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Blacklegged ticks, Ixodes scapularis, reduce predation risk by eavesdropping on communication signals of Formica oreas thatching ants

Gooding, Claire1; Pinard, Charlotte1; Gries, Regine1; Anand, Devireddy1; Gries, Gerhard1

Published Dec 15, 2023 on Dryad. https://doi.org/10.5061/dryad.fbg79cp21

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Dec 15, 2023 version files 58.14 KB

Abstract

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.