Institute for Biodiversity and Ecosystem Dynamics

PhD in the spotlight: Peter Demaeght

20 January 2015

Peter Demaeght (1984) will be awarded his doctorate degree at the University of Amsterdam (UvA) on 23 January. During his doctoral research at the Institute for Biodiversity and Ecosystem Dynamics (IBED), he studied how the two-spotted spider mite develops resistance against different types of pesticides. The knowledge gained will enable more effective prevention of mite infestations.

You investigated two-spotted spider mites – what are they?

‘They are spider-like insects, approximately half a millimetre in size. They are found throughout the world and infestations can damage a wide variety of plants, including economically important crops such as soy, corn and cotton. The mites suck out the contents of the leaf cells, causing the leaves to shrivel up. The economic damage that mites cause is enormous. Pesticides such as acaricides can help to control mite populations. However, the main problem with spider mites is that their short life span and high fertility enables them to rapidly develop resistance against new pesticides. This therefore reduces the effectiveness of the agents. I wanted to know how the two-spotted spider mite achieves this resistance.’

How did you investigate this?

‘In the lab, I cross-bred two-spotted spider mites that are resistant to the pesticide etoxazole with non-resistant mites. In this way, I wanted to find out how etoxazole works. Using genetic technology, I identified the area of the genome that is responsible for the resistance. I found out that resistance to etoxazole is caused by a mutation of a single gene: the chitin synthase gene. I then applied the same technique to mite populations that are resistant to two other pesticides. These resistances were also caused by the chitin synthase gene. The mutation that causes resistance occurs all over the world. The information obtained by my research will enable screening of mite populations.’



Two-spotted spider mites. Photo: Jan van Arkel

What exactly do the pesticides do?

‘They disrupt the production of chitin by switching off the chitin synthase protein. As a result, the mite is unable to fully develop an exoskeleton and dies during ecdysis. The point mutation prevents the pesticides from damaging the chitin synthase protein. Mites with the mutation are therefore able to develop an exoskeleton, so the pesticide does not harm them. Part of the reason that this had not yet been discovered is that the full genome of the spider mite wasn’t sequenced until 2011. I have tried to get the most out of this genomic information by, amongst other methods, identifying the exact location in the genome that is responsible for resistance.’

You worked at Ghent University and will obtain your doctorate from the UvA, right?

‘I conducted all of my research at Ghent University. My supervisor, Thomas van Leeuwen, used to work at Ghent University but currently works at the UvA. I will therefore be receiving my doctorate in Amsterdam. My plan for the future is to continue in the field of research. I have always found science fascinating, which is why I decided to get my doctorate. What attracted me to this research is its huge importance to society. Mite infestations are an increasingly large problem, due in part to global warming. Mites like dry, warm weather, so in the Netherlands, they are mostly restricted to greenhouses. However, this may well change in the future. The more we know about the mites' resistance mechanisms, the more effectively we will be able to combat them.’

Text: Carin Röst

Published by  Faculty of Science