Förderung der funktionellen Biodiversität zur Bekämpfung der Kohlmottenschildlaus

Die Kohlmottenschildlaus (Aleyrodes proletella) hat sich innerhalb kurzer Zeit zu einem Hauptschädling im ökologischen und integrierten Kohlanbau entwickelt. Ein Grund ist der einseitige Nutzen des stetig gestiegenen Winterrapsanbaus für A. proletella nicht aber für dessen natürliche Gegenspieler. Projektziel war die spezifische Förderung dieser Gegenspieler mittels Banker Plants und Blühstreifen, um so den A. proletella-Befall, den ökonomischen Schaden und den Insektizideinsatz nachhaltig zu reduzieren. Zunächst wurden mit einer bundesweiten Erhebung die wichtigsten natürlichen Gegenspieler von A. proletella ermittelt und potentielle Banker Plant-Systeme zusammengestellt. Im Feld wurden zum einen einjährige Banker Plant-Systeme gegeneinander getestet. Zum anderen wurde die Überwinterung und Populationsdynamik von Alternativwirten und Gegenspielern auf mehrjährigen Banker Plants untersucht. Ein Versuch zur Kombination von Banker Plants mit einem spezifisch zusammengestellten Blühstreifen erfolgte im letzten Projektjahr. Der bedeutendste Parasitoid von A. proletella, Encarsia tricolor, wurde für die Entwicklung der Banker Plant-Systeme gewählt. Das beste ein-jährige System setzte sich aus E. tricolor (Gegenspieler) und Trialeurodes vaporariorum (Al-ternativwirt/-beute) auf Hokkaido-Kürbis zusammen. Im Feld erreichte dieses System auf kur-zer Distanz eine Reduktion des A. proletella-Befalls um durchschnittlich 28%. Um durchschnittlich 52% stieg die Parasitierung von A. proletella und auch das Vorkommen von Schwebfliegenlarven und Marienkäfern auf dem Kohl konnte erhöht werden. Mit einer kombi-nierten Strategie von Banker Plants mit Blühstreifen konnte kein zusätzlicher Erfolg beobachtet werden. Nelkenwurz (Geum urbanum) lieferte die besten Ergebnisse als mehrjährige Banker Plant zur permanenten Ansiedlung von Alternativwirten (Aleyrodes lonicerae) und natürlichen Gegenspielern. Die Ergebnisse zeigen, dass durch den Einsatz von Banker Plant-Sys-temen eine dauerhafte Förderung der funktionellen Biodiversität und eine signifikante Befallsreduktion von A. proletella erzielt werden kann. Möglichkeiten zur weiteren Optimierung der Banker Plant-Systeme und Vorschläge für zukünftige Untersuchungen bis zum praxistauglichen Einsatz werden diskutiert

Blue and UV light-emitting diodes (LEDs) disturb the greenhouse whitefly (Trialeurodes vaporariorum) from its host

Push–pull strategy is a well-known and widely used technique for integrated pest management, leading to the reduction of insecticides. This strategy involves the use of mostly visual and chemical stimuli to repel pests from a valuable crop (push) and attract them to an appealing target, e.g., a trap, (pull). Based on former results, this study explored the effect of light-emitting diodes (LEDs) as repelling factors of whiteflies (push). Wavelengths of blue and ultraviolet (UV) were investigated in different light intensities and exposure times in no-choice experiments, under controlled conditions. Whiteflies were exposed directly to LEDs on the underside of tomato leaves and number of repelled insects was counted. The results showed that light intensity and insect repellency were positively related. Insect repellency increased up to tenfold with longer light exposure period. Wavelength of blue and combination of blue + UV repelled more than 87% of whiteflies in light conditions. In darkness, results were only slightly different. The results reveal the property of blue light to repel whiteflies from its host and that addition of UV to blue enhances this effect. They further demonstrate that whitefly vision is dependent on wavelength, light intensity and exposure period. The contribution of the results on understanding the visual behavior of whiteflies and their possible implementation on pest control strategies is discussed

Blue LED trap and commercial lure improve western flower thrips (Frankliniella occidentalis) monitoring in cucumber crops

Blue sticky traps contribute substantially to monitoring the western flower thrips, Frankliniella occidentalis Pergande (Thysanoptera: Thripidae), in greenhouses. Although sticky traps can detect the initial presence of thrips reliably, an estimation of the actual thrips density in the crop by counting number of thrips on the traps is often not accurate. To overcome this issue, we compared blue sticky traps and newly developed sticky LED-enlightened traps in combination with the commercial thrips kairomone Lurem-TR under commercial growing conditions. Therefore, an experiment was conducted in cucumber, Cucumis sativus L. (Cucurbitaceae), crop stands in greenhouse cabins investigating the correlation between thrips caught on (LED) traps and the thrips density in the crop for an accurate and reliable thrips monitoring. Additionally, experiments aiming to understand underlying mechanisms of thrips orientation towards traps in different scenarios were conducted under controlled conditions. Results show that thrips catches on sticky LED enlightened coloured traps correlated strongly positive with number of thrips in the crop, especially at low thrips population densities. Adding Lurem to this trap type further improved accuracy of the correlation in the greenhouse cabin experiment. Moreover, LED traps with and without Lurem were more attractive towards thrips in small follow-up experiments compared to standard blue sticky traps. The results are discussed in the context of general orientation of thrips and its behaviour towards visual and olfactory cues when considering different scenarios. Our study shows the successful integration of blue LEDs into an existing trapping system and underlines the advantages compared with standard sticky plates. In conclusion, sticky LED enlightened coloured traps have a potential as an improved thrips monitoring device that might improve pest management decisions

Conservation of Non-Pest Whiteflies and Natural Enemies of the Cabbage Whitefly Aleyrodes proletella on Perennial Plants for Use in Non-Crop Habitats

Aleyrodes proletella causes severe economic damage to several Brassica crops. Its naturally occurring enemies often immigrate late in the season or appear in low numbers on cabbage. This field study aims to permanently increase the local abundance of A. proletella’s natural enemies by providing the non-pest whitefly Aleyrodes lonicerae as an alternative and overwintering host/prey. Therefore, the population dynamics of natural enemies on different perennial herbaceous plants pre-infested with A. lonicerae were determined at two field locations over two winter periods. Most A. lonicerae colonized (on average 166.22 puparia per m2) and overwintered (342.19 adults per m2 ) on wood avens Geum urbanum. Furthermore, the abundance of A. proletella main parasitoid Encarsia tricolor (28.50 parasitized puparia per m2 ) and spiders (12.13 per m2 ) was 3–74 times and 3–14 times higher, respectively, on G. urbanum compared to the other experimental plants. Conclusively, G. urbanum pre-infested with A. lonicerae permanently promoted natural enemies of A. proletella by serving as shelter, reproduction, and overwintering habitat. A potential implementation of G. urbanum in conservation biological control strategies (e.g., tailored flower strips, hedgerows) against A. proletella are discussed and suggestions for future research are given

Neue Ansätze zur Bekämpfung der Kohlmottenschildlaus (Aleyrodes proletella), einem Problemschädling im Kohlanbau

Die Kohlmottenschildlaus hat sich zum einem wichtigen Schädling im Kohlanbau entwickelt und der Befall kann insbesondere durch Verschmutzung des Ernteguts zu hohen ökonomischen Verlusten führen. In diesem Projekt wurde eine alternative Bekämpfungsstrategie an der Modellpflanze Rosenkohl entwickelt. Als Alternative zu bestehenden Methoden wurde ein präventiver und modularer Ansatz genutzt, der aus den Modulen nicht anfällige Sorten, Fangpflanzen und Blühstreifen bestand. Diese Bekämpfungsmodule wurden separat in Vorversuchen erprobt (Wahl- und no-choice-Versuche im Gewächshaus, Klimakammer und Freiland, um nicht-anfällige Rosenkohlsorten und attraktive Fangpflanzen zu selektieren) und dann in zwei Jahren in Freiland-Parzellenversuchen als kombinierte Bekämpfungsstrategie getestet. Als ausreichend geeignete Fangpflanze hat sich nur Markstammkohl (B. oleracea var. medullosa), als nicht anfällige Rosenkohlsorten können mit Einschränkungen 'Octia', 'Genius' und 'Esperal' empfohlen werden, wobei diese Resistenz allein nicht ausreicht, um einen Befall zu begrenzen. Diese Sorten wurden am wenigsten präferiert und hatten die geringsten Verschmutzungen, konnten aber bei der Antibiosis (Wirtseignung) nur teilweise überzeugen. Bei den Parzellenversuchen konnte im ersten Jahr keinerlei Wirkung erzielt werden (gleicher Befall in allen Varianten), während im zweiten Jahr eine (teilweise signifikante) Befallsreduktion von im Durchschnitt 30 bis 60 % erreicht werden konnte. Auch hatte diese Befallsreduktion eine signifikante Auswirkung auf die Verschmutzung, nicht aber auf den Ertrag. Außerdem wurden grundlegende Arbeiten zur Biologie der Kohlmottenschildlaus in Bezug auf Wirtspflanzenfindung (Orientierung nach optischen und olfaktorischen Signalen) und bakterielle Endosymbionten durchgeführt. Es konnten neben dem weiße Fliegen spezifischen primären Endosymbionten Portiera aleyrodidarum nur zwei sekundäre Endosymbionten nachgewiesen werden, die häufig in Kombination auftraten: Wolbachia und Arsenophonus. Über die Funktion bzw. den Nutzen dieser Endosymbionten ist noch nichts bekannt

Banker plants promote functional biodiversity and decrease populations of the cabbage whitefly Aleyrodes proletella

In this study, potential banker plant systems against the cabbage whitefly Aleyrodes proletella Linnaeus (Hemiptera: Aleyrodidae) were developed under controlled conditions. The two most promising banker plant systems, that is, the parasitoid Encarsia tricolor Förster (Hymenoptera: Aphelinidae) either with Aleyrodes lonicerae Walker on European columbine (columbine system) or with Trialeurodes vaporariorum Westwood (Hemiptera: Aleyrodidae) on Hokkaido squash (pumpkin system), were further evaluated in the field. Although the pumpkin system produced three times more parasitoids than the columbine system, both banker plants led to an 1.5-fold increase in A. proletella parasitism rates. However, only the pumpkin system increased the abundance of syrphid larvae on cabbage by 61.5% and reduced A. proletella populations on average by 4.4%–25.8% depending on the respective assessment date. In conclusion, the pumpkin system revealed to be a promising (supplementary) control measure against A. proletella. Options for further improvement and standardization of the pumpkin system as well as a potential implementation in cabbage production are discussed. © 2020 The Authors. Journal of Applied Entomology published by Wiley-VCH Gmb

Leaf age is important for assessment of resistance in chrysanthemum against Frankliniella occidentalis

Feeding behaviour of pest insects on host plants depends on the plant morphology and chemical composition. So far, leaf position was demonstrated important for estimation of thrips resistance in Capsicum, where resistant associations showed a higher resistance in the youngest leaves compared to old leaves. In the current study, the feeding behaviour of female Frankliniella occidentalis, a major pest of chrysanthemum, and the egg-laying activity was assessed in a non-choice experiment in the climate chamber. We hypothesize that the physiological status, i.e. the age of chrysanthemum leaves, is an important resistance factor influencing thrips silver damage and the number of offspring. In general, the results show significantly higher feeding damage on old (basal) leaves of susceptible cultivars compared to resistant cultivars on the abaxial side of the leaf. In contrast, we detected no significant differences on the adaxial side of the leaves neither for old nor for young leaves. However, feeding damage on different leaf positions is an important factor for resistance level determination. Additionally, we detected significant differences in reproductive activity, i.e. number of hatched larvae on old leaves compared to young leaves for all cultivars. Overall, on old leaves we detected more larvae. The comparison between the old leaves of all cultivars exhibited a significant difference between one resistant and one susceptible cultivar. Contrary to that, the comparison between the young leaves of all cultivars exhibited no significant differences. All findings are important for advancing future resistance screenings in chrysanthemum

The role of plant physiology and cultivar of chrysanthemum in the resistance against Western flower thrips

Western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), is an economically important pest insect in vegetable and ornamental cultivation worldwide. Little is known about host plant resistance in the vegetative and generative phases of chrysanthemum [Chrysanthemum × morifolium (Ramat.) Hemsl. (Asteraceae)] and the role of resistance factors such as flavonols, flower color, and flower shape. We screened a broad range of chrysanthemum cultivars across two seasons to quantify resistance against Western flower thrips. Resistance was based on silver damage on the leaves, and relative flavonol content was measured using a Dualex Scientific 4 hand-held sensor. There was significant variation in silver damage between cultivars, indicating different levels of resistance. There was no correlation between the relative flavonol content in middle leaves and plant silver damage. A clearer resistance level discrimination by flavonols in resistant and susceptible cultivars would be possible in the future by comparing multiple leaf positions during the ontogenetic phases of plant development. Moreover, the influence of flower color and shape on resistance to thrips was investigated by counting the adult thrips and larvae on flowers. The results showed significant differences in flower color preference by adults, but not by larvae. Flower shape influenced thrips larvae and females, but not males. The importance of the results for resistance determination is discussed

Does apple replant disease affect the soil patch selection behaviour and population growth of Collembolans?

Apple replant disease (ARD) is common to all major apple-growing regions in the world. It occurs when new apple trees are replanted on sites where previously the same or closely related crop species were grown. Biotic (fungi, bacteria and nematodes) and abiotic soil factors (poor soil structure, nutrition) contribute to the development and severity of ARD. However, the aetiology of ARD and effects on higher trophic levels are still unknown. In that sense, Collembola might play an important role, since they are one of the dominant mesofauna groups in many soils. They act as decomposer, fungivores and predators, representing different trophic levels in soil food webs. Therefore, any effect of ARD on the occurrence of Collembola could have ecological impacts on the soil quality and health. Here, we examined the colonization behaviour of two Collembolan species, Folsomia candida and Sinella curviseta, in choice tests and population growth tests using Apple Replant Diseased soil (ARD) and non-ARD soil samples from different field sites and standardized laboratory bioassays. Additionally, Collembola behaviour was quantified by continuous video observations to investigate short-term behavioural changes. Results showed that both Collembolan species significantly preferred colonization of the non-ARD soils compared with ARD soils, independent of the origin of the soil samples or specific disinfection treatments. Moreover, the detailed video analysis of the foraging behaviour indicates rapid colonization of soil samples and low dispersal rates. Most likely, volatile compounds and to a lesser extent feeding stimulants play a vital role for the colonization process for both Collembolan species. Finally, results showed negative effects of ARD on population growth of both Collembolan species already after an 8-week period, implying strong nutritional deficiencies in ARD affected soils. The hypothesis that ARD causing microorganisms directly affected orientation, colonization and population development of Collembola is discussed

Importance of antixenosis and antibiosis resistance to the cabbage whitefly (Aleyrodes proletella) in brussels sprout cultivars

The cabbage whitefly Aleyrodes proletella (L.) (Hemiptera: Aleyrodidae) is an important pest of a wide range of vegetable Brassicas. Since the control of this pest is still challenging, new approaches such as the use of resistant cultivars are required. For this, we screened 16 commercialised Brussels sprout cultivars for resistance against this species. Antibiosis was tested with no-choice experiments in a climate chamber, using reproduction, mortality, longevity, developmental time and weight as parameters. Antixenosis was screened in three choice experiments with circular design in a greenhouse to detect cultivar preferences. A field trial with both antibiosis and antixenosis tests was done to verify results under natural conditions. Finally, for several cultivars, also the leaf glucosinolate concentrations were analysed. Cabbage whiteflies showed on certain cultivars significantly increased mortality, prolonged developmental times and reduced weights. Besides, some cultivars were significantly less infested. However, the incidence of antibiosis and antixenosis as well as the glucosinolate patterns were partly inconsistent. Although a number of moderately resistant cultivars could be identified, the detected resistance is certainly not strong and consistent enough as an exclusive measure of a plant protection strategy but might become a component of a multi-layered strategy against cabbage whiteflies