## 2 Bees as Chemical Biosensors in the Laboratory and in the Field
### Constrained Bees as Chemical Biosensors  
In about 2000, Inscentinel, Ltd., a United Kingdom-based biotechnology company, began specializing in harnessing the olfactory ability of insects for trace vapor detection with _parts per trillion_ sensitivity [31]. Based on an adaptation of the PER assay methodology described briefly above, the company developed a bench-top, environmentally stable cassette and bee-holder, using a camera and image processing to monitor the PER behavior of sets of three bees. Working with another company, Panchromos, Ltd., a hand-held, battery-powered, bee-holder and detector for field testing was later produced. Named the Inscentinel VASOR (Volatile Analysis by Specific Odour Recognition), the device held 36 bees, could be switched from filtered to unfiltered air intake, and used a step-wise change in odor concentration to elicit PER. In both the bench-top and field-portable devices, sets of bees were used as the specific odor recognition biosensors. Under the US Defense Advanced Research Projects Agency's (DARPA) Controlled Biological and Biomimetics Systems Program, Inscentinel scientists came to work in the USA; first with us at the University of Montana (UM), and later with researchers at the US Department of Energy's Los Alamos National Laboratory.  
Inscentinel's goal was to commercialize PERs for civilian and defense-related monitoring. Their systems used environmentally controlled containers fitted with bees trained to specific compounds. Bee PER response was derived from data obtained by video processing systems. Despite demonstrated technical feasibility of the system, logistical constraints appear to have stalled the acceptance of Inscentinel's PERs detector. However, interest in PERs by other investigators remains high, with a renewed focus on standardizing procedures [32,33].  
Our own use of PERs has been mainly for screening bees' ability to detect chemicals of military concern. We have also assisted researchers in plant crop genetics and pollination in the US and New Zealand. These biologists use PERs to screen plant varieties for attractiveness to bees and to identify the chemicals to which bees are attracted. From collaborations with a US seed company and now with researchers in New Zealand, we have good evidence that [PERSON] and the Russians were correct: bees can be directed to pollinate specific crops using appropriate conditioning methods.  
Figure 1: PERs results for chemical detection of fertilizer, fertilizer-based bombs, and decomposition products of animal carcasses compared to anise, a floral scent.  
PERs has typically been used to study associative learning in honey bees, especially with respect to floral scents. More recently, the method has been extended to studying the effects of pesticides on learning [34,35], and the following chart (Figure 1) presents PERs results for a sample of novel compounds that can be detected by bees at low concentrations. This data is from a short trial from our military studies whereby chemicals associated with dead bodies (cadaverine, putrescine), fertilizer-based Improvised Explosive Devices (IEDs) (fuel/nitrate), and fertilizer (ammonium nitrate) are compared to anise, a plant attractant to which bees are readily conditioned.