Behavioral and Antennal Responses of Drosophila suzukii (Diptera: Drosophilidae) to Volatiles From Fruit Extracts

Host selection by thrips is affected by the floral volatile profile of sunflower

Thrips, Frankliniella intonsa, is a highly polyphagous pest with a worldwide distribution. F. intonsa-infested sunflower seeds show marked visual damage. The study findings revealed that significantly more F. intonsa infested confection sunflower compared to oilseed sunflower, via olfactometer bioassay studies, we found that compared with the flower and pollen of oilseed sunflowers, those of confection sunflowers attract F. intonsa. Considering this discrepancy in the preference of F. intonsa on oilseed and confection sunflowers, the volatiles of the flower and pollens of two sunflowers were analysed by gas chromatography-mass spectroscopy. The behavioural responses of F. intonsa were assessed for these compounds using Y-tube bioassays. Geranyl bromide, a unique volatile component of oilseed sunflowers, induced an assertive approach-avoidance behaviour in F. intonsa, whereas the unique component ethyl isovalerate in confection sunflowers attracted F. intonsa. F. intonsa adults demonstrated significant attraction to the blends of confection sunflowers. Furthermore, field verification revealed that intercropping confection and oilseed sunflowers could effectively control F. intonsa. The study provided insights into the chemical cues used by F. intonsa in locating hosts. Therefore, oilseed sunflowers can be used as repellent plants to prevent F. intonsa invasion.

Methyl N,N-dimethylanthranilate and ethyl propionate: repellents effective against spotted wing drosophila, Drosophila suzukii

BACKGROUND

Spotted wing drosophila, Drosophila suzukii (Matsumura) (Diptera: Drosophilidae), is an economically important pest of soft and stone fruit crops. The aim of this study was to identify repellents, formulated in dispensers, which could protect crops from D. suzukii. Fourteen potential repellents were screened against summer- and winter-morph D. suzukii through electroantennography and behavioural bioassays. Repellents effective in the laboratory were tested in polytunnels to determine their efficacy in reducing catches in fruit-baited traps. Further trials of three potential repellents were conducted to determine the distances over which repellent dispensers could reduce D. suzukii emergence in a strawberry crop.

RESULTS

All 14 chemicals screened were detected by the antennae of both D. suzukii morphs. Hexyl acetate and geosmin both elicited a significantly greater corrected EAG response in summer morphs than winter morphs. Summer-morph D. suzukii were repelled by butyl acetate, ethyl propionate, methyl N,N-dimethyl anthranilate, geosmin, methyl salicylate, DEET and benzaldehyde at one or more doses test in laboratory bioassays. Winter morphs were repelled by ethyl propionate, methyl anthranilate, methyl N,N-dimethyl anthranilate, DEET, benzaldehyde and butyl anthranilate at one or more of the doses tested in the laboratory. Ethyl propionate, methyl N,N-dimethylanthranilate and benzaldehyde repelled both morphs from fruit-baited traps in polytunnel trapping trials. Ethyl propionate and methyl N,N-dimethylanthranilate reduced emergence of D. suzukii in a strawberry crop over 3-5 m.

CONCLUSIONS

Ethyl propionate and methyl N,N-dimethylanthranilate may protect strawberry crops against D. suzukii. Future work should test these repellents in combination with attractants in a 'push-pull' strategy. © 2024 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Chemical and Electrophysiological Characterisation of Headspace Volatiles from Yeasts Attractive to Drosophila suzukii

Chemical control of Drosophila suzukii (Diptera: Drosophilidae) based on the use of insecticides is particularly challenging as the insect attacks ripening fruits shortly before harvest. An alternative strategy may rely on the use of yeasts as phagostimulants and baits, applied on canopy as attract-and-kill formulations. The aim of this research was to identify the most attractive among six yeast species for D. suzukii: Saccharomyces cerevisiae, Hanseniaspora uvarum, Clavispora santaluciae, Saccharomycopsis vini, Issatchenkia terricola, and Metschnikowia pulcherrima. The volatile profile of C. santaluciae was described for the first time. Behavioural experiments identified H. uvarum and S. vini as the most attractive yeasts. The characterization of yeast headspace volatiles using direct headspace (DHS) and solid-phase microextraction (SPME) revealed several strain-specific compounds. With DHS injection, 19 volatiles were characterised, while SPME revealed 71 compounds constituting the yeast headspace. Both analyses revealed terpenoids including β-ocimene, citronellol, (Z)-geraniol (nerol), and geranial as distinct constituents of S. vini. H. uvarum and S. vini were further investigated using closed-loop stripping analysis (CSLA) and electroantennography. Out of 14 compounds quantified by CSLA, ethyl acetate, isoamyl acetate, β-myrcene, benzaldehyde and linalool were detected by D. suzukii antennae and might generate the strong attractiveness of S. vini and H. uvarum. Our results highlight a strong attraction of D. suzukii to various yeasts associated with both the flies and their habitat and demonstrate how different sampling methods can impact the results of volatile compound characterization. It remains to be demonstrated whether the distinct attraction is based on special adaptations to certain yeasts and to what extent the metabolites causing attraction are interchangeable.

Olfactory behavioral responses of two Drosophila species and their pupal parasitoid to volatiles from bananas

BACKGROUND

Behavior-based manipulation is an essential part of Drosophila integrated pest management (IPM). Effective compounds are useful for improving the efficiency of baits and the development of attract-and-kill or push-pull strategies to manage Drosophila populations. Here, we investigated the olfactory behavior of two Drosophila species, as well as their pupal parasitoid, to volatiles from bananas, for the identification of effective compounds to control fly populations.

RESULTS

The results showed that overripe bananas were most attractive to both flies, with a higher attraction index (AI) in Drosophila melanogaster than in Drosophila suzukii. The profiles of volatile organic compounds (VOCs) from bananas with three different ripening stages were compared, and six VOCs were selected for behavioral tests. D. suzukii showed significantly different responses to isoamyl alcohol with D. melanogaster. The effects of ethyl butyrate and ethyl isovalerate on the two flies were dose-dependent, with lower concentrations acting as repellent and higher concentrations acting as attractant. Isoamyl acetate, isoamyl butyrate and isoamyl isovalerate (0.005-0.05% v/v) were attractive to both flies. The parasitoid wasp Pachycrepoidus vindemmiae was repelled by isoamyl alcohol and ethyl butyrate, and attracted by ethyl isovalerate, but showed no significant response to isoamyl acetate, isoamyl butyrate and isoamyl isovalerate at the tested concentration.

CONCLUSION

This study indicated that the behavioral response of Drosophila to the odor of chemical compounds is dose-dependent. Isoamyl alcohol and isoamyl acetate at certain concentrations could be used as repellents, whereas ethyl isovalerate as an attractant in control strategy design for D. suzukii. © 2023 Society of Chemical Industry.

Evaluating global Vaccinium germplasm for resistance against invasive Drosophila suzukii (Diptera: Drosophilidae)

Control of spotted-wing Drosophila, Drosophila suzukii, in small fruits emphasizes biological, cultural, and chemical approaches, whereas studies of host plant resistance as a form of genetic control are just getting underway. The identification of resistance patterns among genotypes of host plants whose fruit, leaves, roots, stems, or seeds are specifically targeted by an invasive pest is the first step in the development of an effective genetic control. Therefore, a detached fruit bioassay was developed to screen for D. suzukii oviposition and larval infestation within berries from 25 representative species and hybrids of wild and cultivated Vaccinium. Ten Vaccinium species showed strong resistance; among them, two wild diploids originating from within the fly's native range: V. myrtoides and V. bracteatum. Other resistant species came from the sections Pyxothamnus and Conchophyllum. They included New World V. consanguineum and V. floribundum. Large-cluster blueberry, V. amoenum, and three Floridian genotypes of related rabbiteye blueberry, V. virgatum, were the only hexaploids expressing strong resistance against D. suzukii. Most screened blueberry genotypes from managed lowbush and cultivated highbush types were susceptible to the flies' attacks (i.e., oviposition). Tetraploid blueberries tended to host the most eggs, whereas diploids and hexaploids harbored 50%-60% fewer eggs, on average. D. suzukii cannot lay eggs or complete development in the smallest, sweetest, and firmest diploid fruits. Likewise, certain genotypes of large-fruited tetraploid and hexaploid blueberry strongly curbed D. suzukii egg-laying and larval growth, indicating the possibility of heritable resistance operating against this invasive fly species.

Open field trials of food-grade gum in California and Oregon as a behavioral control for Drosophila suzukii Matsumura (Diptera: Drosophilidae)

The invasion of Drosophila suzukii, spotted-wing drosophila, across Europe and the US has led to economic losses for berry and cherry growers, and increased insecticide applications to protect fruit from damage. Commercial production relies heavily on unsustainable use of conventional toxic insecticides. Non-toxic insecticide strategies are necessary to alleviate the disadvantages and non-target impacts of toxic conventional insecticides and improve Integrated Pest Management (IPM). A novel food-grade gum deployed on dispenser pads (GUM dispensers) was evaluated to mitigate D. suzukii crop damage in five commercial crops and nine locations. Trials were conducted at a rate of 124 dispensers per hectare in cherry, wine grape, blueberry, raspberry, and blackberry in California and Oregon, USA during 2019 and 2020. The majority of trials with the food-grade gum resulted in a reduction of D. suzukii egg laying in susceptible fruit. In some cases, such damage was reduced by up to 78%. Overall, results from our meta-analysis showed highly significant differences between GUM treatments and the untreated control. Modeling simulations suggest a synergistic reduction of D. suzukii damage when used in combination with Spinosad (Entrust SC) insecticide. These data illustrate commercial value of this tool as a sustainable alternative to manage D. suzukii populations within a systems approach.

Drosophila suzukii energetic pathways are differently modulated by nutritional geometry in males and females

As a polyphagous pest, Drosophila suzukii has a variety of host fruits available for feeding and oviposition, but how the nutritional geometry of different hosts influences its metabolism is still poorly understood. This work aimed to evaluate how D. suzukii metabolic and transcriptional pathways are influenced by feeding on different host fruits, and how sex influences these responses. Adult flies were allowed to feed on five different fruit-based media. Lipids, glucose, glycogen, and energy pathways-associated gene expression, were quantified. Females showed an energetic metabolism easily adaptable to the food's nutritional characteristics; in contrast, males' energetic metabolism was particularly influenced by food, predominantly those fed on raspberry media who showed changes in glucose levels and in the expression of genes associated with metabolic pathways, suggesting activation of gluconeogenesis and trehaloneogenesis as a result of nutritional deficiency. Here we present novel insight into how D. suzukii's energetic pathways are modulated depending on fruits' nutritional geometry and sex. While the females showed high adaptability in their energetic metabolism to the diet, males were more feeding-sensitive. These findings might be used not only to control this pest population but to better advise producers to invest in less suitable fruits based on the hosts' nutritional geometry.

Factors Influencing the Efficacy of Novel Attract-and-Kill (ACTTRA SWD) Formulations Against Drosophila suzukii

In the continental United States, the invasive spotted-wing drosophila (SWD), Drosophila suzukii Matsumura, has become a primary pest of multiple stone and soft-skinned fruits. A new innovative adjuvant formulation, ACTTRA SWD, mixed with a suitable insecticide, constitutes a novel attract-and-kill tactic to manage D. suzukii in fruit crops. We hypothesized that background odors present in crop fields, particularly odors from host fruits, negatively affect the effectiveness of this attract-and-kill formulation, as odors from these sources can compete for insect attraction. Additionally, we evaluated the influence of adult D. suzukii sex and physiological status (age and mating status), and fruit ripeness on its response to the ACTTRA SWD formulation. For this, we used two-choice bioassays to test the response of adult D. suzukii to three ACTTRA SWD formulations (named OR1, TD, and HOOK SWD) in the presence and absence of host fruits (blueberries, raspberries, blackberries, and strawberries). Odors from raspberries were significantly more attractive than those from the TD formulation mixed with spinosad (Entrust). For the HOOK SWD formulation and OR1+Entrust formulation, odors from all the fruit types tested were significantly more attractive than the adjuvants. Compared with females, male D. suzukii were more attracted to the TD formulation over the blueberry fruits. Additionally, age and female mating status but not fruit ripeness influenced D. suzukii attraction to both OR1 and TD formulations. The results from this study indicate that D. suzukii physiological status and host fruit availability impact the efficacy of new attract-and-kill adjuvants such as ACTTRA SWD.

Drosophila suzukii Management in Latin America: Current Status and Perspectives

Spotted-wing drosophila, Drosophila suzukii Matsumura, was first established in Latin America in Mexico in 2011. The vinegar fly has since been detected in 296 municipalities in Argentina, Brazil, Chile, Mexico, and Uruguay. Drosophila suzukii is polyphagous and is found on 64 host plants in 25 families in Latin America, with most hosts also exotic species. In Latin America, D. suzukii is attacked by 14 species of parasitoid wasps in the families Diapriidae, Figitidae, and Pteromalidae, which are promising native parasitoids for control of the pest. This article analyzes results from studies on monitoring, biological, chemical, and cultural control, and sterile insect techniques to provide a basis for the development of area-wide and sustainable D. suzukii management programs in Latin America. The review examines how D. suzukii has been managed in Latin America and how research conducted in this region can contribute to management of the species in other parts of the world.

Antennae of psychodid and sphaerocerid flies respond to a high variety of floral scent compounds of deceptive Arum maculatum L

Insect-pollinated plants often release complex mixtures of floral scents to attract their pollinators. Yet scent compounds eliciting physiological or behavioural responses in pollinators have only been identified in few plant species. The sapromyiophilous aroid Arum maculatum releases a highly diverse dung-like scent with overall more than 300 different compounds recorded so far to attract its psychodid and other fly pollinators. The volatiles’ role in pollinator attraction is mostly unknown. To identify potential behaviourally active compounds, we recorded electroantennographic responses of four Psychodidae and one Sphaeroceridae species to (1) inflorescence scents of A. maculatum and (2) the scents released by cow dung, likely imitated by the plant species. Here we show that these flies are sensitive to 78 floral volatiles of various chemical classes, 18 of which were also found in cow dung. Our study, which for the first time determined physiologically active compounds in the antennae of Psychoda spp. and Sphaeroceridae, identified various volatiles not known to be biologically active in any floral visitors so far. The obtained results help deciphering the chemical basis that enables A. maculatum and other plants, pollinated by psychodids and sphaerocerids, to attract and deceive their pollinators.

Behavioral Responses of Drosophila suzukii (Diptera: Drosophilidae) to Blends of Synthetic Fruit Volatiles Combined With Isoamyl Acetate and β-Cyclocitral

Baits and lures for trapping and monitoring the invasive vinegar fly Drosophila suzukii Matsumura (Diptera: Drosophilidae) are currently derived from fermentation volatiles. Volatile organic compounds from alternative sources could improve monitoring efforts and optimize capture of gravid females. Through electroantennography and behavioral assays, we evaluated male and female D. suzukii responses to blends of selected synthetic fruit volatiles in combination with the fruit compound isoamyl acetate and the strawberry leaf terpenoid β-cyclocitral. Blends that were attractive to both male and female D. suzukii were then evaluated for attractiveness to a non-target drosophilid, Drosophila melanogaster. A simple 3-component blend of isoamyl acetate, β-cyclocitral and methyl butyrate was attractive to D. suzukii, particularly females, relative to fresh blueberry volatiles. The 3-component blend was not attractive to D. melanogaster. Additional research is needed to determine the effectiveness of this blend to attract D. suzukii under field conditions.

Mass Trapping Drosophila suzukii, What Would It Take? A Two-Year Field Study on Trap Interference

Simple Summary

Drosophila suzukii is an invasive fruit fly that have became a key pest of soft-skinned fruits during the past decade. Today, the control of this pest relies strongly on broad-spectrum insecticides. Deploying attractive traps to control the pest population (mass trapping) could be part of the management strategy of D. suzukii. The present study analyses whether mass trapping with different attractants could be viable for D. suzukii control and how far traps should be maximally spaced in a grid. Traps in a grid compete for the same insects when they are spaced close enough and their radii of attraction overlap. Since the traps on the corners of a grid have fewer competing traps around than fully surrounded centre traps, the ratio of the catches in the corner traps and the centre traps indicates whether the traps are spaced close enough. By quantifying that trap interference in 4 × 4 trapping grids, it was found in this two-year field study that workable trap densities can be expected to control D. suzukii. From June onwards, synthetic lures in dry traps show equal or better results than the same traps with a reference liquid bait (apple cider vinegar).

Abstract

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.

Sodium Chloride Added to Diluted Concord Grape Juice Prior to Fermentation Results in a Highly Attractive Bait for Drosophila suzukii (Diptera: Drosophilidae)

At the interface of behavioral chemical ecology and pest management lays the evaluation of kairomones that can be used for either, monitoring or attract-and-kill of insect pests. Diluted Concord grape juice (DGJ) was previously reported to be highly attractive to male and female D. suzukii. Here, we conducted cage and field studies aimed at (1) comparing the attractiveness of fresh DGJ against that of commercial lures over a 3-year period in multiple locations, (2) quantifying the effects of DGJ aging for 1 and 2 weeks on D. suzukii attraction, and (3) ascertaining the effects of adding sodium chloride to DGJ prior to fermentation on the outcome. For all field studies, captures of non-target insects were recorded. Combined findings from the cage and field studies comparing DGJ and commercial lures indicate that fresh DGJ is as attractive or more attractive than the commercial lures that were evaluated. The results of the aging studies revealed that 7- and 14- day old DGJ baits are at least twice as attractive to female D. suzukii when compared to fresh DGJ. The response of other Drosophilids to the aged olfactory treatments mirrored that of D. suzukii. Remarkably, the addition of 2% sodium chloride to DGJ prior to aging resulted in a fourfold increase in attractiveness to male and female D. suzukii while reducing the number of non-target insects captured in traps. In conclusion, DGJ is an effective bait that can be deployed in traps and, when 2% sodium chloride is added, the resulting material outcompetes the performance of commercial lures and greatly reduces captures of non-target insects, thereby increasing bait selectivity. Overall, our findings increase our understanding of D. suzukii olfactory-driven behavior in response to fruit-based odor and demonstrate the potential use of a low-cost attractant for farmers who are not able to monitor for D. suzukii when commercially produced lures are expensive or less accessible.

Nutritional phenotype underlines the performance trade-offs of Drosophila suzukii on different fruit diets

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Drosophila suzukii exhibits contrasting performance trade-offs when confined to fruit diets of different protein-to-sugar ratios.

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These trade-offs can only be established when we examined performance parameters in both larvae and adults.

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The diet-specific nutritional phenotype readily explains the performance trade-offs.

Animals confined to different dietary conditions often exhibit distinct, sometimes contrasting, nutritional phenotypes and performance outcomes. This is especially true for many oviparous insects whose developmental diets can vary depending on the mother's egg-laying site selection. Much research on the relationship between preference and performance in insects has focused on larval success, which overlooks the complexities of dietary effects on diverse performance parameters across life stages and potential trade-offs between those parameters. Furthermore, the connection between diet-induced nutritional phenotype and performance trade-offs is not well understood. Here, using Drosophila suzukii, we quantify multiple performance indices of larvae and adults reared on five host fruits of different protein-to-sugar ratios (P:S) which have previously been shown to differ in attractiveness to fly foraging and oviposition. Our results demonstrate robust diet-specific performance trade-offs, with fly fecundity, larval development time, pupal size, and adult weight superior in flies reared on the high P:S raspberry diet, in contrast to the low P:S grape diet; but the reverse was found in terms of adult starvation resistance. Notably, the contrasting performance trade-offs are readily explained by the fly nutritional phenotype, reflected in the protein and energy (glucose and lipid) contents of flies reared on the two fruits. Together, our results provide experimental evidence for metabolic plasticity of D. suzukii reared on different fruits and the possibility of using adult nutritional phenotype as a marker for diet and performance outcomes.

Olfactory Cues From Host- and Non-host Plant Odor Influence the Behavioral Responses of Adult Drosophila suzukii (Diptera: Drosophilidae) to Visual Cues

While trapping methods for Drosophila suzukii Matsumura (Diptera: Drosophilidae) have typically relied on fermentation volatiles alone or in association with a visual stimulus, the relative contribution of visual and olfactory stimuli to the food- and host-seeking behavior of D. suzukii is poorly understood. This study quantified the type of response exhibited by male and female D. suzukii to color and the effects that volatiles (fermentation, fresh fruit, and leaf) exert on the outcome. Seven-, four- and two-choice assays were used to quantify interactions between visual and olfactory cues. When no volatiles were present in a seven-choice assay, D. suzukii preferred red, black, and green pigments. Black and red were preferred when yeast odors were present, and black alone was the most attractive color when blueberry odor was present. A strawberry leaf terpenoid, β-cyclocitral, seemed to have overridden the flies' response to color. In four-choice assays, blueberry odor was more likely to interact synergistically with color than yeast or β-cyclocitral. This study demonstrates that D. suzukii modulates the response to multimodal sensory modalities (vision and olfaction) depending, to some extent, on the type of olfactory stimuli. Our findings also provide insight into the relative importance of vision as a function of odor quality in this invasive species.

Identification of Blackberry (Rubus fruticosus) Volatiles as Drosophila suzukii Attractants

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.

Assessment of Attractant Lures and Monitoring Traps for Drosophila suzukii (Diptera: Drosophidae) Using Electrophysiology, Laboratory Choice Assays, and Field Trials

Monitoring is critical to control efforts for Drosophila suzukii Matsumura, an invasive polyphagous fly that has the potential to cause significant losses in commercial soft fruit and berry production worldwide. We used an iterative process to identify trap colors, trap designs, and volatile mixtures to improve monitoring efforts in commercial blueberry, raspberry, and blackberry crops. Our results suggest that the selection of trap color and design and attractant lures should be customized to the crop in which they are deployed. In raspberries grown in high tunnel systems, DrosaLure paired with Drosal traps painted green and purple were highly specific to D. suzukii although actual capture counts were low. However, in field grown raspberries, BioLure and Multilure traps were most effective, but with significant nontarget bycatch. In blueberries, we had greatest success with a 5 µg:50 ng mixture of ethyl acetate-acetoin in a green/purple-colored jar-style trap with large (5 cm) mesh covered openings.

The attractant, but not the trap design, affects the capture of Drosophila suzukii in berry crops

Drosophila suzukii (Matsumura) (Diptera: Drosophilidae) is recognized as an invasive pest in Europe and North America. In Mexico, it is one of the main insect pests of soft-skinned fruits such as blueberries, strawberries, raspberries, blackberries, plums, and guava. Previous studies have shown that D. suzukii uses visual and chemical cues during host plant searching. This knowledge has been used to develop traps and attractants for monitoring D. suzukii. In this study, five trap designs were evaluated to monitor D. suzukii under field conditions. Traps were baited with SuzukiiTrap®, Z-Kinol, an attractant based on acetoin and methionol, or apple cider vinegar (ACV) enriched with 10% ethanol (EtOH) with the synergistic action of carbon dioxide (CO2). Our results suggested that the attractant was the determining factor in capturing D. suzukii, while trap design seemed to play a modest role. We found that traps baited with Z-Kinol captured the highest number of D. suzukii compared to that caught by traps baited with SuzukiiTrap®, or ACV + EtOH + CO2. The highest catch numbers occurred in blackberry, followed by strawberry, raspberry, and blueberry. Traps captured more females than males. The results obtained may be useful for monitoring D. suzukii populations in Mexico and elsewhere, particularly in states where soft fruit crops are a component of agricultural activities.

Field Evaluation of Different Attractants for Detecting and Monitoring Drosophila suzukii

Drosophila suzukii, more commonly known as the spotted-wing drosophila (SWD), is an invasive pest of soft, thin-skinned fruit responsible for significant economic losses for growers worldwide. To detect and monitor this pest, several host attractants have been developed for use in trapping SWD; however, they lack selectivity. Therefore, there is a significant need for more selective monitoring devices to enable growers to make timely pest management decisions to properly protect vulnerable crops. Previous studies identified a quinary blend (QB), based on fermenting apple juice odors, which offers significantly higher selectivity by reducing non-target captures compared with the standard apple cider vinegar bait commonly used by growers in the orchards. In this study, the selectivity and efficacy of a home-made QB dispenser was compared to an industry formulated version of the QB components (ChemTica) and two commercially available (Scentry and Trécé) SWD dispensers across blueberry and raspberry fields in Maryland, West Virginia, and New Jersey in different seasons. Controlled-release dispensers of the QB (home-made and ChemTica) consistently had higher selectivity within the blueberry and raspberry field sites compared with the two commercial dispensers; although efficacy was compromised such that total SWD captures per trap tended to be lower. The selectivity ratio range of SWD to non-targets (all non-SWD) for a QB-based (ChemTica) dispenser averaged from 15 to 57% compared with other commercial dispensers that ranged from 1 to 30% based on location and year. Due to high selectivity of the controlled-release dispenser of the QB, the potential for this dispenser to be utilized by growers as a SWD detection and monitoring tool is high.

Antennal and Behavioral Responses of Drosophila suzukii to Volatiles from a Non-Crop Host, Osyris wightiana

Drosophila suzukii (Diptera: Drosophilidae) infests a variety of commercial fruits, including cherries and other soft-skinned fruits. After the cropping season of most cultivated crop hosts, it heavily infests the fruit of a wild host-plant, Osyris wightiana in southwest China. Here, we employ gas chromatography-electroantennographic detection (GC-EAD) together with behavioral bioassays and a trapping experiment to identify volatile semiochemicals emitted by O. wightiana that are involved in D. suzukii attraction. GC-EAD recordings of D. suzukii antenna showed responses to 13 compounds, including α-pinene, 3-methylbutyl acetate, 2-hexanol, E-β-ocimene, Z-3-hexenol, β-caryophyllene, α-humulene, and six unidentified compounds. The flies were attracted by seven individual EAD-active compounds at low doses (0.01 and 0.1 μg), but were repelled at high doses (10 and 100 μg). In a similar manner, a blend of seven EAD-active compounds at low doses (0.1 and 1 μg) was attractive to female flies, but became repulsive at high doses (10 μg). The low dose of the blend was as attractive as the fruit volatiles, although both were less attractive than the fruits. The blend attracted both female and male D. suzukii and other Drosophila flies. The percentage of D. suzukii out of all flies captured by the blend was significantly greater than that captured by the control. These results indicate that the EAD-active volatile compounds emitted by fruits of O. wightiana play an important role in D. suzukii attraction, and have the potential to be used for management of D. suzukii.

Selection of Lactic Acid Bacteria Species and Strains for Efficient Trapping of Drosophila suzukii

Simple Summary

The spotted wing drosophila (SWD) is an invasive fruit fly that causes serious economic damage to many fruit crops. Monitoring is the first step for any management program to determine the characteristics of a pest. For this purpose, there are no efficient baits registered to date. Certain bacteria release chemical compounds that attract SWD. We studied the bacterial impact on the enhanced attractiveness of a commercial bait (Droskidrink^®) under field and laboratory conditions. At first, Oenococcus oeni belonging to lactic acid bacteria (LAB) was found to release chemical compounds that were highly attractive for SWD. The attractiveness of Droskidrink^® bait was increased by O. oeni culture, resulting in a higher capture rate of SWD in traps. Therefore, our findings suggest the use of the bacterial culture inside the commercial SWD baits. The use of these kinds of baits can minimize the risk of pest outbreaks in fruit orchards in both domestic and wild environments. Our pest management approach is farmer-friendly in all aspects, as well as the food sector.

Abstract

(1) Monitoring of Drosophila suzukii is based on the use of effective traps and baits. The current baits are insufficient to provide efficient monitoring. The use of bacteria as bio-catalyzers to produce bioactive volatiles may improve flies’ attraction. Thus, we conducted this work to improve Droskidrink^® bait’s attractiveness using lactic acid bacteria. (2) Different baits that were based on the use of Droskidrink^® were assessed for flies’ attraction in a Droso-Trap^® in a vineyard. Oenococcus oeni, Pediococcus spp., and Lactobacillus spp. were used. The performance of the most attractive species, O. oeni, inoculated into Droskidrink^® was assessed in laboratory tests. The responses of female flies to volatiles produced by Droskidrink^® with O. oeni strains were recorded by electroantennography. (3) Preliminary field assessment of baits recorded O. oeni as the most attractive species. Three strain groups showed adaptation to test conditions. Volatiles extracted by the headspace of baits inoculated with O. oeni, elicited electroantennographic responses from fly antennae. (4) Droskidrink^® inoculated with O. oeni is a highly attractive bait for monitoring. These findings will be useful for improving the attractiveness of D. suzukii commercial baits based on the utilization of LAB volatiles in a strain-dependent manner.

Liquid Baits with Oenococcus oeni Increase Captures of Drosophila suzukii

Simple Summary

Among the challenges arising from climate change and the transformation of agroecosystems is that agricultural production is heavily affected by invasive insect species. Invasive insects can establish in new areas where their development can progress due to a suitable climate and lack of natural enemies. Farmers have few options to mitigate those insects’ attacks. Current control tactics using pesticides must be replaced with more sustainable methods to counter invasive insect species. We approached the control of the invasive spotted-wing drosophila Drosophila suzukii, using a baiting system that manipulates insect behavior without use of toxic or non-sustainable chemicals. The results of our work are utilized for the monitoring and mass trapping of this devastating invasive species. In our innovative smart-design trap system, we use odors that attract flies and decrease damage in open field scenarios. Our trapping system can efficiently detect the first spring arrival of D. suzukii in agricultural fields and as a such, represents a good early monitoring tool. We conducted four years of laboratory and open-field trials in different berry crops. As a source of odor attraction, we used a mixture of wine, apple cider vinegar, and different commercially available strains of lactic acid bacteria.

Abstract

The spotted-wing drosophila (SWD), Drosophila suzukii Matsumura (Diptera: Drosophilidae), native to Eastern Asia, is an invasive alien species in Europe and the Americas, where it is a severe pest of horticultural crops, including soft fruits and wine grapes. The conventional approach to controlling infestations of SWD involves the use of insecticides, but the frequency of application for population management is undesirable. Consequently, alternative strategies are urgently needed. Effective and improved trapping is important as an early risk detection tool. This study aimed to improve Droskidrink^® (DD), a commercially available attractant for SWD. We focused on the chemical and behavioral effects of adding the bacterium Oenococcus oeni (Garvie) to DD and used a new trap design to enhance the effects of attractive lures. We demonstrate that microbial volatile compounds produced by O. oeni are responsible for the increase in the attractiveness of the bait and could be later utilized for the development of a better trapping system. Our results showed that the attractiveness of DD was increased up to two-fold by the addition of commercially available O. oeni when combined with an innovative trap design. The new trap-bait combination increased the number of male and especially female catches at low population densities.

Physicochemical Characteristics and Superficial Damage Modulate Persimmon Infestation by Drosophila suzukii (Diptera: Drosophilidae) and Zaprionus indianus

Drosophila suzukii (Matsumura) (Diptera: Drosophilidae) and Zaprionus indianus Gupta (Diptera: Drosophilidae) were recently observed co-infesting persimmons in Brazil. We evaluate the infestation susceptibility of persimmons at different ripening stages (unripe, UN; early ripe, ER; orange ripe, OR, and overripe, OV) by D. suzukii and Z. indianus in the field and laboratory conditions. Additionally, we determined the influence of physicochemical characteristics (e.g., resistance to penetration force, fruit skin color, acidity (pH), TSS concentration, total titratable acidity [TTA]) and the type of damage that facilitates infestation by D. suzukii or Z. indianus. In the field, the natural infestation capacity and biological development of D. suzukii and Z. indianus were verified in whole fruits at the ripening stages ER, OR, and OV. The natural infestation was directly related to the physicochemical characteristics of the fruits (resistance to penetration force, pH, and total soluble solids). In the no-choice bioassay, the oviposition rate of D. suzukii did not differ between the ripening stages of the fruit. However, in the choice bioassay, there was a higher preference for oviposition in OV fruits. Regarding Z. indianus, the highest preference for oviposition was observed in OR and OV fruits in both bioassays. The presence of mechanical damage did not increase the susceptibility of the fruits to D. suzukii. However, it favored the oviposition of Z. indianus in OR and OV fruits. The damage caused by D. suzukii or mechanical damage favored the infestation by Z. indianus. This is the first report of the capacity of D. suzukii to infest whole persimmons in Brazil.

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

Simple Summary

Adult flies of the invasive fruit pest, Drosophila suzukii, commonly known as spotted wing drosophila, showed susceptibility towards several natural plant products tested in bioassays under laboratory conditions. Depending on the compound tested, contact toxicity, modified food uptake, or reduction in numbers of eggs deposited and hatched was found. The natural plant substances thereby identified will be further assessed under field conditions and can be used to develop innovative pest control strategies.

Abstract

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.

Deterrent Effects of Essential Oils on Spotted-Wing Drosophila (Drosophila suzukii): Implications for Organic Management in Berry Crops

Simple Summary

Spotted-wing drosophila (Drosophila suzukii Matsumura; SWD) poses a significant threat to small fruit production world-wide. Though frequent applications of insecticides is the dominant strategy to manage this pest, insecticide resistance is a concern. Resistance has already been reported for one of the only consistently effective insecticides labeled for organic production systems, spinosad, underscoring the need to diversify management strategies. Botanical products, such as essential oils, contain volatile organic compounds (VOCs) which could interfere with SWD preference for or ability to locate host fruit. We conducted laboratory and field studies to determine the efficacy of botanical products (lavender oil, catnip oil, KeyPlex Ecotrol^® PLUS, and KeyPlex Sporan^® EC²) on preventing SWD infestation in raspberry and blueberry crops. Under laboratory conditions lavender oil, Ecotrol, and Sporan deterred SWD from diet. In the field trials, Ecotrol deterred SWD from raspberries; however, no differences were seen in blueberry infestation. To optimize essential oil deterrents for SWD, such as how to maintain effective concentrations for longer periods of time, further research is needed. Botanical deterrents represent a promising alternative pest management strategy that could be implemented without additional equipment investment from growers, while decreasing the use of broad-spectrum insecticides.

Abstract

Due to concerns about frequent applications of spinosad and other broad spectrum insecticides for managing spotted-wing drosophila (Drosophila suzukii Matsumura, SWD), we investigated the use of essential oils as an alternative to current insecticides. Essential oils from a number of plant species have been studied for their attraction and deterrence of SWD. However, these botanical products have not been thoroughly tested in the field. We conducted laboratory and field studies to determine the efficacy of botanical products, including lavender (Lavandula angustifolia Mill.) oil, catnip (Nepeta cataria L.) oil, KeyPlex Ecotrol^® PLUS, and KeyPlex Sporan^® EC² on preventing SWD infestation in raspberry (Rubus idaeus L.) and blueberry (Vacciniumcorymbosum L.) crops. In a two-choice laboratory bioassay, lavender oil, Ecotrol, and Sporan treatments deterred SWD from a yeast-cornmeal-sugar based fly diet. In the field trials, raspberry fruit treated with Ecotrol had lower SWD infestation (6%), compared to the control (17%), and was comparable to spinosad (6%). No differences were seen in blueberry infestation. The combination of essential oils in Ecotrol may work to decrease SWD fruit infestation under certain conditions in the field, however more research is needed on the longevity of these products.

Agricultural-Grade Apple Cider Vinegar Is Remarkably Attractive to Drosophila suzukii (Diptera: Drosophiliadae) in Mexico

Due to its availability and low cost, apple cider vinegar (ACV) is a frequently used as an attractant for monitoring the invasive spotted wing drosophila, Drosophila suzukii. In laboratory cage experiments, the attraction of ACV alone was compared with ACV in mixtures with different concentrations of acetic acid, propionic acid, different hydrolyzed proteins, synthetic fruit flavors (strawberry, blackberry and apple) and the addition of fruit nectars (grape, pineapple and apple). The addition of 5% apple nectar to ACV significantly increased fly captures, whereas other combinations were similar to or less attractive than ACV alone. Apple flavored vinegar was not attractive to flies. Captures did not vary significantly among the brands of ACV commonly sold in Mexico, except for one poorly-performing brand, but cup traps baited with an agricultural-grade ACV unfit for human consumption captured approximately two-fold more flies than the commercial attractants Suzukii Trap, Suzukii Trap Max Captures or ACV alone in cage experiments. Field trials performed in polytunnels planted with raspberry crops in Mexico resulted in two-fold to ten-fold higher numbers of D. suzukii captured by the agricultural-grade ACV compared to Droskidrink (a mixture of ACV, red wine and sugar), Suzukii Trap, Suzukii Trap Max Captures or edible grade ACV alone. The species selectivity of the agricultural grade ACV was similar to that of other attractants tested. Agricultural-grade ACV also captured higher numbers of female than male flies in field trials. We conclude that the remarkably high attractiveness and low cost of agricultural-grade ACV makes it a useful tool for monitoring D. suzukii populations in berry crops.

Peppermint essential oil inhibits Drosophila suzukii emergence but reduces Pachycrepoideus vindemmiae parasitism rates

Spotted Wing Drosophila (Drosophila suzukii; Matsumura) is an invasive fruit fly with the ability to oviposit in a broad range of agriculturally valuable fruits. Volatile organic compounds (VOCs) produced by botanical oils may reduce D. suzukii’s attraction to hosts and decrease survival, but it is unknown whether their efficacy varies across D. suzukii life stages or affects the survival and success of higher trophic levels. Through a series of laboratory bioassays, we evaluated the effects of peppermint (Mentha arvensis L.) oil produced VOCs on D. suzukii survival and the survival of and parasitism rates by a pupal parasitoid wasp, Pachycrepoideus vindemmiae (Rondani). First, we determined whether fumigation with peppermint oil VOCs at the pupal stage reduced adult emergence, and whether this depended on environmental conditions (i.e. soil moisture). Second, we evaluated whether fumigation with peppermint oil VOCs reduced or enhanced parasitism by the pupal parasitoid and whether this depended on the timing of peppermint oil VOC exposure (i.e. before, during, or after parasitoid access). Fumigation with VOCs of 4.5 mg of peppermint oil reduced D. suzukii emergence under moist soil conditions but dry soil had a similar effect on reducing adult emergence as peppermint oil presence. Peppermint oil VOC fumigation was toxic to adult P. vindemmiae, but developing P. vindemmiae were unaffected by peppermint oil VOC fumigation. Using peppermint essential oil as a fumigant may reduce D. suzukii emergence from the pupal stage. However, this could negatively impact P. vindemmiae dependent on the timing of application.

Sex-biased gene expression in antennae of Drosophila suzukii

Drosophila suzukii differs from other members of the genus Drosophila in its host preference and oviposition behavior. The flies are attracted to ripening fruits, and females have a serrated ovipositor enabling eggs to be laid inside the fruit. In addition to its huge economic impact, its unique chemoecological, morphological, and physiological characteristics have garnered considerable research interests. In this study, we analyzed D. suzukii antennal transcriptomes to identify sex-biased genes by comparison of differential gene expressions between male antennae (MA) and female antennae (FA). Among 13,583 total genes of the fly genome, 11,787 genes were expressed in either MA or FA. There are only 132 genes (9 in MA, 7 in FA, and 116 in both, FPKM >1) were expressed in antennae exclusively, and 2,570 genes (9 in MA, 0 in FA, and 2,561 in both) were enriched in antennae containing 185 and 113 sex-biased genes in MA and FA, respectively. Interestingly, many immune-related genes were highly expressed in MA, whereas several chemosensory genes were at high rank in FA. We identified 27 sex-biased chemosensory genes including odorant and gustatory receptors, odorant-binding proteins, chemosensory proteins, ionotropic receptors, and cytochrome P450s, and validated the gene expressions using quantitative real-time PCR. The highly expressed sex-biased genes in antennae are likely involved in the fly specific mating, host-finding behaviors, or sex-specific functions. The molecular results demonstrated here will facilitate to find the unique chemoreception of D. suzukii, as well as on the development of new management strategies for this pest.

Diurnal and Seasonal Activity Patterns of Drosophilid Species (Diptera: Drosophilidae) Present in Blackberry Agroecosystems With a Focus on Spotted-Wing Drosophila

Drosophilid species with different life histories have been shown to exhibit similar behavioral patterns related to locating and utilizing resources such as hosts, mates, and food sources. Drosophila suzukii (Matsumura) is an invasive species that differs from other frugivorous drosophilids in that females lay eggs in ripe and ripening fruits instead of overripe or rotten fruits. We hypothesized that there may be diurnal and/or seasonal patterns associated with the movement of drosophilid species into and out of crop fields and their attraction to fermentation-odor-based monitoring traps, and that D. suzukii would conform to similar patterns. To test these hypotheses, we deployed passive, 2-headed Malaise traps between crop fields and wooded edges to simultaneously catch flies moving into and out of crop fields. We also deployed monitoring traps with a fermentation-based bait between crop fields and wooded edges and within crop rows. Traps were deployed weekly in June-August in 2014 and 2015 at two commercial blackberry farm in Cleveland County, NC, and were checked hourly for 24 h, except during darkness. Both D. suzukii and other drosophilid species moved between crop fields and wooded edges and were attracted to monitoring traps primarily during the morning and evening hours. Whereas other drosophilids were captured in traps throughout the season, few D. suzukii were caught in traps until early to mid-July in both years and increased as the season progressed. Understanding D. suzukii movement and activity patterns is essential for the development of effective management strategies.

Laboratory and Field Evaluation of Host-Related Foraging Odor-Cue Combinations to Attract Drosophila suzukii (Diptera: Drosophilidae)

The invasive spotted-wing drosophila, Drosophila suzukii (Matsumura), is a major pest of soft-skinned fruits. Since its introduction into North America and Europe, significant progress has been made in understanding the volatile cues used by this fly during food, oviposition site, and mate finding. Despite this progress, commercially available lures are non-selective. Here, we tested two Hanseniaspora uvarum (Niehaus) yeast compounds (isoamyl acetate and isobutyl acetate) and a leaf compound β-cyclocitral alone and in combination with a blend of four fermentation compounds ('Fermentation lure': acetic acid, ethanol, methionol, and acetoin) to improve D. suzukii attraction and selectivity. In laboratory assays, males and females were attracted to all seven individual compounds, although in electrophysiological assays, their antennae exhibited a dose-dependent response to only four of these compounds. In two-choice cage studies, the Fermentation lure was more attractive to D. suzukii than water controls, whereas β-cyclocitral and the mixture of isoamyl acetate and isobutyl acetate were not attractive in this larger-cage study. Moreover, adding the two-component H. uvarum compound blend to the Fermentation lure reduced D. suzukii attraction to the Fermentation blend. When these experiments were repeated in blueberry, raspberry, blackberry, and cherry orchards across several states in the United States over 2 yr, similar outcomes were observed: β-cyclocitral or the mixture of the H. uvarum blend did not improve the attractiveness of the Fermentation lure or its selectivity. This study demonstrates that cues from different sources may interfere with each other and reduce D. suzukii attraction to otherwise attractive odor combinations.

Color preference of the spotted wing Drosophila, Drosophila suzukii

Drosophila suzukii Matsumura (Diptera: Drosophilidae) is a significant invasive pest in soft-skin fruits and berries in Asia, Europe, and North and South America. Many herbivorous insects use multiple cues for host selection, particularly olfactory and visual stimuli. The visual system of closely-related Drosophila melanogaster is well-documented, expressing strong sensitivity to short-wavelength colors (ultraviolet to green) and only limited sensitivity to long-wavelength colors (red to infrared). Our results suggest that D. suzukii have limited ability to distinguish red consistent with visual sensitivity range within the melanogaster subgroup. We propose that color contrast rather than color appearance may be of greater importance in orientation and attraction. We propose that differences in reflectance between light wavelengths important for color opponency are key to color discrimination to provide color contrast between foreground and background, as occurs between fruit and foliage, during host-finding.

Electrophysiological and Behavioral Responses of Drosophila suzukii (Diptera: Drosophilidae) Towards the Leaf Volatile β-cyclocitral and Selected Fruit-Ripening Volatiles

The spotted-wing drosophila, Drosophila suzukii Matsumura (Diptera: Drosophilidae), is attracted to numerous volatile organic compounds (VOCs) emitted from several ripening, small fruit crops. However, the strawberry leaf terpenoid, β-cyclocitral, is reportedly very attractive to D. suzukii (but not to all Drosophila spp.). This suggests that leaf and fruit VOCs may be critical sources needed to further develop a more species-specific D. suzukii monitoring lure, or semiochemically based attract-and-kill systems. This study investigated the electrophysiological responses of male and female D. suzukii towards selected host fruit-ripening VOCs and β-cyclocitral, along with behavioral responses toward combined fruit VOCs with β-cyclocitral. Electroantennogram (EAG) results revealed a positive dose-response, for both sexes, as concentrations increased for all VOCs tested. For β-cyclocitral, hexyl acetate and methyl butyrate, the mean male EAG responses were significantly greater than the female responses at lower doses. In caged behavioral bioassays, only in the β-cyclocitral treatments were the mean number of flies captured (sexes combined) significantly greater than that captured in solvent (mineral oil) controls. Our study has demonstrated that while single fruit-based VOCs alone are not enough to cause a strong behavioral attraction by both male and female D. suzukii, the addition of β-cyclocitral did produce a significant attraction response from both sexes. In both bioassays, males had higher responses to β-cyclocitral than females, which suggest a greater sensitivity to this compound. Further studies are needed to ascertain the role β-cyclocitral may play in the development of a more species-specific D. suzukii monitoring lure.

Oviposition Preference and Larval Performance of Drosophila suzukii (Diptera: Drosophilidae), Spotted-Wing Drosophila: Effects of Fruit Identity and Composition

A better understanding of the factors affecting host plant use by spotted-wing drosophila (Drosophila suzukii) could aid in the development of efficient management tools and practices to control this pest. Here, proxies of both preference (maternal oviposition behavior) and performance (adult emergence) were evaluated for 12 different fruits in the form of purees. The effect of the chemical composition of the fruits on preference and performance traits was then estimated. We synthesized the literature to interpret our findings in the light of previous studies that measured oviposition preference and larval performance of D. suzukii. We show that fruit identity influences different parts of the life cycle, including oviposition preference under both choice and no-choice conditions, emergence rate, development time, and number of emerging adults. Blackcurrant was always among the most preferred fruit we used, while grape and tomato were the least preferred fruits. Larvae performed better in cranberry, raspberry, strawberry, and cherry than in the other fruits tested. We found that fruit chemical compounds can explain part of the effect of fruit on D. suzukii traits. In particular, oviposition preference under choice conditions was strongly influenced by fruit phosphorus content. In general, the consensus across studies is that raspberry, blackberry, and strawberry are among the best hosts while blackcurrant, grape and rose hips are poor hosts. Our results generally confirm this view but also suggest that oviposition preferences do not necessarily match larval performances. We discuss opportunities to use our results to develop new approaches for pest management.

Spotted-Wing Drosophila (Diptera: Drosophilidae) Adult Movement, Activity, and Oviposition Behavior in Maine Wild Blueberry (Vaccinium angustifolium; Ericales: Ericaceae)

Over a period of 5 yr (2012-2016), we conducted laboratory and field studies on activity, movement, and response to trap placement of adult Drosophila suzukii (Matsumura) in wild blueberry, Vaccinium angustifolium Aiton, fields in Maine. When measuring temporal patterns in fruit infestation, we found that D. suzukii females are most active in the morning and that they are 10 times more likely to lay eggs in blueberries at the top of the plant canopy compared with berries located in the lower part of the bush. Flies were found to be more abundant in fruit-bearing (crop) fields compared with pruned (vegetative) fields based on trap capture of adults. They are also most abundant along edges of fields compared with interiors. Trap efficiency is significantly better in traps 1.2 m above the ground and above the crop canopy of this low-growing crop plant than within the crop canopy. Three experiments involving the marking of laboratory-reared flies with fluorescent marker, their release, and capture with traps along a grid in fields suggest that: 1) fluorescent markers do not affect the distance moved of marked flies, 2) dispersal rates are not different between sexes, 3) there is little difference in the dispersal pattern through pruned fields and fruit-bearing fields, and 4) flies disperse at a low rate of 0.1-30 m per day, with an average of 5 m per day, but that long-distance dispersal over 1-2 km is feasible based on statistical model extrapolation.

β-cyclocitral synergizes the response of adult Drosophila suzukii (Diptera: Drosophilidae) to fruit juices and isoamyl acetate in a sex-dependent manner

Semiochemicals play a pivotal role in the location, evaluation, and utilization of hosts by herbivorous insects. Mixtures of host plant-derived compounds are often required to elicit appropriate levels of response to olfactory stimuli. In multiple-choice bioassays, we characterized the response of adult Drosophila suzukii to foliage- and fruit-based synthetic compounds tested alone and in association with grape and tart cherry juices, and assessed whether synergistic interactions among olfactory stimuli are involved in the olfactory-driven behavior of D. suzukii. Our results established (1) significant attraction of females (but not males) to β-cyclocitral and isoamyl acetate when tested singly, (2) the presence of a synergistic interaction between β-cyclocitral and cherry juice only for females, and (3) the presence of a synergistic interaction between β-cyclocitral and isoamyl acetate but only in the case of males. Our findings increase our understanding of male and female D. suzukii olfactory responses to synthetic compounds and fruit juices as sources of attractants. Combinations of foliage- and fruit-based compounds may be needed to increase SWD attraction.

Olfactory Preference of Drosophila suzukii Shifts between Fruit and Fermentation Cues over the Season: Effects of Physiological Status

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.

Raspberry as a Source for the Development of Drosophila suzukii Attractants: Laboratory and Commercial Polytunnel Trials

Several commercial products and home-made attractants have been developed for monitoring and mass-trapping of the spotted wing drosophila, Drosophila suzukii. Growers in Mexico have adopted an attractant based on a fermenting mixture of raspberry pulp and sucrose, with anecdotally promising results. We compared the capture rates of traps baited with raspberry pulp + sucrose with captures from a range of alternative attractants. Raspberry pulp alone or with sucrose was more attractive than apple cider vinegar (ACV) or SuzukiiTrap and similar to baker's yeast + sucrose in laboratory cage studies. Synthetic raspberry aroma (0.1-10% concentration), in water or mixed with ACV, did not improve capture rates in the laboratory. Traps baited with raspberry + sucrose or ACV had similar captures of D. suzukii in raspberry or blackberry polytunnels in Michoacán, Mexico. Raspberry + sucrose baited traps captured significantly higher numbers of other drosophilid species, leading to higher total numbers of captured flies (all species), which may explain why Mexican growers favor the raspberry-based attractant. The commercial products SuzukiiTrap and Z-Kinol had lower captures than ACV in polytunnels, although SuzukiiTrap had the highest selectivity in captures of D. suzukii (81% of flies captured). A two-component trap (2C trap) baited with ACV + ethanol as the drowning solution and raspberry pulp + sucrose or baker's yeast + sucrose in a ventilated tube device was markedly more effective than the trap currently used by growers. We conclude that raspberry pulp + sucrose is as effective for the attraction of D. suzukii as ACV under commercial polytunnel conditions. The 2C trap performed better than the transparent cup trap currently used by berry producers in Mexico.

Evaluation of Protein Bait Manufactured From Brewery Yeast Waste for Controlling Drosophila suzukii (Diptera: Drosophilidae)

We evaluated a protein bait based on an enzymatically hydrolyzed beer yeast and two widely used baits including a sugar + vinegar + wine mixture and apple cider vinegar for their ability to trap Drosophila suzukii (Matsumura) in the laboratory and outdoors. The protein bait was a more attractive lure than the other tested baits, with the protein bait capturing significantly more female and male adults at different developmental stages than the other baits. Furthermore, the protein bait with 20% vinegar attracted significantly more adult flies than the other baits, and the protein bait without dilution attracted the most adults. Except for the addition of 0.05% spinosad, increased insecticide content in protein bait reduced its attractiveness to adult flies. Moreover, we found that D. suzukii has a bimodal activity pattern in visiting protein bait, where maximum activity occurs during 8:00-10:00 a.m. and 14:00-16:00 p.m. The antennae and maxillary palpi played an important role in detecting the chemicals emitted from the protein bait, as the number of intact flies that responded to new protein bait was significantly higher than the number of flies without antennae that responded, but almost 15% of defective flies still responded to the protein bait. Our results suggested that the protein bait based on spent brewery yeast could be a promising alternative for D. suzukii population monitoring and for managing this pest when combined with bioinsecticides, providing guidance for using this protein bait as a component of integrated pest management.

Detection of Volatile Constituents from Food Lures by Tephritid Fruit Flies

Tephritid fruit flies require protein for sexual and gonotrophic development. Food-based lures are therefore widely used in strategies to detect and control fruit flies in the Tephritidae family. However, these baits are attractive to a broad range of insect species. We therefore sought to identify volatiles detected by the fly antennae, with the goal to compose lures that more specifically target tephritids. Using gas chromatography-coupled electroantennographic detection (GC-EAD) we screened for antennal responses of four important tephritid species to volatile compounds from five commercially available protein-based baits. Antennal active compounds were reconstituted in synthetic blends for each species and used in behavioral assays. These species-based blends were attractive in olfactometer experiments, as was a blend composed of all antennally active compounds from all the four species we observed (tested only in Bactrocera dorsalis, Hendel). Pilot field tests indicate that the blends need to be further evaluated and optimized under field conditions.

Multistate Comparison of Attractants and the Impact of Fruit Development Stage on Trapping Drosophila suzukii (Diptera: Drosophilidae) in Raspberry and Blueberry

Spotted-wing drosophila, Drosophila suzukii Matsumura (Diptera: Drosophilidae), is an invasive pest of soft-skinned fruits across the globe. Effective monitoring is necessary to manage this pest, but suitable attractants are still being identified. In this study, we combined lures with fermenting liquid baits to improve D. suzukii trapping specificity and attractiveness. We also measured the efficiency and specificity of baits/lures during different times of the season; the reproductive status of females among baits/lures; and the effects of locations and crop type on these response variables. We developed a metric that combined mating status and fat content to determine differences in types of females attracted. Lures utilizing yeast and sugar-based volatiles trapped the most D. suzukii. The addition of a commercial lure to yeast and sugar-based lures increased catches in most locations, but was also the least specific to D. suzukii. Apple juice-based chemical lures tended to be most specific to D. suzukii, while lures comprised of a singular attractant tended to trap more D. suzukii with a higher reproductive potential than combinations of attractants. Trap catch and lure specificity was lower during fruit development than fruit ripening. While catch amounts varied by geographic location and crop type, attractants performed similarly relative to each other in each location and crop. Based on the metrics in this study, the yeast and sugar-based attractants were the most effective lures. However, further work is needed to improve early season monitoring, elucidate the effects of physiological status on bait attraction, and understand how abiotic factors influence bait attraction.

A Multiple-Choice Bioassay Approach for Rapid Screening of Key Attractant Volatiles

Fermentation volatiles attract a wide variety of insects and are used for integrated pest management. However, identification of the key behavior modifying chemicals has often been challenging due to the time consuming nature of thorough behavioral tests and unexpected discrepancies between laboratory and field results. Thus we report on a multiple-choice bioassay approach that may expedite the process of identifying field-worthy attractants in the laboratory. We revisited the four-component key chemical blend (acetic acid, ethanol, acetoin, and methionol) identified from 12 antennally active wine and vinegar chemicals for Drosophila suzukii (Matsumura) (Diptera: Drosophilidae). The identification of this blend took 2 yr of continuous laboratory two-choice assays and then similarly designed field trials. This delay was mainly due to a discrepancy between laboratory and field results that laboratory two-choice assay failed to identify methionol as an attractant component. Using a multiple-choice approach, we compared the co-attractiveness of the 12 potential attractants to an acetic acid plus ethanol mixture, known as the basal attractant for D. suzukii, and found similar results as the previous field trials. Only two compounds, acetoin and, importantly, methionol, increased attraction to a mixture of acetic acid and ethanol, suggesting the identification of the four-component blend could have been expedited. Interestingly, the co-attractiveness of some of the 12 individual compounds, including a key attractant, methionol, appears to change when they were tested under different background odor environments, suggesting that background odor can influence detection of potential attractants. Our findings provide a potentially useful approach to efficiently identify behaviorally bioactive fermentation chemicals.

Advances in the Chemical Ecology of the Spotted Wing Drosophila (Drosophila suzukii) and its Applications

Significant progress has been made in understanding the cues involved in the host and mate seeking behaviors of spotted wing drosophila, Drosophila suzukii (Matsumura). This insect pest has been discovered in many fruit growing regions around the world since 2008. Unlike closely related Drosophila species, D. suzukii attacks fresh fruit and has become a severe pest of soft fruits including strawberry, cherry, blackberry, blueberry, raspberry, and may pose a threat to grapes. Prior to 2008, little was known about the courtship and host-seeking behaviors or chemical ecology of this pest. Since then, researchers have gained a better understanding of D. suzukii attraction to specific odors from fermentation, yeast, fruit, and leaf sources, and the visual cues that elicit long-range attraction. Several compounds have also been identified that elicit aversive behaviors in adult D. suzukii flies. Progress has been made in identifying the constituent compounds from these odor sources that elicit D. suzukii antennal responses in electrophysiological assays. Commercial lures based on food volatiles have been developed to attract D. suzukii using these components and efforts have been made to improve trap designs for monitoring this pest under field conditions. However, current food-based lures and trap technologies are not expected to be specific to D. suzukii and thus capture large numbers of non-target drosophilids. Attractive and aversive compounds are being evaluated for monitoring, mass trapping, and for the development of attract-and-kill and push-pull techniques to manage D. suzukii populations. This review outlines presently available research on the chemical ecology of D. suzukii and discusses areas for future research.

Identification of attractive blend for spotted wing drosophila, Drosophila suzukii, from apple juice

Drosophila suzukii, commonly known as the spotted wing drosophila (SWD), is an exotic fruit fly from Southeast Asia that was introduced to the temperate regions of North America and Europe in 2008. It attacks a wide variety of fruits and has become a devastating pest of soft-skinned fruit crops. Due to the rapid spread of SWD across the newly invaded continents, fresh fruit markets have a zero-tolerance policy regarding D. suzukii infestation. Specific and efficient D. suzukii detection tools are urgently needed so that farmers can deliver timely management interventions to meet market demands. Since SWD is known to be attracted to damaged and rotting fruits, headspace volatiles from fresh and fermented apple juices were collected and analyzed by gas chromatography-mass spectrometry. Special attention was given to the compounds produced and/or enriched during the fermentation process. After performing a series of laboataory and field tests, we identified a quinary blend, which is more efficient and selective for D. suzukii than the currently standard apple cider vinegar and commercially available SWD lure under field conditions. Identification of SWD attractant will help growers accurately detect D. suzukii adult infestations in orchards, thereby allowing for timely pest management interventions while reducing conventional insecticidal usage to protect our crops, environment, and ecosystem.

Comparative Antennal and Behavioral Responses of Summer and Winter Morph Drosophila suzukii (Diptera: Drosophilidae) to Ecologically Relevant Volatiles

Drosophila suzukii (Matsumura) (Diptera: Drosophilidae) is a devastating global pest of berry crops and cherries. Little is understood about its biology during the winter in northern temperate regions, including potential resources that it may utilize during this period. In this study, olfactory and behavioral responses of female D. suzukii to six volatiles (methionol, acetic acid, linalool, bornyl acetate, isoamyl acetate, and geosmin) were evaluated separately for electroantennogram (EAG) and behavioral assays between summer and winter morphs. Results of EAG indicated that isoamyl acetate, acetic acid, and geosmin elicited significantly higher olfactory responses from the antennae of female summer morph D. suzukii compared with those of female winter morph D. suzukii. Winter morph D. suzukii showed reduced antennal response to the volatiles overall. Geosmin and bornyl acetate elicited significantly different behavioral responses from the two morphs in no-choice laboratory behavioral assays. T-maze behavioral assays with geosmin further revealed that summer morphs had a significant aversion, while winter morphs showed no significant aversion to geosmin. Overall, we demonstrate that responses of the two seasonally induced morphs to environmental stimuli are different, and future studies are justified to further understand how these physiological and behavioral differences may contribute to improved pest management of D. suzukii.

Toxicity, Phytochemical Composition, and Enzyme Inhibitory Activities of Some Indigenous Weed Plant Extracts in Fruit Fly, Drosophila melanogaster

Drosophila melanogaster being used as model organism is considered as pest of homes, restaurants, and fruit markets. The damaged fruits are also reported to serve as a carrier for various diseases. The current study was designed to evaluate the toxicity of petroleum extract of some weed plants, namely, Euphorbia prostrata, Parthenium hysterophorus, Fumaria indica, Chenopodium murale, and Azadirachta indica, against D. melanogaster. Mortality at 10, 20, and 30% concentrations after 24 and 48 hours was found comparatively low. E. prostrata caused high mortality (51.64%) at 30% concentration and was found more toxic (LC₅₀ 27.76; P value 0.00) after 72 hours. A. indica showed high LC₅₀ value (P value 0.15) compared to other weed plants. The combination of E. prostrata and Bti showed highest mortality (100%; LC₅₀ 12.49; P value 0.00) after 72 hours. Similarly, the same combination caused maximum reduction in the activity of AChE, AcP, AkP, α-Carboxyl, and β-Carboxyl enzymes. Phytochemical analysis showed the presence of flavonoids, saponins, tannins, steroids, cardiac glycosides, alkaloids, anthraquinones, and terpenoids. FTIR analysis of E. prostrata showed the presence of phenolic compounds. It is suggested that further studies are needed in order to incorporate weed plant extracts in combination with Bti for the management of fruit flies.

Comparison of Commercial Lures and Food Baits for Early Detection of Fruit Infestation Risk by Drosophila suzukii (Diptera: Drosophilidae)

Drosophila suzukii (Matsumura; Diptera: Drosophilidae) is one of the most serious invasive pests of berries and cherries worldwide. Several adult monitoring systems are available to time foliar application of insecticides with the expectation of detecting the presence of D. suzukii before they infest susceptible crops. We tested this by comparing four different trapping systems based on two homemade baits, apple cider vinegar (ACV) or fermenting dough, and two fermentation volatile-based commercial lures, Scentry and Trécé. Traps baited with dough or Scentry captured more D. suzukii than traps baited with ACV or Trécé in blueberries and traps baited with Trécé in raspberries. In blueberries, traps baited with Scentry, Trécé and dough provided 11-21 d of warning prior to first detection of fruit infestation. However, these traps were not as effective in summer floricane raspberries. The Scentry lure baited traps detected D. suzukii on the same week as the first detection of fruit infestation and other trapping systems detected the fly 4 to 11 d after the first detection, suggesting the need for an improved D. suzukii detection system in raspberries. Both synthetic lures (Scentry and Trécé) were significantly more selective for D. suzukii than dough bait, although the selectivity of all four tested lures/baits were relatively low at <20%. Our results suggest that in locations where D. suzukii adults are not trapped in late winter and spring, adult monitoring of D. suzukii using a sensitive trapping system may provide early warning of pending infestation risk thereby potentially reducing unnecessary insecticide applications.