Morphology and distribution of antennal sensilla on Spodoptera frugiperda (Lepidoptera: Noctuidae) larvae and adults

Abstract The fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) is an important and devastating insect pest feeding on extensive species of plants and causing serious economic losses in crops worldwide. The antennal sensilla of insect adults and larvae play an important role in the recognition and perception of plant odors and chemical pheromones. In this study, the antennal morphology, and sensilla types on the antennae of both FAW larvae and adults were examined using an optical microscope and scanning electron microscope. The results showed that FAW larval antennae possessed smell pores, sensilla pegs, and 5 types of antennal sensilla, i.e., sensilla trichodea I and II, sensilla basiconica I and II, sensilla chaetica, sensilla cavity

The fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) is an important and devastating insect pest feeding on extensive species of plants and causing serious economic losses in crops worldwide. The antennal sensilla of insect adults and larvae play an important role in the recognition and perception of plant odors and chemical pheromones. In this study, the antennal morphology, and sensilla types on the antennae of both FAW larvae and adults were examined using an optical microscope and scanning electron microscope. The results showed that FAW larval antennae possessed smell pores, sensilla pegs, and 5 types of antennal sensilla, i.e., sensilla trichodea I and II, sensilla basiconica I and II, sensilla chaetica, sensilla cavity, and sensilla styloconicum. Among them, smell pores and sensilla cavity were first identified in Lepidoptera larvae. The size of the antennal sensilla on 5th-instar larvae was significantly larger than those of 3rd-instar larvae. The antennae of FAW adults were thread-like and the flagellum consisted of 69-73 subsegments. The adult antennae were covered by imbricate scales and most sensilla were on the ventral side of the flagellum. There were smell pores and 12 types of sensilla were identified on adult antennae, i.e., sensilla trichodea, sensilla basicaonica, sensilla auricillica, sensilla cavity, sensilla placodea, sensilla ligulate, Böhm bristles, sensilla chaetica, sensilla squamous, sensilla coeloconica, sensilla styloconicum, and sensilla uniporous peg. Among them, sensilla uniporous peg were only distributed in females. Sensilla cavity, sensilla placodea, sensilla ligulate, sensilla uniporous peg, and smell pores were first identified in FAW adults. To further explore the host location mechanism and courtship behavior of FAW, the possible functions of these antennal sensilla were also discussed. The present work not only provides valuable information for a comprehensive understanding of the type and function of antennal sensilla in FAW, but also assists the development of novel pest control strategies such as pest behavior control technology for the prevention of this invasive pest.

Introduction
The fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), originated in America, is a major migratory pest with strong fecundity, high migration ability, a wide range of hosts, and great difficulty in control (Montezano et al., 2018). In China, FAW is first found in Yunnan Province in January 2019, and by October 2019, it has already spread to 26 Chinese provinces (R. L. Wang et al., 2020). Due to its widespread occurrence, serious damage, difficult prevention, and social concern, FAW has been listed in Category One List of Crop Diseases and Pests in China by the Ministry of Agriculture and Rural Affairs of China (https://www.moa.gov.cn/govpublic/ZZYGLS/202009/t20200917 6352227.htm). In China, FAW adults possibly move northward via seasonal monsoons in spring and summer to enter wheat, corn, and other major crop production areas along the Yangtze River Basin, the Yellow River Basin, and the northeast region of China (Wu, 2020). Therefore, in addition to feeding on corn, FAW is posing a serious threat to potential economic losses to other staple crops such as wheat, soybean, cabbage, and tomato (W. W. Wang et al., 2020) It is well known that the olfactory system plays an important role in the process of host location and the antenna is the most important olfactory organ for perceiving odors (Cardoso & Linardi, 2006;Rebora, Piersanti, & Gaino, 2008). Insect antennae generally have a variety of sensilla, which play an important role in various behaviors such as foraging, courtship, and oviposition (Cardoso & Linardi, 2006;Rebora et al., 2008). There are lots of studies describing the antennal sensilla of various insect species, for example, Earias vittella (Rani et al., 2021), Glenea cantor (Dong, Yang, et al., 2020), Allotraeus asiaticus , andCallidiellum villosulum (Dong, Dou, et al., 2020). In Lepidoptera insects, the research on antennal sensilla of adults is far more than that of larvae, which may be related to the task of population reproduction undertaken by adults (L. Y. Ma, Hu, Li, Liu, & Yuan, 2019;Sun, Wang, & Zhang, 2011). As an important invasive pest in the world, the study on the antennal sensilla of FAW has also attracted the attention of some scholars (Ge et al., 2019;Lei et al., 2021;Tian, Huang, Wang, Zhang, & Li, 2020). However, several types and nomenclatures of FAW sensilla are conflicting among researchers, and are inconsistent with the antennal sensilla of other Lepidoptera insects reported. For instance, the morphological characteristics of the sensilla chaetica of FAW named by Lei et al. (2021) and the same sensilla named by Tian et al. (2020) are completely different. These maybe seriously affect the subsequent studies on the sensilla function as well as academic communications. Therefore, in this study, we used optical and scanning electron microscopy to observe the antennal sensilla of 3rd (Represented the younger larvae) and 5th (Represented the older larvae) instar larvae (L3 and L5) as well as adults of FAW in detail. We also investigated whether the type and size of sensory types of L3 and L5 changed with instars. Moreover, we also discussed the potential function of antennal sensilla of FAW that may be involved in host localization and host receptive behavior. The present work not only provides valuable information for a comprehensive understanding of the type and function of antennal sensilla in FAW larvae and adults, but also assists the development of novel pest control strategies such as pest behavior control technology for the prevention of this invasive pest.

Insect culture
In July 2019, about 10 FAW egg masses were collected from a maize field in Yangling, Shaanxi Province, China. All egg masses were incubated at 25, and about 100 newly hatched neonate larvae were raised separately with maize leaves in plastic boxes (4x3x3 cm) in an artificial climate greenhouse (26+-1, 60%+-5% RH, a photoperiod of 14L:10D). Maize seeds (Shaandan 636) were purchased from Yangling Nongcheng Seed Supplement Company (Yangling, China), and sown in plastic pots (10x15 cm) with a 3:1:1 mixture of commercial peat moss (Pindstrup Mosebrug A/S, Ryomgaard, Denmark), perlite and vermiculite in the same climate room. The maize seedlings of 14 days old were used in the experiments.

Statistical analysis
The differences in the length or width of antennae between female and male adults, and the size of antennal sensilla between third and fifth instar larvae of FAW were analyzed by t-test. The experimental data were analyzed using the package SPSS Statistics 28.0 (IBM, USA).

Sensilla trichodea (ST)
Sensilla trichodea was like hair with a slender shape. Its base fit into a socket slightly elevated above the cuticle, and gradually became thinner to the tip with a smooth surface (Fig. 2C). The ST had two subtypes: sensilla trichodea I (ST I) and sensilla trichodea II (ST II). The ST I was blunter and more curved than ST II. The lengths of ST I (t = 29.421,df = 28, p < 0.0001) and ST II (t = 11.915, df = 28, p < 0.0001) in L5 were significantly greater than that of L3 (Table 1).

Sensilla basiconica (SB)
Sensilla basiconica was erected on the top surface of the antennae. Its base was thicker and the tip was blunter. The outer wall of SB had longitudinal lines (Fig. 2F) and smell pores (Fig. 2B, 2E). The SB included two subtypes, i.e., sensilla basiconica I (SB I) and sensilla basiconica II (SB II). The pedicel had 2 SB I (Fig. 2C), and the flagellum had 1 SB I and 1 SB II (Fig. 2B). The length of SB I of L5 was significantly greater than that of L3 (t = 3.976,df = 28, p = 0.0004), while there was no significant difference in length of SB II between L5 and L3 (t = 1.643,df = 28, p = 0.1114) ( Table 1).

Sensilla chaetica (SCh)
There were 2 SCh, erected on the top surface of the antenna, and the base of SCh was thicker and without a basal socket. The tip of SCh was sharper than SB II (Fig. 2B, 2D). The length of SCh in L5 was significantly longer than that of L3 (t = 2.859, df = 28,p = 0.0079) ( Table 1).

Sensilla styloconicum (SSt)
The antennae of FAW larvae only had 1 SSt with a smooth surface. The base of SSt was thicker and erected on the antennal top surface, and its tip was sharper and a little curved (Fig. 2B, 2E). The basal column height (t = 2.062, df = 28, p = 0.0486) and peg height (t = 3.009, df = 28, p = 0.0055) of SSt in L5 was significantly longer than that of L3 (Table 1).

Sensilla cavity (SCa)
The cuticle around the SCa was sunken, and the center of SCa bulged like a mound with longitudinal lines on the surface ( Fig. 2A, 2F). The diameter of SCa in L5 was significantly greater than that of L3 (t = 17.065, df = 28, p< 0.0001) ( Table 1).  The data are mean ± SE. * indicates a significant difference between third-instar and fifth-instar larvae (p < 0.05). The data are collected from 15 samples.

General description of antennae of FAW adults
The antennae of both male and female adults were thread-like, consisting of the scape, pedicel, and flagellum ( Fig. 3A). The scape was thick and short, and the pedicel was thinner and shorter than the scape (Fig. 3B).
The flagellum was long and thin, consisting of 69-73 subsegments (Fig. 3B, 3C). The antennae of males were slightly longer than that of females, but there was no significant difference (t = 1.069,df = 28, p = 0.2940) ( Table 2). The antennal dorsal surface was covered with imbricate scales. The subsegments of flagellum were covered by two rows of scales (Fig. 3C, 3D).  The data are mean ± SE. The data are collected from 15 samples.
3.4 The antennal sensilla type and distribution of Spodoptera frugiperda adults The antennae of FAW adults had smell pores and 12 types of sensilla, i.e., sensilla trichodea, sensilla basicaonica, sensilla auricillica, sensilla cavity, sensilla placodea, sensilla ligulate, Böhm bristles, sensilla chaetica, sensilla squamous, sensilla coeloconica, sensilla styloconicum, and sensilla uniporous peg. Most of the sensilla were distributed on the ventral surface of the antenna, and only SCh and sensilla squamous were distributed on the dorsal scale (Fig. 3D). The end of the flagellum had more amount of SCh, and there was 1 specialized SSt on the tip of the flagellum (Fig. 3E, 3F).

Böhm bristles (BB)
Böhm bristles were distributed on both bilateral sides of the scape and the base of the pedicel (Fig. 4A).
The BB was spiny with a smooth and non-porous surface, and its base was thicker and tapered to the tip. According to the length and the basal socket, The BB was divided into two subtypes: BB I and BB II (Fig.  4B). The thick and long BB I inserted a socket slightly above the antennal cuticle. The length of BB I in females was significantly longer than that of male adults (t = -2.762, df = 28, p< 0.0001). The basal diameter of BB I between female and male adults had no significant difference (t = -1.611, df = 28,p = 0.1183). BB II was more numerous and distributed in clusters around BB I. The short and thin BB II had no socket at the base. There was no significant difference in the length of BB II between female and male adults (t = 0.076, df = 28, p = 0.9399) ( Table 3).

Sensilla trichodea (ST)
Sensilla trichodea was borne in the basal socket with a hair-like shape, and was the most abundant and widely distributed on the lateral and ventral sides of the flagellum. The base of ST was thicker and the tip was blunt round (Fig. 4C). The basal surface of ST had thicker longitudinal lines, with spiral lines above the base. The ST surfaces had small, shallow pores evenly borne between lines (Fig. 4D). There was a thick-walled hollow structure inside ST (Fig. 4E). The length (t = -0.399, df = 28, p = 0.6931) and basal diameter (t = -1.576, df = 28, p = 0.1262) of ST between female and male adults were no significantly different (Table 3).

Sensilla basiconica (SB)
Sensilla basiconica had a cone-shaped structure, dispersedly distributed on the flagellum, protruding from a circular socket, and had a clear gap with the edges of the socket. The near base of SB shrank slightly and became thicker, and the end was blunt round. There were longitudinal lines on the surface of SB, and a row of dense small holes was visible between the longitudinal lines (Fig. 4F). The length of SB between female and male adults had no significant difference (t = -0.503, df = 28, p = 0.619). The diameter of the circular socket in males was significantly larger than that of females (t= 2.643, df = 28, p = 0.0133) ( Table 3).

Sensilla chaetica (SCh)
The SCh was straight and had a spine-like tip, with longitudinal lines on the surface and a socket at the base. Both females and males had 6 SCh evenly surrounding each flagellum subsegment (Fig. 4H, 5A), and the end flagellum subsegment had 12 SCh (possibly 2 subsegments fused into 1) (Fig. 3E). The angle between SCh and the antennal surface was greater than those of other sensilla (Fig. 4G). The sensilla length of males was significantly larger than that of the females (t = -4.103,df = 28, p < 0.0003) ( Table 3).

Sensilla coeloconica (SCo)
The SCo was shaped like a daisy, and each subsegment of flagellum was distributed with 2-6 SCo (Fig.  5A). The SCo was a shallow circular cavity formed by the inward depression of the antennal surface, and the cavity center had a vertical sensory cone with a blunt round tip that protruded out of the epidermal depression. There were 11-13 petal-shaped marginal pegs around the cavity, and the marginal pegs bent toward the central pegs in a semilunar shape. There were longitudinal lines on the surface of all the marginal pegs and sensory cones (Fig. 4I). The sensilla cavity diameters of females and males were no significantly different (t = -0.817, df = 28, p= 0.4208) ( Table 3). Sensilla styloconicum was also called the cylinder sensilla, and distributed on the edge of the end of the subsegment of the flagellum, extending from the former to the latter (Fig. 5A). The tip of the end flagellum subsegment had 1 SSt (Fig. 3E, 3F). The shape of SSt was similar to a thumb. The base was cylindrical with raised pleated mesh-like structure, and the tip was thick with a small cavity on the top, and 1-3 small papillary bulges in the cavity. There was a constriction on the middle surface of SSt (Fig. 5B, 5C). The sensilla height of males was significantly larger than that of the females (t = -4.619, df = 28, p < 0.0001) ( Table 3).

Sensilla cavity (SCa)
Sensilla cavity was less distributed on the flagellum, and its surface was sunken to form a cavity. The base of SCa was mound-shaped and the middle surface has lines (Fig. 5D). The sensilla diameters between females and males were no significant difference (t = -0.188,df = 28, p = 0.8522) ( Table 3).

Sensilla squamous (SSq)
Sensilla squamous was distributed in whole antennae (Fig. 5E). The SSq was similar to the scale, but thinner and longer than the scale, with a socket at the base. The surface of SSq had 5-7 parallel longitudinal ridges, and there were evenly distributed discontinuities on each longitudinal ridge. The length (t = -1.417, df = 28,p = 0.1675) and basal diameter (t = 1.388, df = 28,p = 0.1760) of SSq between females and males were no significantly different (Table 3). Moreover, there were smell pores distributed around the SSq (Fig. 5E).
3.4.9 Sensilla auricillica (SA) Sensilla auricillica was scattered in the middle and posterior of the subsegment of the flagellum near the inner scale site, generally 1-2 SA per subsegment (Fig. 5A). The shape of SA was similar to an outward curling scale, the base was inserted in a socket shaped nest, the end was in the shape of a bell mouth, and the surface had a longitudinal pattern (Fig. 5F). The sensilla length between females and males was no significant difference (t = -1.840, df = 28, p = 0.0763) ( Table 3).

Sensilla ligulate (SL)
Sensilla ligulate was distributed on the ventral surface of the antennae and curved towards the antenna surface (Fig. 5G). The SL had small pores and grooves on the surface. The base of SL was embedded in a socket, and gradually became thinner from the base to the end, and the end was blunt. The sensilla length of females was significantly larger than that of the males (t = 2.319, df = 28, p = 0.0279). There was no significantly different between the basal diameters of females and males (t = 1.495, df = 28, p = 0.1461) ( Table 3).

Sensilla uniporous peg (SU)
Sensilla uniporous peg was only distributed on the subsegments of the female flagellum, and there were 2-6 SU on each subsegment. The SU was papillate and embedded in deep socket. The base of SU was enlarged, with a small hole at the end, and there were longitudinal notches around the hole (Fig. 5H). The SU peg was the smallest type of sensilla in FAW (Table 3).

Sensilla placodea (SPl)
Sensilla placodea was located in the sensilla fossa formed by the epidermal depression, which was long and oval in shape, with longitudinal lines and small holes on the surface. The width of SPl from the base to the end was basically the same, and the end was blunt round (Fig. 5I). The length (t = -1.948, df = 28, p = 0.0615), basal diameter (t = 0.503, df = 28, p = 0.6186) and width (t = -1.226, df = 28, p = 0.2304) of SPl between females and males were no significant difference (Table 3).   The data are mean ± SE. * indicates a significant difference between females and males (p < 0.05). The data are collected from 15 sensilla samples.

Discussion
The antennae are important organs for insects to perceive changes in the environment and regulate their behavior, for example, recognizing plant odors, pheromones, and other substances through the sensilla borne on them (Ronderos & Smith, 2009). In this study, scanning electron microscopy was used to observe the ultrastructure of larvae and adult antennae of FAW, and the results showed that the larvae of FAW had sensilla pegs, smell pores, and 5 types of sensilla. Among them, smell pores and sensilla cavity were reported for the first time in Lepidoptera larvae. FAW adult antennae possessed smell pores and 12 types of sensilla. Among them, sensilla uniporous peg were only distributed on the flagellum of FAW females. Moreover, sensilla cavity, sensilla uniporous peg, sensilla ligulate sensilla placodea, and smell pores were firstly found in FAW adults. In general, the antennal sensilla of insect adults is more than that of larvae because adults need to complete more complex feeding, mating, oviposition, and other behaviors (Li, Xiao, Liu, Yin, & Liu, 2018;Liu, 2021).
Lepidopteran larvae mainly use the head sensilla to select host plants and then complete feeding activities (Li et al., 2018;Xu, Pei, Wang, Ren, & Zong, 2017). Our results showed that the sensilla of FAW larvae were concentrated on the pedicel and flagellum of the antennae, and the sensilla trichodea, sensilla chaetica, and sensilla basiconica were the most widely distributed sensilla types. The results are consistent with the findings of Zhang et al. (2019) in Spodoptera lituralarvae and Qin et al. , (2020) in Ectropis grisescenslarvae. Furthermore, we found smell pores and sensilla cavity on FAW larval antennae, which have not been reported in Lepidoptera larvae. Smell pores have chemosensory functions in Hymenoptera (Ahmed, Zhang, Wang, He, & Bai, 2013), but their function in Lepidoptera insects is not clear. Lepidopteran larvae rely on sensilla trichodea of mandibles and maxillae sensing mechanical stimuli to determine the type and nature of the food (Dey, Singh, & Chakraborty, 2011). Xu et al. (2017) reported that sensilla styloconicum on the maxillary palp of Cossidae larvae can be used in gustatory perception. Albert (2003) confirmed that sensilla basiconica on the maxillary palp ofChoristoneura fumiferana larvae can be used as detectors and receivers of odor substances. Paul et al. (2016) proposed that multiporous sensilla chaetica on mandibles of Antheraea assamensis can perceive chemical stimuli, whereas this sensillum on FAW larval antennae is nonporous. The specific functions of these sensilla in FAW larvae need further study.
Lepidoptera adults can sense external stimuli through olfactory and tactile sensilla, thus sensilla play an important role in the selection of host plants and reproduction (Ansebo et al., 2005;Isidoro, Bartlet, Ziesmann, & Williams, 1998). According to the physiological functions, insect sensilla can be divided into chemoreceptors, mechanoreceptors, thermo-, and hygroreceptors. Chemoreceptors such as olfactory and tactile sensilla play a key role in finding habitat and mates (Ruschioni et al., 2015). The surface of sensilla trichodea possesses small, shallow pores, which give play to olfactory function (Binyameen et al., 2012;Roh, Park, Oh, & Park, 2016). Sensilla basiconica has many pores on its surface, indicating that they are a class of olfactory sensilla (Binyameen et al., 2012). Sensilla auricillica may play an important role in the host localization of female moths in Scoliopteryx libatrix (Anderson, Hallberg, & Subchev, 2000;Ansebo et al., 2005). Sensilla placodea is reported on the antennae of Coleophora obducta with having a gustatory function (Yang, Yan, & Liu, 2009). These sensilla are also distributed on the antennae of FAW, but their functions have not been studied. Since the morphological characteristics of these sensilla are similar to those reported, we speculate that they may play similar functions on the antennae of FAW. Moreover, our results showed that these sensilla are more abundant in females than in males of FAW. This could explain the fact that FAW females are more sensitive to the environment and more easily find host plants to oviposit.
Mechanoreceptors sense host movement and body size, providing accurate and necessary information to insects (L. Y. Ma et al., 2019;Nacro & Nénon, 2009). Previous studies have found that Böhm bristles, sensilla chaetica, and sensilla squamous have the function of sensing mechanical stimuli (Dong, Yang, et al., 2020;Li et al., 2018). Böhm bristles are related to the mechanical rotation of the antennae in fir longhorn beetle (Dong, Dou, et al., 2020). Böhm bristles of Holcocerus hippophaecolus can detect changes in the positions of the antennae and are essential for flight control in moths (Wang, Zhang, Xu, Zong, & Luo, 2015). Böhm bristles in FAW were distributed on the base of the scape and pedicel, suggesting that they may play the role in sensing position, velocity, and acceleration. Sensilla chaetica responds to mechanical shocks, and play the role in the selection of suitable sites, behavioral environments, and courtship microenvironments (Dong, Yang, et al., 2020). However, Jiang et al. (2015) reported that sensilla chaetica is sensitive to D-fructose and has a gustatory function. In the present study, we found that sensilla chaetica of FAW were located on the ventral and dorsal surfaces of antennae, which were much more prominent than other sensors, so they might be the first to encounter objects. Therefore, we speculate that they may play functions in the perception of mechanical stimuli. In addition, the sensilla chaetica of FAW males were longer than that of females, which may be helpful for males to better perceive the movement and status of females. Sensilla squamous are thought to have mechanoreceptive functions (Chang, Zhang, Lv, & Wang, 2015;Ndomo-Moualeu, Ulrichs, Radek, & Adler, 2014). Sensilla squamous of FAW were distributed on the scape, the pedicel, and the dorsal surface of the flagellum, which might be related to sensory mechanical stimulation and reduction of mechanical damage.
The temperature and humidity sensing abilities of insects are closely related to sensilla styloconicum, sensilla uniporous peg, and sensilla coeloconica. Sensilla styloconicum is usually non-porous and has the function of sensing temperature and humidity (Altner & Loftus, 1985), which is widely distributed on the antennae of Lepidopteran insects such as Copitarsia consueta(Castrejón-Gómez, Valdez-Carrasco, Cibrian-Tovar, Camino-Lavin, & Rodolfo Osorio, 1999) and Plutella xylostella (Wee et al., 2016). Our results showed that the sensilla styloconicum morphology of FAW was absent of pores, so it might have the function of sensing environmental changes. The sensilla uniporous peg is distributed on the antennae of Earias vittella and S. littoralis females, which may sense humidity or be sensitive to CO 2 (Seada, 2015). Sensilla cavity have been reported in Hymenoptera, but lack of study of function (Bai, Chen, Chen, Liang, & Zeng, 2012). In this study, sensilla uniporous peg were mainly distributed on the ventral surface of the flagellum in FAW females, suggesting that they may play a role in perceiving the temperature and humidity changes of the host habitat. Sensilla coeloconica is commonly found on the antennae in Lepidoptera (Roh et al., 2016;Sun et al., 2011), and can be divided into more subtypes in Sitotroga cerealella (M. Ma, Chang, Lu, Lei, & Yang, 2017). Shanbhag et al. (1995) reported that sensilla coeloconica of Drosophila melanogaster has no pore-like structures on the walls and sense cone, and possesses the function of sensing temperature and humidity in the environment. In the present study, we found that FAW had only one type of sensilla coeloconica on its antennae, and the walls of the sensilla had no pores, but the surrounding annular microtrichia on the surface of the sensilla might serve to protect the inner central sense cone from physical damage produced by the external environment.

Conclusions
In summary, insect sensilla contain a variety of sensory spectra to identify quite complex substances such as plant secondary substances, salts, sugars, amino acids, and so on, and thus select suitable host plants. Spodoptera frugiperda is a worldwide agricultural pest, and its larvae can feed on more than 350 species of host plants. In this study, we comprehensively reported smell pores, sensilla pegs, and 5 types of sensilla on the antennae of FAW larvae and 12 types of sensilla on the antennae of FAW adults. Though the antennal sensilla of FAW were similar to those of other Lepidoptera in morphology, there were some differences in size and surface microstructure. Furthermore, the actual physiological function and the role in host localization and receptive behavior of each sensillum in FAW have not been well studied. Therefore, in the future, it is of great significance to use electrophysiological techniques such as electroantennography or single-cell recording techniques to deeply study the functions of these sensilla, which will assist the development of new pest control strategies such as pest behavioral control technology for more effective control of this invasive pest.