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\begin{document}

\title{Observation on the ultrastructure of the oral appendages of Glenea
cantor Fabricius (Coleoptera: Lamiinae)}



\author[1]{yao wu}%
\author[1]{Zhixin Li}%
\author[2]{Liangshan Ming}%
\author[3]{Zhongyan Huang}%
\author[1]{Gaochuan Zhang}%
\author[3]{WEN LU}%
\author[1]{Hongning Liu}%
\author[1]{ZISHU DONG}%
\affil[1]{Jiangxi University of Traditional Chinese Medicine}%
\affil[2]{no affiliation}%
\affil[3]{Guangxi University}%


\vspace{-1em}



  
  \date{May 25, 2024}


\begingroup
\let\center\flushleft
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\selectlanguage{english}
\begin{abstract}
We investigated the gross and ultrastructure morphology of the
mandibles, labial palpus and mandibular palpus of adult male and female
\emph{Glenea cantor} beetles using scanning electron microscopy. There
were significant differences between males and females in the gross and
ultrastructure morphology of these parts. Observation of the gross
morphology of the mandible, labial palpus and mandibular palpus revealed
that their lengths were significantly greater in females, which is
mainly related to the oviposition mechanism. In terms of the
ultrastructural morphology of the mandibles, labial palpus and
mandibular palpus, seven types of sensilla were found on these parts:
sensilla twig basiconica (STB I, II, III, and IV), sensilla chaetica
(SCh IV and V), B\selectlanguage{ngerman}öhm's bristles (Bb), sensilla placodea (SP), sensilla
trichodea (ST II), sensilla plate (SP), sensilla coeloconica (SC) and
sensilla campaniformia (SCa). Females have significantly more ST I and
SCh III on their mandibles than males. The mechanical sensors SCh and
Bb, olfactory sensor ST II, taste sensor STB IV, and carbon dioxide
sensor and temperature and humidity sensors SC, SP and SCa were
significantly more developed on female than male labial and maxillary
palps, which also further explained the important role of the oral
appendages in oviposition behavior. These results will help us further
understand the host selection and oviposition behavior of adult \emph{G.
cantor} and promote the information-based design of pest control
methods.%
\end{abstract}\selectlanguage{ngerman}%



\sloppy


\textbf{Observation on the ultrastructure of the oral appendages
of\emph{Glenea cantor} Fabricius (Coleoptera: Lamiinae)}

Yao Wu\textsuperscript{1}, Zhixin Li\textsuperscript{1}, Liangshan Ming,
Zhongyan Huang\textsuperscript{2}, Gaochuan Zhang\textsuperscript{1},
Wen Lu\textsuperscript{2}, Hongning Liu\textsuperscript{1}*, Zishu
Dong\textsuperscript{1}*

\emph{\textsuperscript{1}Advanced Research Institute, Jiangxi University
of Chinese Medicine, Nanchang, China;}

\emph{\textsuperscript{2} Guangxi Key Laboratory of Agric-Environment
and Agric-Products Safety, National Demonstration Center for
Experimental Plant Science Education, College of Agriculture,Guangxi
University, Nanning, Guangxi, China.}

*Corresponding author. Email: lhn0791@139.com, dongzishu1668@163.com;
Address: \emph{Advanced Research Institute, Jiangxi University of
Chinese Medicine, Nanchang 330004, China} .

\emph{Two corresponding authors contributed equally.}

\textbf{Observation on the ultrastructure oftheoral appendages
of}\emph{Glenea cantor} \textbf{Fabricius}

\textbf{(Coleoptera: Lamiinae)}

\textbf{ABSTRACT}

We investigated the gross and ultrastructure morphology of the
mandibles, labial palpus and mandibular palpus of adult male and female
\emph{Glenea cantor} beetles using scanning electron microscopy. There
were significant differences between males and females in the gross and
ultrastructure morphology of these parts. Observation of the gross
morphology of the mandible, labial palpus and mandibular palpus revealed
that their lengths were significantly greater in females, which is
mainly related to the oviposition mechanism. In terms of the
ultrastructural morphology of the mandibles, labial palpus and
mandibular palpus, seven types of sensilla were found on these parts:
sensilla twig basiconica (STB I, II, III, and IV), sensilla chaetica
(SCh IV and V), B\selectlanguage{ngerman}öhm's bristles (Bb), sensilla placodea (SP), sensilla
trichodea (ST II), sensilla plate (SP), sensilla coeloconica (SC) and
sensilla campaniformia (SCa). Females have significantly more ST I and
SCh III on their mandibles than males. The mechanical sensors SCh and
Bb, olfactory sensor ST II, taste sensor STB IV, and carbon dioxide
sensor and temperature and humidity sensors SC, SP and SCa were
significantly more developed on female than male labial and maxillary
palps, which also further explained the important role of the oral
appendages in oviposition behavior. These results will help us further
understand the host selection and oviposition behavior of adult \emph{G.
cantor} and promote the information-based design of pest control
methods.

\textbf{KEYWORD}

\emph{Glenea cantor} , oral appendage, scanning electron microscopy,
plant protections, stem boring insects

\textbf{RESEARCH HIGHLIGHTS}

\begin{enumerate}
\tightlist
\item
  The external morphology and distribution of the oral appendages of
  \emph{G. cantor} between sexes has been researched through scanning
  electron microscopy (SEM) for the first time.
\item
  Several significant differences between males and females has been
  found by analyzing the oral appendages of \emph{G. cantor} with SEM.
\item
  The differences in the structure of oral appendages of \emph{G.
  cantor} between sexes reflect functional differences in reproductive
  behaviors.
\end{enumerate}

\textbf{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). \emph{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 disturb\emph{G. 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 \emph{Oedaleus decorus asiaticus}Bey-Bienko (Wang et
al., 2022) and \emph{Locusta migratoria manilensis}Meyen (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 \emph{G. cantor} plays an important role in reproductive behavior
(Dong et al., 2020), but the ultrastructure of labial palpus and
mandibular palpus of \emph{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.

\textbf{2 MATERIAL AND METHOD}

\textbf{2.1 Insects}

In July 2020, we collected three kapok branches that had withered in the
upper stalk due to \emph{G. cantor} infestation from Qingxiu Mountain
(22°12\selectlanguage{english}'-23deg32\selectlanguage{english}'N, 107deg45\selectlanguage{english}'-108deg51\selectlanguage{english}'E), Guangxi Zhuang Autonomous Region
Nanning, China. The stems were incubated in four bubble containers in
the yarn in a cage (50 cm x 70 cm x 80 cm) and sprayed with water every
5 days in a controlled environment (25 +- 1degC, 75 +- 5\% RH, 14 L: 10 D;
Lu et al., 2011). After 2 months, five males and five females were
randomly selected from our caged adults and transferred to separate
glass containers (5 cm diameter x 16 cm length) in a refrigerator at -20
degC. After 25 minutes, the adult insect returned to normal and its
mandibles, labial papules and mandibular papules were cut under a
stereomicroscope PX-1 (Camsonar Technology Co., Ltd., Beijing, China).
The mandibles, labial papules and mandibular papules are prepared.

\textbf{2.2 Preparation of Specimens}

The mandibles, labial papules and mandibular papules prepared as above
were cleaned three times in an ultrasonic bath JP-010T (Skymen Cleaning
Equipment CO., Ltd., Shenzhen, China) at 250 W for 350 s each time. The
mandibles, labial papules and mandibular papules were fixed with 3\%
glutaraldehyde at 5\selectlanguage{english} for 15 h, and dehydrated with 60\%, 70\%, 80\%,
90\%, and 100\% liters of ethanol, with an interval of 8 min. The
prepared mandibles, labial papules and mandibular papules were stored in
glass containers which was already cleared and dried for 36 h. After
drying, the specimens were mounted on a holder using double-sided sticky
tape (dorsal, ventral), sputter coated with gold-palladium.
Subsequently, the prepared were scanned by using an electron microscope
(model S-3400N, Hitachi, Ibaraki, Japan) at an accelerating voltage of
3-10 kV. The images were named separately and stored on a computer.

\textbf{2.3 Data Analysis}

In this paper, according to the morphological criteria described by
Moeck (1968) mainly introduce the terminology and classification of
sensilla length and the intermediate width of mandibles, labial papules
and mandibular papules, and various sensillum was quantified using Image
J Launcher Version software at 1.44p (Broken Symmetry Software, National
Institutes of Health, Bethesda, MD). On the basis of scanning electron
microscopy images, the general morphological characteristics of
mandibles, labial papules and mandibular papules of\emph{G. cantor} were
studied. The differences in the distribution patterns of these sensillum
were accurately described by Adobe Photoshop CC 2019 software. T-test (t
= 0.05) was used to compare the length, width, and number of each
individual sensilla subtype in adults between sexes using SPSS 25.0
(IBM, Armonk, NY) and GraphPad Prism 5 (GraphPad Software, Inc., La
Jolla, CA). Values are reported as mean +- SE (standard error).

\textbf{3 RESULT}

\textbf{3.1 Gross Morphology of oral appendages}

\textbf{3.1.1 Mandible}

The length and basal width of the mandibles of females are significantly
more developed than those of males, but there is no significant
difference in basal thickness (Table 1).

Table 1 Lengths, base widths and base thickness of mandible of both
sexes in \emph{G. cantor}\selectlanguage{english}
\begin{longtable}[]{@{}lllll@{}}
\toprule
Index (mm) & Sex & Sex & Significance & Significance\tabularnewline
&  &  & \emph{t} & \emph{P}\tabularnewline
Lengths & 1.71 \selectlanguage{ngerman}± 0.07* & 1.26 \selectlanguage{ngerman}± 0.03 & 5.92 & 0.00\tabularnewline
base widths & 1.09 \selectlanguage{ngerman}± 0.05* & 0.88 \selectlanguage{ngerman}± 0.03 & 3.45 & 0.00\tabularnewline
base thickness & 0.67 \selectlanguage{ngerman}± 0.04 & 0.59 \selectlanguage{ngerman}± 0.03 & 1.46 & 0.16\tabularnewline
\bottomrule
\end{longtable}

Note: Data are presented as means \selectlanguage{ngerman}± SE, n = 10. *Indicating significant
difference between males and females at 0.05 level.

\textbf{3.1.2 Labial palpus}

The length and basal width of the mandibles of females were
significantly more developed than those of males, but there was no
significant difference in basal thickness. Figure 1 shows that the
length and width of the female labial palpus are different from those of
males. The basal segment 1 of the labial palpus is shorter, the terminal
segment is expanded and conical at the top, and the base of each segment
forms an articulated structure that is embedded within the terminal part
of the preceding segment, and it is flexible, soft and bendable (Table
2).

Table 2 Lengths and base widths of labial palpus of both sexes in
\emph{G. cantor}\selectlanguage{english}
\begin{longtable}[]{@{}lllllllll@{}}
\toprule
Labial palpus & Length (mm) & Length (mm) & Significance & Significance
& Width (mm) & Width (mm) & Significance & Significance\tabularnewline
&  &  & \emph{t} & \emph{P} &  &  & \emph{t} &
\emph{P}\tabularnewline
1\textsuperscript{st} & 0.17 \selectlanguage{ngerman}± 0.01c & 0.14 \selectlanguage{ngerman}± 0.01b & 3.22 & 0.01 & 0.09
\selectlanguage{ngerman}± 0.01b & 0.06 \selectlanguage{ngerman}± 0.00b & 6.45 & 0.00\tabularnewline
2\textsuperscript{nd} & 0.52 \selectlanguage{ngerman}± 0.02b & 0.42 \selectlanguage{ngerman}± 0.02a & 3.13 & 0.01 & 0.10
\selectlanguage{ngerman}± 0.01a & 0.08 \selectlanguage{ngerman}± 0.01a & 4.69 & 0.00\tabularnewline
3\textsuperscript{rd} & 0.60 \selectlanguage{ngerman}± 0.01a & 0.46 \selectlanguage{ngerman}± 0.01a & 7.11 & 0.00 & 0.10
\selectlanguage{ngerman}± 0.01a & 008 \selectlanguage{ngerman}± 0.01a & 5.87 & 0.00\tabularnewline
Whole & 1.28 \selectlanguage{ngerman}± 0.03 & 1.02 \selectlanguage{ngerman}± 0.02 & 7.91 & 0.00 & 0.09 \selectlanguage{ngerman}± 0.00a & 0.07 \selectlanguage{ngerman}±
0.00 & 8.87 & 0.00\tabularnewline
\bottomrule
\end{longtable}

Note: Data are presented as means \selectlanguage{ngerman}± SE, n = 10; Different letters in
each column indicate significant difference at 0.05 level using Tukey's.

\textbf{3.1.3 Mandibular palpus}

There is also clear dimorphism in the mandibular palpus of male and
female adults, especially in length, with each subsegment and overall
length showing significant differences, except for the basal width of
segment 4 of the mandibular palpus, which is not significantly different
(Table 3).

Table 3 Lengths and base widths of mandibular palpus of both sexes in

\emph{G. cantor}\selectlanguage{english}
\begin{longtable}[]{@{}lllllllll@{}}
\toprule
Mandibular palpus & Length (mm) & Length (mm) & Significance &
Significance & Width (mm) & Width (mm) & Significance &
Significance\tabularnewline
&  &  & \emph{t} & \emph{P} &  &  & \emph{t} &
\emph{P}\tabularnewline
1\textsuperscript{st} & 0.22 \selectlanguage{ngerman}± 0.01d & 0.19 \selectlanguage{ngerman}± 0.01d & 2.84 & 0.01 & 0.08
\selectlanguage{ngerman}± 0.00b & 0.07 \selectlanguage{ngerman}± 0.00a & 2.39 & 0.03\tabularnewline
2\textsuperscript{nd} & 0.46 \selectlanguage{ngerman}± 0.01b & 0.34 \selectlanguage{ngerman}± 0.01b & 7.17 & 0.00 & 0.10
\selectlanguage{ngerman}± 0.01a & 0.08 \selectlanguage{ngerman}± 001a & 5.31 & 0.00\tabularnewline
3\textsuperscript{rd} & 0.41 \selectlanguage{ngerman}± 0.01c & 0.30 \selectlanguage{ngerman}± 0.01c & 8.46 & 0.00 & 0.10
\selectlanguage{ngerman}± 0.00a & 0.08 \selectlanguage{ngerman}± 0.00a & 3.75 & 0.00\tabularnewline
4\textsuperscript{th} & 0.60 \selectlanguage{ngerman}± 0.01a & 0.48 \selectlanguage{ngerman}± 0.00a & 12.53 & 0.00 &
0.09 \selectlanguage{ngerman}± 0.00ab & 0.08 \selectlanguage{ngerman}± 001a & 1.11 & 0.28\tabularnewline
Whole & 1.47 \selectlanguage{ngerman}± 0.02 & 1.13 \selectlanguage{ngerman}± 0.02 & 12.64 & 0.00 & 0.10 \selectlanguage{ngerman}± 0.00 & 0.08 \selectlanguage{ngerman}±
0.00 & 4.27 & 0.00\tabularnewline
\bottomrule
\end{longtable}

Note: Data are presented as means \selectlanguage{ngerman}± SE, n = 10; Different letters in
each column indicate significant difference at 0.05 level using Tukey's.

\textbf{3.2 Ultrastructural morphology of oral appendages}

\textbf{3.2.1 Mandible}

The mandible sensors of adult \emph{G. cantor} are relatively simple and
highly ossified and are mainly used for feeding and making oviposition
grooves. The lateral and medial sides of the palate have numerous
receptive hair areas, with a small number of hair-shaped sensors type I
(ST I) distributed on the outer side (Fig. 1), while the ventral and
dorsal edges of the palate have sensilla chaetica (SCh) III in addition
to ST I, and the dorsal surface has significantly more sensilla than the
ventral surface (Fig. 2). Females have significantly more ST I and SCh
III on their mandibles than males.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image1/image1}

\end{center}
\end{figure}

Fig. 1 The morphological characteristics of mandible of both sexes of

\emph{G. cantor}

A, Venter view of mandible of female; B, Lateral view of mandible of
female; C, Interior view of mandible of female; D, Dorsal view of
mandible of female; E, Venter view of mandible of male; F, Lateral view
of mandible of male; G, Interior view of mandible of male; H, Dorsal
view of mandible of male. (Scale bars): A, E = 1000 \selectlanguage{greek}μ\selectlanguage{english}m; B, F = 500 \selectlanguage{greek}μ\selectlanguage{english}m;
C, D, G = 200 \selectlanguage{greek}μ\selectlanguage{english}m; H = 50 \selectlanguage{greek}μ\selectlanguage{english}m.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image2/image2}

\end{center}
\end{figure}

\par\null

Fig. 2 Numbers and distributions of sensilla on the mandible of both
sexes of \emph{G. cantor}

Lateral; Dorsal; Venter, n = 10. ** Indicating significant difference
between males and females at 0.01 level, * indicates significant
difference between males and females at 0.05 level, n = 10.

\textbf{3.2.2 Labial palpus}

The labial palps of \emph{G. cantor} have a rich variety of sensor
species, with no differences between male and female sensor types but
some variability in the number of sensors (Fig. 3). The sensor species
on the labial palps can be divided into seven main groups (11 subtypes):
sensilla chaetica (SCh IV, SCh V), sensilla twig basiconica (STB I, STB
II, STB III, STB IV), B\selectlanguage{ngerman}öhm's bristle sensor (Bb), sensilla trichodea (ST
II), sensilla plate (SP), sensilla coeloconica (SC) and sensilla
campaniformia (SCa) (Table 4).

Table 4 The morphological characteristics of sensilla on the labial
palpus of both sexes in \emph{G. cantor}\selectlanguage{english}
\begin{longtable}[]{@{}llllllll@{}}
\toprule
Type & Subtype & Sex & Length (\selectlanguage{greek}μ\selectlanguage{english}m) & Width (\selectlanguage{greek}μ\selectlanguage{english}m) & Morphological
character & Morphological character & Morphological
character\tabularnewline
& & & & & Tip & Basal & Wall\tabularnewline
Sensillia Twig Basiconica & STB I &  & 2.21 \selectlanguage{ngerman}± 0.08 & 2.09 \selectlanguage{ngerman}± 0.07 & Flat
blunt cavity & None & Smooth\tabularnewline
& &  & 2.70 \selectlanguage{ngerman}± 0.10* & 2.04 \selectlanguage{ngerman}± 0.05 & & &\tabularnewline
& STB II &  & 2.37 \selectlanguage{ngerman}± 0.22 & 1.81 \selectlanguage{ngerman}± 0.05 & Rounded blunt projection &
None & Smooth\tabularnewline
& &  & 3.52 \selectlanguage{ngerman}± 0.12* & 1.78 \selectlanguage{ngerman}± 0.04 & & &\tabularnewline
& STB III &  & 2.52 \selectlanguage{ngerman}± 0.12 & 1.50 \selectlanguage{ngerman}± 0.04 & Finger-shaped protrusions &
None & Smooth\tabularnewline
& &  & 2.85 \selectlanguage{ngerman}± 0.16 & 2.03 \selectlanguage{ngerman}± 0.08* & & &\tabularnewline
& STB IV &  & 2.88 \selectlanguage{ngerman}± 0.20 & 1.78 \selectlanguage{ngerman}± 0.08* & Rounded blunt & None &
Smooth\tabularnewline
& &  & 2.70 \selectlanguage{ngerman}± 0.11 & 1.54 \selectlanguage{ngerman}± 0.08 & & &\tabularnewline
Sensilla Chaetica & SCh IV &  & 52.58 \selectlanguage{ngerman}± 1.96 & 3.37 \selectlanguage{ngerman}± 0.23 & Sharp
pointed & dense & V-shaped\tabularnewline
& &  & 50.79 \selectlanguage{ngerman}± 2.04 & 3.15 \selectlanguage{ngerman}± 0.18 & & &\tabularnewline
& SCh V &  & 249.79 \selectlanguage{ngerman}± 32.10 & 9.08 \selectlanguage{ngerman}± 0.67* & Sharp pointed & dense &
V-shaped\tabularnewline
& &  & 185.09 \selectlanguage{ngerman}± 22.23 & 5.65 \selectlanguage{ngerman}± 0.23 & & &\tabularnewline
B\selectlanguage{ngerman}öhm bristles & Bb &  & 10.90 \selectlanguage{ngerman}± 1.28 & 2.46 \selectlanguage{ngerman}± 0.16 & Sharp pointed &
Loose & Smooth\tabularnewline
& &  & 11.30 \selectlanguage{ngerman}± 0.99 & 2.45 \selectlanguage{ngerman}± 0.12 & & &\tabularnewline
Sensilla Trichodea & ST II &  & 58.57 \selectlanguage{ngerman}± 3.33 & 4.38 \selectlanguage{ngerman}± 0.16* & Blunt &
Loose & V-shaped\tabularnewline
& &  & 59.14 \selectlanguage{ngerman}± 2.92 & 3.61 \selectlanguage{ngerman}± 0.14 & & &\tabularnewline
Sensilla Plate & SP &  & 20.63 \selectlanguage{ngerman}± 1.44 & 1.77 \selectlanguage{ngerman}± 0.10 & Board shape &
Loose & Smooth\tabularnewline
& &  & 31.31 \selectlanguage{ngerman}± 0.88* & 1.88 \selectlanguage{ngerman}± 0.11 & & &\tabularnewline
Sensilla Coeloconica & SC &  & ------ & 0.43 \selectlanguage{ngerman}± 0.03 & Hole cavity &
None & Folded\tabularnewline
& &  & ------ & 0.37 \selectlanguage{ngerman}± 0.02 & & &\tabularnewline
Sensilla Campaniformia & SCa &  & ------ & 2.87 \selectlanguage{ngerman}± 0.17* & Rounded blunt
protrusion & loose & Smooth\tabularnewline
& &  & ------ & 1.80 \selectlanguage{ngerman}± 0.11 & & &\tabularnewline
\bottomrule
\end{longtable}

Note: Data are presented as means \selectlanguage{ngerman}± SE, n = 10. * Indicating significant
difference between males and females at 0.05 level (The same to the
following table). ``------'' indicate the sensilla were absent.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image3/image3}

\end{center}
\end{figure}

Fig. 3 Numbers and distributions of sensilla on the labial palpus of
both sexes of \emph{G. cantor}

\textbf{Sensillia twig basiconica}

Sensilla twig basiconica (STB) is found only at the apical end of adult
labial palps and consists of four subtypes (STB I, STB II, STB III, and
STB IV). The shape of these sensors varies markedly between subtypes
(Fig. 4): STB I has a smooth surface and a flat and deeply concave
apical part with a distinct chamber and no basal fossa; STB II has a
generally smooth surface and a rounded apical part with chrysanthemum
shaped granules and no basal fossa; STB III has a smooth surface and a
flower-like wrapping around a finger-like projection at the tip; STB IV
has an overall smooth surface and a rounded apical part with a dome.

The terminal tapered inductor of the labial palpus exhibits external
morphological features that are significantly longer in males than in
females, including STB I (\emph{t} = -4.00, \emph{P} \textless{} 0.01)
and STB II (\emph{t} = -4.59, \emph{P} \textless{} 0.01), while the
basal width of STB III (\emph{t} = -5.76, \emph{P} \textless{} 0.01) in
males is similarly significantly wider than in females; however, the STB
IV basal width (\emph{t} = 2.15, \emph{P} \textless{} 0.05) in females
was significantly wider than males. Quantitatively, females had
significantly more STB IV than males (Fig. 3).\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image4/image4}

\end{center}
\end{figure}

Fig. 4 The ultrastructural of labial palpus of both sexes of \emph{G.
cantor}

A, Labial palpus of female beetle; B, Sensilla on
3\textsuperscript{rd}of labial palpus of female beetle; C, Sensilla
styloconica on 3\textsuperscript{rd} of labial palpus of female beetle;
D, Labial palpus of male beetle; E, Sensilla on 3\textsuperscript{rd} of
labial palpus of male beetle; F,Sensilla styloconica on
3\textsuperscript{rd}of labial palpus of male beetle.Scale bars: A, D =
300 \selectlanguage{greek}μ\selectlanguage{english}m, B, E = 50 \selectlanguage{greek}μ\selectlanguage{english}m, C, F = 10 \selectlanguage{greek}μ\selectlanguage{english}m.

\textbf{Sensilla chaetica}

The sensilla chaetica of the adult labial palpus differ from those on
the antennae, with two subtypes (SCh IV, SCh V). SCh IV is found on
segments 2 and 3 of the labial palpus, while SCh V is found on segment 2
of the labial palpus. These two subtypes of inductors differ
considerably in length and basal width (Table 4).

The basal width of the SCh V on the labial palpus of females was
significantly wider than that of males. In contrast, the number of SCh
IV ( = 250.00 \selectlanguage{ngerman}± 10.32, \selectlanguage{english} = 304.20 +- 7.69, \emph{t} = -4.21, \emph{P} =
0.00) on the third segment of the labial palpus was significantly
greater in males than in females (Fig. 3).

\textbf{Bohm bristles}

Bohm's bristle sensor (Bb) is present at the base of the labial palpus
and mandibular palpus only at the junction of the base of the first
segment with the mouthparts, and the sensor has a smooth epidermal wall
with an acute tip and a loose basal fossa (Fig. 5). This sensor is a
relatively common sensor at the junction of insect organs, and no
subtypes exist, which it shows no significant differences between males
and females as a whole (Fig. 3).

\textbf{Sensilla trichodea}

The adult labial palps have a relatively small number of sensilla
trichodea, with only one subtype, ST II, which is more abundant and is
found in all segments of the labial palpus in both sexes. It has a blunt
apex, a V-shaped pattern in the epidermal wall and a loose basal fossa
(Fig. 4).

There was no significant difference in the number of labial palpus ST II
between males and females (Fig. 3), but the basal width of ST II was
significantly wider in females than in males.

\textbf{Sensilla placodea}

The sensilla placodea (SP) of brown-spotted \emph{G. cantor} was long
and lamella-plate-shaped with a loose basal fossa and smooth epidermal
walls (Figs. 4, 6), and in adults, the labial palpus and mandibular
palpus sensilla placodea were distributed on the outer side of the
terminal segment.

Females had significantly more SP than males in both labial palps (\selectlanguage{english} =
17.00 +- 0.32, \selectlanguage{english} = 12.80 +- 0.58, \emph{t} = 6.33, \emph{P} \textless{}
0.01) (Fig. 2), but the length of the SP of the labial palpus was
significantly longer in males than in females (Table 4).

\textbf{Sensilla coeloconica}

Sensilla coeloconica (SC) are found mainly at the top of the terminal
segments of the labial palpus of adults, scattered and interspersed
along the outer edges of the terminal conical sensor group. The shape of
the sensor is elevated to form a chamber, with a raised and ruffled
surface (Fig. 4).

\textbf{Sensilla campaniformia}

Sensilla campaniformia (SCa) are more common on the labial palpus and
mandibular palpus of insects of the family Araneae and are named after
their bell-shaped appearance. The sensor consists of a broad basal fossa
and a rounded, blunt projection with a smooth epidermal wall and is
found mainly on the terminal segments of the labial palpus and
mandibular palpus of adults.

There is clear male and female dimorphism in the morphological
characteristics of the insect. The basal width of the SCa was
significantly greater in females than in males (Table 4), and the number
of SCa (\selectlanguage{english} = 29.40 +- 2.52, \selectlanguage{english} = 19.20 +- 1.07, \emph{t} = 3.73,
\emph{P}\textless{} 0.05) was significantly greater in females than in
males (Fig. 3).

\textbf{3.2.3 Mandibular palpus}

The mandibular palps of \emph{G. cantor} also have a rich variety of
sensor types, with no difference between male and female sensor types
but some variation in the number of sensors (Fig. 5). The sensor species
on mandibular palps can also be divided into seven main groups (11
subtypes): sensilla chaetica, sensilla twig basiconica, Bohm's bristle
sensor (Bb), sensilla trichodea (ST II), sensilla plate (SP), sensilla
coeloconica (SC) and sensilla campaniformia (SCa) (Table 5).

Table 5 The morphological characteristics of sensilla on mandibular
palpus of both sexes in \emph{G. cantor}\selectlanguage{english}
\begin{longtable}[]{@{}llllllll@{}}
\toprule
Type & Subtype & Sex & Length (\selectlanguage{greek}μ\selectlanguage{english}m) & Width (\selectlanguage{greek}μ\selectlanguage{english}m) & Morphological
character & Morphological character & Morphological
character\tabularnewline
& & & & & Wall & Basal & Tip\tabularnewline
Sensillia Twig Basiconica & STB I &  & 2.26 \selectlanguage{ngerman}± 0.10 & 2.04 \selectlanguage{ngerman}± 0.04 & Flat
blunt cavity & None & Smooth\tabularnewline
& &  & 2.33 \selectlanguage{ngerman}± 0.10 & 1.96 \selectlanguage{ngerman}± 0.05 & & &\tabularnewline
& STB II &  & 2.35 \selectlanguage{ngerman}± 0.13 & 1.74 \selectlanguage{ngerman}± 0.08 & Rounded blunt projection &
None & Smooth\tabularnewline
& &  & 2.69 \selectlanguage{ngerman}± 0.14 & 1.60 \selectlanguage{ngerman}± 0.06 & & &\tabularnewline
& STB III &  & 2.42 \selectlanguage{ngerman}± 0.16 & 1.89 \selectlanguage{ngerman}± 0.10 & Finger-shaped protrusions &
None & Smooth\tabularnewline
& &  & 2.63 \selectlanguage{ngerman}± 0.13 & 2.01 \selectlanguage{ngerman}± 0.10 & & &\tabularnewline
& STB IV &  & 3.21 \selectlanguage{ngerman}± 0.10* & 2.28 \selectlanguage{ngerman}± 0.12 & Rounded blunt & None &
Smooth\tabularnewline
& &  & 2.62 \selectlanguage{ngerman}± 0.08 & 1.71 \selectlanguage{ngerman}± 0.10 & & &\tabularnewline
Sensilla Chaetica & SCh IV &  & 50.24 \selectlanguage{ngerman}± 1.57* & 2.99 \selectlanguage{ngerman}± 0.13 & Sharp
pointed & dense & V-shaped\tabularnewline
& &  & 42.56 \selectlanguage{ngerman}± 1.07 & 3.46 \selectlanguage{ngerman}± 0.14 & & &\tabularnewline
& SCh V &  & 226.98 \selectlanguage{ngerman}± 12.67* & 7.40 \selectlanguage{ngerman}± 0.26 & Sharp pointed & dense &
V-shaped\tabularnewline
& &  & 81.31 \selectlanguage{ngerman}± 4.93 & 3.29 \selectlanguage{ngerman}± 0.09 & & &\tabularnewline
B\selectlanguage{ngerman}öhm bristles & Bb &  & 8.62 \selectlanguage{ngerman}± 0.96 & 2.49 \selectlanguage{ngerman}± 0.07* & Sharp pointed &
Loose & Smooth\tabularnewline
& &  & 8.46 \selectlanguage{ngerman}± 0.58 & 1.92 \selectlanguage{ngerman}± 0.07 & & &\tabularnewline
Sensilla Trichodea & ST II &  & 37.19 \selectlanguage{ngerman}± 4.09 & 2.84 \selectlanguage{ngerman}± 0.18 & Blunt &
Loose & V-shaped\tabularnewline
& &  & 50.68 \selectlanguage{ngerman}± 3.85* & 3.04 \selectlanguage{ngerman}± 0.09 & & &\tabularnewline
Sensilla Plate & SP &  & 29.39 \selectlanguage{ngerman}± 0.84 & 2.65 \selectlanguage{ngerman}± 0.14* & Board shape &
Loose & Smooth\tabularnewline
& &  & 30.75 \selectlanguage{ngerman}± 0.76 & 1.27 \selectlanguage{ngerman}± 0.05 & & &\tabularnewline
Sensilla Coeloconica & SC &  & ------ & 0.35 \selectlanguage{ngerman}± 0.02 & Hole cavity &
None & Folded\tabularnewline
& &  & ------ & 0.45 \selectlanguage{ngerman}± 0.02* & & &\tabularnewline
Sensilla Campaniformia & SCa &  & ------ & 2.60 \selectlanguage{ngerman}± 0.13* & Rounded blunt
protrusion & loose & Smooth\tabularnewline
& &  & ------ & 1.95 \selectlanguage{ngerman}± 0.13 & & &\tabularnewline
\bottomrule
\end{longtable}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image5/image5}

\end{center}
\end{figure}

Fig. 5 Numbers and distributions of sensilla on mandibular palpus of
both sexes of \emph{G. cantor}

\textbf{Sensillia twig basiconica}

Similar to the labial palps, sensilla twig basiconica (STB) also occur
only at the apical end of adult mandibular palps and can also be divided
into four subtypes (STB I, STB II, STB III, and STB IV). The shape of
these sensors varies markedly between subtypes (Fig. 6).

The terminal tapered inductor of the mandibular palpus showed little
overall difference in external morphological features, but females
likewise differed significantly from males in the length of STB IV
(\emph{t} = 4.54, \emph{P} \textless{} 0.01). In terms of number, STB I
(\emph{t} = -5.62, \emph{P} \textless{} 0.01) were more numerous in
males than females, while females had significantly more STB IV
(\emph{t} = 2.63, \emph{P} \textless{} 0.05) than males.

\par\null\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image6/image6}

\end{center}
\end{figure}

Fig. 6 The ultrastructure of mandibular palpus of both sexes of \emph{G.
cantor}

A, mandibular palpus of female beetle; B, Sensilla on 4th of mandibular
palpus of female beetle; C, Sensilla styloconica on 4th of labial palpus
of female beetle; D, mandibular palpus of male beetle; E, Sensilla on
4th of mandibular palpus of male beetle; F, Sensilla styloconica on
mandibular palpus of male beetle Scale bars: A, D = 500 \selectlanguage{greek}μ\selectlanguage{english}m, B, C, E, F =
50 \selectlanguage{greek}μ\selectlanguage{english}m.

\textbf{Sensilla chaetica}

The sensilla chaetica of the adult mandibular palpus has two subtypes
(SCh IV, SCh V). SCh IV is found on segments 2, 3 and 4 of the
mandibular palpus, while SCh V is found on segments 2 and 3 of the
mandibular palpus. These two inductor subtypes differ considerably in
length and basal width (Table 5).

The lengths of SCh V and SCh IV of the female mandibular palpus were
both longer than those of the males, but there were no significant
differences in width. Quantitatively, females outnumbered males only in
SCh IV ( = 226.98 \selectlanguage{ngerman}± 12.67 \selectlanguage{greek}μ\selectlanguage{english}m,  = 81.31 \selectlanguage{ngerman}± 4.93 \selectlanguage{greek}μ\selectlanguage{english}m, \emph{t} =
10.71,\emph{P} \textless{} 0.01) in segment 4 of the mandibular palpus,
whereas males outnumbered females in SCh IV ( = 321.60 \selectlanguage{ngerman}± 1.21, \selectlanguage{english} =
24.60 +- 1.47, \emph{t} = 7.58, \emph{P} \textless{} 0.01), and SCh V (\selectlanguage{english}
= 22.00 +- 2.79, \selectlanguage{english} = 48.60 +- 4.12, \emph{t} = -5.35, \emph{P} \textless{}
0.01) were significantly more numerous in males than in females, and SCh
IV (\selectlanguage{english} = 193.60 +- 6.52, \selectlanguage{english} = 226.60 +- 5.84, \emph{t} = -3.77,
\emph{P}\textless{} 0.05) and SCh V (\selectlanguage{english} = 14.80 +- 3.38, \selectlanguage{english} = 31.60 +-
1.44,\emph{t} = -4.57, \emph{P} \textless{} 0.01) in segment 3 of the
mandibular palpus were significantly more numerous in males than in
females. Bohm's bristle sensor (Bb) also occurred at the junction of the
base of the first segment with the mouthparts. There were no significant
numerical differences in Bb between males and females in the labial
palpus and mandibular palpus as a whole (Fig. 5).

\textbf{Bohm bristles}

The Bohm's bristle sensor (Bb) also founded that it just exists at the
junction of the base of the 1st segment with the mouthparts.There were
no significant numerical differences between males and females in the
labial papuls and mandibular papuls as a whole (Figs. 5). The overall
variability in morphological characters was also not significant, except
for the presence of a significantly wider Bb base width (\selectlanguage{english} = 2.49 +- 0.07
\selectlanguage{greek}μ\selectlanguage{english}m,  = 1.92 \selectlanguage{ngerman}± 0.07 \selectlanguage{greek}μ\selectlanguage{english}m, \emph{t} = 5.81, \emph{P} \textless{} 0.01) in
the mandibular palpus of females than males (Tables 5).

\textbf{Sensilla trichodea}

Sensilla trichodea also occur in a small number in adult mandibular
palps but only in one subtype, ST II. The length of female mandibular
palpus ST II was significantly greater than that of males; female
mandibular palpus segment 2 ( = 15.40 \selectlanguage{ngerman}± 0.81, \selectlanguage{english} = 7.80 +- 0.66,
\emph{t}= 7.25, \emph{P} \textless{} 0.01), segment 3 (\selectlanguage{english} = 25.40 +- 1.50,
\selectlanguage{english} = 7.80 +- 0.37, \emph{t} = 11.36, \emph{P} \textless{} 0.01) and
segment 4 (\selectlanguage{english} = 53.80 +- 7.45, \selectlanguage{english} = 17.60 +- 0.68, \emph{t} = 4.84,
\emph{P}\textless{} 0.01) were significantly more numerous in ST II
(Fig. 5).

\textbf{Sensilla placodea}

In the mandibular palpus, the SP (\selectlanguage{english} = 2.65 +- 0.14 \selectlanguage{greek}μ\selectlanguage{english}m,  = 1.27 \selectlanguage{ngerman}± 0.05
\selectlanguage{greek}μ\selectlanguage{english}m, \emph{t} = 9.20, \emph{P} \textless{} 0.01) was significantly wider
basally in females than in males. The basal width of the SP of the
mandibular palpus was significantly wider in females than in males, but
the length of the SP of the labial palpus was significantly longer in
males than in females (Table 5). The number of SP in females was much
greater than that in males in the mandibular palpus ( = 21.20 \selectlanguage{ngerman}± 1.02, \selectlanguage{english}
= 12.40 +- 0.24, \emph{t} = 8.39, \emph{P} \textless{} 0.01) (Figs. 3).

\textbf{Sensilla coeloconica}

Sensilla coeloconica (SC) also mainly occurred at the top of the
terminal segments of the mandibular palpus of adults (Fig. 6).

\textbf{Sensilla campaniformia}

Both the basal width and the number of SCa in the mandibular palpus were
significantly greater in females than in males (Table 5). SCa in the
mandible palpus in females were all significantly more numerous than in
males (\selectlanguage{english} = 82.60 +- 1.17, \selectlanguage{english} = 13.20 +- 1.07, \emph{t} = 43.89,
\emph{P}\textless{} 0.01) (Figs. 5).

\textbf{4 DISCUSSION}

As largely consistent with reports for other pests, the olfactory system
of \emph{G. cantor} is also an ideal target for pest control (Wu et al.,
2022). In this study, by analyzing the oral appendages of \emph{G.
cantor} with scanning electronic microscopy, we found several
significant differences between males and females. On the one hand, in
the gross morphology of the mandible, we found that the length and basal
width of the mandibles of females were significantly more developed than
those of males, but there was no significant difference in basal
thickness. This suggests that the functional differences between the
ossified parts of the mandible of males and females are mainly the depth
of groove production and have little effect on their shared feeding
behavior. This is because the palate of females is involved in the
grooving process and has a greater demand for mechanical sensing,
especially for sensing the force required by the palate during the
grooving process, so it is related to the sex difference in basal width
and length. This has also been reported in insects such as the desert
locust \emph{Schistocerca gregaria} Forskal (Katel et al., 2021), in
which the mandible participates in the grooving process, and there are
some behavioral differences between males and females. On the other
hand, in the ultrastructural morphology of the mandible, we found that
the number of ST I in the female mandible was significantly higher than
that in the male mandible. As an olfactory sensor, ST I can help females
identify and confirm oviposition grooving more quickly through its
olfactory in addition to feeding function. This result indicated that
this olfactory sensor could help females recognize more chemical odors,
which is consistent with the results of previous studies on other
insects (Dong et al., 2020).

In addition, the oral appendages of adult \emph{G. cantor} (labial
palpus and mandibular palpus) are mainly involved in host selection,
oviposition, mating and other behaviors (Zhang et al., 2018; Hall et
al., 2019). In the gross morphology of the labial palpus and mandibular
palpus, we also found that there was obvious dimorphism, which is
consistent with \emph{Aphis gossypii} Glover and \emph{Diaphorina citri}
Kuwayama \selectlanguage{english}(Ettay et al.\selectlanguage{english},2001\selectlanguage{english};Bento et al.\selectlanguage{english},2017\selectlanguage{english}), especially in terms
of length. Each subsegment and overall length showed obvious
differences, and only the basal width of the fourth segment of
mandibular palps did not show significant sex differences. This is
related to the dominant role of labial and mandibular papillae in female
oviposition.

It is worth mentioning that our results on the ultrastructural
morphology of the labial palpus and mandibular palpus also confirmed
this conjecture, and we found that the SCh V, SCh IV and Bb of female
beetles are more developed than those of male beetles. A large number of
studies have shown that the main function of the SCh is to focus on
force and vibration induction, and the sex difference in the Bb
in\emph{G. cantor} is mainly related to its function of sensing the
position and movement frequency of labial and mandibular cumulus hair
during oviposition (Sun et al., 2011). Therefore, we hypothesized that
this was because \emph{G. cantor} needs more developed mechanical
sensors to detect the vibration frequency and force of the oral
appendages in the process of oviposition localization and recognition.
Other sensilla showing female superiority mainly distributed in the
labial and mandibular palpus of \emph{G. cantor} also include ST II, STB
IV, SC, SP and SCa. The functions of ST II have been confirmed in at
least two different types of olfactory sensilla cells in the antennae of
male cotton bollworms (Lopes et al., 2002; Dong et al., 2020). Similar
functions of this sensor have also been confirmed in our study of the
labial palpus and mandibular palpus of \emph{G. cantor} . Moreover, some
studies have shown that STB IV in \emph{Liriomyza sativae} Blanchard is
a kind of contact chemosensory apparatus and has taste function (Zhang
et al., 2017). Based on this, we conducted a further investigation and
found that STB IV shows female superiority in external morphology and
quantity both in the labial palpus and mandibular palpus of \emph{G.
cantor.} In addition, SC, SP and SCa have been reported in a variety of
insects, such as \emph{Dyseriocrania subpurpurella} and \emph{Pissodes
yunnanensis} (Faucheux et al., 2008), showing that the main functions
are carbon dioxide sensing and temperature and humidity sensing. We
found that these functions also apply to the reproductive behavior
of\emph{G. cantor} because the oviposition process is highly complex,
which requires the female to be sensitive to the appropriate
temperature, humidity and carbon dioxide concentration in the
environment, which is also in line with their relatively developed
results in females.

In summary, the present study investigated the external morphology of
the sensillum types of the oral appendages of \emph{G. cantor} using
scanning electron microscopy to contribute to a better understanding of
host selection and courtship behavior in \emph{G. cantor} and to future
studies linking these behaviors to electrophysiological mechanisms. The
observed differences in sensillum distribution and function will greatly
facilitate the design of more effective standardized control methods
against this pest.

\textbf{5 CONCLUSION}

We investigated, by means SEM, the external morphology and distribution
of the oral appendages of \emph{G. cantor} . We find that the gross
morphology and ultrastructural morphology of mandible, labial and
mandibular palpus are significantly different between sexes of \emph{G.
cantor} using scanning electron microscopy. Observation of the gross
morphology of the mandible, labial palpus and mandibular palpus revealed
that their lengths were significantly greater in females. In terms of
the ultrastructural morphology of the mandibles, females have
significantly more ST I and SCh III on their mandibles than males. The
mechanical sensors SCh and Bb, olfactory sensor ST II, taste sensor STB
IV, and carbon dioxide sensor and temperature and humidity sensors SC,
SP and SCa were significantly more developed on female than male labial
and maxillary palps. These play an important role in reproductive
behavior to provide new insights for the pest control and forest
protection.

\textbf{AUTHOR CONTRIBUTION}

Yao Wu: Conceptualization, Methodology, Data curation , Investigation,
Validation, Formal analysis, Writing - original draft; Zhixin Li:
Software; Liangshan Ming: Validation; Zhongyan Huang: Software,
Resources; Gaochuan Zhang: Visualization; Wen Lu: Supervision, Writing -
review \& editing; Hongning Liu: Project administration, Writing -
review \& editing; Zishu Dong: Conceptualization, Methodology, Data
curation , Funding acquisition, Project administration, Resources,
Writing - original draft, Conceptualization, Methodology, Data curation
, Funding acquisition, Project administration, Resources, Writing -
original draft

\textbf{ACKNOWLEDGEMENT}

This research was supported by Jiangxi University of Chinese Medicine
Science and Technology Innovation Team Development Program (CXTD22007).
The Science and Technology Project of Education Department of Jiangxi
Province of China (No. GJJ211271). The Science and Technology Project of
Jiangxi Provincial Health Commission (No. 202311135).

\textbf{DISCLOSURE STATEMENT}

The authors declare no conflict of interest. The authors alone are
responsible for the content and writing of the paper.

\textbf{ORCID}

Yao Wu iD http://orcid.org/0000-0002-5413-4333

Zishu Dong iD http://orcid.org/0000-0002-4194-3422

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