Kirsten Köppler

Evidence for a recent horizontal transmission and spatial spread of Wolbachia from endemic Rhagoletis cerasi (Diptera: Tephritidae) to invasive Rhagoletis cingulata in Europe.

The widespread occurrence of Wolbachia in arthropods and nematodes suggests that this intracellular, maternally inherited endosymbiont has the ability to cross species boundaries. However, direct evidence for such a horizontal transmission of Wolbachia in nature is scarce. Here, we compare the well‐characterized Wolbachia infection of the European cherry fruit fly, Rhagoletis cerasi, with that of the North American eastern cherry fruit fly, Rhagoletis cingulata, recently introduced to Europe. Molecular genetic analysis of Wolbachia based on multilocus sequence typing and the Wolbachia surface protein wsp showed that all R. cingulata individuals are infected with wCin2 identical to wCer2 in R. cerasi. In contrast, wCin1, a strain identical to wCer1 in R. cerasi, was present in several European populations of R. cingulata, but not in any individual from the United States. Surveys of R. cingulata from Germany and Hungary indicated that in some populations, the frequency of wCin1 increased significantly in just a few years with at least two independent horizontal transmission events. This is corroborated by the analysis of the mitochondrial cytochrome oxidase II gene that showed association of wCin1 with two distinct haplotypes in Germany, one of which is also infected with wCin1 in Hungary. In summary, our study provides strong evidence for a very recent inter‐specific Wolbachia transmission with a subsequent spatial spread in field populations.

The hitchhiker's guide to Europe: the infection dynamics of an ongoing Wolbachia invasion and mitochondrial selective sweep in Rhagoletis cerasi

Wolbachia is a maternally inherited and ubiquitous endosymbiont of insects. It can hijack host reproduction by manipulations such as cytoplasmic incompatibility (CI) to enhance vertical transmission. Horizontal transmission of Wolbachia can also result in the colonization of new mitochondrial lineages. In this study, we present a 15‐year‐long survey of Wolbachia in the cherry fruit fly Rhagoletis cerasi across Europe and the spatiotemporal distribution of two prevalent strains, wCer1 and wCer2, and associated mitochondrial haplotypes in Germany. Across most of Europe, populations consisted of either 100% singly (wCer1) infected individuals with haplotype HT1, or 100% doubly (wCer1&2) infected individuals with haplotype HT2, differentiated only by a single nucleotide polymorphism. In central Germany, singly infected populations were surrounded by transitional populations, consisting of both singly and doubly infected individuals, sandwiched between populations fixed for wCer1&2. Populations with fixed infection status showed perfect association of infection and mitochondria, suggesting a recent CI‐driven selective sweep of wCer2 linked with HT2. Spatial analysis revealed a range expansion for wCer2 and a large transition zone in which wCer2 splashes appeared to coalesce into doubly infected populations. Unexpectedly, the transition zone contained a large proportion (22%) of wCer1&2 individuals with HT1, suggesting frequent intraspecific horizontal transmission. However, this horizontal transmission did not break the strict association between infection types and haplotypes in populations outside the transition zone, suggesting that this horizontally acquired Wolbachia infection may be transient. Our study provides new insights into the rarely studied Wolbachia invasion dynamics in field populations.

Multiple Wolbachia infections in Rhagoletis pomonella

Rhagoletis pomonella Walsh (Diptera: Tephritidae) is a model species for sympatric speciation through host race formation on apple and hawthorn. The bacterial endosymbiont Wolbachia, a manipulator of arthropod reproduction, has been considered to contribute to speciation in several species. A potential role of Wolbachia in sympatric speciation of R. pomonella remains to be tested despite an earlier detection by PCR. In this study, we isolated Wolbachia from R. pomonella individuals from both host species using multi‐locus sequence typing (MLST) and the surface protein wsp. By cloning and sequencing of 311 plasmids, we found sequence types of at least four wPom strains. A complete MLST profile was obtained only for wPom1, whereas MLST loci of the other putative strains were difficult to assign because of multiple infections and low sample numbers. wPom1 occurs in both host races, whereas different sequence types were found at low frequencies only in apple‐infesting R. pomonella. This warrants further investigation as it cannot be excluded that Wolbachia plays a part in this model of sympatric speciation.

Substantial progress made in the rearing of the European cherry fruit fly, Rhagoletis cerasi

Successful and reproducible rearing of Rhagoletis cerasi L. (Diptera: Tephritidae) is imperative for substantiated research on this main pest in cherries in Europe, for instance for the applied research on control of the pest, as well as for basic research on its physiology, behaviour, or reproduction. Temperate Rhagoletis species with an obligatory diapause are more difficult to rear in the laboratory than most of the tropical or subtropical fruit fly species (Boller, 1989). The host range of the monoor oligophagous Rhagoletis species comprises a few main host plants, for R. cerasi these are sweet cherry [Prunus avium L. (Rosaceae)], tart cherry (Prunus cerasus L.), and fly honeysuckle [Lonicera xylosteum L. (Caprifoliaceae); Boller & Bush, 1974]. Rearing of Rhagoletis spp. included an adequate oviposition device and a suitable larval diet. In previous studies, Boller and Haisch et al. worked intensively on both aspects for R. cerasi. Boller and Prokopy developed black-dyed ceresin wax domes for oviposition (Prokopy & Boller, 1970, 1971; Boller & Ramser, 1971; Katsoyannos et al., 1977; Boller, 1984). However, this wax is no longer available. Hence, a new wax with similar or improved features had to be found. Boller (1984) and Haisch (1975) described different larval diets based mainly on brewer’s yeast, wheat germ, sugar, organic acids, and vitamins. Both authors reported pupation rates between 40 and 46%, but no reports on repeated or continuous laboratory rearing were published until now. In the experiments reported here, we could not reproduce these pupation rates. Furthermore, a Rhagoletis diet is sold by Bio-Serv (Frenchtown, NJ, USA) without information on its efficacy. For decades, the lack of a reproducible rearing method has hampered progress in R. cerasi research. The urgent need of applied research on R. cerasi becomes increasingly obvious because of the ongoing re-evaluation of pesticide usage in the EU. New and environmentally sound control strategies of this pest rely on the knowledge ascertained from basic research, wherefore successful rearing is a prerequisite. Based on present rearing knowledge, a reproducible rearing method was developed with an alternative for the formerly used, but now unavailable, wax for egg devices, and with optimised larval diets. Adult emergence, oviposition, and larval development until pupation of R. cerasi were quantified in this study.

Bait spray for control of European cherry fruit fly: an appraisal based on semi-field and field studies.

BACKGROUND The European cherry fruit fly, Rhagoletis cerasi, is the major insect pest of sweet and tart cherries. Its management is becoming increasingly difficult in many countries as formerly effective but broad-spectrum insecticides are removed from the market. With the objective of identifying suitable and environmentally safe alternatives, we investigated bait sprays containing two families of plant-derived insecticides: azadirachtins (NeemAzal-T(®) and NeemAzal-T/S(®) ) and pyrethrins (Spruzit Neu(®) ). RESULTS In 12 semi-field trials conducted within cages, weekly applications of 0.0001 or 0.0005% neem in a bait formulation effectively reduced fruit infestation. However, addition of 0.000125-0.001% pyrethrins did not improve the efficacy of the neem formulations, and when used alone pyrethrins were less effective than neem alone. Two years of field trials were also conducted within orchards wherein an insecticidal barrier of treated trees excluded immigration of fertile R. cerasi from elsewhere. In blocks treated with 0.0005% neem in a bait formulation, we observed 94% (2011) or 86% (2012) reduction of fruit infestation over control blocks. CONCLUSION Bait sprays containing neem are a promising alternative for the management of R. cerasi, especially where the risk of immigration of fertilized females is low, as in isolated orchards or as part of area-wide treatments.

Demonstrationsvorhaben „Einnetzen von Obstkulturen zum Schutz gegen die Kirschessigfliege (Drosophila suzukii)“ : Förderkennzeichen: 2815MD010 ; Ergebnisse des ersten Projektjahres 2017 ; Berichtszeitraum 15. Februar 2017 – 28. Februar 2018

Eine technische Moglichkeit, Obstkulturen vor Befall durch die Kirschessigfliege, Drosophila suzukii, zu schutzen, bietet die Verwendung von Insektenschutznetzen. Um dieses Verfahren zu validieren, zu optimieren und verstarkt in die Praxis zu bringen, startete im Jahr 2017 das vom Bundesministerium fur Ernahrung und Landwirtschaft (BMEL) geforderte Demonstrationsprojekt „Einnetzen von Obstkulturen zum Schutz gegen die Kirschessigfliege“. Die Leitung obliegt dem Julius Kuhn-Institut, beteiligt sind die Lander Baden-Wurttemberg, Niedersachsen und Nordrhein-Westfalen mit bis zu sieben Betrieben, die bereits Netze installiert haben, unter Berucksichtigung der Kulturen Kirschen, Himbeeren, Brombeeren und Heidelbeeren. Der Bericht fuhrt in das Projekt ein und fasst die Ergebnisse aus dem ersten Projektjahr zusammen.

Demonstrationsvorhaben „Einnetzen von Obstkulturen zum Schutz gegen die Kirschessigfliege (Drosophila suzukii)”. Projektjahr 2017 – Probleme und Besonderheiten

Recent studies on endophytic Kosakonia radicincitans DSM 16656T demonstrated a wide plant growth-promoting activity. The application of this Gram-negative bacterium as a biofertilizer is limited due to the lack of adequate formulation that protects the cells during drying and storage and supports plant colonization. Here we set out to elucidate the compatible solutes accumulation influence of K. radicincitans triggered by osmotic stress on its capacity as an endophyte in radish plants. We found that physiological modifications by osmotic stress treatments and accumulation of compatible solutes during cultivation, improve the capability of K. radicincitans formulated in dry beads to colonize and to promote radish growth. Thus, pre-conditioning of cells with NaCl 4% and by adding compatible solutes such as hydroxyectoine during cultivation induced a positive effect on relative gene expression response, enhancing significantly the ability to colonize plant tissue up to 10 fold. Additionally, when this osmolyte was added, either dry matter of tuber or leaves increased by 3 % and 13.59 %, respectively in comparison to beads without the bacterium. These first results indicate that a systematic approach to cultivation and formulation may increase the endophytic capacity of this bacterium.

Report about the German-Chinese Workshop on Prevention and Control of Spotted Wing Drosophila, Drosophila suzukii,held in China, June 16–20, 2015

Institute Julius Kühn-Institut (JKI), Institut für Pflanzenschutz in Obstund Weinbau, Dossenheim, Germany1 Julius Kühn-Institut (JKI), Institut für Biologischen Pflanzenschutz, Darmstadt, Germany2 Landwirtschaftliches Technologiezentrum Augustenberg (LTZ), Karlsruhe, Germany3 Regierungspräsidium Gießen, Dez. 51.4 Pflanzenschutzdienst, Wetzlar, Germany4 Dienstleistungszentrum Ländlicher Raum (DLR) Rheinpfalz, Neustadt/Wstr., Germany5 Landwirtschaftskammer Nordrhein-Westfalen, Fachbereich 62 – Pflanzenschutzdienst, Obstbau, Münster, Germany6 German-Chinese Agricultural Center (DCZ), Zhong Ou Hotel, Chaoyang District, Beijing, PR China7