Sniffing out Insect Invaders

Biosecurity screening in Australia includes detector dogs that search for potential biological hazards arriving in luggage and mail. To further improve biosecurity screening, we propose that these detector dogs could be used to screen for high-risk invasive insects; in particular, the brown marmorated stink bug Halyomorpha halys (BMSB) (Hemiptera: Pentatomidae). This research project investigated the feasibility of the use of training aids as odour proxies when conditioning dogs to detect live, exotic insects that are inaccessible for training purposes. Chemical odour comparisons using headspace gas chromatography-mass spectrometry (GC-MS) in combination with canine scent detection testing were used to assess two potential training aids – a novel scent extract and dead specimens - for their efficacy in training for live insect detection.<br>
A locally abundant pentatomid species, the bronze orange bug Musgraveia sulciventris (BOB) (Hemiptera: Tessaratomidae), was used as an experimental model to test these training aids and provide a proof-of-concept for future application of these training aids in BMSB detection training. Headspace GC-MS analyses identified considerable similarities in volatile organic compounds (VOCs) between live BOB specimens and both BOB training aids. Following this, canine scent detection testing demonstrated that among biosecurity detector dogs (n = 4), most were able to generalize from scent extract (2/2) or dead specimens (1/2) to live specimens of that species (p = 0.008). A follow-up experiment further assessed the use of scent extract and investigated how dogs might generalize between different insect species for insect detection training. This experiment revealed that, after being trained with only BOB scent extract, all biosecurity detector dogs (n = 4) generalized to dead BOB specimens (p < 0.05), and only one dog generalized to dead BMSB specimens with sufficient accuracy (p < 0.05). However, contrary to expectations, the dogs also all falsely responded to several unrelated insect species in the following trials.<br>
Subsequent experiments compared chemical odour profiles of BMSB training aids and live BMSB specimens using headspace GC-MS and revealed substantial VOC similarities, supporting their use for canine BMSB detection. In particular, BMSB scent extract appeared to have a very similar composition to live specimens.<br>
Finally, using a novel method - a habituation-dishabituation paradigm – we tested dogs’ (n = 13) detection threshold of the BMSB scent extract, revealing dogs’ apparent ability to perceive the scent extract at very low concentrations - between the lowest concentration tested, a 1:1000 extract-pentane dilution, and 1:500 dilution. The novel application of this paradigm for determining canine odour thresholds had not been tested previously.<br>
Overall, the findings of this research suggest that scent extract and dead specimens may be effective and practical training aids for training biosecurity detector dogs for live BMSB detection, and these training aids are now being used to train biosecurity detector dogs to screen for BMSB in Australia. Following future research, this method may also be applicable for other species of high-risk insect pests.