22 August 2013 Examining the cues: volatile organic compound triggers in insects

Plants and animals produce volatile organic compounds (VOCs) in response to a range of biological and environmental triggers. These compounds play a role in signalling within and between plant and animal species, but in many cases, the exact role, and the identity of the compounds produced is unknown.

Researchers Mette-Cecilie Nielson, Dr Jessica Dohmen-Vereijssen and Dr Michael Rostas are involved in three innovative projects investigating the role of various plant and insect induced VOCs and their potential in the field of bio-protection. Ms Nielsen’s work focuses on thrips in horticulture, Dr Dohmen-Vereijssen’s on foliar feeding insect pests and Dr Rostás’ on root feeding ones.

Western flower thrips are a major pest of horticultural crops worldwide. This pest is difficult to manage due to its small size, cryptic habits and resistance to a number of insecticides. Because of this, there is growing interest in finding ways of utilising the odour cues that the thrips use (to find their hosts) for applied pest management.

Ms Nielsen’s PhD project is investigating how selected intrinsic and extrinsic factors affect the response of resident and non-resident thrips to odour cues that are used in host finding. The ultimate aim of her study is to develop applied pest management tools.  The work is being carried out in labs and greenhouses in New Zealand and Europe.

Dr Jessica Dohmen-Vereijssen’s work is focused on VOCs and egg-laying in the pasture pest Argentine stem weevil. Oviposition rates decline as adult weevil densities increase, possibly as a response to some sort of spacing pheromone in the grass or possibly due to other factors such as odours created by other weevils or damaged plants. Whatever the cause, this phenomenon has implications for understanding and maintaining the stability of parasitoid-based weevil suppression.

Dr Dohmen-Vereijssen’s research involves offering male and female weevils a choice of damaged and undamaged ryegrass plants, with or without other weevils present. They cannot see the plants, so any choices are made solely on what odours they can detect.

The project run by Dr Rostás is addressing three issues: whether grass grub larvae are able to use their sense of smell to differentiate between endophyte-free and endophyte-infected fescue plants below-ground and then avoid feeding on roots that contain the endophyte’s toxic alkaloids; whether the VOCs induced by different numbers of feeding larvae affect host choice; and finally, interactions between larvae and endophytes. A key challenge will be to isolate and identify the plant root VOCs, as only very small amounts are emitted.

This work is novel as it explores plant root VOCs in the context of host selection by an insect herbivore and investigates how endophytic fungi and intraspecific competition interfere with this process.

For more information, read the full article on page 77 of the University’s research profile publication Transform.