0 Female Pheromones and Infection May Affect Tick Behavior

Image: Researcher drags white
flannel to collect questing ticks. 

Recently I came across an abstract for the paper, "The correlation between tick (Ixodes persulcatus Sch.) questing behaviour and synganglion neuronal responses to odours".

I'm looking forward to reading the full text, as the abstract demonstrates two findings on tick behavior which may reveal who is more likely to be bitten by ticks.

In this experiment, the taiga tick or Ixodes persulcatus is used - a tick common in parts of Russia. It is unknown if other Ixodes ticks would respond to the same odors the same way, and I think the same experiment should be conducted in Western Europe and North America with local Ixodes ticks to see if there would be a similar outcome.

The researchers experimented with seeing which odors would attract and repel ticks, focusing on seeing how ticks respond to synthetic hormones and insecticides/acaricides. Osmopherone®, Osmopherine®, DEET®, ethanol, and water were placed in a simple maze, and changes in their synganglia - basically their entire central nervous system, as ticks do not have a brain as we think of one - were measured to reflect whether they were attracted, repelled, or neutral to the specific odor tested.

Also, researchers tested which odors were most likely to encourage the maximum height ticks could reach during questing behavior by placing ticks on glass rods which were held at a 75 degree angle.

Two notable findings came from these experiments:

1. Ticks were, as expected, repelled by DEET® and ethanol. It's good to have further confirmation that DEET® works as a repellent. But what was interesting is that ticks were totally neutral to Osmopherone® and water - and attracted to Osmopherine® .
   
   
2. Questing ticks were studied not only for their attraction to certain odors but were tested for whether or not they were infected with Borrelia burgdorferi sensu lato and tickborne encephalitis virus. It was found that not only did those ticks which were most attracted to Osmopherine® reach the highest questing height - but also those ticks which were infected with Borrelia burgdorferi sensu lato were more likely to reach the highest questing height.
   

What is the difference between Osmopherone® and Osmopherine®? Osmopherone® is a synthetic sex pheromone that is meant to mirror the scent human males give off. Osmopherine® is a synthetic sex pheromone that is meant to mirror the scent human females give off. Each of these pheromones are found in their natural form on people and are not an obvious smell people give off - they are registered on a subconscious level and may act as an attractant to the opposite sex.

In these experiments, it appears the female sex pheromone, Osmopherine®, attracts ticks, and ticks infected with Borrelia burgdorferi sensu lato are more likely to have the highest questing height in a laboratory.

What is not known is whether or not the same behavior occurs in the wild, outside a lab - and how much other factors may play into ticks' behavior when questing. Different ticks have different behavior in the wild to begin with, such as Amblyomma americanum tends to be more aggressive in searching out a blood meal and Ixodes scapularis is a more passive questing tick.

Ticks are already attracted to the source of their blood meal through detecting heat and carbon dioxide (CO₂) given off by exhalation. One thing I would hope the full text of this article would explain is how the presence of warm blooded, CO₂ exhaling researchers was shielded so they did not have any influence on these ticks. It may be that these indicators of the next potential dinner may play a bigger role than the gender of the potential host in front of them and whether or not the tick is currently infected with Borrelia burgdorferi s.l. 

Certainly more research is needed to determine what the case is in the wild, but in the meantime these findings provide one with more food for thought as to how a tick host's gender and the tick's state of infection might play a role in tick behavior.

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