Use of a parasitic wasp as a biosensor.

Dawn Olson,Glen Rains

doi:10.3390/bios4020150

Abstract

Screening cargo for illicit substances is in need of rapid high-throughput inspection systems that accurately identify suspicious cargo. Here we investigate the ability of a parasitic wasp, Microplitis croceipes to detect and respond to methyl benzoate, the volatile component of cocaine, by examining their response to training concentrations, their sensitivity at low concentrations, and their ability to detect methyl benzoate when two concealment substances (green tea and ground coffee) are added to the testing arena. Utilizing classical associative learning techniques with sucrose as reward, we found that M. croceipes learns individual concentrations of methyl benzoate, and they can generalize this learning to concentrations 100× lower than the training concentration. Their sensitivity to methyl benzoate is very low at an estimated 3 ppb. They are also able to detect methyl benzoate when covered completely by green tea, but were not able to detect methyl benzoate when covered completely by coffee grounds. Habituation to the tea and coffee odors prior to testing improves their responses, resulting in effective detection of methyl benzoate covered by the coffee grounds. With the aid of the portable device called ‘the wasp hound’, the wasps appear to have potential to be effective on-site biosensors for the detection of cocaine.

Highlights

Screening cargo for illicit substances has been time constrained, in part due to false positive responses, so that high-throughput inspection systems that rapidly screens and accurately identifies suspicious cargo are still required [1]
Lai et al [1] showed that solid phase microextraction (SPME) coupled to ion mobility spectrometry (IMS) was effective at detecting methyl benzoate, but some interference compounds produced false positives so that higher levels of specificity of SPME are being investigated
Wasps trained to methyl benzoate at 1000 g/mL, and tested to 1 g/mL, 10 g/mL, 100 g/mL, and 1000 g/mL showed a significant increase in turning (F3/79 = 93.33, p < 0.001) or time spent at the odor portal (F3/79 = 87.73, p < 0.001) of the training concentration and the 10× and 100× lower concentrations, but not the 1000× lower concentration (Figure 1c)

Summary

Introduction

Screening cargo for illicit substances has been time constrained, in part due to false positive responses, so that high-throughput inspection systems that rapidly screens and accurately identifies suspicious cargo are still required [1]. Chemical detection requires that the substance has volatile properties and for cocaine detection, the volatile component is methyl benzoate [2,3,4]. The two trace detection systems that are most commonly employed at US checkpoints are canines and ion mobility spectrometry (IMS) [1]. Lai et al [1] showed that solid phase microextraction (SPME) coupled to IMS was effective at detecting methyl benzoate, but some interference compounds produced false positives so that higher levels of specificity of SPME are being investigated. There remains a need for sensitive and accurate means of identifying suspicious cargo

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Conclusion