Hidden Wolbachia diversity in field populations of the European cherry fruit fly, Rhagoletis cerasi (Diptera, Tephritidae)

The European cherry fruit fly Rhagoletis cerasi has been a field model for cytoplasmic incompatibility since the mid 1970s. Two Wolbachia strains were detected in this tephritid species and w Cer2 was described as the CI inducing agent dividing European populations into two unidirectional incompatible groups, i.e. southern females produce viable offspring with northern males, whereas the reciprocal cross results in incompatibility. We detected three new Wolbachia strains by sequencing a multitude of plasmids derived from Wolbachia surface protein gene ( wsp ) polymerase chain reaction (PCR) products. Strain-specific primers were developed allowing individual diagnosis without need for cloning. Hybridization of specific PCR products with a wsp oligonucleotide enhanced the detection limit significantly and revealed the presence of low-titre infections in some strains, in different ontogenetic stages and in adults of different age. We then performed a survey of strain prevalence and infection frequency in eight European regions. w Cer1 was fixed in all populations, whereas w Cer2 was detected only in the South. w Cer3 frequency was the lowest without a clear distribution pattern. The abundance of w Cer4 was homogenous across Europe. Like w Cer2, w Cer5 showed significant differences in spatial distribution. Our new findings of previously undetected and recombinant Wolbachia strains in R. cerasi reveal a major caveat to the research community not to overlook hidden Wolbachia diversity in field populations. Low-titres and geographical variability in Wolbachia diversity are expected to influence the outcome of Wolbachia population dynamics and Wolbachia- based insect population control and may create invasion barriers for expanding and artificially introduced Wolbachia strains.     

A second case of genetic host races in Rhagoletis? A population genetic comparison of sympatric host populations in the European cherry fruit fly,Rhagoletis cerasi

Despite an increasing acceptance in the biological community for sympatric speciation as a mode of species formation, well documented examples of sympatrically evolved ‘incipient species’ remain rare. The sympatric host races of apple maggot, Rhagoletis pomonella (Walsh), represent one of the most prominent case studies for sympatric speciation via a host shift. The European cherry fruit fly, R. cerasi (L.), shows strong ecological similarities to R. pomonella: (1) infestation of two different host plants, Lonicera xylosteum L. and Prunus avium L., and (2) divergent phenological and behavioral adaptations of flies on different hosts. The population genetic study presented here addresses whether the host associated populations of R. cerasi also represent genetically differentiated true host races. Out of a total of 29 allozyme loci examined, six were polymorphic and used to analyze six sympatric pairs of R. cerasi populations on Lonicera and Prunus from Switzerland and Germany. A direct comparison of allele frequencies between sympatric sites showed no pattern indicative of host races in R. cerasi. However, the hierarchical F‐statistic for one locus, mannose 6‐phosphate isomerase (Mpi), showed significant population differentiation that was in accordance with host race differentiation. Mpi is one of several loci that are also diagnostic for host race differentiation in R. pomonella. Results from Mpi suggest the formation of sympatric host races in R. cerasi, but additional polymorphic markers are necessary.     

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

We examined phenyl propionate as an attractant for trapping navel orangeworm, Amyelois transitella (Walker) (Lepidoptera: Pyralidae) adults, with the objective of developing a method of trapping both sexes more effectively than with almond meal. Two initial experiments maximized the total number of adults captured using phenyl propionate released from glass vials with cotton wicks. A third experiment compared the numbers of males and females captured using these glass dispensers in either bucket or sticky traps. The glass vial dispensers captured more adults than 0.1% phenyl propionate in water (as both attractant and killing agent), and far more adults were captured with glass vial phenyl propionate dispensers than with almond meal. On rare occasion, the glass vial dispensers captured as many adults as traps baited with virgin females, but usually phenyl propionate in glass vials captured fewer adults than virgin‐baited traps. Glass vial phenyl propionate dispensers were equally effective in sticky traps or bucket traps. The majority of females captured were mated, and the proportion of males captured increased over time within flights (generations). We conclude that phenyl propionate released from glass vials captured A. transitella adults more effectively than currently available options, and will be useful in research projects where capturing intact adults and comparing mating status are important. Developing a cost‐effective phenyl propionate‐based alternative to the egg traps currently used for commercial monitoring will be more difficult.     

Characterization of microsatellite loci for the western cherry fruit fly, Rhagoletis indifferens (Diptera: Tephritidae)

The western cherry fruit fly (Rhagoletis indifferens) is a major pest of cherry crops in western North America, yet relatively little is known about its population structure or movement patterns due to the difficulty of studying these parameters directly in the field. We isolated and characterized a set of 16 polymorphic microsatellite loci specific to R. indifferens that display sufficient polymorphism to assess genetic structure and movement patterns. All 16 loci amplified in one or more other Rhagoletis species, indicating that they are useful tools for genetic analysis in other members of the genus, many of which are also agricultural pests.     

Host plant‐related genomic differentiation in the European cherry fruit fly,Rhagoletis cerasi

Elucidating the mechanisms and conditions facilitating the formation of biodiversity are central topics in evolutionary biology. A growing number of studies imply that divergent ecological selection may often play a critical role in speciation by counteracting the homogenising effects of gene flow. Several examples involve phytophagous insects, where divergent selection pressures associated with host plant shifts may generate reproductive isolation, promoting speciation. Here, we use ddRADseq to assess the population structure and to test for host‐related genomic differentiation in the European cherry fruit fly, Rhagoletis cerasi (L., 1758) (Diptera: Tephritidae). This tephritid is distributed throughout Europe and western Asia, and has adapted to two different genera of host plants, Prunus spp. (cherries) and Lonicera spp. (honeysuckle). Our data imply that geographic distance and geomorphic barriers serve as the primary factors shaping genetic population structure across the species range. Locally, however, flies genetically cluster according to host plant, with consistent allele frequency differences displayed by a subset of loci between Prunus and Lonicera flies across four sites surveyed in Germany and Norway. These 17 loci display significantly higher F_ST values between host plants than others. They also showed high levels of linkage disequilibrium within and between Prunus and Lonicera flies, supporting host‐related selection and reduced gene flow. Our findings support the existence of sympatric host races in R. cerasi embedded within broader patterns of geographic variation in the fly, similar to the related apple maggot, Rhagoletis pomonella, in North America.     

Microsatellite and Wolbachia analysis in Rhagoletis cerasi natural populations: population structuring and multiple infections

Rhagoletis cerasi (Diptera: Tephritidae) is a major pest of sweet and sour cherries in Europe and parts of Asia. Despite its economic significance, there is a lack of studies on the genetic structure of R. cerasi populations. Elucidating the genetic structure of insects of economic importance is crucial for developing phenological‐predictive models and environmental friendly control methods. All natural populations of R. cerasi have been found to harbor the endosymbiont Wolbachia pipientis, which widely affects multiple biological traits contributing to the evolution of its hosts, and has been suggested as a tool for the biological control of insect pests and disease vectors. In the current study, the analysis of 18 R. cerasi populations collected in Greece, Germany, and Russia using 13 microsatellite markers revealed structuring of R. cerasi natural populations, even at close geographic range. We also analyzed the Wolbachia infection status of these populations using 16S rRNA‐, MLST‐ and wsp‐based approaches. All 244 individuals screened were positive for Wolbachia. Our results suggest the fixation of the wCer1 strain in Greece while wCer2, wCer4, wCer5, and probably other uncharacterized strains were also detected in multiply infected individuals. The role of Wolbachia and its potential extended phenotypes needs a thorough investigation in R. cerasi. Our data suggest an involvement of this symbiont in the observed restriction in the gene flow in addition to a number of different ecological factors.     

Susceptibility of different life stages of the European cherry fruit fly,Rhagoletis cerasi,to entomopathogenic fungi

The effects of six fungus isolates on the mortality of different life stages of the European cherry fruit fly, Rhagoletis cerasi (Diptera: Tephritidae), were assessed in a series of laboratory experiments to find an isolate suitable for biological control. In a first step, the effects of fungus treatments on mortality, mycosis and fecundity of adult flies at a concentration of 10⁷ conidia/ml were evaluated. All fungus isolates caused mycosis but virulence varied considerably among the isolates. Beauveria bassiana and Isaria fumosorosea caused 90–100% mortality and had the strongest influence on fecundity. Metarhizium anisopliae also induced high rates of mortality, while the pathogenicity of Isaria farinosa was low. The effects of lower conidia concentrations and the influence of the age of flies were assessed in a second step. Higher conidia concentrations generally resulted in a higher mortality. B. bassiana was most efficient at low concentrations. Young flies showed lower mortality rates than older flies but, sub‐lethal effects on eclosion rate of eggs were greater in younger flies. Finally, the effects on L₃ larvae were tested: none of the fungus isolates induced mortality in more than 25% of larvae. As L₃ larvae and pupae are not susceptible to fungus infection, field control of R. cerasi should be focused on adult flies.     

Tarsal contact chemoreceptor for the host marking pheromone of the cherry fruit fly, Rhagoletis cerasi: responses to natural and synthetic compounds

Abstract. The European cherry fruit fly (Rhagoletis cerasi L.; Diptera, Tephritidae) marks cherries (Prunus avium L.) after oviposition with a host marking pheromone (HMP). The marking trail prevents additional oviposition by the same or other females into the same fruit. On the ventral side of the tarsi of both sexes, contact-chemoreceptor sensilla were identified which contain a receptor cell selectively sensitive to HMP. The HMP receptors of males were slightly more sensitive than those of females, suggesting that the more general term ‘host-marking pheromone’ is more appropriate than the previously used ‘oviposition deterring pheromone (ODP)’. The four structural isomers of the HMP, N(15R, S(β-glucopyranosyl)-oxy-8RS-hydroxypalmitoyl)-taurine, and various derivatives were synthesized and tested in an electrophysiological bioassay. Both the 8R,15R and the 8S,15RS isomers of the HMP were equally active with a threshold of about 2 times 10^-10M, and were shown to be present in the female faeces in similar proportions. The two 15S HMP isomers were about 13 times less active. Testing synthetic derivatives of the HMP molecule revealed that the presence of the four moieties of the molecule are important for the activity: taurine, palmitic acid, C₍₈₎ hydroxyl group, and glucose (C₍₁₅₎). The chain length of the fatty acid, the hydroxyl group at C₍₈₎ and the position of glucose at C₍₁₅₎ also influenced the activity. Only minor loss of activity (factor 2) relative to the natural molecule was observed when the methyl group in the C₍₁₅₎ position was removed. The removal of the β-glycosidically linked glucose (replaced by a hydroxyl group) resulted in about a 4-fold loss of activity. The cation of the HMP molecule seemed to have no effect on its activity, whereas both low and high pH reduced it significantly. Based on these results, field experiments have been initiated to control oviposition by cherry fruit flies on cherries applying the 15-desmethyl-HMP derivative.     

Transinfection of the olive fruit fly Bactrocera oleae with Wolbachia: towards a symbiont‐based population control strategy

The olive fruit fly Bactrocera oleae is responsible for worldwide economic damage. In this report, we describe the first B. oleae lines transinfected with the Wolbachia strain wCer2, an endosymbiont of the cherry fruit fly Rhagoletis cerasi. Immunostaining followed by confocal microscopy, detects high numbers of Wolbachia in embryos as well as in ovarioles and sperm from individuals of both transinfected lines. wCer2 was uniformly distributed in B. oleae egg chambers and the cortex of preblastoderm embryos. Wolbachia is known to manipulate host reproduction with several strategies, one of which is cytoplasmic incompatibility (CI), resulting in embryonic mortality in incompatible crosses. Wolbachia was found to induce complete CI in the novel host, suggesting that symbiont‐based approaches can be used as novel environmentally friendly tools for the control of natural olive fruit fly populations.     

Host marking pheromone of Rhagoletis cerasi: field deployment of synthetic pheromone as a novel cherry fruit fly management strategy

We tested the efficacy of synthetic host marking pheromone (HMP) of the European cherry fruit fly (R. cerasi) as a fruit-infestation-reducing-agent in an experimental cherry orchard. Two different pheromone deployment strategies were compared: covering entire tree canopies with synthetic HMP or treating only one half (top to bottom or lower half) of the tree canopy. Pheromone application caused a tenfold reduction in fruit infestation if the entire tree canopy was covered (0.226 vs 0.021 pupae/fruit in untreated and treated trees, respectively). Results show, nevertheless, that a significant reduction in fruit infestation can be achieved by treating only one half of tree canopies (top to bottom) (0.021 vs 0.048 pupae/fruit when comparing totally vs partially treated trees). We conclude that synthetic cherry fruit fly HMP has potential as a fruit fly management tool, especially in cases where organically grown fruit reaches high market values.     

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.     

Genetic and cytogenetic analysis of the fruit fly Rhagoletis cerasi (Diptera: Tephritidae).

The European cherry fruit fly, Rhagoletis cerasi, is a major agricultural pest for which biological, genetic, and cytogenetic information is limited. We report here a cytogenetic analysis of 4 natural Greek populations of R. cerasi, all of them infected with the endosymbiotic bacterium Wolbachia pipientis. The mitotic karyotype and detailed photographic maps of the salivary gland polytene chromosomes of this pest species are presented here. The mitotic metaphase complement consists of 6 pairs of chromosomes, including one pair of heteromorphic sex chromosomes, with the male being the heterogametic sex. The analysis of the salivary gland polytene complement has shown a total of 5 long chromosomes (10 polytene arms) that correspond to the 5 autosomes of the mitotic nuclei and a heterochromatic mass corresponding to the sex chromosomes. The most prominent landmarks of each polytene chromosome, the "weak points", and the unusual asynapsis of homologous pairs of polytene chromosomes at certain regions of the polytene elements are also presented and discussed.     

Stable coexistence of incompatible Wolbachia along a narrow contact zone in mosquito field populations

In arthropods, the intracellular bacteria Wolbachia often induce cytoplasmic incompatibility (CI) between sperm and egg, which causes conditional embryonic death and promotes the spatial spread of Wolbachia infections into host populations. The ability of Wolbachia to spread in natural populations through CI has attracted attention for using these bacteria in vector‐borne disease control. The dynamics of incompatible Wolbachia infections have been deeply investigated theoretically, whereas in natural populations, there are only few examples described, especially among incompatible infected hosts. Here, we have surveyed the distribution of two molecular Wolbachia strains (wPip11 and wPip31) infecting the mosquito Culex pipiens in Tunisia. We delineated a clear spatial structure of both infections, with a sharp contact zone separating their distribution areas. Crossing experiments with isofemale lines from different localities showed three crossing types: wPip11‐infected males always sterilize wPip31‐infected females; however, while most wPip31‐infected males were compatible with wPip11‐infected females, a few completely sterilize them. The wPip11 strain was thus expected to spread, but temporal dynamics over 7 years of monitoring shows the stability of the contact zone. We examined which factors may contribute to the observed stability, both theoretically and empirically. Population cage experiments, field samples and modelling did not support significant impacts of local adaptation or assortative mating on the stability of wPip infection structure. By contrast, low dispersal probability and metapopulation dynamics in the host Cx. pipiens probably play major roles. This study highlights the need of understanding CI dynamics in natural populations to design effective and sustainable Wolbachia‐based control strategies.     

Effects of Wolbachia on fitness of the Mediterranean fruit fly (Diptera: Tephritidae)

Wolbachia pipientis is a widespread endosymbiont of insects and other arthropods exerting a wide range of biological effects on their hosts. A growing number of recent studies document the influence of Wolbachia on reproduction and lifespan of insect host species. However, little is known regarding effects of Wolbachia on the demographic traits of different host populations. Moreover, whether different Wolbachia strains exert different effects on fitness components of their hosts remains largely unknown. We studied the effects of (a) the Wolbachia strain wCer2 on fitness components of two laboratory lines of the Mediterranean fruit fly, Ceratitis capitata (Diptera: Tephritidae) and (b) two different Wolbachia strains (wCer2 and wCer4) on one of the Mediterranean fruit fly lines. Wolbachia infection (wCer2) shortens the egg‐to‐adult developmental duration of both C. capitata lines, although it prolongs embryonic development. In one of the two lines, egg‐to‐adult mortality increased. Wolbachia infection shortens adult lifespan (to a different extent in males and females) and reduces female fecundity. The different Wolbachia strains differentially affect both immature mortality and developmental duration, and adult longevity and female fecundity. Our findings demonstrate both differential response of two C. capitata lines to Wolbachia infection and differential effects of two Wolbachia strains on the same Mediterranean fruit fly line. Practical and theoretical implications of our findings are discussed.     

Relative air humidity influences the function of the tarsal chemoreceptor cells of the cherry fruit fly (Rhagoletis cerasi)

ABSTRACT. Electrophysiological recordings from the tarsal D-sensilla of mature, 5–7-day-old female European cherry fruit fly ( Rhagoletis cerasi L.) revealed that a large proportion of sensilla showed no sensory activity in response to stimulation with the oviposition deterring pheromone ('ODP') or sucrose. In contrast, good recordings were obtained from almost all sensilla in freshly emerged, 1-day-old flies. Ageing, nutritional state and contamination were excluded as possible major factors influencing the responsiveness of the D-sensilla. The study of the variability in responsiveness of the sensilla of 1-day-old flies among different tarsomers, among tarsi of the same individual and among individuals, revealed that the major source of variability was among individuals.
Individual flies were also affected by the humidity in the holding cages: relative air humidity of less then 75% for 4–6 days was shown to reduce the number of D-sensilla giving recordings with a good signal-to-noise ratio. The D-sensilla on the most distal tarsomers were affected most by the reduced (30–55% r. h.) air humidity. Flies which had contact with plant leaves showed less reduction in responsiveness at low air humidity (40% r. h.) then flies without leaf contact.     

Life cycle,phenology and economic importance of the walnut husk fly Rhagoletis completa Cresson (Diptera: Tephritidae) in northern Italy

The walnut husk fly Rhagoletis completa Cresson, a pest originating from North-America, was detected for the first time in Europe in 1991. The life cycle and phenology of R. completa were studied, during two successive seasons, in two commercial orchards located in northern Italy. The pest develops one generation per year. Fly emergence lasted from early July to the second half of August. Oviposition was detected from late July to early September, with peaks between August 5 and 18. First instar larvae were recorded from early August and mature larvae left husks from late August onwards to pupate in the soil. The seasonal patterns of nuts infestation showed rapid growths in August following oviposition peaks. Nuts infestation levels in the untreated plots of the two orchards, ranged from 74–91% in the first year to 89–91% in the following season. Relatively dark shell surfaces were linked to a weight reduction in nuts and kernels and to an increase in darkened and mouldy kernels. Observations made in an untreated orchard for additional 3 years confirmed these trends. Baited Pherocon AM were effective in monitoring flies but catches on woody green spheres were better correlated with the first relevant oviposition phases. When pesticides were sprayed with the correct timing, i.e. against eggs or first instar larvae, infestation was kept to acceptable levels with a single application. Considering average yields, nuts prices and costs for insecticide use, 1–2 insecticide treatments are economically viable. Other Implications are discussed.     

Genetic and cytogenetic analysis of the American cherry fruit fly, Rhagoletis cingulata (Diptera: Tephritidae)

The American eastern cherry fruit fly, Rhagoletis cingulata, a pest of cherries in the western hemisphere, invaded Europe in 1983, and since then dispersed to several European countries. Information on the genetics and cytogenetics of this pest is very scarce. The mitotic karyotype and detailed photographic maps of the salivary gland polytene chromosomes of R. cingulata are presented here. The mitotic metaphase complement consists of six pairs of chromosomes with the sex chromosomes being very small and similar in size. The analysis of the salivary gland polytene complement shows a total number of five long chromosomes (10 polytene arms), which correspond to the five autosomes of the mitotic nuclei and an extrachromosomal heterochromatic mass, which corresponds to the sex chromosomes. The banding patterns and the most characteristic features and prominent landmarks of each polytene chromosome are presented and discussed. Chromosomal homologies between R. cingulata, R. completa and R. cerasi are also proposed, based on the comparison of chromosome banding patterns. Furthermore, the detection and characterization of Wolbachia pipientis in the R. cingulata population studied is presented and the potential correlation with the asynaptic phenomena found in its polytene complement is discussed. In addition, 10 out of 24 microsatellite markers developed for other Rhagoletis species are cross-amplified, evaluated and proposed as useful markers for population and genetic studies in R. cingulata.     

Habitat-specific flight period in the cherry fruit fly Rhagoletis cingulata (Loew) (Diptera: Tephritidae)

Flight periods of the cherry fruit fly, Rhagoletis cingulata (Loew), were compared in the major sweet and tart cherry-growing regions of Michigan, among neglected orchards, managed orchards, and natural areas containing the ancestral host, black cherry. Traps were deployed from early June to late September 2005 and 2006. Captures indicated that cherry fruit fly has an early flight (June-July) in neglected orchards, a mid-season flight peaking immediately after harvest (June-August) in managed orchards, and an extended flight covering most of the season (June-September) in natural areas. We found that the period of fruit infestation mirrored the flight period in neglected and managed orchards. In natural areas, we found infestation late in the season only. The relative emergence periods for adults reared from pupae collected from the three habitats and maintained under the same conditions coincided with adult flight periods for each habitat. We also studied factors related to fruit availability that may have a role in shaping the flight periods. Fruit abundance decreased rapidly early in the season in neglected orchards, whereas in managed orchards, fruit left after harvest remained on the trees until late August. Measurements of fruit size and skin firmness revealed that fly activity in neglected and managed orchards began immediately after fruit increased in size and skin firmness decreased, whereas in natural areas, the flight began before fruit matured. In managed orchards, fruit harvest and insecticide sprays likely maintain the late flight period of resident fly populations by preventing the use of fruit earlier in the season. However, a significant proportion of these resident flies may still emerge before harvest and increase the risk of costly fruit infestation.     

Optimized composite microspheres containing insecticide and attractant for control of Rhagoletis batava obseuriosa Kol. (Diptera: Tephritidae)

Ammonium carbonate is used as an attractant for many fruit flies since it releases ammonia in humid atmospheres, which is attractive to them. For integrated pest management in the field, and as part of an ‘attract-and-kill’ strategy, it is necessary to prolong the release period of ammonia from the ammonium carbonate and combine it with an insecticide. To achieve this, we combined ammonium carbonate with spinosad in slow-release microspheres. The microspheres were prepared using gelatin and polylactic acid as capsule materials. An orthogonal test was used to optimize the parameters needed for production. Particles produced using the optimal parameters were uniform in size (55.5 μm diameter), the spinosad encapsulation rate was 98.1%, the encapsulation concentration of ammonium carbonate was 2.6 mg/g, and they had a longer release period than when the components were not encapsulated. In a field experiment, rates of damage to sea buckthorn by Rhagoletis batava obseuriosa Kol. (Diptera, Tephritidae) (RBO) were 16.05 ± 1.15% in the treatment subplots compared with 81.75 ± 1.50% in the control subplot; the mean number of RBO trapped per trap per day was 21.2 ± 6.3 (SE) in the treatment subplots and 130.8 ± 27.5 (SE) in the control subplot, respectively. Therefore, using composite microspheres has potential as an effective method for control of RBO.     

The effect of temperature on the post-diapause development of four geographical populations of the European cherry fruit fly (Rhagoletis cerasi)

Pupae of Rhagoletis cerasi (L.) from Austria, Czechoslovakia, Switzerland and Italy were stored at 4° for 155 days and then transferred to eleven constant and four cycling temperature regimes until the flies emerged. No flies emerged in 324 days at 8° constant but mean emergence was 84% for the remaining regimes. Female flies emerged slightly earlier than males and flies from Italy were the last to start emerging. Reduced to a common mean base temperature of 6.8°, temperature sums in day degrees C to 10% emergence of female flies were 331 (Austria), 319 (Czechoslovakia), 359 (Italy) and 321 (Switzerland). The equivalent sums are also given for first, 50% and 90% emergence. When tested with soil temperature data from Switzerland 321 day degrees above 6.8° and 430 day degrees above 5° gave effectively the same estimates for practical forecasting purposes.

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Zusammenfassung Puppen von Rhagoletis cerasi L. aus üOsterreich, der Slovakei, der Schweiz und aus Italien, welche aus infizierten Kirschen gewonnen worden waren, wurden wüahrend 155 Tagen bei 4\dg gelagert und anschliessend füur die Weiterentwicklung in 11 konstanten und 4 fluktuierenden Temperaturregimen untersucht. Keine Fliegen schlüupften nach 324 Tagen Inkubationsdauer bei 8\dg, wüahrend die durchschnittliche Schlüupfrate bei den üubrigen Temperaturbedingungen 84% betrug. Die beobachteten und berechneten Werte füur die Entwicklungsdauer bis zur Erreichung der Schlüupfraten von 10% und 50% sind nach Geschlechtern und Herküunften getrennt in Tabellen aufgefüuhrt. Lineare Regressionsgleichungen wurden berechnet füur die Kurven der Entwicklungsraten und verwendet füur die Berechnung der Entwicklungsnullpunkte und effektiven Temperatursummen. Weibliche Fliegen schlüupften früuher als Müannchen und Puppen aus Italien entwickelten sich von allen vier Herküunften am langsamsten. Berechnet auf der Basis eines durchschnittlichen Entwicklungsnullpunktes von 6.8\dg als Schwellenwert benüotigten die Weibchen der verschiedenen Herküunfte bis zum Erreichen der Schlüupfrate von 10% folgende Temperatursummen in Gradtagen: üOsterreich 331\dg, Slovakei 319\dg, Italien 359\dg und die Schweiz 321.Die entsprechenden Werte für das Erreichen des Zeitpunktes von Schlüpfbeginn, 50% und 90% Schlüpfrate sind ebenfalls in Tabellenform dargestellt. Der normalerweise füur Prognosezwecke verwendete Schwellenwert von 5\dg wurde zu Vergleichszwecken ebenfalls in die Analyse der experimentellen Daten einbezogen, doch zeigte es sich, dass er zu tief liegt. Die üUberprüufung der Prognosemethode in der Schweiz mittels Bodentemperaturen in 5 cm Bodentiefe unter Anwendung des neuen Schwellenwertes von 6.8\dg und der effektiven Temperatursumme von 321 Gradtagen füuhrte jedoch zu den gleichen Schlussfolgerungen wie die Verwendung des traditionellen Schwellenwertes von 5\dg und der Summe von 430 Gradtagen. Da die Berechnungen auf der Basis von 5\dg einfacher sind und gute üUbereinstimmung mit den Fangresultaten im Freiland zeigen, besteht keine Veranlassung füur die praktische Anwendung den alten Schwellenwert zu üandern.