Peripheral regulation by ecdysteroids of olfactory responsiveness in male Egyptian cotton leaf worms, Spodoptera littoralis

Physiological and behavioral plasticity allows animals to adapt to changes in external (environmental) and internal (physiological) factors. In insects, the physiological state modulates adult behavior in response to different odorant stimuli. Hormones have the potential to play a major role in the plasticity of the olfactory responses. To explore if peripheral olfactory processing could be regulated by steroid hormones, we characterized the molecular, electrophysiological, and behavioral response to changes in endogenous hormone levels in adult male Spodoptera littoralis. The expression of the receptor complex (EcR/USP) was localized by in situ hybridization in the olfactory sensilla of antennae. Injections of 20-hydroxyecdysone (20E) induced an ecdysteroid signaling pathway in antennae and increased expression of the nuclear receptors EcR, USP and E75. Diacylglycerol kinase (DGK) and CaM expression were also up-regulated by 20E. Taken together, these molecular, electrophysiological, and behavioral results suggest a hormonal regulation of the peripheral olfactory processing in S. littoralis.

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► The nuclear receptors of the 20E signalling pathway (EcR, USP and E75) are expressed in trichodea sensillae of S. littoralis male antennae during the entire adult's life.
► An increase of 20E haemolymphatic concentrations during the scotophase close to concentrations observed during the photophase leads to an induction of the 20E signalling pathway and the up-regulation of olfactory regulator as calmodulin and DGK.
► A modification of the timing of repolarization in electro-antennographical (EAG) recording was measured after 20E injection which conduces to a decrease of the responsiveness to the major pheromonal compound in S. littoralis.