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Method Article
Ganaspis brasiliensis-a larval parasitoid of Drosophila suzukii (a global invasive fruit crop pest)-has been approved or is considered for introduction into Europe and the United States for biological control of this pest. This article provides protocols for both small-scale and large-scale rearing of this parasitoid.
Native to East Asia, the spotted-wing drosophila, Drosophila suzukii (Matsumura) (Diptera: Drosophilidae), has established widely in the Americas, Europe, and parts of Africa over the last decade, becoming a devastating pest of various soft-skinned fruits in its invaded regions. Biological control, especially by means of self-perpetuating and specialized parasitoids, is expected to be a viable option for sustainable area-wide management of this highly mobile and polyphagous pest. Ganaspis brasiliensis Ihering (Hymenoptera: Figitidae) is a larval parasitoid that is widely distributed in East Asia, and has been found to be one of the most effective parasitoids of D. suzukii.
Following rigorous pre-introduction evaluations of its efficacy and potential non-target risks, one of the more host-specific genetic groups of this species (G1 G. brasiliensis) has been approved recently for introduction and field release in the United States and Italy. Another genetic group (G3 G. brasiliensis), which was also commonly found to attack D. suzukii in East Asia, may be considered for introduction in the near future. There is currently enormous interest in rearing G. brasiliensis for research or in mass-production for field release against D. suzukii. This protocol and associated video article describe effective rearing methods for this parasitoid, both on a small scale for research and a large scale for mass-production and field release. These methods may benefit further long-term research and use of this Asian-native parasitoid as a promising biological control agent for this global invasive pest.
Native to East Asia, the spotted-wing drosophila, Drosophila suzukii (Matsumura) (Diptera: Drosophilidae), has established widely in the Americas, Europe, and parts of Africa1,2. The fly is extremely polyphagous, being capable of utilizing various cultivated and wild fruits with soft and thin skins in its native and invaded regions1,2,3. Current management strategies for this pest rely heavily on the frequent use of insecticides that target adult flies in crop fields when susceptible fruit are ripening. Repeated sprays are often used, possibly due to consistent spillover of reservoir fly populations from non-crop habitats and lack of effective natural enemies resident in the invaded regions1,4. Biological control, especially by means of self-perpetuating specialized parasitoids, may help suppress fly populations at the landscape level and play a critical role for sustainable area-wide management of this highly mobile and polyphagous pest4,5,6.
Over the past decade, researchers have focused efforts to discover co-evolved parasitoids of Drosophila suzukii in the fly's native ranges in East Asia7,8,9, as well as effective but newly associated parasitoids in the fly's invaded regions in the Americas and Europe4,5,6. In the fly's newly invaded regions, commonly occurring larval Drosophila parasitoids, such as Asobara c.f. tabida (Nees) (Hymenoptera: Braconidae), Leptopilina boulardi (Barbotin et al.), and L. heterotoma (Thompson) (Hymenoptera: Figitidae), are unable to develop from or have low parasitism levels on D. suzukii due to the fly's strong immune resistance10. Only some cosmopolitan and generalist pupal parasitoids such as Pachycrepoideus vindemiae (Rondani) (Hymenoptera: Pteromalidae) and Trichopria drosophilae (Perkins) (Hymenoptera: Diapriidae) in North America and Europe, and Trichopria anastrephae Lima in South America can readily develop from this fly4. In contrast, explorations in East Asia have discovered a number of larval parasitoids from D. suzukii4,5,6. Among them, Asobara japonica Belokobylskij, Ganaspis brasiliensis Ihering, and Leptopilina japonica Novković & Kimura are the dominant larval parasitoids7,8,9,11. In particular, the two figitids (L. japonica and G. brasiliensis) were the major parasitoids predominantly found in fresh fruits infested by D. suzukii and/or other closely related drosophilids in natural vegetation7,8,9. These three Asian larval parasitoids were imported to quarantine facilities in the USA and Europe, and evaluated for their relative efficiency12,13,14,15,16,17, climatic adaptability18, potential interspecific competitive interactions19, and, most importantly, host specificity8,20,21,22.
Quarantine evaluations showed that Ganaspis brasiliensis was more host-specific to Drosophila suzukii than other tested Asian larval parasitoids, although it likely consists of different biotypes or cryptic species with varying host specificity8,21,22,23,24. Nomano et al.22 grouped Ganaspis individuals from different geographical regions into five genetic groups (named as G1-G5) based on molecular analyses of the mitochondrial cytochrome oxidase I gene fragment. The G2 and G4 groups are reported only from a few south Asian tropical locations, and the G5 group was reported from Asia and other regions (e.g., Argentina, Brazil, Hawaii, and Mexico) from unknown host(s) (Buffington, personal observation). Field collections of wild fruits infested by D. suzukii in South Korea7, China8, and Japan9,23,25 found G1 alone or a mixture of specimens representing groups G1 and G3. The two groups seem to be sympatric and co-exist on the same host plants inhabited by D. suzukii and other closely related host flies. Nonetheless, some differences have been observed between the two groups, with G1 seemingly having a higher degree of host- or host-habitat-specificity to D. suzukii than G3, although they both attack a number of closely related species in the quarantine tests21,22. Further detailed molecular analyses may help determine the species status, especially for the G1 and G3 groups. This study refers to them as G1 G. brasiliensis and G3 G. brasiliensis. Some early studies also named the G1 G. brasiliensis as G. cf. brasiliensis14,21,22. The G1 G. brasiliensis has recently been approved for field release against D. suzukii in the USA and Italy (several other European countries are also currently considering its introduction), while the G3 G. brasiliensis may be considered for field release in the near future. Recent surveys also found adventive populations of both L. japonica and G1 G. brasiliensis in British Columbia, Canada26, and Washington State, USA (Beers et al., unpublished data), and adventive L. japonica populations in Trento province, Italy27.
Given the significant interest in the development of biological control programs for Drosophila suzukii management and the substantial biological control potential of adventive and deliberate introductions of Ganaspis brasiliensis, there is a need to develop efficient rearing methods for this larval parasitoid for future long-term research and/or field release. This protocol and associated video article describe two sets of rearing methods for this parasitoid: (1) small-scale laboratory rearing in flasks using a mixture of host fruit (blueberry) and artificial diet for the culture of D. suzukii. The methods were developed using G3 material originally collected from Kunming, China8. (2) Mass rearing for field release in large cages using host fruit (blueberry) for the culture of D. suzukii. The genetic group used for the large-scale rearing was G1 stock originating in Tokyo, Japan9,22. Other scales of rearing methods, such as using vials or small containers for both groups, are also briefly discussed.
1. Methods for small-scale laboratory rearing of G3 Ganaspis brasiliensis
2. Methods for large-scale rearing of G1 Ganaspis brasiliensis
Figure 4 shows representative results of the small-scale laboratory rearing of G3 Ganaspis brasiliensis using two different parasitoid densities (six or 10 pairs) and two different exposure times (5 or 10 days) at the quarantine facility of the USDA-ARS Beneficial Insects Introduction Unit (Newark, Delaware). There were 14 replicates for each combination of parasitoid density and exposure time. In total, the 64 flasks produced 4,018 wasps (71.7 ± 4.9 offspring per flask) with 4...
Long-term research and subsequent field releases of a biological control agent depend on the availability of effective and economical rearing techniques. The described methods in this study have proven to be efficient protocols for both small-scale and large-scale rearing of Ganaspis brasiliensis. The small-scale rearing protocol has been developed over several years to optimize the amount of labor and reduce specialized equipment needed to maintain the parasitoid and host colonies simultaneously. It is suitable...
The authors have no conflicts of interest to disclose.
The authors thank Lukas Seehausen and Marc Kenis (CABI, Switzerland) for kindly providing G1 G. brasiliensis. Funding in Italy was provided by Provincia Autonoma di Trento, Trento, Italy, and in the US by the National Institute of Food and Agriculture, USDA Specialty Crops Research Initiative award (#2020-5118-32140), USDA Animal and Plant Health Inspection Service (Farm Bill, fund 14-8130-0463), and USDA ARS CRIS base funds (project 8010-22000-033-00D). The USDA is an equal-opportunity provider and employer and does not endorse products mentioned in this publication.
Name | Company | Catalog Number | Comments |
Active dry yeast | Fleischmanns Yeast, Cincinatti, OH, USA | None | Used to cover fruit to reduce mold growth and enhance the frui attraction to the flies |
Bacteriological agar | Merk Life Science S.r.l., Milan, Italy | A1296 - 5KG | Used to prepare the Standard Drosophila Medium |
Bleach solution | Clorox Company, Oakland, CA, USA | None | Used to disinfect flesh fruit |
Blue stopper | Azer Scientific, Morgantown, PA, USA | ES3837 | Used for sealing the tube while allowing ventilation for insects |
Blueberries | Grocery Store, Newark, DE, USA | None | Provided as host fruit for the flies (various other fruit can also be used) |
BugDorm insect rearing cage (W24.5 x D24.5 x H63.0 cm) | Mega View Science Co. Ltd., Taichung, Taiwan | 4E3030 | Used for rearing parasitoids (parasitism cage) |
BugDorm insect rearing cage (W32.5 x D32.5 x H32.5 cm) | Mega View Science Co. Ltd., Taichung, Taiwan | 4E4590 | Used for rearing flies |
BugDorm insect rearing cage (W32.5 x D32.5 x H32.5 cm) | Mega View Science Co. Ltd., Taichung, Taiwan | 4E4545 | Used for rearing parasitoids (eclosion cage) |
Chicken wire (0.64 cm, 19 gauge) | Everbilt, OH, USA | 308231EB | Used to lift up the fruit to allow maximum parasitoid oviposition |
Cornmeal | Grocery Store, Trento, TN, Italy | None | Used to prepare the Standard Drosophila Medium |
Dental cotton roll (1 x 3.8 cm) | Gima S.p.A., Gessate, MI, Italy | 35000 | Used for providing water to the parasitoids within the storage container |
Drosophila diet | Frontier Scientific, Newark, DE, USA | TF1003 | Custom diet used to rear flies |
Drosophila vial narrow, Polystirene (2.5 x 9.5 cm) | VWR International, LLC., Radnor, PA, US | 75813-160 | Used for providing water to the parasitoids within the cage |
Drosophila vial plugs, Cellulose acetate (2.5 cm) | VWR International, LLC., Radnor, PA, US | 89168-886 | Used for providing water to the parasitoids within the cage |
Erlenmeyer flask (250 mL) | Carolina Biological, Burlington, NC, USA | 731029 | Used for rearing flies and parasitoids |
Falcon-style centrifuge tube (50 mL) | VWR International, LLC., Radnor, PA, US | VWRI525-0611 | Modified to ship adult parasitoids |
Foam stopper | Jaece Industries, North Tanawanda, NY, USA | L800-C | Used for sealing the flasks while allowing ventilation for insects |
Honey | Grocery Store, Newark, DE, USA | None | Provided as food for parasitoids |
Identi-Plug plastic foam stopper | Fisher Scientific Company, L.L.C., Pittsburg, PA, US | 14-127-40E | Used as feeder for parasitoids and to seal the storage container |
Industrial paper towel | Grocery Store, Newark, DE, USA | None | Provided as a pupation substrate for pupae and mitigated moisture |
Micron mesh fabric (250 mL) | Industrial Netting, Maple Grove, MN, USA | WN0250-72 | Used to make ventilation lid for insects |
Nutritional yeast (flakes) | Grocery Store, Trento, TN, Italy | None | Used to prepare the Standard Drosophila Medium |
Paper coaster (10.2 cm) | Hoffmaster, WI, USA | 35NG26 | Porvided as pupation substrate for flies and parsitized pupae |
Plastic cup (Ø 13.3 cm, 800 mL) | Berry Superfos, Taastrup, Denmark | Unipak 5134 | Modified to store adult parasitoids |
Plastic lid (Ø 13.3 cm) | Berry Superfos, Taastrup, Denmark | PP 2830 | Modified to store adult parasitoids |
Propionic acid | Merk Life Science S.r.l., Milan, Italy | P1386 - 1L | Used to prepare the Standard Drosophila Medium |
Saccharose | Grocery Store, Trento, TN, Italy | None | Used to prepare the Standard Drosophila Medium |
Soup cup with lid (475 mL) | StackMan, Vietnam | DC1648 | Used for parasitized larvae to pupate |
Soybean flour | Grocery Store, Trento, TN, Italy | None | Used to prepare the Standard Drosophila Medium |
White felt washer (0.64 cm thick, 5 mm ID x 20 mm OD) | Quiklok, Lincoln, NH, US | WFW/.25 x 5 x 20 mm | Used as feeding ring for parasitoids |
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