DOI: 10.5061/dryad.fbg79cp21
title: Blacklegged ticks, Ixodes scapularis, reduce predation risk by eavesdropping on communication signals of Formica oreas thatching ants

description: Ticks spend most of their life inhabiting leaf litter and detritus where
 they are protected from sun but preyed upon by ants. Ants secrete chemical
 communication signals to coordinate group tasks such as nest defense.
 Ticks that avoid ant semiochemicals – as indicators of ant presence –
 would reduce predation risk by ants. We tested the hypotheses that (1)
 chemical deposits from the thatching ant Formica oreas deter blacklegged
 ticks, Ixodes scapularis, (2) deterrent semiochemicals originate from the
 ants’ poison and/or Dufour’s gland(s), and (3) tick-deterrent
 semiochemicals serve as alarm-recruitment pheromone components in F.
 oreas. In two-choice olfactometer bioassays, filter paper soiled with ant
 chemical deposits significantly deterred female and male ticks. Poison and
 Dufour’s gland extracts deterred ticks in combination but not alone. Gas
 chromatographic-mass spectrometric analyses of gland extracts revealed
 formic acid as the major constituent in the poison gland and 8
 hydrocarbons as constituents in the Dufour’s gland. Synthetic formic acid
 and hydrocarbons deterred ticks only when combined. F. oreas workers
 sprayed both formic acid and hydrocarbons when distressed. A synthetic
 blend of these compounds elicited alarm-recruitment responses by F. oreas
 in behavioural bioassays. All results combined indicate that ticks
 eavesdrop on the ants’ communication system.
description: # Blacklegged ticks, *Ixodes scapularis*, reduce predation risk by
 eavesdropping on communication signals of Formica oreas thatching ants
 **Experiment
 Descriptions:** 1. Exp1 - Female blacklegged ticks, *Ixodes scapularis*,
 responding in olfactometers to filter paper previously soiled (treatment),
 or not (control), with chemical deposits of 20 Formica oreas worker ants
 2. Exp2 - Male blacklegged ticks, *Ixodes scapularis*, responding in
 olfactometers to filter paper previously soiled (treatment), or not
 (control), with chemical deposits of 20 Formica oreas worker ants 3. Exp3
 - Female blacklegged ticks, *Ixodes scapularis*, responding in
 olfactometers to *Formica oreas* poison gland extract (treatment) or
 dichloromethane (solvent control) 4. Exp4 - Male blacklegged ticks,
 *Ixodes scapularis*, responding in olfactometers to *Formica oreas* poison
 gland extract (treatment) or dichloromethane (solvent control) 5. Exp5 -
 Female blacklegged ticks, *Ixodes scapularis*, responding in olfactometers
 to *Formica oreas* Dufour's gland extract (treatment) or
 dichloromethane (solvent control) 6. Exp6 - Male blacklegged ticks,
 *Ixodes scapularis*, responding in olfactometers to *Formica oreas*
 Dufour's gland extract (treatment) or dichloromethane (solvent
 control) 7. Exp7 - Female blacklegged ticks, *Ixodes scapularis*,
 responding in olfactometers to *Formica oreas* Dufour's gland extract
 + poison gland extract (treatment) or dichloromethane (solvent control) 8.
 Exp8 - Male blacklegged ticks, *Ixodes scapularis*, responding in
 olfactometers to *Formica oreas* Dufour's gland extract + poison
 gland extract (treatment) or dichloromethane (solvent control) 9. Exp9 -
 Female blacklegged ticks, *Ixodes scapularis*, responding in olfactometers
 to formic acid (treatment) or dichloromethane (solvent control) 10. Exp10
 - Male blacklegged ticks, *Ixodes scapularis*, responding in olfactometers
 to formic acid (treatment) or dichloromethane (solvent control) 11. Exp11
 - Female blacklegged ticks, *Ixodes scapularis*, responding in
 olfactometers to hydrocarbons (treatment) or dichloromethane (solvent
 control) 12. Exp12 - Male blacklegged ticks, *Ixodes scapularis*,
 responding in olfactometers to hydrocarbons (treatment) or dichloromethane
 (solvent control) 13. Exp13 - Female blacklegged ticks, *Ixodes
 scapularis*, responding in olfactometers to hydrocarbons + formic acid
 (treatment) or dichloromethane (solvent control) 14. Exp14 - Male
 blacklegged ticks, *Ixodes scapularis*, responding in olfactometers to
 hydrocarbons + formic acid (treatment) or dichloromethane (solvent
 control) 15. Exp15 - Visits by *Formica oreas* worker ants, tested in
 groups of 5 (n = 20), to paired filter paper discs treated with either a
 synthetic pheromone blend (treatment) or dichloromethane (solvent control)
 **Interpretation of data sheets:** Exp1-14: * rep - replicate * species -
 species of tick tested * sex - male (M) or female (F) * start.time - time
 experiment was started * side - side treatment stimulus was placed on
 (R=right, L=left) * trmt - treatment stimulus tested * dose - dose of
 treatment stimulus used * choice - stimulus chosen by tick (T=treatment,
 C=control, NR=non-responder) Exp15: * rep - replicate * species - ant
 species tested * start.time - time experiment was started * side - side
 treatment stimulus was placed on (R=right, L=left) * trmt - treatment
 stimulus tested * dose - dose of treatment stimulus used * choice - T
 (filter paper disc treated with pheromone blend) or C (filter paper disc
 treated with solvent control) * responders - number of visits made by ants
 to each filter paper disc **R Code** Exps 1-14 were analyzed and figures
 were prepared using the provided code entitled
 "exp1-14-stats-and-graphics.R" Exp 15 was analyzed and figures
 were prepared using the provided code entitled
 "exp15-stats-and-graphics.R"