Analyses of factors influencing the population dynamics of cereal aphids and their relevance to model extensions

Aphids annually infest winter wheat, Triticum aestivum L., in late spring and early summer in Central Europe, but densities leading to strong yield losses are reached only occasionally (Basedow et al., 1994). Three aphid species, Sitobion avenae Fabr., Metopolophium dirhodum Walk. and R. padi L., usually occur in cereal crops with increasing densities from late spring onwards (Basedow et al., 1994). Modelling population levels of cereal aphids is a key tool in integrated pest management for winter wheat. Over the last 30 years, considerable efforts have been made to investigate the population dynamics of aphids (DeWit and Rabbinge, 1979; Entwistle and Dixon, 1987). In Central Europe to date, two models have attained greater importance in late spring: LAUS (Friesland, 1986) and GETLAUS01 (Gosselke et al., 2001). The first one estimates the population level of S. avenae in spring in winter wheat fields and has obtained regional significance in practical plant protection. In contrast, the model GETLAUS01 is a scientific model, not designed for practical plant protection. It describes in great detail the population dynamics of S. avenae, R. padi and M. dirhodum. Both models have been improved over time and extended with several factors, e.g. by including the effects of antagonists, fertilisation, crop density, plant protection agents and meteorological parameters on population development. The objective of this study was to analyse the following three factors in terms of their impact on population and migration characteristics: cultivar, proximity between winter and summer hosts and migration (according to meteorological parameters).Getreideblattläuse (Hemiptera: Aphididae) sind die bedeutendsten Schädlinge von Winterweizen im Frühjahr und Sommer. Sie führen jedoch nur zu signifikanten Ertragsausfällen, wenn biotische und abiotische Faktoren ein optimales Populationswachstum erlauben. Einige dieser Faktoren sind bereits in Simulationsmodellen berücksichtigt. In der vorliegenden Arbeit wurden Sorteneinflüsse, die Nähe von Winter- zu Sommerwirten und meteorologische Parameter bezüglich der Migrations- und Populationsentwicklung als weitere mögliche Faktoren im Hinblick auf Modellerweiterungen untersucht. 8 Winterweizensorten zeigten weder bezüglich der Entwicklung von Nachkommen (in Klippkäfigen, BBCH-Stadium 32 und 69), noch während der Erstbesiedelungsphase von geflügelten Getreideblattläusen (Ende Mai, Anfang Juni) bedeutende Unterschiede. Die Nähe von Winter- zu Sommerwirten beeinflusste in unterschiedlicher Weise den Populationsaufbau der wirtswechselnden Arten im Winterweizen. In Jahren mit hoher Populationsentwicklung auf den Winterwirten konnte nur für Rhopalosiphum padi L. signifikant erhöhte Populationsdichten im Winterweizen in nächster Nähe zu Prunus padus L. festgestellt werden. Die frühe Migration wurde anhand von Saugfallendaten verschiedener Standorte der letzten Jahre untersucht. Das Erstauftreten von R. padi (1. Fänge in Saugfallen) zeigte sich dabei recht konstant am 13. Mai eines Jahres. Die Beziehungen zwischen den weiteren Migrationsereignissen und meteorologischen Parametern waren jedoch eher schwach ausgeprägt (R²<0,21, p=0,01); wobei hier Globalstrahlung (R²=0,21), Temperatur (R²=0,18) und Windgeschwindigkeit (R²=0,14) die deutlichsten Beziehungen zeigten

Blue-green opponency and trichromatic vision in the greenhouse whitefly (Trialeurodes vaporariorum)

Visual orientation in the greenhouse whitefly ( Trialeurodes vaporariorum Westwood, Hemiptera: Aleyrodidae) is the result of 9wavelength-specific behaviours9. Green-yellow elicits 9settling behaviour9 while ultraviolet (UV) radiation initiates 9migratory behaviour9. Electroretinograms of the photoreceptors9 spectral efficiency showed peaks in the green and the UV range and whitefly vision was said to be dichromatic. In order to study the visual behaviour of T. vaporariorum , nineteen narrow-bandwidth LEDs covering the UV-A and visible range were used in combination with light scattering acrylic glass screens in a small-scale choice arena under greenhouse conditions. Multiple-choice and dual-choice assays were performed, resulting in LED-based behavioural action spectra of settling (green) and migratory behaviour (UV). A potential inhibitory blue-green chromatic mechanism was studied by combining yellow with different blueish LEDs. Intensity dependencies were illustrated by changing LED intensities. Regarding the 9settling response9, highest attraction was achieved by a green LED with a centroid wavelength of 550 nm, while a blue LED with 469 nm proved to be most inhibitory. Behaviour was distinctly intensity dependent. 9Migratory behaviour9 was elicited the most by the UV LED with the shortest available wavelength of 373 nm. The results clearly prove the presence of a green and a yet undescribed blue sensitive photoreceptor and a blue-green opponent mechanism. Furthermore, empirical colour choice models were built and receptor peaks were estimated around 510 - 520 nm (green), 480 - 490 nm (blue) and 340 - 370 nm (UV). Consequently, Trialeurodes vaporariorum possesses a trichromatic receptor setup

Effect of narrow-banded blue LED device on host plant settlement by greenhouse whitefly and currant-lettuce aphid

Manipulating phytophagous insects with light-based repelling techniques has shown its potential to be a useful tool in integrated pest management systems in the future. Underlying optical mechanisms can be applied in field and in protected cultivation, with reflecting materials or emitting light sources, such as LEDs. Many pest insects are characterised by their cryptic lifestyle to avoid intervening pest protection measurements. In addition, there is a high degree of resistance mechanisms against insecticides in certain species. The idea of most light-repelling techniques is to reduce the immigration and the settlement of pest species on hostplants before population growth even starts. We conducted experiments with narrow-banded blue LEDs arranged around the plants and emitting radiation towards the sky. For compact rosette Lactuca sativa and upright-branched Euphorbia pulcherrima, we tested the suitability of the measure on settlement of Trialeurodes vaporariorum in 2 choice experiments. In further choice experiments with reduced number of untreated plants, T. vaporariorum and Nasonovia ribisnigri were evaluated for the effect on hostplant settlement of the light barrier on lettuce plants under more practical conditions. The light barrier shows high repellent impact on hostplant settlement by greenhouse whitefly, independent of different plant architectures. The modified choice experiment showed strong decrease in hostplant settlement for greenhouse whitefly. For currant-lettuce aphid, tendencies are shown, but no statistical effect could be demonstrated. Possible applications and differences between the insect species used for the experiments are discussed

Inheritance genetics of the trait vector competence in Frankliniella occidentalis (Western flower thrips) in the transmission of Tomato spotted wilt virus

The complexity of tospovirus–vector–host plant interaction is linked to a range of factors influencing vector's efficacy in virus transmission, leading to high variability in the transmission efficiency within vector populations. Main shortcomings of most studies are the missing information on the intrinsic potential of individual insects to serve as efficient vectors, both at phenotypic and at genotypic levels. Moreover, detailed analysis of vector competence heredity and monitoring the splitting of both genotypes and phenotypes in filial generations has not been reported. In this study, using the model system Frankliniella occidentalis and Tomato spotted wilt virus, we evaluated the inheritance and stability of the trait vector competence in a population through basic crossings of individually characterized partners, as well as virgin reproduction. We hypothesized that the trait is heritable in F. occidentalis and is controlled by a recessive allele. From the results, 83% and 94% of competent and noncompetent males respectively, inherited their status from their mothers. The trait was only expressed when females were homozygous for the corresponding allele. Furthermore, the allele frequencies were different between males and females, and the competent allele had the highest frequency in the population. These suggest that the trait vector competence is inherited in single recessive gene in F. occidentalis, for which the phenotype is determined by the haplodiploid mechanism. These findings are fundamental for our understanding of the temporal and spatial variability within vector populations with respect to the trait vector competence and at the same time offer an essential basis for further molecular studies.DFG/207/37-

Reducing initial aphid infestation by use of coloured mulch foils and newly developed biodegradable spray-films

A newly invented biodegradable sprayable film based on renewable raw materials was modified in colour to reduce the landing and settlement of alate aphids (Macrosiphum euphorbiae, Nasonovia ribisnigri) on iceberg lettuce (Lactuca sativa L., var. crispa). The sprayable films were compared with green and black conventional PE-foils and the cultivation on bare soil. In field trials, migration and host settlement of insect pests were investigated with special consideration of colour contrasts and light reflection. The lettuce was evaluated for alate aphid infestation at the time of initial infestation and at the time of harvest. The aim was to reduce the initial infestation number with alate individuals and to minimize the demand for additional intervening measurements for plant protection. The black-grey spray film led to reduced numbers of aphids at initial infestation date. Evaluation at harvest time shows the need of secondary measurements for reliable pest control. The quality of the lettuce heads was not negatively affected by the spray treatment.Eine neu entwickelte, biologisch abbaubare, sprühfähige Folie auf Basis nachwachsender Rohstoffe wurde farblich modifiziert, um den Zuflug und die Ansiedlung von Blattläusen (Macrosiphum euphorbiae, Nasonovia ribisnigri) auf Eisbergsalat (Lactuca sativa, var. crispa) zu reduzieren. Die sprühfähigen Folien wurden mit grünen und schwarzen konven­tionellen PE-Folien und dem Anbau auf Boden verglichen. In Feldversuchen wurden der Zuflug und die Ansiedlung von Schadinsekten unter besonderer Berücksichtigung von Farbkontrasten und Lichtreflexion untersucht. Der Salat wurde auf den Befall mit Blattläusen zum Zeitpunkt des Erstbefalls und zum Zeitpunkt der Ernte untersucht. Ziel war es, den Erstbefall mit Blattläusen zu reduzieren und den Bedarf an zusätzlichen Maßnahmen zum Pflanzenschutz zu minimieren. Der schwarzgraue Sprühfilm führte zu einer reduzierten Anzahl von Blattläusen zum Zeitpunkt des Erstbefalls. Die Auswertung zum Erntezeitpunkt zeigt die Notwendigkeit von zusätzlichen Maßnahmen für eine zuverlässige Schädlingsbekämpfung. Die Qualität der Salatköpfe wurde durch die Sprühfolien nicht negativ beeinflusst

Manipulation of landing behaviour of two whitefly species by reflective foils

Whiteflies are major pests on several vegetable and ornamental crops. Landing behaviour is strongly influenced by wavelength (nm) of reflected light from ground and surrounding vegetation. This paper deals with manipulation of whitefly landing behaviour in semi-field greenhouse experiments using background foils, either white foils with high reflection of short wavelength radiation or green foils reducing contrast between target plants and background (soil). The reactions of two different whitefly species were compared to detect possible differences between specialist (Aleyrodes proletella) and generalist (Trialeurodes vaporariorum) species. Dual-choice experiments were performed in a greenhouse using ice-lettuce, Lactuca sativa var. capitata (T. vaporariorum) and broccoli, brassica oleracera var. Italica P (A. proletella) as model plants. The results show strong impact of the white reflective foil in controlling landing behaviour of both species, whereas the effect of the contrast-minimising foil was much lower. Light influence was stronger on generalist than on specialist species. Mechanisms behind these effects and opportunities for inclusion in an integrated pest management strategy are discussed. © 2020, The Author(s)

Systemic slow-release neem formulations: the future of cabbage aphids, Brevicoryne brassicae control

The efficacy and dose-response, residual effect, and effect on the fecundity of neem formulations on cabbage aphid Brevicoryne brassicae applied systemically through root tissues of Brussels sprouts (Brassica oleracea), were studied in the greenhouse. Two formulations were tested; NeemAzal granules containing 7% azadirachtin (AZA), at 75, 150, 225 and 300 mg per kilogram of the substrate and a water-based formulation, NeemAzal-T (1% AZA) at 1, 1.5, 2 and 2.5 ml/kg of substrate. The efficacy of the neem formulations was dose-dependent, with the highest doses of NeemAzal granules and NeemAzal T, (300 mg and 2.5 ml/kg of substrate) respectively, having up to 0% survival of aphids by 14 days after treatment. The manufacturer’s recommended doses, NeemAzal granules at 150 mg and NeemAzal-T at 1 ml/kg of substrate, were used to evaluate the persistence and bioresidual effect of the azadirachtin on cabbage aphid over time. After treatments, plants were infested with one-day-old aphid larvae on the same day (D0), three days (D4) and eight days (D8) after treatment. There was a sharp decrease in persistence with NeemAzal-T when plants were infested 8 days after treatment, and there was no significant difference in the survival of aphids with control plants. However, there were no differences in the survival rate of cabbage aphid larvae if exposed 0, 4 or 8 days after treatment with NeemAzal granules but the survival rate was significantly lower compared to that in the control. The fecundity of aphids decreased significantly after the application of azadirachtin. In conclusion, results show high efficacy of soil-applied NeemAzal against cabbage aphid, with NeemAzal granules, which is a slow-release formulation, giving the longest period of bioactivity hence offering the longest period of protection

Restriction fragment length polymorphisms of different DNA regions as genetic markers in the hoverfly Episyrphus balteatus (Diptera: Syrphidae)

A polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis using mitochondrial (A + T-rich region; mtDNA) and genomic (zen-region; nDNA) DNA was performed on 182 female individuals of Episyrphus balteatus (DeGeer), a widespread aphidophagous hoverfly with supposed migratory behaviour. Specimens originated from 13 sampling sites in six European countries. The analyses revealed 12 and 18 haplotypes, respectively, for the two DNA types, several of them with a wide distribution, although seven and eight haplotypes, respectively, occurred only in one location. In contrast to other studies on mobile insects, the genetic diversity was relatively high. However, lack of population subdivision, low genetic distances between populations, the very high gene flow rates, and the complete lack of isolation by distance suggest that E. balteatus populations are largely connected and that there is an absence of large-scale geographic structuring. These results support the hypothesis that E. balteatus is a migratory hoverfly species, capable of moving over large distances. These findings related to the seasonal migrations of this species are discussed. © CAB International, 2005

Differential proteomics analysis of Frankliniella occidentalis immune response after infection with Tomato spotted wilt virus (Tospovirus)

Tomato spotted wilt virus (TSWV) is mainly vectored by Frankliniella occidentalis Pergande, and it potentially activates the vector's immune response. However, molecular background of the altered immune response is not clearly understood. Therefore, using a proteomic approach, we investigated the immune pathways that are activated in F. occidentalis larvae after 24 h exposure to TSWV. Two-dimensional isoelectric focusing/sodium dodecyl sulfate polyacrylamide gel electrophoresis (2D-IEF/SDS/PAGE) combined with mass spectrometry (MS), were used to identify proteins that were differentially expressed upon viral infection. High numbers of proteins were abundantly expressed in F. occidentalis exposed to TSWV (73%) compared to the non-exposed (27%), with the majority functionally linked to the innate immune system such as: signaling, stress response, defense response, translation, cellular lipids and nucleotide metabolism. Key proteins included: 70 kDa heat shock proteins, Ubiquitin and Dermcidin, among others, indicative of a responsive pattern of the vector's innate immune system to viral infection. © 2016 Elsevier Lt

Optimizing Western Flower Thrips Management on French Beans by Combined Use of Beneficials and Imidacloprid

Western flower thrips (WFT), Frankliniella occidentalis (Pergande), is an important pest of vegetable crops worldwide and has developed resistance to many insecticides. The predatory mites Neoseiulus (=Amblyseius) cucumeris (Oudemans), the entomopathogenic fungus Metarhizium anisopliae (Metsch.), and an insecticide (imidacloprid) were tested for their efficacy to reduce WFT population density and damage to French bean (Phaseolus vulgaris L.) pods under field conditions in two planting periods. Metarhizium anisopliae was applied as a foliar spray weekly at a rate of one litre spray volume per plot while imidacloprid was applied as a soil drench every two weeks at a rate of two litres of a mixture of water and imidacloprid per m(2). Neoseiulus cucumeris was released every two weeks on plant foliage at a rate of three mites per plant. Single and combined treatment applications reduced WFT population density by at least three times and WFT damage to French bean pods by at least 1.7 times compared with untreated plots. The benefit-cost ratios in management of WFT were profitable with highest returns realized on imidacloprid treated plots. The results indicate that M. anisopliae, N. cucumeris, and imidacloprid have the potential for use in developing an integrated pest management program against WFT on French beans.BMZ/GIZ/07.7860.5-001.0