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 beetleās 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.