Putting insect pheromones to use: New strategies for engineering trap crops?

Trap cropping is an integrated pest management technique that uses properties of an economically unimportant plant to lure a pest away from a cash crop. Often these properties include the emission of volatile organic compounds such as terpenoids. The harlequin bug, Murgantia histrionica, a stink bug (Hemiptera: Pentatomidae), is a growing pest problem on crucifer crops in the Unites States and can be partially managed by trap cropping. In contact with a host plant, male harlequin bugs produce the bisabolene–type sesquiterpenoid aggregation/sex pheromone, murgantiol. Bisabolene-type aggregation or sex pheromones are common in other pentatomids such as the invasive brown marmorated stink bug. We assume that these terpene pheromones are produced de novo by the insect and are not products of host plant metabolites. We hypothesize that the biosynthetic pathway in murgantiol biosynthesis consists of two steps catalyzed by a bi- functional prenyltransferase/terpene synthase and a cytochrome P450 epoxidase. Comparative next generation sequencing of male and female harlequin bug RNA has identified a putative bi-functional prenyltransferase/terpene synthase gene with a possible role in murgantiol biosynthesis. We are in the process of functionally characterizing this enzyme with the long term goal to metabolically engineer the murgantiol biosynthetic pathway into a harlequin bug- attracting trap crop such as mustard (Brassica juncea). This study will also provide new insight into the mechanism and evolution of volatile terpene biosynthesis in insects in comparison to plants and other organisms.