The vast majority of sexually reproductive animals propagate through mating. For insects diverse mating positions have evolved to deliver sperm ejaculates, with the female-above pattern as the groundplan (Huber et al., 2007; Huber, 2010), from which all other deviations evolved through rotations or flexions of the terminal abdomen of males (McAlpine et al., 1981; Bickel, 1990; Huber, 2010). The evolution of mating position and other behavioral traits involved in mating are regarded to relate to sexual conflict in insects (Chapman et al., 2003; Parker, 2006).
Most Mecoptera are characterized by their interesting sexual behaviors, including various mating positions, nuptial feeding or forced copulation by modified grasping devices (Thornhill, 1973, 1980, 1981; Thornhill and Sauer, 1991; Sauer et al., 1998; Engqvist and Sauer, 2001, 2003; Byers, 2002; Engqvist, 2007, 2009, 2011; Kock et al., 2009; Gao and Hua, 2013; Zhong and Hua, 2013; Zhong et al., 2015a, b). Of the nine families, five have been studied with respect to their mating behaviors and/or copulatory mechanisms (Cooper, 1974; Thornhill, 1981; Byers and Thornhill, 1983; Thornhill and Sauer, 1991; Ma et al., 2010; Zhong and Hua, 2013; Zhong et al., 2015a, b). The male of Boreidae uses his paired hook-shaped wings to secure the female dorsally to form a typical female-above mating position (Cooper, 1974). In Bittacidae the male temporarily twists his abdomen by 180º to maintain a belly-to-belly mating position to control the nuptial gift (Gao and Hua, 2013). Most males of Panorpidae provide a salivary mass as a nuptial gift and sustain a V-shaped mating position (Thornhill, 1981; Byers and Thornhill, 1983; Zhong et al., 2015a). The male of Panorpa liui Hua, 1997 offers the female only prey rather than salivary mass as a nuptial gift owing to the less-developed salivary glands of males (Ma and Hua, 2011). The species of Furcatopanorpa (Panorpidae) (Zhong et al., 2015b) and Chorista (Choristidae) (Byers and Thornhill, 1983) adopt an O-shaped mating position for the male lacking a notal organ to help control the female. Similarly in the males of Panorpodidae the notal organ is vestigial or thoroughly lacking (Carpenter, 1953; Byers and Thornhill, 1983; Tan and Hua, 2008; Zhong et al., 2011; Krzeminski and Soszynska-Maj, 2012), but their mating behavior has not been satisfactorily studied thus far.
Panorpodidae is the sister group of Panorpidae (Willmann, 1987; Friedrich et al., 2013), and consists of only 13 extant species in two genera: Brachypanorpa Carpenter, 1931 occurring in North America and Panorpodes MacLachlam, 1875 almost exclusively distributed in eastern Asia (Pollmann et al., 2008; Hu and Hua, 2016). Panorpodes colei Byers, 2005 from western North America is the only exception (Byers, 2005). The male of Brachypanorpa does not provide any nuptial gift, and starts mating with the female in a V-shaped mating position at any time of the day but usually in the evening (Carpenter, 1953; Byers, 1997). As far as we know, however, the mating behavior in Panorpodes has not been reported to date.
In this study, we investigated the mating behavior and copulatory mechanism of the short-faced scorpionfly Panorpodes kuandianensis Zhong, Zhang and Hua, 2011 and found an unusual mating pattern in Mecoptera.