Molluscs on the menu: Prey preference and predating behaviours of a slug-killing Allison Bistline-East and Michael J. Gormally Applied Ecology Unit, Centre for Environmental Science, NUI Galway [email protected] | @ABEentomology

Background Results: Prey preference

Slugs are major agricultural pest of vegetable and cereal elata larvae showed no significant crops throughout temperate zones. In Europe, three of species preference across trials (Fig. 2), including the most important species are Deroceras reticulatum, its original host species D. reticulatum. 1 Arion hortensis, and Tandonia budapestensis . The only instance of feeding occurring Under the Horizon 2020 effort towards more sustainable significantly more frequently than no predation agriculture, we examined a conservation biological was on D. reticulatum in no-choice trials control approach for pest slugs using the natural enemy (p = 0.04). Deroceras reticulatum was the only (Diptera: ) in Ireland. prey species killed during trials. One of the most important aspects to consider for any Larvae most often attacked the first slug which 2 biocontrol agent is its host/prey range and preference they encountered in trials, often attacking or to determine both its efficacy in controlling the target feeding on it until the larva was dislodged, came pest and identifying potential non-target effects. This into contact with another slug, or until the end Fig. 2. Proportion of feeding events by Tetanocera elata feeding on each study addresses both of these aspects for T. elata. of the trial. potential prey species in no-choice, 2-choice, and 3-choice trials. The big questions: Results: Predating behaviours Deroceras reticulatum was the most easily predated of the three potential prey species (Fig. 3). Feeding on D. reticulatum What is T. elata larval prey preference? 1 was significantly more rapid than on either Arion hortensis (p < 0.001) or Tandonia budapestensis (p = 0.006). 2 Which slugs will T. elata larvae predate? Feeding took place significantly more frequently at the head region compared to mid-body or tail regions for all slug species (p < 0.001), suggesting attacks to this region are more effective. What are T. elata predatory behaviours? 3 Several distinct behavioural patterns were observed in larvae, including Searching (active head-tapping), Random Movement Methods (locomotion without searching or specific directionality), and Waiting (no movement)4. If larvae were dislodged they DR AH TB DR AH TB DR AH TB Lab-reared third instar Tetanocera elata larvae were feeding successful before attacksMean no. frequently chased the individual they had been attacking. No-Choice 2-Choice 3-Choice exposed to Deroceras reticulatum (DR), Arion hortensis Larvae most often demonstrated ambush predation, waiting or (AH), and Tandonia budapestensis (TB) slugs in three Fig. 3. Mean number of attacks before the first moving randomly and attacking the first slug they contacted. treatment types: successful feeding event by T. elata larvae on each Tetanocera elata larvae did not display trail-following 1. No-choice (DR n=10; AH n=13; TB n=15) slug species across all treatment types. behaviours as observed in other Sciomyzidae species5. 2. Two-choice (DR/AH n=12; DR/TB n= 11; TB/AH n=13) 3. Three-choice (DR/AH/TB n=14) Conclusions: Exposures were run in darkness with infrared lights and recorded for three hours. Video capture and analysis was performed using EthoVision XT software v. 10.1 Tetanocera elata larvae typically attacked the first slug encountered, regardless of species 1 (Fig.1). Statistics were performed using R in R Studio3.

Feeding was most rapid and successful on D. reticulatum, the only slug killed during trials 2

Ambush predation was the most common tactic rather than searching or trail-following 3

Acknowledgements References Thanks to Prof. Mike Gormally and members 1. Howlett, S.A. 2012. CAB Reviews 7(51): 1-10. of the Applied Ecology Unit, NUI Galway for 2. Babendreier, D., F. Bigler, and U. Kuhlmann. 2006. CABI Publishing pp. 1-14. logistic and technical support. 3. R Core Team. 2013. http://www.R-project.org/. Funding provided by the Government of 4. Hynes, T.M., I. Giordani, M. Larkin, R.J. McDonnell, and M.J. Gormally. Ireland Postgraduate Award and the Thomas 2014. Biocontrol Science and Technology 24(9): 1077-1082. Crawford Hayes Research Fund (NUI Galway). 5. McDonnell, R.J., T.D. Paine, and M.J. Gormally. 2007. Journal of Behaviour 20(3): 367-376.

Fig. 1. Diagram of experimental setup of a 3- choice trial and EthoVision video capture.