Institute for Biodiversity and Ecosystem Dynamics

Photographer: FNWI

Mr A.J. (Bram) Knegt MSc

PhD Candidate
  • Faculty of Science
    Institute for Biodiversity and Ecosystem Dynamics
  • Visiting address
    Science Park A
    Science Park 904  Room number: C3.218
  • Postal address:
    Postbus  94248
    1090 GE  Amsterdam

I started my PhD in December 2012, supervised by dr. Martijn Egas. My research focuses on the plant-eating arthropod Tetranychus evansi - a spider mite. This spider mite species originated in South America but has recently become an invasive species in many parts of the world. The rapid spread of this species is of concern for agriculture, because it likes to eat many commercially grown crops, such as tomato, potato, aubergine and pepper. 

One reason why T. evansi can so easily infest these plants is that it can suppress their defense. The exact mechanism behind this is unknown, but it causes the infested plants to be very edible compared to other plants. Upon infestation, the spider mites quickly multiply, and cover the plant with dense webbing. Within 2-3 weeks the plant dies, and the mites disperse to find new host plants.

Suppression of plant defense is not new for science, but the extent to which T. evansi can suppress plant defense is unprecedented. Why is T. evansi so keen on suppressing plant defense? What evolutionary forces have driven this species to become such an aggressive suppressor? In my research I aim to find answers to these questions.

Tetranychus evansi female (left) and male (right). Picture downloaded from

A.J. (Bram) Knegt MS

PhD Candidate

Population Biology - Institute for Biodiversity and Ecosystem Dynamics

University of Amsterdam


Visiting address

Science Park 904

1098 XH Amsterdam

Room C3.218



a.j.knegt (at)




  • Kant, M. R., Jonckheere, W., Knegt, B., Lemos, F., Liu, J., Schimmel, B. C. J., ... Alba, J. M. (2015). Mechanisms and ecological consequences of plant defence induction and suppression in herbivore communities. Annals of Botany, 115(7), 1015-1051. DOI: 10.1093/aob/mcv054  [details] 


  • Knegt, B., Alba, J. M., Ataide, L. M. S., Barbosa, T. A., Bernardo, A. M. G., Chafi, R., ... Egas, M. (2017). Meta-analysis reveals intraspecific variation in herbivores for plant-mediated interactions. Poster session presented at Gordon Research Conference "Plant - Herbivore Interactions", Ventura, CA, USA, United States.
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