1 INTRODUCTION
Cerambycidae is one of the main members of the order Coleoptera, with more than 36,000 recorded species worldwide, and it is one of the most important pests of forests, street trees, and fruits (Lu et al., 2007; Wang et al., 2017). Glenea cantor Fabricius is a member of the subfamily Lamiinae, which is mainly distributed in southern China and Southeast Asia countries (Lu et al., 2013a). It is a stem-boring insect pest that survives as a larva by burrowing into tree trunks or branches. However, traditional control methods, such as pesticide application, have a poor effect on preventing and controlling stem-boring insects (Brockerhoff et al., 2006). Research has shown that pheromones can be used to disturbG. cantor (Lu et al., 2013b), including two main types of pheromone reception, short-distance and contact pheromones (Wong et al., 2017), which has been reported on a number of longhorns, including the subfamily Lamiinae (Zhang et al., 2003; Li et al., 2008). So many ideas are to prevent the stem-boring insect pest by blocking the reception of pheromones. This step belongs to the field of insect chemical ecology, which has attracted an increasing number of scholars aiming to provide theoretical guidance for the prevention of multiple pests.
The structural basis of pheromone chemosensory recognition is the sensilla ultrastructure. Studies have shown that the common sensilla types of beetles include sensilla basiconica, sensilla chaetica, sensilla twig basiconica, sensilla coeloconica, sensilla trichodea, sensilla campaniformia, sensilla placodea (Wu et al., 2018; Ma et al., 2019). Furthermore, a large amount of these sensilla are mainly distributed in the antennae, labial papilla, mandibular papilla and ovipositor (MacKay et al., 2014; Wang et al., 2014; Liu et al., 2018; Dong et al., 2020). The morphology, distribution, number and function of the different sensors differ, and the different functions of the sensilla work in synergy to receive and recognize signals (Dong et al., 2020), which are converted into electrical signals and transmitted to the brain for unified regulation, thus ensuring that the various behaviors are carried out efficiently and smoothly. For example, the main function of the spiny sensor is mechanosensory (Zhang et al., 2003; MacKay et al., 2014) sensilla trichodea and sensilla twig basiconica have olfactory functions (Dong et al., 2020); and the plate sensor, bell sensor and cavity sensor are reported to be mainly distributed in the plate. Moreover, the bell and cavity sensors were reported to be mainly located in the labial palpus and mandibular palpus and mainly functioned to sense carbon dioxide and temperature and humidity ( Ochieng et al., 2000; Dong et al., 2020). To date, however, research on these sensilla has focused on the beetle’s antennae, and sensillum in specific parts of the antennae have been shown to be involved in the recognition of oviposition sites (Peng et al., 2012). In addition, studies have also reported that labial palpus and mandibular palpus have similar roles. For instance, in Oedaleus decorus asiaticusBey-Bienko (Wang et al., 2022) and Locusta migratoria manilensisMeyen (Zhang et al., 2020), the labial palpus and mandibular palpus of female beetles may also play a certain role in finding spawning sites.
Studies further have shown that the labial palpus and mandibular palpus of G. cantor plays an important role in reproductive behavior (Dong et al., 2020), but the ultrastructure of labial palpus and mandibular palpus of G. cantor has not been reported. Therefore, the purpose of our study was to analyze the ultrastructure of the oral appendages of male and female longhorn beetles through scanning electron microscopy and to determine the structural differences between male and female longhorn beetles and their specific role in reproductive behavior to provide new insights for pest control and forest protection.