Detection of phytoecdysteroids by gustatory sensilla on chelicerae of the brown dog tick Rhipicephalus sanguineus

Ecdysteroids are polyhydroxylated steroids that act as moulting hormones in arthropods and regulate several important life‐cycle processes. Phytoecdysteroids are ecdysteroid analogues produced by some plants that disrupt the growth and development of insects feeding on them, and can be perceived by the taste receptors of insects. The present study tested the hypothesis that the blood‐feeding tick Rhipicephalus sanguineus (Latreille, 1806) (Acari: Ixodidae) is capable of detecting phytoecdysteroids. By recording from the chelicerae, six phytoecdysteroids are tested: α ‐ecdysone, 20‐hydroxyecdysone, ponasterone A, makisterone A, inokosterone and pterosterone. In unfed ticks, makisterone A and pterosterone elicit frequencies of neural impulses higher than in a negative control (a KCl solution at 10 −3 m ), with detection thresholds of 10 −6 m and 10 −12 m , respectively. The spike amplitudes of the responses to these compounds, and also for 20‐hydroxyecdysone and ponasterone A, are higher than in the control, indicating that a different neurone may be involved: perhaps a deterrent cell, as observed in insects. In fed ticks, only pterosterone at 10 −4 m remains active. In behavioural attachment assays, no difference is observed between electrophysiologically active compounds and the negative control. These results show the capability of R. sanguineus ticks to detect phytoecdysteroids, although they do not clarify the role of ecdysteroids in tick biology, for which further studies are required.