Drosophila suzukii in Argentina: State of the Art and Further Perspectives

Drosophila suzukii (Matsumura) (Diptera: Drosophilidae), commonly known as spotted-wing drosophila or SWD, is an invasive, severe, and damaging pest, which is able to inflict huge economic losses on soft thin-skinned fruits worldwide. Argentina was not excluded from the rapid invasion of this new and aggressive pest. Berries and cherries are among the most economically important fruits, showing an increasing demand from both domestic and export markets, which make necessary the application of effective and early protection measures. Although SWD is currently established almost everywhere in Argentina, the scarcity of research on and rapid regulatory actions against this pest have probably contributed to its fast spread throughout the country. In view of that, the article reviews first the current threat status of SWD in Argentina, provides summarized information on crop and non-crop host fruits, seasonal variation and population dynamics, resident natural enemy assemblages, and describes control actions implemented to date. Finally, the need to focus local control actions within an integrated national SWD management program is emphasized. The development and application of complementary eco-friendly strategies, such as Sterile Insect Technique, biological control, mass trapping, and the use of innovative lactone-derived synthetic insecticides with extremely low toxicity for SWD parasitoids, in environmentally distinguishable Argentinian regions is also highlighted.

Pathogenicity and Virulence of Different Concentrations of Brazilian Isolates of Entomopathogenic Nematodes Against Drosophila suzukii

The invasive pest Drosophila suzukii (Matsumura) (Diptera: Drosophilidae) was recently recorded in Brazil and constitutes a threat to fruit growing, mainly for small, soft fruits. Recent advances in research on ways of controlling D. suzukii involve the use of entomopathogenic nematodes (EPNs). In this context, the objective of this study was to evaluate the pathogenicity and virulence of four isolates in different concentrations against D. suzukii pupae. The EPN isolates used in trials were Steinernema brazilense IBCBn 06, S. carpocapsae IBCBn 02, Heterorhabditis bacteriophora HB, and H. amazonensis IBCBn 24. Both H. amazonensis IBCBn 24 and H. bacteriophora HB were effective in controlling D. suzukii as they caused a mortality rate of 86.25% and 80.0%, and virulence of 549.75 IJs/pupae and 787.75 IJs/pupae in the concentrations of 1800 IJs/ml and 5400 IJs/ml, respectively. The lowest lethal concentrations (LC50) of juveniles were found in host pupae with 771.63 IJs/ml of H. bacteriophora HB and 1115.49 IJs/ml of H. amazonensis IBCBn 24. Results showed that both EPNs, H. amazonensis IBCBn 24 and H. bacteriophora HB, could be promising eco-friendly biological agents to control D. suzukii.

Integrated Pest Management Education: a Video-Game to Improve Management of Drosophila suzukii, Soft-Skin Fruit Pest

The transition from the conventional global agriculture to an agroecological model poses a teaching and learning challenge to facilitate the wide variety of practices and the many biological processes involved. Games, such as board games, video-games, or mobile apps, are elements that may be used for teaching agroecology, environmental education, or animal conservation. Here, we present a video-game designed to contribute to integrated pest management education. The Spotted-Stop-It video-game is a single-player game which encourages participation, disseminates knowledge on the pest problem and its potential solutions (i.e., harvest frequency, sanitation, and management of alternative non-crop plants), and highlights the importance of good practices from an agroecological perspective at the farmer scale. In a farm-tech regional fair, we presented the game to its users and performed a simple retrospective survey. The survey results showed that most participants did not know about the fly prior to playing the game (34 ind., 68%), but were able to recognize the species among other flies after playing (23 ind., ~ 65%). Also, 21 individuals correctly responded about the effects of this pest on soft-skin fruits ("the fly lays eggs inside the fruit"). The training of future generations on new insect invasions and IPM practices with elements of their own environment may prove to be important to transmit concepts and practices at the service of sustainable crop protection.

Improvement on the genetic engineering of an invasive agricultural pest insect, the cherry vinegar fly, Drosophila suzukii

Background

The invasive fly Drosophila suzukii has become an established fruit pest in Europe, the USA, and South America with no effective and safe pest management. Genetic engineering enables the development of transgene-based novel genetic control strategies against insect pests and disease vectors. This, however, requires the establishment of reliable germline transformation techniques. Previous studies have shown that D. suzukii is amenable to transgenesis using the transposon-based vectors piggyBac and Minos, site-specific recombination (lox/Cre), and CRISPR/Cas9 genome editing.

Results

We experienced differences in the usability of piggyBac-based germline transformation in different strains of D. suzukii: we obtained no transgenic lines in a US strain, a single rare transgenic line in an Italian strain, but observed a reliable transformation rate of 2.5 to 11% in a strain from the French Alps. This difference in efficiency was confirmed by comparative examination of these three strains. In addition, we used an attP landing site line to successfully established φC31-integrase-mediated plasmid integration at a rate of 10% and generated landing site lines with two attP sequences to effectively perform φC31-Recombinase Mediated Cassette Exchange (φC31-RMCE) with 11% efficiency. Moreover, we isolated and used the endogenous regulatory regions of Ds nanos to express φC31 integrase maternally to generate self-docking lines for φC31-RMCE. Besides, we isolated the promoter/enhancer of Ds serendipity α to drive the heterologous tetracycline-controlled transactivator (tTA) during early embryonic development and generated a testes-specific tTA driver line using the endogenous beta-2-tubulin (β2t) promoter/enhancer.

Conclusion

Our results provide evidence that the D. suzukii strain AM derived from the French Alps is more suitable for piggyBac germline transformation than other strains. We demonstrated the feasibility of using φC31-RMCE in the cherry vinegar fly and generated a set of lines that can be used for highly efficient integration of larger constructs. The φC31-based integration will facilitate modification and stabilization of previously generated transgenic lines that carry at least one attP site in the transgene construction. An early embryo-specific and a spermatogenesis-specific driver line were generated for future use of the binary expression system tet-off to engineer tissue- and stage-specific effector gene expression for genetic pest control strategies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12863-020-00940-5.

Combining sterile and incompatible insect techniques for the population suppression of Drosophila suzukii

The spotted wing Drosophila, Drosophila suzukii, has recently invaded Europe and the Americas, and it is a major threat for a wide variety of commercial soft fruits both in open field and greenhouse production systems. D. suzukii infests a wide range of ripening fruits, leading to substantial yield and revenue losses. As the application of insecticides close to the harvest period poses great concerns, the development of an efficient environment-friendly control approach to fight D. suzukii is necessary. In this study, we exploited the sterile insect technique (SIT) in combination with Wolbachia symbiosis as a population suppression approach that can constitute a potential component of an area-wide integrated pest management program. We aimed to establish a combined SIT/incompatible insect technique (IIT) protocol that would require lower irradiation doses as a complementary tool for D. suzukii management. Two D. suzukii lines trans-infected with the Wolbachia wHa and wTei strains were irradiated at doses four times less than usual (e.g., 45 Gy), and the egg hatching and adult emergence were determined. Our results indicated that wHa and wTei females as well as wHa males were sterile at this low dose. The longevity, adult emergence and flight ability of adults were evaluated, and no major effect caused by irradiation was detected. Our data indicate that a SIT/IIT protocol can be a competent approach for D. suzukii management.

Plant-Based Natural Product Chemistry for Integrated Pest Management of Drosophila suzukii

Since the first reports of damage by Drosophila suzukii, the spotted-wing Drosophila (SWD), over a decade ago in Europe, widespread efforts have been made to understand both the ecology and the evolution of this insect pest, especially due to its phylogenetic proximity to one of the original model organisms, D. melanogaster. In addition, researchers have sought to find economically viable solutions for the monitoring and management of this agricultural pest, which has now swept across much of Europe, North America and Asia. In a new direction of study, we present an investigation of plant-based chemistry, where we search for natural compounds that are structurally similar to known olfactory cues from parasitoid wasps that in turn are well-described ovipositional avoidance cues for many Drosophila species. Here we test 11 plant species across two plant genera, Nepeta and Actinidia, and while we find iridoid compounds in both, only those odorants from Actinidia are noted to be detected by the insect antenna, and in addition, found to be behaviorally active. Moreover, the Actinidia extracts resulted in oviposition avoidance when they were added to fruit samples in the laboratory. Thus we propose the possible efficacy of these plants or their extracted chemistry as a novel means for establishing a cost-effective integrated pest management strategy towards the control of this pest fly.

Sterile insect technique and Wolbachia symbiosis as potential tools for the control of the invasive species Drosophila suzukii

Drosophila suzukii, a vinegar fly originated from Southeast Asia, has recently invaded western countries, and it has been recognized as an important threat of a wide variety of several commercial soft fruits. This review summarizes the current information about the biology and dispersal of D. suzukii and discusses the current status and prospects of control methods for the management of this pest. We highlight current knowledge and ongoing research on innovative environmental-friendly control methods with emphasis on the sterile insect technique (SIT) and the incompatible insect technique (IIT). SIT has been successfully used for the containment, suppression or even eradication of populations of insect pests. IIT has been proposed as a stand-alone tool or in conjunction with SIT for insect pest control. The principles of SIT and IIT are reviewed, and the potential value of each approach in the management of D. suzukii is analyzed. We thoroughly address the challenges of SIT and IIT, and we propose the use of SIT as a component of an area-wide integrated pest management approach to suppress D. suzukii populations. As a contingency plan, we suggest a promising alternative avenue through the combination of these two techniques, SIT/IIT, which has been developed and is currently being tested in open-field trials against Aedes mosquito populations. All the potential limiting factors that may render these methods ineffective, as well as the requirements that need to be fulfilled before their application, are discussed.

Evaluation of Off-season Potential Breeding Sources for Spotted Wing Drosophila (Drosophila suzukii Matsumura) in Michigan

It has been suggested that fruit wastes including dropped and unharvested fruits, and fruit byproducts (i.e., pomace) found in fruit plantings and cideries or wine-making facilities could serve as potential off-season breeding sites for spotted wing Drosophila (Drosophila suzukii Matsumura (Diptera: Drosophilidae)). This idea, however, has yet to be widely tested. The goal of our study was to determine the potential of dropped fruit and fruit wastes as Fall spotted wing Drosophila breeding resources in Michigan, USA. Fruit waste samples were collected from 15 farms across the lower peninsula of Michigan and were evaluated for spotted wing Drosophila and other drosophilid emergence and used in host suitability bioassays. All of the dropped apples, pears, grapes, and raspberries and 40% of apple and 100% of grape fruit pomace evaluated were found to contain spotted wing Drosophila with the highest numbers collected from dropped grapes and pears. Greater spotted wing Drosophila recovery was found in fruit wastes at sites attached with cideries and wine-making facilities and with multiple cultivated fruit crops than sites with no cideries and only one crop. Females oviposited in raspberry, pear, apple, grape, apple pomace and grape pomace samples with the highest rates of reproduction in raspberries. Our results demonstrate that fruit wastes including dropped berry, pomme and stone fruits, as well as fruit compost may be important late season reproductive resources for spotted wing Drosophila.

Diurnal Activity of Drosophila suzukii (Diptera: Drosophilidae) in Highbush Blueberry and Behavioral Response to Irrigation and Application of Insecticides

Spotted wing Drosophila, Drosophila suzukii Matsumura (Diptera: Drosophilidae), is an invasive vinegar fly that has become a primary direct pest of berry crops worldwide. We conducted 2 yr of behavioral studies in blueberry plantings to determine how fly activity varied throughout the day. Observations of diurnal activity of adult D. suzukii found the greatest activity in the morning hours between 0600 and 0800 hours, when the majority of flies were on the berries. Flies were also active in the evening mainly between 1800 and 2000 hours; however, this trend was more prominent in 2015, which had cooler and more humid evenings. Experiments examining the effect of irrigation on D. suzukii behavior showed that flies remained active during and after irrigation. The effect of insecticide treatments alone and in combination with irrigation revealed that treatment with spinosad had limited effects on the number of flies per bush, whereas spinetoram reduced the number flying and on the bushes in some cases. Zeta-cypermethrin caused longer and more consistent reduction in D. suzukii flying and on bushes. In all treatments, we observed surviving flies flying near and on treated bushes, indicating that these insecticides do not completely deter fly activity. Irrigation did not influence the effects of zeta-cypermethrin on fly behavior during daily observations up to 3 d after application. Our results highlight that the diurnal patterns of activity of D. suzukii on host plants are flexible and are relatively unaffected by irrigation or insecticide applications.

Basal tolerance to heat and cold exposure of the spotted wing drosophila, Drosophila suzukii

The spotted wing Drosophila, Drosophila suzukii, is a new pest in Europe and America which causes severe damages, mostly to stone fruit crops. Temperature and humidity are among the most important abiotic factors governing insect development and fitness. In many situations, temperature can become stressful thus compromising survival. The ability to cope with thermal stress depends on basal level of thermal tolerance. Basic knowledge on temperature-dependent mortality of D. suzukii is essential to facilitate management of this pest. The objective of the present study was to investigate D. suzukii basal cold and heat tolerance. Adults and pupae were subjected to six low temperatures (-5-7.5 °C) and seven high temperatures (30-37 °C) for various durations, and survival-time-temperature relationships were investigated. Data showed that males were globally more cold tolerant than females. At temperature above 5 °C, adult cold mortality became minor even after prolonged exposures (e.g., only 20% mortality after one month at 7.5 °C). Heat tolerance of males was lower than that of females at the highest tested temperatures (34, 35 and 37 °C). Pupae appeared much less cold tolerant than adults at all temperatures (e.g., Lt50 at 5° C: 4-5 d for adults vs. 21 h for pupae). Pupae were more heat tolerant than adults at the most extreme high temperatures (e.g., Lt50 at 37 °C: 30 min for adults vs. 4 h for pupae). The pupal thermal tolerance was further investigated under low vs. high humidity. Low relative humidity did not affect pupal cold survival, but it reduced survival under heat stress. Overall, this study shows that survival of D. suzukii under heat and cold conditions can vary with stress intensity, duration, humidity, sex and stage, and the methodological approach used here, which was based on thermal tolerance landscapes, provides a comprehensive description of D. suzukiithermal tolerance and limits.

Drosophila suzukii population response to environment and management strategies

Drosophila suzukii causes economic damage to berry and stone fruit worldwide. Laboratory-generated datasets were standardized and combined on the basis of degree days (DD), using Gompertz and Cauchy curves for survival and reproduction. Eggs transitioned to larvae at 20.3 DD; larvae to pupae at 118.1 DD; and pupae to adults at 200 DD. All adults are expected to have died at 610 DD. Oviposition initiates at 210 DD and gradually increases to a maximum of 15 eggs per DD at 410 DD and subsequently decreases to zero at 610 DD. These data were used as the basis for a DD cohort-level population model. Laboratory survival under extreme temperatures when DD did not accumulate was described by a Gompertz curve based on calendar days. We determined that the initiation of the reproductive period of late dormant field-collected female D. suzukii ranged from 50 to 800 DD from January 1. This suggests that D. suzukii females can reproduce early in the season and are probably limited by availability of early host plants. Finally, we used the DD population model to examine hypothetical stage-specific mortality effects of IPM practices from insecticides and parasitoids at the field level. We found that adulticides applied during the early season will result in the largest comparative population decrease. It is clear from model outputs that parasitism levels comparable to those found in field studies may have a limited effect on population growth. Novel parasitoid guilds could therefore be improved and would be valuable for IPM of D. suzukii.