Detection and monitoring of Drosophila suzukii in raspberry and cherry orchards with volatile organic compounds in the USA and Europe.

Spotted wing drosophila (SWD) causes significant economic loss in fruit crops to growers worldwide. There is immediate need for efficacious and selective monitoring tools that can detect infestations early. Previously, volatile organic compounds derived from apple were studied and a quinary chemical component blend (QB) was identified as the key SWD attractant in a blueberry orchard in the United States. This study's aim was to determine whether previously observed QB efficacy, selectivity, and early detection levels could be attained within raspberry and cherry fields in the USA and Europe. Results demonstrated that sticky trap baited QB dispenser provided earlier SWD detection potential than the usually adopted apple cider vinegar (ACV) trap. The number of SWD captured/trap by QB baited trapping systems was significantly lower than that of the ACV trap. However, percent SWD/trap of QB baited traps was same within cherry. Lower non-target capture will save farmer/grower's labor and time allocated to traps installation and drosophila species identification. Within the USA, SWD selectivity of QB baited liquid traps was consistently greater than sticky trap in raspberry field, suggesting that the QB dispenser can be an alternative to the standard ACV lure and that trap design could improve selectivity further.

Search for Alternative Control Strategies of Drosophila suzukii (Diptera: Drosophilidae): Laboratory Assays Using Volatile Natural Plant Compounds.

Drosophila suzukii (Diptera: Drosophilidae), is native to southeastern Asia and invaded Europe during the past decade. It causes serious economic damage in cherries and soft fruits. Control strategies rely on few insecticides with varying success. Due to environmental concern, the use of synthetic chemicals is restricted. Therefore, research effort is put into the quest for alternative substances applicable in chemical pest control. In laboratory assays, we tested 17 volatile plant compounds from different chemical classes for their contact toxicity, feeding modification, and oviposition repellency. Toxicity through contact with treated surfaces was evaluated after 1 h, 4 h, and 24 h; effects on food uptake were observed with capillary feeding (CAFE)-tests and oviposition trials compared egg numbers laid in raspberry medium with or without treated filter paper. Cinnamon oil and its components had the highest contact toxicity with an LC90 = 2-3%, whereas lemongrass oil, its main components, and farnesol were less toxic (LC90 = 7-9%), and geraniol was the least toxic. In CAFE tests, feeding stimulation was observed through 0.1% and 1% solutions of citronellol, lemongrass oil and farnesol. Cinnamon oil, cinnamaldhyde, and ethyl cinnamate were not consumed at a concentration of 1%. In the presence of citral, eugenol, and lemongrass oil, oviposition was reduced, and in the presence of limonene, no eggs were deposited. The natural products found most efficient in either bioassay will be further tested under field conditions.

A Whole-Genome Scan for Association with Invasion Success in the Fruit Fly Drosophila suzukii Using Contrasts of Allele Frequencies Corrected for Population Structure.

Evidence is accumulating that evolutionary changes are not only common during biological invasions but may also contribute directly to invasion success. The genomic basis of such changes is still largely unexplored. Yet, understanding the genomic response to invasion may help to predict the conditions under which invasiveness can be enhanced or suppressed. Here, we characterized the genome response of the spotted wing drosophila Drosophila suzukii during the worldwide invasion of this pest insect species, by conducting a genome-wide association study to identify genes involved in adaptive processes during invasion. Genomic data from 22 population samples were analyzed to detect genetic variants associated with the status (invasive versus native) of the sampled populations based on a newly developed statistic, we called C2, that contrasts allele frequencies corrected for population structure. We evaluated this new statistical framework using simulated data sets and implemented it in an upgraded version of the program BayPass. We identified a relatively small set of single-nucleotide polymorphisms that show a highly significant association with the invasive status of D. suzukii populations. In particular, two genes, RhoGEF64C and cpo, contained single-nucleotide polymorphisms significantly associated with the invasive status in the two separate main invasion routes of D. suzukii. Our methodological approaches can be applied to any other invasive species, and more generally to any evolutionary model for species characterized by nonequilibrium demographic conditions for which binary covariables of interest can be defined at the population level.

Effects of photoperiod and relative humidity on diapause termination and post-winter development of Rhagoletis cerasi pupae.

The European cherry fruit fly, Rhagoletis cerasi (Diptera: Tephritidae), is a univoltine species that undergoes obligatory summer-winter diapause at pupal stage in the soil (2-5 cm) beneath host trees. To study the effects of photoperiod and relative humidity on diapause termination and post-winter developmental duration of R. cerasi, pupae collected from Dossenheim (Germany) were exposed to different photoperiod or relative humidity regimes during a chilling period ranging from 2 to 8.5 months. Specifically, pupae were exposed to four photoperiod regimes: (a) light conditions (24L:00D), (b) dark conditions (00L:24D), (c) short photoperiod (08L:16D) and (d) long photoperiod (16L:08D), as well as to three relative humidity regimes: (a) low (40% RH), (b) medium (60% RH) and (c) high (70-80% RH). Data revealed that relative humidity is not a significant predictor of diapause termination, but it affects the post-winter developmental period. Higher relative humidity promotes post-winter pupae development. On the other hand, photoperiod significantly affected both diapause termination and post-winter development of R. cerasi pupae. Light conditions (24L:00D) accelerate adult emergence, particularly for females. Regardless of the photoperiod (24L:00D, 00L:24D, 08L:16D), rates of adult emergence were high (>75%) for chilling intervals longer than 6.5 months. Nonetheless, exposure to a long day photoperiod (16L:08D), during chilling, dramatically reduced the proportion of adult emergence following 6 months exposure to chilling. Our findings broaden the understanding of factors regulating diapause responses in European cherry fruit fly, local adaptation and synchronization of adult emergence with the ripening period of major hosts.

Explorative Data Analysis of Drosophila suzukii Trap Catches from a Seven-Year Monitoring Program in Southwest Germany.

Over the last decade, Drosophila suzukii Matsumura, an invasive pest of soft-skinned fruits, gradually established itself in Europe, often resulting in significant economic losses. In 2011, when D. suzukii was first described for Germany, the Julius Kühn Institut (JKI) started a monitoring program in southwest Germany to study the occurrence and activity of the fly. Capture data from late 2011⁻early 2018 from 100 traps were analyzed for the effect of weather and immediate habitat on trap captures at different times of the year. We identified five phases in the annual population development cycle of D. suzukii. We found that the mild winter of 2013/2014 helped the thorough establishment of D. suzukii in Germany. Habitat types in the immediate vicinity of the trap and local weather conditions had a strong influence on trap captures. Forest borders and hedges were found to provide adequate overwintering shelter for the flies. Trap captures in forests and hedges were generally higher than those of vineyards and orchards, even during the fruiting seasons. Summer capture rates were correlated with the number of heat days and precipitation. We also discuss briefly the limitations of using trap captures as representative of fly density in the field.

Wolbachia in Parasitoids Attacking Native European and Introduced Eastern Cherry Fruit Flies in Europe.

The eastern cherry fruit fly, Rhagoletis cingulata Loew (Diptera: Tephritidae), is an economically important pest of cherries in North America. In 1983 it was first reported in Europe where it shares its ecological niche with the native European cherry fruit fly, Rhagoletis cerasi L. (Diptera: Tephritidae). Their coexistence in Europe led to the recent horizontal transmission of the Wolbachia strain wCer1 from R. cerasi to R. cingulata Horizontal Wolbachia transmission is mediated by either sharing of ecological niches or by interacting species such as parasitoids. Here we describe for the first time that two braconid wasps, Psyttalia rhagoleticola Sachtleben (Hymenoptera: Braconidae) and Utetes magnus Fischer (Hymenoptera: Braconidae), naturally parasitizing R. cerasi, use the invasive R. cingulata in Europe as a new host. In contrast, no parasitoids that parasitize R. cingulata in its native American range were detected in the introduced European range. Diagnostic Wolbachia PCR screening and sequence analyses demonstrated that all P. rhagoleticola individuals were infected with the newly described Wolbachia strain wRha while all U. magnus individuals were uninfected. wRha is different from wCer1 but had an Wolbachia surface protein (wsp) gene sequence that was identical to wCer2 of R. cerasi and wCin2 of R. cingulata. However, multi locus sequence typing revealed differences in all loci between wRha and the tephritid's strains. The horizontal transmission of wCer1 between the two tephritid species did not result in fixed heritable infections in the parasitoids. However, the parasitoids may have acted as a transient wCer1 vector.

Validation of Individual-Based Markov-Like Stochastic Process Model of Insect Behavior and a "Virtual Farm" Concept for Enhancement of Site-Specific IPM.

The paper reports application of a Markov-like stochastic process agent-based model and a "virtual farm" concept for enhancement of site-specific Integrated Pest Management. Conceptually, the model represents a "bottom-up ethological" approach and emulates behavior of the "primary IPM actors"-large cohorts of individual insects-within seasonally changing mosaics of spatiotemporally complex faming landscape, under the challenge of the local IPM actions. Algorithms of the proprietary PESTonFARM model were adjusted to reflect behavior and ecology of R. cerasi. Model parametrization was based on compiled published information about R. cerasi and the results of auxiliary on-farm experiments. The experiments were conducted on sweet cherry farms located in Austria, Germany, and Belgium. For each farm, a customized model-module was prepared, reflecting its spatiotemporal features. Historical data about pest monitoring, IPM treatments and fruit infestation were used to specify the model assumptions and calibrate it further. Finally, for each of the farms, virtual IPM experiments were simulated and the model-generated results were compared with the results of the real experiments conducted on the same farms. Implications of the findings for broader applicability of the model and the "virtual farm" approach-were discussed.

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.

Comparison of a synthetic chemical lure and standard fermented baits for trapping Drosophila suzukii (Diptera: Drosophilidae).

We determined the attractiveness of a new chemical lure compared with fermented food baits in use for trapping Drosophila suzukii Matsumura, spotted wing drosophila (Diptera: Drosophilidae), in Connecticut, New York, and Washington in the United States and at Dossenheim in Germany. The chemical lure (SWD lure) and food baits were compared in two types of traps: the dome trap and a cup trap. Regardless of trap type, numbers of male and female D. suzukii trapped were greater with the SWD lure compared with apple cider vinegar (ACV) baits at the Washington and New York sites, and were comparable with numbers of D. suzukii captured with a wine plus vinegar bait (W + V) at Germany site and a combination bait meant to mimic W + V at the Connecticut site. Averaged over both types of attractants, the numbers of D. suzukii captured were greater in dome traps than in cup traps in New York and Connecticut for both male and female D. suzukii and in Washington for male D. suzukii. No such differences were found between trap types at the Washington site for female and Germany for male and female D. suzukii. Assessments were also made of the number of large (>0.5 cm) and small (<0.5 cm) nontarget flies trapped. The SWD lure captured fewer nontarget small flies and more large flies compared with ACV bait in New York and fewer nontarget small flies compared with W + V in Germany, although no such differences were found in Washington for the SWD lure versus ACV bait and in Connecticut for the SWD lure versus the combination bait, indicating that these effects are likely influenced by the local nontarget insect community active at the time of trapping. In New York, Connecticut, and Germany, dome traps caught more nontarget flies compared with cup traps. Our results suggest that the four-component SWD chemical lure is an effective attractant for D. suzukii and could be used in place of fermented food-type baits.

In Focus: Spotted wing drosophila, Drosophila suzukii, across perspectives.

In August 2008, the first detection of the spotted wing drosophila, Drosophila suzukii, to the North America mainland in California caused great concern, as the fly was found infesting a variety of commercial fruits. Subsequent detections followed in Oregon, Washington, Florida and British Columbia in 2009; in Utah, North Carolina, South Carolina, Michigan, and Louisiana in 2010; and in Virginia, Montana, Wisconsin, Pennsylvania, New Jersey, Maryland and Mexico in 2011. In Europe, it has been detected in Italy and Spain in 2009 and in France in 2010. Economic costs to the grower from D. suzukii include the increased cost of production (increased labor and materials for chemical inputs, monitoring and other management tools) and crop loss. An effective response to the invasion of D. suzukii requires proper taxonomic identification at the initial phase, understanding basic biology and phenology, developing management tools, transferring information and technology quickly to user groups, and evaluating the impact of the research and extension program on an economic, social, and environmental level. As D. suzukii continues to expand its range, steps must be initiated in each new region to educate and inform the public as well as formulate management tactics suitable for the crops and growing conditions in each.

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.