Spider mites escape bacterial infection by avoiding contaminated food
To fight infection, arthropods rely on the deployment of an innate immune response but also upon physical/chemical barriers and avoidance behaviours. However, most studies focus on immunity, with other defensive mechanisms being relatively overlooked. We have previously shown that the spider mite Tetranychus urticae does not mount an induced immune response towards systemic bacterial infections, entailing very high mortality rates. Therefore, we hypothesized that other defence mechanisms may be operating to minimize infection risk. Here, we test (a) if spider mites are also highly susceptible to other infection routes—spraying and feeding—and (b) if they display avoidance behaviours towards infected food. Individuals sprayed with or fed on Escherichia coli or Pseudomonas putida survived less than the control, pointing to a deficient capacity of the gut epithelium, and possibly of the cuticle, to contain bacteria. Additionally, we found that spider mites prefer uninfected food to food contaminated with bacteria, a choice that probably does not rely on olfactory cues. Our results suggest that spider mites may rely mostly on avoidance behaviours to minimize bacterial infection and highlight the multi-layered nature of immune strategies present in arthropods.
KeywordsParasitism Immunity Behavioural avoidance Tetranychus urticae
We thank Miodrag Grbic for the “bubble machine” and José Feijó for the air pump, both of which were necessary to make the parafilm bubbles (feeding experiments). We thank Arne Jansen and Luísa Vasconcelos for the material needed to make the Y olfactometer, and Francisco Dionísio for providing access to his laboratory, material and reagents for bacterial work. We also thank members of the Sucena and Magalhães labs for useful discussions and suggestions. This work was funded by an FCT-Tubitak agreement (FCT-TUBITAK/0001/2014) to SM and Ibrahim Cakmak. FZ was funded through an FCT Post-Doc fellowship (SFRH/BPD/125020/2016). Funding agencies did not participate in the design or analysis of experiments.
Author contribution statement
Experimental conception and design: FZ, GM, ES, SM; acquisition of data: GM, AF, CE, CP, TL; statistical analyses: FZ; paper writing: FZ, GM, SM, with input from all authors. Funding: ES and SM. All authors have read and approved the final version of the manuscript.
Compliance with ethical standards
Conflict of interest
We declare that we do not have any conflict of interest.
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