26 Mar 2019
Cassie Sims is a PhD student at Rothamsted Research, Hertfordshire, and the University of Nottingham. She is the Vice-Chair of our Agri-Food Early Careers Committee and a member of our Agrisciences group. Currently, Cassie is completing a digital media internship at SCI.
Here, she details her PhD research at Rothamsted.
Pest control & pesticides
Significant crop yields are lost per year due to the impact of pests. Pest control traditionally includes the use of pesticides; however, many pests have very quick lifecycles, and a combination of this with heavy use of a limited range of pesticides has resulted in a significant increase in pesticide resistance in recent years.
Additionally, legislation changes have limited the range of pesticides further. In 2013, the European Commission severely restricted the use of treated seeds and other plant protection products containing three neonicotinoid pesticides (clothianidin, imidacloprid and thiamethoxam). The regulation was extended in 2018 despite recommendations from leading scientists.
Scientists have predicted that we have not yet seen the full effect of the European ban and that some issues could become much more prevalent in years to come, such as the barley yellow dwarf virus (BYDV) which is transmitted by aphids.
Aphids are an insect pest that feed on crops worldwide. They are prolific herbivores and cause significant crop damage through three main means.
Firstly, they suck the sap from the phloem of the plants, depriving the plant of vital nutrients. Secondly, they secrete a sweet and stick honeydew, which attracts a fungus that grows over the plant and blocks out sunlight for photosynthetic. Finally, aphids transmit plant viruses that can cause severe damage, such as BYDV.
Aphids are prevalent pests of horticultural and agricultural crops. Image: Pixabay
Aphid communication is mainly through olfaction – their sense of smell. The aphid utilises pheromones – communication chemicals between organisms of the same species. There are two main aphid pheromones – the sex pheromone – a combination of two iridoids (4aS,7S,7aR)-nepetalactone and (1R,4aS,7S,7aR)-nepetalactol – and the alarm pheromone (E)-β-farnesene.
The most effective and recommended form of pest control is Integrated Pest Management (IPM). This involves using a combination of control strategies, that may include chemical control, biocontrol, push-pull strategies and management practises. IPM is effective and reduces the risk of pesticide resistance developing.
Despite best efforts, resistance still occurs, and novel methods of pest-control are needed. One form of pest-management involves using the insect’s communication systems against them, such as utilising pheromones in traps. New olfactory ligands are needed, and my PhD research is looking to the insect olfactory systems to help us develop these, with a focus on aphids.
In insects, olfaction occurs in the antennae. There are proteins found in the antennae responsible for odor detection – odorant receptors and odorant-binding proteins (OBPs). OBPs are found in a high concentration in insect antennae, but their role is not very well understood. They are believed to be important for odor recognition.
We need to find smart strategies than using chemical control alone to avoid pesticide resistance. Image: Pixabay
My work focuses on elucidating the role of OBPs, including determining their importance in molecular recognition by insects. The project involves using chemical techniques, including mass-spectrometry and nuclear magnetic resonance spectroscopy (NMR) to study the protein-ligand interactions.
If my work is successful in determining the role of these proteins, and we can use this knowledge to test novel odorants or develop sensor technologies that can determine the presence of aphids.