Stored product insect pests, such as the red flour beetle (Tribolium castaneum), produce pheromones and other volatile chemicals that can betray their presence. They also detect these odours with high sensitivity to find mates or suitable food sources. This sensitivity and specificity relies on odorant receptors (ORs) and would be ideal for detecting infestations for targeted pest management.

There are 259 potential OR genes annotated in the T. castaneum genome (Engsontia et al., 2008, Insect Biochem. Mol. Biol. 38: 387) and we aim to find one or more that can detect infestation odours. To improve our chances of finding a suitable OR, we are using two complementary approaches: one is presented at the 2011 Science Exchange by Kelly Bailey and the other is outlined here.

This approach is based on the observation that 35 OR genes are expressed in both adult and larvae heads (Engsontia et al., 2008). We hypothesised that both larvae and adults can detect infestation odours in order to find food or breeding sites. This hypothesis was confirmed by behavioural studies in an olfactometer with infestations of T. castaneum or two other grain pests: Rhyzopertha dominica or Sitophilus granarius. Therefore, this relatively small set of genes can be targeted.

To find a specific OR, we also need a specific odour. We are now testing several individual chemicals associated with infestation odours, such as aggregation pheromones. Chemicals that can be detected by both life stages are likely to be recognised by one or more of the 35 shared OR genes.

We aim to implicate OR genes in chemical detection by using RNA interference to attenuate the expression of each OR in turn. Without normal expression of the necessary OR, we hypothesise that beetles will loose their behavioural response to a chemical. In addition to these olfactometry studies, we are also investigating electroantennagraphy as a method of discerning recognition. With these approaches we aim to identify ORs for application in protecting stored products, such as grain in silos or railcars, through early detection of infestation.