Agricultural intensification has led to dramatic losses of species and associated ecosystem services. In the European Union, agri‐environment schemes (AESs) have been developed to mitigate these ...challenges. There are two opposing AES strategies, targeting either production or non‐production areas. Organic farming focuses on production and conservation on the same land‐use area, whereas flower strips adjacent to crop fields are in favour of intensified conventional production combined with conservation strips outside the cultivated area.
We investigated pest and natural enemy abundances of organic farming versus establishing flower strip in 10 agricultural landscapes in Central Germany along a gradient of mean field size (1.24–6.78 ha). We focused on three winter wheat fields per landscape: conventional field (control), conventional field with adjacent flower strip and organic field. We sampled crop pests such as cereal leaf beetles (CLBs) and cereal aphids as well as their natural enemies.
Our results indicated that the abundance of CLB larvae was more than two times higher in conventional farming with and without flower strip than that in the organic farming. The abundance of natural enemies was supported by landscapes with small mean field size, that is their numbers increased c. threefold when field size decreased from 7 to 2 ha.
Aphid abundance was lower in organic fields and conventional control fields than in conventional fields with flower strips suggesting a potential disservice of flower strips. Parasitoids and natural enemies benefited from flower strips, but they were obviously not able to control the aphids.
Synthesis and applications. The major pests in cereals, aphids and CLBs infested organic farming less than flower strips along conventional fields. However, the abundance of natural enemies of pests benefited from flower strips and, in addition, from decreasing field size in agricultural landscapes. Hence, enhancing predator populations for more effective biological pest control may be best with decreasing field sizes combined with organic farming and flower strips. Altogether, organic farming might contribute much more to low pest damage than a conventional farming strategy with flower strips.
The major pests in cereals, aphids and cereal leaf beetles infested organic farming less than flower strips along conventional fields. However, the abundance of natural enemies of pests benefited from flower strips and, in addition, from decreasing field size in agricultural landscapes. Hence, enhancing predator populations for more effective biological pest control may be best with decreasing field sizes combined with organic farming and flower strips. Altogether, organic farming might contribute much more to low pest damage than a conventional farming strategy with flower strips.
The larvae of the cereal leaf beetle (Oulema melanopus L., CLB) are one of the major pests of small grains in the Northern Hemisphere. Besides other cereals, winter wheat (Triticum aestivum L.) is ...among the preferred host plants of CLB larvae. In this two-year study, which was carried out in central Hungary, we examined the influence of an increasing initial number of CLB larvae on the extent of both flag leaf and all-leaf defoliation and the effects of this defoliation on the yield of winter wheat cultivars ‘Alcantara’ and ‘Altigo’. We used asymptotic nonlinear regression models for analysing the impact of the initial number of CLB larvae on flag leaf and all-leaf defoliation, and linear regression models to quantify the effect of defoliation on the yield. The asymptotic nonlinear regression models predicted mean maximal defoliation values of ca. 25% for flag leaves and ca. 20% for all leaves. In 2017, CLB defoliation had a severe impact on the yield, with 10% flag leaf defoliation causing ca. 0.17 g and 10% all-leaf defoliation causing ca. 0.241 g reduction in yield per ear for both cultivar types. However, CLB defoliation did not have any significant effects on the yield in the following study year. The predicted mean maximal defoliation levels are consistent with results reported in previous studies, whereas the strong negative effect on the yield found in 2017 is considerably higher than yield losses reported in previously published studies. Our results suggest that even high abundances of CLB larvae only cause rather low degrees of defoliation, but can still generate severe yield losses in winter wheat. However, the biological mechanisms behind both phenomena are yet unknown and highlight the need for further research.
•We found an asymptotic relationship between the number of cereal leaf beetle larvae and their defoliation in winter wheat.•This defoliation affected all leaves, that is both flag and other leaves.•Our models predicted average maximal defoliation levels below 30% for both flag and all leaves.•These overall low levels of defoliation, however, still caused severe yield losses (around or even above 50%) in many cases.
The article presents the results of studies of the resistance of the breeding material of winter soft wheat (Triticum aestivum L.) to the phytophagous beetle, cereal leaf beetle (Oulema melanopus ...Z.). The research was conducted in 2019-2021 at the FSBI SCNIIGPSH VNC RAS. The objects of research were 128 varieties of winter soft wheat from the VIR collection, of various ecological and geographical origin. The purpose of the research is to study the gene pool of winter soft wheat and create a new source material for breeding for resistance to cereal leaf beetle. There are 31.3% of varieties that are resistant. They are Torrild, Mereke 70, Zhadyra, Kobra, Soraja, Fenezia, Dorota, Olivin, Zaritsa, Muza, Areal, Teslo, Kredo, Bizel, Frontana, Renan, Zysk, Biggar, AK biday, Alacris, Cina 7, Solara, Chornobrova, Batko, Zvytyaga, Astella, Lilit, Verita, Batum, Khmel'nychanka, Vatazbok, Markola, Zolotoy bezosty, Omskaya 5, Pionerskaya 32, Nebokrai, Lasuma, Blago, Kamyshlanka 4, Jadvisia. The correlation coefficient between the degree of leaf damage and an ear length is -0.56 (negative, average), between the degree of leaf damage and the number of grains in an ear is -0.68 (negative, strong), between the degree of leaf damage and the weight of the grain from an ear and the plant productivity index (PPI) is negative and very high -0.93 and -0.86, respectively. All productivity elements had significant correlation coefficients, but the highest are r = -0.93 (with the weight of grain from an ear) and r = -0.86 (plant productivity index). The source material for use in breeding programs for resistance to cereal leaf beetle has been isolated.
One of the earliest responses of plants to insects’ attack is generation of reactive oxygen species. However, the elevated level of ROS can elicit oxidative burst within plant tissues, and plants ...employ antioxidant systems against these radicals. Due to their chemical structures, polyphenols are able to diminish the level of ROS. Thus, we investigated the role of phenolic compounds in oxidative stress within winter triticale caused by Sitobion avenae and Oulema melanopus. It was found, that infestation by insects induced a high increase in the content of hydrogen peroxide and superoxide anion radical within resistant Lamberto cv. 24 hpi, whereas in sensitive Marko cv., an increase in H2O2 content was found within two days of aphid feeding. Moreover, resistant plants showed earlier and much greater induction of l-phenylalanine and l-tyrosine ammonia lyases and chalcone synthase activities, as well as accumulation of phenolic compounds in response to insect feeding than susceptible Marko. On the other hand, strong positive influence of hydrogen peroxide and superoxide radical contents on chalcone synthase activity and furthermore flavonoid biosynthesis was detected in the susceptible cultivar. Negative relationships between level of o-coumaric acid or flavonoid compounds and content of hydrogen peroxide or superoxide radical suggest their antioxidant capacity. Luteolin and o-coumaric acid may attend in scavenging of hydrogen peroxide, whereas quercetin, apigenin and (+)-catechin probably participate in reduction of superoxide anion radical content.
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•The grain aphid induced in triticale higher levels of H2O2 and O2•− than beetle.•Generation of ROS was earlier and higher in resistant than susceptible plants.•Chalcone synthase in the susceptible cv. is up-regulated by H2O2, O2•−, and TAL.•In the susceptible plants, flavonoids play crucial roles in diminishing of ROS.•In resistant triticale cv., phenolic compounds act as prooxidants against insects.
Abstract Background Since the 1980s, soils in a 22-km 2 area near Lake Neuchâtel in Switzerland have been recognized for their innate ability to suppress the black root rot plant disease caused by ...the fungal pathogen Thielaviopsis basicola . However, the efficacy of natural disease suppressive soils against insect pests has not been studied. Results We demonstrate that natural soil suppressiveness also protects plants from the leaf-feeding pest insect Oulema melanopus . Plants grown in the most suppressive soil have a reduced stress response to Oulema feeding, reflected by dampened levels of herbivore defense-related phytohormones and benzoxazinoids. Enhanced salicylate levels in insect-free plants indicate defense-priming operating in this soil. The rhizosphere microbiome of suppressive soils contained a higher proportion of plant-beneficial bacteria, coinciding with their microbiome networks being highly tolerant to the destabilizing impact of insect exposure observed in the rhizosphere of plants grown in the conducive soils. We suggest that presence of plant-beneficial bacteria in the suppressive soils along with priming, conferred plant resistance to the insect pest, manifesting also in the onset of insect microbiome dysbiosis by the displacement of the insect endosymbionts. Conclusions Our results show that an intricate soil–plant-insect feedback, relying on a stress tolerant microbiome network with the presence of plant-beneficial bacteria and plant priming, extends natural soil suppressiveness from soilborne diseases to insect pests.
Wheat (
) is one of the most economically important crops in the world. During the routine monitoring of wheat pest, the cereal leaf beetle (CLB,
Coleoptera, Chrysomelidae), in the Greater Poland ...region, it was observed that some leaves wounded by CLB also displayed brownish lesions with clear margins and yellow halo, disease symptoms resembling a bacterial infection. The aim of this study was therefore to investigate those symptoms to establish a causal agent of the disease. The identification based on the results of the Biolog's Gen III system, 16S rRNA, and
B genes sequencing, revealed the presence of eight strains of
bacteria. Four strains were derived from wheat leaves (Ta024, Ta027, Ta030, Ta046), and four from the CLB's oral secretion (OUC1, OUD2, OUF2, and OUG1). They shared the nucleotide identity ranging from 99 to 100% to
strains deposited in the GenBank database. Additionally, the multi-locus sequence analysis (MLSA) of concatenated sequences of partial
D,
A,
B,
B, and
B genes was performed. All
strains isolated in Poland, grouped into one cluster supported with high bootstrap value. Pathogenicity tests performed on four varieties of wheat plants have identified
strains as a causal agent of wheat disease. To our knowledge, this is the first report of
affecting wheat plants.
The yearly timing of the life cycle of a parasitoid is a key element of its life‐history strategy. I examine here factors influencing the expression of partial bivoltinism in Tetrastichus julis ...Walker (Hymenoptera: Eulophidae), a specialist parasitoid introduced to North America to attack its univoltine host, the cereal leaf beetle, Oulema melanopus (L.) (Coleoptera: Chrysomelidae). The varying tendency was assessed of individuals of this gregarious larval parasitoid to either emerge as adults in the same summer they mature, or to enter diapause to emerge the following year. Parasitized hosts were obtained by rearing cereal leaf beetles collected as mature larvae from grain fields in northern Utah (western USA) throughout the growing seasons in 2013 and 2014. Cocoons spun by these beetles were held to determine patterns over the spring and summer in the tendency of the parasitoid to forgo larval diapause. A high percentage (nearly 90% in 2013) of parasitoid individuals were found to forgo diapause and emerge in the same summer from earliest maturing hosts. This percentage rapidly declined to 20% or less of individuals forgoing diapause and emerging from cocoons as the summer advanced. The percentage of parasitoid individuals forgoing diapause increased significantly at a given time of season (early or late) as the number of conspecifics with which an individual shared a host larva increased. These results may reflect a trade‐off for individual parasitoids in which greater success in finding – and ovipositing in – host larvae the following spring vs. in summer, is countered by reduced survivorship in diapausing over the winter vs. emerging in the same summer in which the parasitoid matures. Expression of partial bivoltinism of T. julis, as affected strongly by both season and within‐host density, results in high rates of parasitism of cereal leaf beetles both early and late in the season.
The percentage of individuals of the gregarious endoparasitoid Tetrastichus julis (Hymenoptera: Eulophidae) forgoing larval diapause over the winter to emerge instead in the same summer that they developed within their host, the cereal leaf beetle Oulema melanopus (Coleoptera: Chyrsomelidae), was examined for field populations of the parasitoid and host in northern Utah (USA). This percentage decreased as the season advanced from spring through summer, and increased for a given time of season as the number of individuals sharing the host increased.
Semi‐natural habitats (SNHs) are becoming increasingly scarce in modern agricultural landscapes. This may reduce natural ecosystem services such as pest control with its putatively positive effect on ...crop production. In agreement with other studies, we recently reported wheat yield reductions at field borders which were linked to the type of SNH and the distance to the border. In this experimental landscape‐wide study, we asked whether these yield losses have a biotic origin while analyzing fungal seed and fungal leaf pathogens, herbivory of cereal leaf beetles, and weed cover as hypothesized mediators between SNHs and yield. We established experimental winter wheat plots of a single variety within conventionally managed wheat fields at fixed distances either to a hedgerow or to an in‐field kettle hole. For each plot, we recorded the fungal infection rate on seeds, fungal infection and herbivory rates on leaves, and weed cover. Using several generalized linear mixed‐effects models as well as a structural equation model, we tested the effects of SNHs at a field scale (SNH type and distance to SNH) and at a landscape scale (percentage and diversity of SNHs within a 1000‐m radius). In the dry year of 2016, we detected one putative biotic culprit: Weed cover was negatively associated with yield values at a 1‐m and 5‐m distance from the field border with a SNH. None of the fungal and insect pests, however, significantly affected yield, neither solely nor depending on type of or distance to a SNH. However, the pest groups themselves responded differently to SNH at the field scale and at the landscape scale. Our findings highlight that crop losses at field borders may be caused by biotic culprits; however, their negative impact seems weak and is putatively reduced by conventional farming practices.
Understanding how semi‐natural habitats influence provisioning ecosystem services of agricultural fields should be a key argument in debates about economic profits versus biodiversity conservation in agricultural landscapes. Therefore, we studied the effect of pest infestation as a biotic culprit to yield losses close to hedgerows and kettle holes using a structural equation model. We found arable weed cover being associated with yield losses along the transects, however, only in the proximate distances to the field border.
Cereal leaf beetles (CLBs) are described as an invasive pest of small grain cereals in many regions worldwide. Prediction models aimed to prevent yield losses caused by these feeding insects have ...been developed by researchers all over the world. As a foundation for many of these prediction models, it is known that a specific number of heat units, or growing degree days (GDDs), is required for an insect to complete a certain physiological process. In this paper, we overview the existing GDD models for CLBs. Furthermore, we used our Belgian input data to compare model predictions with our own observations.Though, the existing models were not able to predict the seasonal trends present in our data: the occurrence of various life stages were monitored earlier then the model predicted. Hence, a weighted GDD model was tested on the data as well: the accumulated GDDs during certain periods were balanced according to the significance of this period for the insect. Rainfall and/or relative humidity were included as well. Based on these selected variables, multiple linear regression models, ridge regression models, and regression trees were fitted. This approach performed considerably better compared to the simple accumulation of GDD. However, based on cross-year cross-location validation method, to gain insight in the future performance of the models, the accuracy was still too low to serve as an accurate warning tool.
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