For animals that exhibit a scramble competition mating system, sexual selection pressures on mate searching ability are expected to be strong. Scramble competition mating systems evolve when populations provide females with equal accessibility to all male competitors, yet sex ratio and population density influences mating systems and varies seasonally. The stick insect species,Clitarchus hookeri, is frequently found in copula, yet very little is known about it’s mating behaviour. We preformed behavioural tests and assayed antennal sensory morphology to determine whether males used chemosensory cues to detect females. Through natural field observations we found populations to be significantly male-biased earlier in the season, while later, populations began to display equal sex ratios. With increasing female availability mating pair proportions steadily increased, while copulation duration declined. These results supportC. hookerias a scramble competitor, and demonstrate males may alter their behaviour in response to the seasonal variation in female density.

We describe two new species of Clitarchus Stål from Northland, New Zealand. Clitarchus rakauwhakanekeneke sp. nov. is described from the Poor Knights Islands and Clitarchus tepaki sp. nov. is described from the Te Paki / North Cape area and the Karikari Peninsula at the northernmost tip of New Zealand. Two new synonymies are proposed including Clitarchus multidentatus Brunner (syn. nov.) and Clitarchus tuberculatus Salmon (syn. nov.) as synonyms of Clitarchus hookeri (White). Clitarchus magnus Brunner, recorded from Thailand, is transferred to Ramulus Saussure and given the replacement name Ramulus changmaiense nom. nov. The holotype of C. multidentatus was recorded as being collected from New Caledonia; however we believe this is a labelling error and the specimen was collected from New Zealand. These taxonomic changes render Clitarchus endemic to New Zealand and consisting of three species; C. hookeri, C. rakauwhakanekeneke and C. tepaki. Keys to the adult males and females of Clitarchus species are given in addition to notes on host plants, ecology and geographic distributions.

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