Worldwide monitoring programs of the invasive fruit pest Drosophila suzukii Matsumura (Diptera: Drosophilidae), using fermentation baits like apple cider vinegar (ACV), revealed a counterintuitive period of low trap catches during summer, followed by an autumn peak. In this study, we demonstrate that ACV baited traps indeed provide a distorted image of the D. suzukii population dynamics as it is possible to capture higher numbers during this “low capture period” with synthetic lures. It was hypothesised that the preference of D. suzukii populations for fermentation cues like ACV is most pronounced during autumn, winter and spring, while the flies prefer fresh fruit cues during summer and that this seasonal preference is related to the changing physiology of the flies over the season. To test this hypothesis, the preference between fermentation cues (ACV) and host fruits (strawberries) and the effect of physiology (sex, seasonal morphology and feeding, mating and reproductive status) was investigated both in olfactometer laboratory experiments and a year-round field preference experiment. In olfactometer experiments we demonstrated that protein deprived females, virgin females with a full complement of unfertilised eggs and males show a strong preference for fermentation cues while fully fed reproductive summer morph females generally prefer fruit cues. These findings indicate that D. suzukii is attracted to fermentation volatiles in search of (protein-rich) food and to fruit volatiles in search of oviposition substrates. Winter morph and starved females displayed indiscriminating olfactory behaviour. In the field preference experiment, the hypothesised seasonal shift between fermentation and fruit cues was confirmed. This shift appeared to be highly temperature-related and was similarly observed for summer and winter morphs.

Over the past decade, the spotted-wing drosophila, Drosophila suzukii Matsumara has become one of the most important pests of soft-and stone fruits throughout Europe. Currently, the majority of growers still rely heavily on a limited portfolio of chemical foliar spray insecticides. Alternative strategies such as attract and kill (pull) or behavioral control systems that repel or deter D. suzukii from damaging fruits (push) are less common. We evaluated the potential of hop (Humulus lupulus L.), as a repellent for the Integrated Pest Management of D. suzukii, in controlled greenhouse conditions as well as at commercial field sites. In greenhouse cage tests on fruit or attractant medium, the positive controls thymol and 1-octen-3-ol as well as certain hops significantly reduced larval infestation levels compared to an untreated control, while other hop products showed only numerical reduction in infestation. A controlled field trial on raspberries (Rubus idaeus L.) failed to replicate these results, both for the positive control repellents as for the hop samples. In field experiments in commercial raspberry and blackberry (Rubus fruticosus L.) plantations, no significant reduction in oviposition or differences in population density could be observed for the hop treated plots as compared to the untreated. Through SPME headspace analysis of the hops, a number of compounds were associated with the efficacy observed in the greenhouse, even though different hop varieties were found to have notably different volatile profiles.

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Background Spotted wing drosophila (SWD), Drosophila suzukii (Matsumura) (Diptera: Drosophilidae), is a pest of stone and small fruits causing considerable economic losses. Current management strategies rely primarily on calendar‐based spraying, owing to the poor relationship between monitoring data and damage levels, and the lack of success of mass‐trapping tools. The aim of this study was to evaluate different trap models for SWD, with an emphasis on their fly‐retention capacity. To this end, we examined and quantified the added value of two fly‐retaining trap features; tunnel entries to impede escape and an insecticide‐coated inner surface as a killing agent. Results An insecticide‐coated inner surface resulted in significantly higher trap retention after 24 h in the laboratory (4.9‐ to 7.4‐fold greater, depending on trap type) compared to a noncoated trap. Trapping efficacy was significantly improved in field trials by such a killing agent in the trap (1.2‐ to 4.5‐fold greater). Tunnel entries significantly improved trap retention in the laboratory and field (by 1.5‐fold). Conclusion The outcomes of this study clearly reveal the substantial impact of the fly‐retention capacity of SWD traps on their overall capture performances. It was demonstrated for the first time that an insecticide‐coated inner surface as a killing agent significantly improves trap efficacy for SWD. This finding can readily be implemented in any trap model to improve monitoring and mass trapping of SWD. Also tunnel entries were shown to have a significant influence on the fly retention and, hence, substantially enhance trapping efficacy.

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The spotted wing drosophila, Drosophila suzukii, is an invasive pest species from Southeast Asia that was recently introduced in Europe and North America. As this fruit fly lays its eggs in ripening soft-skinned fruit, it causes great damage to a variety of crops, including cherries, blueberries, blackberries, raspberries, grapes, plums and strawberries. Consequently, there is a great demand for an effective and species-specific lure, which requires the development of successful attractants. Until now, there is no lure available that is species-specific and can detect the presence of D. suzukii before infestation. As blackberry (Rubus fruticosus) is one of the preferred host crops of D. suzukii, the volatile compounds of R. fruticosus berries are here identified and quantified using multiple headspace SPME (solid phase micro extraction) GC-MS (gas chromatography–mass spectrometry). Subsequently, the attractivity of 33 of the identified compounds was tested with a two-choice laboratory bioassay. Acetaldehyde, hexyl acetate, linalool, myrtenol, L-limonene and camphene came out as significantly attractive to D. suzukii. The first four attractive compounds induced the strongest effect and therefore provided the best prospects to be implemented in a potential lure. These findings could contribute towards the development of more effective attractants for monitoring and mass trapping D. suzukii.

The marking of Drosophila suzukii can be an important instrument for studying the ecology and behaviour of this economically important fruit pest, aiding the development of new Integrated Pest Management (IPM) tools or strategies. There is, however, a need for a cost-effective methodology that provides an easily detectable and stable mark. Whereas fluorescent pigment powders are often used in entomological research, the pigments (series, dyes), application techniques, or doses need to be evaluated for each studied species in terms of their efficacy and possible adverse effects on the performance of the insect. The effectiveness of different application techniques and dyes (RadGlo ® TP-series) and their effect on the survival of adult D. suzukii were investigated in the laboratory. Furthermore, the influence of the marking on the behaviour of the flies was examined in laboratory trap assays (olfaction) and a field recapture study (general orientation). The persistence and detectability of the marks was evaluated both on living flies (for different application techniques) and dead flies under trapping/storage conditions. The use of fluorescent powders to mark D. suzukii flies yielded a clearly detectable and highly persistent mark, without any adverse effects on the survival and behaviour of the flies. Insects 2020, 11, 152 2 of 20The spotted wing Drosophila, Drosophila suzukii Matsumura (Diptera: Drosophilidae), native to Asia [5][6][7], has become a worldwide invasive pest of soft-skinned fruit crops over the last decade [8][9][10][11][12][13][14]. Studies on the ecology and behaviour of the species can yield new insights allowing the improvement or development of management strategies. Various methods for marking D. suzukii flies have been proposed and further optimised. An immunomarking technique (i.e., the use of proteins as markers and detection by enzyme-linked immuno-sorbent assays (ELISA) [15]) for both topical application and acquisition of residues on leaves was tested and optimised by Klick et al. in a series of laboratory and semi-field experiments [16]. What makes this technique unique is that vast areas can be sprayed with inexpensive proteins and that detection by ELISA is fairly sensitive to the acquisition of leaf residues. The disadvantages of immunomarking are the possibility of both false positives and false negatives [17], the need for individual analyses of specimens, and the costs and labour required for detection. Trace elements and stable isotopes can be administered to plants to act as systemic markers for herbivorous insects, an approach that was evaluated for D. suzukii with Rb and 15 N. [18]. The added value of these systemic markers lies in the fact that larvae are self-marked while developing inside the host fruits, enabling the linkage of captured adults to their source of larval development [18]. Methods of self-marking are particularly interesting for MC studies in which whole areas or plants are marked, instead of marking the (captured/reared) insects before release. For MR and M...

The invasion of Drosophila suzukii (Matsumura) (Diptera: Drosophilidae) worldwide has disrupted existing or developing integrated pest management (IPM) programs in soft-skinned fruits. Currently, with a reliance on only broad-spectrum insecticides, there is a critical call for alternative control measures. Behavioural control is one of the pillars of IPM, and, in the present study, it is investigated whether mass trapping could be viable for D. suzukii management. By quantifying trap interference in 4 × 4 replicate trapping grids, an estimate of the attraction radius for a certain attractant and context can be obtained. Traps designed for dry trapping (no drowning solution, but a killing agent inside) and synthetic controlled released experimental lures were tested in a two-year field study. Apple cider vinegar (ACV) was included as a reference bait and trials were performed with 5, 10 and 15 m inter-trap spacings at different seasonal timings. Clear trap interference and, hence, overlapping attraction radii were observed both in spring and summer for both the synthetic lures and ACV. In early spring, ACV shows the most potential for mass trapping, however from June onwards, the experimental dry lures show equal or better results than ACV. Based on our findings, workable trap densities are deemed possible, encouraging further development of mass trapping strategies for the control of D. suzukii.