Effects of non-crop habitat on Drosophila suzukii infestation in commercial blackberry fields Katharine A. Swoboda Bhattarai and Hannah J. Burrack

Department of Entomology, North Carolina State University, Raleigh, NC, USA

Objective Determine if proximity to non-crop habitat affects infestation in commercial blackberry fields

Hypothesis Fruit infestation rates will decrease as the distance from non-crop habitat increases

Infestation rates were measured weekly from 25 June to 13 August 2013 along transects that ran from a water source and a wooded edge into crop fields (Fig. 3)

Traps with a fermentation-based bait were used to catch adult D. suzukii at regular intervals along each transect

Samples of 40 ripe, marketable-looking berries were collected near each trap located within a crop field

D. suzukii larvae were reared to adults (Fig. 4) using standard methods3

Drosophila suzukii, the spotted wing drosophila, is a highly invasive vinegar fly that has been detected in many parts of the United States, Canada, Europe, and Mexico since 2008. Females use their saw-like ovipositor to lay eggs in soft-skinned fruits (Fig. 1) and severely threaten the viability of blackberry, raspberry, blueberry, cherry, and strawberry production1. Monitoring programs that predict infestation risk for growers are not currently available. However, it has been suggested that non-crop habitat (Fig 2.) may serve as a source of infesting populations and provide D. suzukii with a refuge from management treatments2.

Fruit infestation rates Larvae (Fig 5.) were first detected on 9 July along both sets of transects (Fig. 3)

High infestation rates on 16 July corresponded with a disproportionate increase in infestation rates in fruit closer to the wooded edge compared to other sample dates (F10,18=3.431, P=0.01111) (Fig. 6), resulting in a significant interaction between sample date and distance from the wooded edge

The sharp drop in infestation rates after 16 July was likely due to the aggressive application of management tactics (i.e., insecticides) in response to infestation

Additionally, infestation rates did not decrease as distance from a water source increased (F3,39=2.25, P=0.0975) (results not pictured)

Female trap captures Higher numbers of females, the damaging sex, were captured in traps (Fig. 7) placed outside crop fields (Figs. 8 and 9)

For traps located within crop fields, there was not a significant relationship between the number of females trapped and infestation rates in fruit surrounding the trap (Wooded edge: F1,82=0.01, P=0.9138, R2=0.0001; Water source: F1,61=0.32, P=0.5764, R2=0.0051)

The hypothesis that fruit infestation rates will decrease as the distance from non-crop habitat increases was only supported when infestation

rates were high in fruit located near a wooded edge

More females were trapped outside of crop fields than within crop fields

No relationship was observed between female trap captures and infestation rates within crop fields

Acknowledgements Douglas McPhie, Dylan Kraus,

and Aurora Toennisson helped process trap and fruit samples

Research was funded by the North Carolina Agricultural Foundation

References 1eFly: The Spotted Wing Drosophila Working Group. 2013. Spotted wing drosophila impacts in the eastern United States. http://www.sripmc.org/WorkingGroups/eFly/index.cfm] 2Cini, A., C. Ioraitti, and G. Anfora. 2012. A review of the invasion of Drosophila suzukii in Europe and a draft research agenda for integrated pest management. Bulletin of Insectology 65: 149-160. 3Burrack, H.J., G.E. Fernandez, T. Spivey, and D.A. Kraus. 2013. Variation in selection and utilization of host crops in the field and laboratory by Drosophila suzukii Matsumara (Diptera: Drosophilidae), an invasive frugivore. Pest Management Science 69: 1173-1180.

Management implications Based on these results, it will be difficult to advise growers where sampling efforts should be focused to detect infestation. However, attention should be given to fruit located closer to wooded edges.

Traps with fermenting baits may be less attractive to D. suzukii females than blackberries and should not be relied upon to predict infestation.

Future studies will address whether results were due to management tactics applied within crop fields or patterns associated with D. suzukii dispersal between crop fields and non-crop habitat.

Fig. 3. Transects running from A) a water source and B) a wooded edge into commercial ‘Navaho’ blackberry fields in western North Carolina. Distance between collection points was 10 m for A) and 20 m for B); distance between transects was ≥ 20 m for both A) and B). Green dots indicate points where larvae were detected on 9 July.

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Fig. 6. Mean infestation rates in fruit collected between 20-40, 60-80, and 100-120 meters away from a wooded edge. Mean infestation was calculated as D. suzukii per berry per day. Means within a circle were not different at α=5% (F2,18=4.32, P=0.0294).

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Fig. 8. Females captured in traps located along one transect that ran from a water source into a blackberry field

Fig. 9. Females captured in traps located along one transect that ran from a wooded edge into a blackberry field

Outside the field

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Fig. 1. Female D. suzukii laying eggs in a blackberry

Fig. 4. Fruit samples were held at 20°C in plastic rearing containers vented on the bottom with mesh

Fig. 2. A commercial blackberry field and non-crop habitat

Introduction

Materials and Methods

Results

Conclusions

Fig. 7. A D. suzukii trap filled with yeast/sugar/water bait

Fig. 5. A blackberry infested with larvae