Methods for Rearing the Parasitoid Ganaspis brasiliensis, a Promising Biological Control Agent for the Invasive Drosophila suzukii

Summary

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.

Abstract

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.

Introduction

Native to East Asia, the spotted-wing drosophila, Drosophila suzukii (Matsumura) (Diptera: Drosophilidae), has established widely in the Americas, Europe, and parts of Africa^1,2. The fly is extremely polyphagous, being capable of utilizing various cultivated and wild fruits with soft and thin skins in its native and invaded regions^1,2,3. 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. Repea....

Protocol

1. Methods for small-scale laboratory rearing of G3 Ganaspis brasiliensis

1. Prepare host diet.
   1. Add 600 mL of distilled water to a 1,500 mL glass container, and heat the water on a hot plate.
   2. Add 88.6 g of commercially available dry diet (made of agar, Brewer's yeast, corn meal, methyl paraben, and sucrose) or prepare diet using the formula published by Dalton et al.²⁸ (see step 2.1.2).
   3. Add 300 mL of distilled water into the dry diet and stir the diet mixture thoroughly.
   4. Add the mixture to the boiling water.
   5. Allow the liquid diet on the hot plate to b....

Results

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.......

Discussion

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.......

Materials

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