of insect pests or constitute a hazard to nontarget organisms, including the microbiota of soil, and increase the selection of toxin-resistant target insects.
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