Larvae of Ochrogaster lunifer Herrich-Schaeffer (Lepidopetera: Thaumetopoeidae), or as it has previously been known, Ochrogaster contraria Walker or Teara contraria Walker, are widely distributed throughout coastal and inland regions of Australia (Turner 1921; Froggatt 1923; Mills 1951; McFarland 1979). Inhabiting mainly acacia and eucalypt vegetation (Van Schagen et al. 1992), larval populations of O. lunifer display a distinctive processionary behaviour by crawling head to tail in single-file to the canopy of its host tree to feed before returning to their nests in much the same way (Floater 1996a; Maier et al. 2003). Previous studies conducted on O. lunifer have focused on the species life history (Floater 1996a), biology (Van Schagen,…show more content… 1992; Floater 1996a). Second through to eighth instar emerge from the egg mass between December and May; ascending the host plant in a single-file procession to feed (Floater 1996a). First instar larvae have been observed to remain within the egg mass not feeding (Floater 1996a; Floater & Zalucki 1999). Final instars leave the host plant during May in larval processions before splitting into subgroups and then later individuals to pupate (Floater 1996a). Individual larvae form an underground cocoon of silk, soil and setae where they will diapause over winter; pupation and emergence does not take place until September or October (Van Schagen et al. 1992; Floater 1996a).
The larval integument of O. lunifer is covered with a multitude of hair types (Floater 1996a; Floater & Zalucki 1999). A typical arthropod hair is embedded in epidermal cells; developed by a trichogen and a tormogen or auxiliary cell, and is connected to neurons for the transmission of sensorial information (Battisti et al. 2011). Urticating hairs, and in particular those classified as true setae, are derived from arthropod hairs (Battisti et al. 2011).
True setae are a distinguishing characteristic of the larval stage of many processionary Lepidoptera (Battisti et al. 2011; Cawdell-Smith et al. 2013; Petrucco Toffolo et al. 2014). They are small, approximately 100-500µm long and 3-7µm in diameter, and barbed (Fenk et al. 2007; Battisti et al. 2011). The cellular