Morphology of T. canadensis The rostrum of spider mites (Tetranychidae) was examined with a scanning electron microscope (SEM) by Summer et al. (1973), Jeppson et al. (1975), Hislop & Jeppson (1976) and Razaq et al. (2000). Lindquist (1985) noted the mouth of spider mites was flanked by hyaline lateral lips and three pairs of usually inconspicuous adoral setae (or 1-3) apically. The rostrum of Raoiella (Tenuipalpidae) were examined with SEM by Beard et al. (2012) who observed 3 pairs of adoral setae around the tip of the rostrum. The rostrums of Bryobia sp., Petrobia sp. and Oligonychus sp. have the same characters as T. canadensis: the tip of rostrum of all spider mites bears three pairs of adoral setae: the lateral and ventral “lips” are modified as leaf-like adoral setae, (or 2 and or 3), and the dorsal lips bearing a pair of spine-like adoral setae (or 1) (Fig 7B). The trichobothrium, a mechanoreceptor, has cup-like socket for setal base (Grandjean 1943). In spider mites the dorsal seta on tibia I has a trichobothridial aspect and seta d on femora I and II sometimes has a similar aspect (Lindquist 1985). In this study, we show the trichobothridial nature of these setae using SEM studies of T. canadensis. Trichobothridial seta, on tibia I, has a cup-shaped base and broken striae on the inner integument (Fig 17B), while normal seta does not has striae on the inner integument (Fig 17C). Leg setation of spider mites (Tetranychidae) provides valuable information for species diagnostics and systematics (Yi et al. 2013, 2017; Yi & Ochoa 2018; Seeman et al. 2017). In recent works on descriptions and ontogeny of spider mites, chaetotaxy data are now more commonly provided than simple setal counts (e.g. Beard & Walter, 2010; Yi & Zhang 2013, 2017; Yi et al., 2017; Li et al. 2017, 2018a, 2018b; Khanjani et al. 2017; Liu & Zhang 2018; Khanjani et al. 2018; Mahdavi et al. 2018). T. canadensis has typical larval chaetotaxy of Tetranychidae provided by Lindquist (1985) and is vastly different from several hypotrichous genera (for which ontogenetic data are available) such as Neonidulus (Beard & Walter 2010), Tribolonychus (Yi et al. 2013), Bryobiella (Yi & Ochoa 2018) and certain species of Eotetranychus (Seeman et al. 2017). On the other hand, it is close to some other species of Eotetranychus (Yi et al. 2017, Seeman et al. 2017) and Oligonychus (Li et al. 2017, 2018; Khanjani et al. 2018), and identical to some Oligonychus (Khanjani et al. 2018).

Published as part of Liu, Man, Yi, Tian-Ci, Gulbronson, Connor, Bauchan, Gary R. & Ochoa, Ronald, 2020, Ontogenetic and morphological studies on Tetranychus canadensis (Acari: Tetranychidae), pp. 215-250 in Zootaxa 4857 (1) on pages 244-245, DOI: 10.11646/zootaxa.4857.1.11, http://zenodo.org/record/4396392