Antennal and ovipositor sensilla of Pseudoligosita yasumatsui (Hymenoptera: Trichogrammatidae)

Journal of Asia-Pacific Entomology 22 (2019) 296–307

Contents lists available at ScienceDirect

Journal of Asia-Pacific Entomology journal homepage: www.elsevier.com/locate/jape

Antennal and ovipositor sensilla of Pseudoligosita yasumatsui (Hymenoptera: Trichogrammatidae) Sian-Sang Wonga, Peter Aun-Chuan Ooib, Wey-Lim Wonga,

T

⁎

a

Department of Biological Science, Universiti Tunku Abdul Rahman, Kampar Campus, Jalan Universiti, Bandar Barat, 31900 Kampar, Perak, Malaysia Department of Agricultural and Food Science, Faculty of Science, Universiti Tunku Abdul Rahman, Kampar Campus, Jalan Universiti, Bandar Barat, 31900 Kampar, Perak, Malaysia

b

A R T I C LE I N FO

A B S T R A C T

Keywords: Scanning electron microscopy Parasitoid Sexual dimorphism Sensillum Morphometry Ultrastructure

Pseudoligosita yasumatsui Viggiani and Subba Rao 1978 (Hymenoptera: Trichogrammatidae) is a common egg parasitoid of rice insect pests. The surface morphology of the antenna and ovipositor on P. yasumatsui was examined using scanning electron microscopy. The antenna of P. yasumatsui is geniculate in shape, hinged at the scape-pedicel joint, approximately 190 μm in length and consists of seven antennomeres. In total, the male and female antennae have ten different types of sensilla: trichoid sensilla type 1, 2, 3, 4, 5, 6, campaniform sensilla, basiconic sensilla, and placoid sensilla type 1 and 2. The flagellum of the female antenna is covered with cuticular pores, which are absent on the male antennal flagellum. The distal extremity of its ovipositor stylet has campaniform sensilla and styloconic sensilla. Trichoid sensilla found on its apical abdomen part may play a role in the host detection and egg placement. The types and distribution of antennal and ovipositor sensilla on the parasitoid were discussed.

Introduction Pseudoligosita yasumatsui is from the family Trichogrammatidae, which members are egg parasitoids (measured about 0.2–1.0 mm in length) and are characterized by three segmented tarsi (Begum and Anis, 2013). Pseudoligosita yasumatsui was previously known as Oligosita yasumatsui when it was first described by Viggiani & Subba Rao and named after Professor Yasumatsu (Pinto, 2006; Pinto and Viggiani, 2004; Viggiani and Subba Rao, 1978). Pseudoligosita yasumatsui parasitizes the eggs of the rice brown planthopper, Nilaparvata lugens (Stål) and the white-backed planthopper, Sogatella furcifera (Horváth). Both planthoppers are important agricultural pests that present in massive outbreaks in Asian countries (Gurr et al., 2011). In Malaysia, surveillance and behavioral studies showed that Anagrus spp. and Oligosita spp. are the two common egg parasitoids emerged from N. lugens eggs, which are found in the rice field (Ooi, 1988; Sivapragasam and Chua, 1992). Members from Pseudoligosita have been studied as the biological control agent for major agricultural pests. For examples, the egg parasitoid, Pseudoligosita babylonica is used to control Dubas bug, Ommatissus lybicus infestation on date palms in Yemen (Hubaishan and Bagwaigo, 2010). In California, the glassy-winged sharpshooter, Homalodisca vitripennis (Germar) is being controlled by Pseudoligosita plebeia (Perkins) (see Lytle et al., 2012). Like other natural enemies, P.

⁎

yasumatsui has a great potential to be studied and deployed as a biological agent to control the pest population in the rice field as part of integrated pest management modules (Ooi and Shepard, 1994). The success of P. yasumatsui to serve as a biological control agent against herbivore pests may depend on its ability to locate its host in the environment. Parasitic wasps have demonstrated the ability to learn and utilize chemical cues, such as herbivore-induced plant volatiles or other volatile organic compounds from the host-plant complex to locate their hosts (Ochieng et al., 2000; Turlings et al., 1990; Zakir et al., 2013). Antenna and ovipositor of parasitic Hymenoptera have long been associated with the detection of chemical cues in host location, host examination and oviposition (Hansson et al., 1999; Ochieng et al., 2000; Shah, 2012). There are many studies done on the ultrastructure on the antenna of Hymenoptera parasitoids (Isidoro et al., 1996; Amornsak et al., 1998; van Baaren et al., 1999; van Baaren et al., 2007; Onagbola and Fadamiro, 2008; Onagbola et al., 2008, 2009; He et al., 2014). However, to our knowledge, only a few studies thus far have investigated the sensilla of Trichogrammatids (Voegelé et al., 1975; Schmidt and Smith, 1987; Olson and Andow, 1993; Amornsak et al., 1998) and none in the genus Pseudoligosita. In most studies, such as in Trichogramma nubilale, Trichogramma maltbyi, Trichogramma brasiliensis and Trichogramma evanescens, only the female antennal sensilla were examined and their male antennae were never studied (Olson and

Corresponding author. E-mail address: [email protected] (W.-L. Wong).

https://doi.org/10.1016/j.aspen.2019.01.002 Received 16 June 2018; Received in revised form 5 December 2018; Accepted 7 January 2019 Available online 08 January 2019 1226-8615/ © 2019 Korean Society of Applied Entomology. Published by Elsevier B.V. All rights reserved.

Journal of Asia-Pacific Entomology 22 (2019) 296–307

S.-S. Wong et al.

Fig. 1. Head and antennae of female P. yasumatsui. Figure shows the scanning electron micrographs of frontal view (A) and dorsal view (B) of the head and antenna. The antennae of P. yasumatsui (C) showing basal radicle (BR), scape (Sc), pedicel (P), basal annelus (BA), funicle (Fu), second flagellomere (Fl. 2), third flagellomere (Fl. 3) and fourth flagellomere (Fl. 4). The club (Cl) of the antenna (D) contains three flagellomeres (Fl), Fl. 2, Fl. 3 and Fl. 4.

from the test tubes. Pseudoligosita yasumatsui were introduced to the rice seedlings containing the fresh and viable host eggs inside the test tubes for parasitization up to two days. A single drop of pure honey was added to the inner wall of the test tube as the food source for the parasitoids. Moist gauzes, which provide water and humidity for the parasitoids, were used to close the test tubes (modified from Lou et al., 2005). The egg parasitoids were removed from the test tubes after two days and introduced to another set of host eggs for parasitization. Rice seedlings containing the parasitized eggs were placed in closed test tubes so that the adult parasitoids can be collected as soon as they emerged from the host eggs.

Andow, 1993; Voegelé et al., 1975). No previous study was conducted on the sensilla of the ovipositor of Trichogrammatids. In the present study, the surface morphology of the male and female antennal sensilla and ovipositor of P. yasumatsui were examined at the ultrastructural level. The distribution and abundance of different antennal sensilla are also compared between the male and female parasitoids. Materials and methods Insects The egg parasitoid, P. yasumatsui was reared using the eggs of N. lugens in the laboratory. Both the parasitoid and its host insect originated from individuals collected from a paddy field in Tanjung Karang (3°28′07.6″N 101°13′32.5″E), Selangor, Malaysia. Nilaparvata lugens was reared on cultured paddy plants of MR220 CL2 variety. Gravid female N. lugens were allowed to lay eggs on two weeks old rice seedlings inside test tubes for about 24 h. The rice seedlings were then examined under a stereo microscope (Motic NSZ-810, China) for the confirmation of oviposition by N. lugens prior to removing the females

Scanning electron microscopy Freshly emerged adult parasitoids were initially anesthetized at low temperature (−20 °C) in a freezer for 30 mins. The adults of P. yasumatsui (n = 20, 10 males and 10 females) were first fixed in 2.5% glutaraldehyde in 1× phosphate-buffered saline (pH 7.4) at 4 °C for 12 h. Then, the insects were dehydrated in a graded ethanol series (25%, 50%, 75%, 95%, 99.9% and 99.9%; 1 h each). After dehydration, 297

Journal of Asia-Pacific Entomology 22 (2019) 296–307

S.-S. Wong et al.

antenna. These sensilla are trichoid sensilla types 1–6, campaniform sensilla, basiconic sensilla, placoid sensilla types 1 and 2. Of these ten sensilla types, trichoid sensilla type 1 and placoid sensilla type 2 are not found on the surface of male antenna (Fig. 4). The distribution and abundance of each type of sensilla on each segment of male and female antenna are listed in Table 1. The major differences between the male and female antennae were observed at the apical tips of the club or flagellomere 4 (Fig. 4). The number and types of sensilla present at the apical tips of the female antenna (Fig. 4B) are more than that found at the tip of the male antenna (Table 1; Fig. 4A). At the apical tip of the male antenna, there are three types of sensilla found with a total of six of them. While at the apical tip of the female antenna, there are six types of sensilla found with a total of eight of them.

the specimens were dried using hexamethyldisilazane solution (modified from Wong et al., 2006). The prepared insects were positioned on a carbon conductive tape attached on a copper stud before coated using platinum in an auto fine coater (Jeol JFC-1600, Japan), and observed with a field emission scanning electron microscope, (Jeol JSM-6701F, Japan), operating at 2 kV. Sensilla measurement and count The terminology used to describe the morphology of antenna and ovipositor, together with the classification of sensilla types in this study were based on the morphological characters described by Schneider (1964). The lengths of antennae, antennal segments, ovipositors and dimensions of sensilla were estimated from the micrographs of ten male and ten female P. yasumatsui. The mean ± standard error (mean ± S.E.) of the mean of the above mentioned structures was determined. Their exact measurements cannot be obtained due to geometric distortion, as most of the ultrastructures were viewed from different angles, which may not be directly perpendicular to the viewer. The approximate numbers of different sensilla on the antenna and ovipositor of the male and female parasitoids (n = 20, 10 males, 10 females) were obtained after examining the parasitoids from multiple angles. We compared the abundance and distribution of different sensilla on the antenna of male and female P. yasumatsui.

Types and distribution of the antennal sensilla of P. yasumatsui Trichoid sensilla Trichoid sensilla are the most prominent and most abundant type of antennal sensilla in P. yasumatsui (Figs. 2 & 3). They are characterized by their hair-like structures, with thicker base extending above the cuticular surface or a socket, and ending with a relatively pointed tip. In this study, different types of trichoid sensilla are categorized based on their length, presence of cuticular pores and presence of socket at their base. A total of six types of trichoid sensilla are identified on the antenna of P. yasumatsui.

Result

Trichoid sensilla type 1. This type of trichoid sensilla is only found in the female antenna. There is only one sensillum of this type located at the tip of the club, opposite to the basiconic sensillum (Figs. 2A & 4B). Its tip is always pointing toward the distal end of the antenna and observed to be slightly curved at the tip. Each sensillum is 9.75 ± 1.38 μm in length and 0.59 ± 0.05 μm in diameter at the base and tapers gradually to a point (Fig. 5A). The base of this trichoid sensillum is inserted into a socket, with a slight elevation of the cuticle. The surface of this trichoid sensillum has no pore, but its cuticle is carved into long cuticular grooves.

General description of P. yasumatsui antenna The two antennae of male and female P. yasumatsui are situated between the two compound eyes on the medial region of their head capsules (Fig. 1A & B). Both the male and female antennae of P. yasumatsui are geniculate and hinged at the scape-pedicel joint (Fig. 1C). The left and right antennae are the mirror image of each other. Each antenna, 191.60 ± 11.89 μm long, consists of an elongated scape with basal radicle followed by pedicel and flagellum. The flagellum contains a basal anellus and four flagellomeres; flagellomere 1 is the funicle and flagellomeres 2–4 make up the apical club (Fig. 1D). The overall structure and dimension of the antennal segments of female (Fig. 2) and male (Fig. 3) are quite similar. The flagellum is 87.93 ± 3.72 μm in length and possesses four segments. These segments are then separated into a funicle and apical club by their structural differences (Fig. 1D). The most distal segment of the flagellum, flagellomere 4 (Figs. 2A & 3A) is conical and pointy while the other three flagellomeres are cylindrical (Figs. 2B, C, 3B & C). Flagellomere 4 is the longest segment within the flagellum, 33.67 ± 0.97 μm in length. The other two flagellomeres, flagellomere 2 and 3 are quite similar in length of 19.24 ± 0.90 μm and 20.26 ± 1.01 μm, respectively. The funicle, 16.86 ± 0.79 μm long (Figs. 2D & 3D), is the shortest segment amongst the four flagellomeres. A small disk-like structure known as anellus, 2.44 ± 0.10 μm in width separates the pedicel and flagellum (Figs. 2E & 3E). The pedicel, 42.20 ± 1.11 μm in length (Figs. 2F & 3F), is jointed to a scape by the scape-pedicel joint that can allow bending at about 180° at one direction only (Fig. 1C). The scape (Figs. 2G & 3G) is the longest antennal segment, 65.39 ± 2.01 μm in length, followed by the shortest antennal segment, which is the basal radicle, 11.34 ± 0.40 μm in length (Figs. 2H & 3H). The antenna is connected to the cuticle just above the frons by the basal radicle. Sexual dimorphism does exist in the morphology of the antennae of P. yasumatsui by the difference in the types and distribution of the sensilla. On the surface of every antennal segment of both the male and female antennae except the anellus, the corrugated cuticular wall possessing different types of sensilla. Based on their shape, size, surface and cuticular attachment, a total of ten different types of sensilla were discovered on the female antenna while eight types on the male

Trichoid sensilla type 2. These trichoid sensilla are the longest and biggest of all sensilla that are found on the male and female antennae. Their tips are always pointing toward the distal end of the antenna. They are usually present at the flagellomere 2 and 3 of both male and female antennae with the number varying from three to six. There is a shorter trichoid sensilla type 2, about 30 μm long, located only at the flagellomere 4 of the female antenna. These sensilla are 45.11 ± 1.11 μm in length and 1.38 ± 0.05 μm in diameter at the base and decrease slowly until the tip (Fig. 2B & C). These sensilla are connected directly to the cuticular surface, with no socket or any elevation of cuticle at the base of sensilla. The surface of these sensilla has numerous cuticular pores, which are approximately 0.1 μm in diameter and separated about 1 μm apart (Figs. 5B & 6B). There are no grooves present on the cuticular surface of the sensilla. These sensilla are slightly curved inward to the center of the antenna and sideward, clockwise on the left antenna and anticlockwise on the right antenna if viewed from the distal end of the antenna (Fig. 1C). Trichoid sensilla type 3. These sensilla are structurally similar to the trichoid sensilla type 1 but longer and bigger. These sensilla measured 28.46 ± 1.12 μm in length and 1.01 ± 0.04 μm in diameter at the base and taper gradually to a point (Fig. 5C). There are about three of this type of sensilla located on the medial side of the second flagellomere next to the trichoid sensilla type 2 (Figs. 2C & 3C). Moreover, there are about three to four of these sensilla discovered on the dorsal side of the first flagellomere (Figs. 2D & 3D). About eight of these sensilla are located at the pedicel (Figs. 2E & 3E) and approximately nine more on the scape (Figs. 2F & 3F). 298

Journal of Asia-Pacific Entomology 22 (2019) 296–307

S.-S. Wong et al.

Fig. 2. Scanning electron micrographs of the distribution of different types of sensilla on the antennal segments of female P. yasumatsui. Figure shows the presence of trichoid sensillum type 1 (Tr. 1), basiconic sensillum (Ba), placoid sensilla (Pl) and placoid sensillum type 2 (Pl. 2) on fourth flagellomere (A); trichoid sensilla type 2 (Tr. 2) and placoid sensillum type 1 (Pl. 1) on third flagellomere (B); trichoid sensilla type 2 and type 3 (Tr. 3) on second flagellomere (C); basiconic sensillum, trichoid sensilla type 3 and type 4 (Tr. 4) on funicle (D); surface cuticular pores (scp) on segments next to basal anellus (BA) (E); campaniform sensillum (Ca), trichoid sensilla type 3 and type 5 (Tr. 5) on pedicel (F); trichoid sensilla type 3 on scape (G); and trichoid sensilla type 5 on basal radicle (H).

Trichoid sensilla type 4. These sensilla are 20.51 ± 1.08 μm in length and 0.96 ± 0.03 μm in diameter measured at the base, connected directly to the cuticular surface, with no socket or any elevation of cuticle at the base of sensilla (Fig. 2D). These sensilla taper gradually to a point and are slightly shorter than trichoid sensilla type 3. Pores are absent on the surface of these trichoid sensilla, but their cuticle is carved into long cuticular grooves (Fig. 5D). There are about two to four of these sensilla found on the medial side of the first and second flagellomere, next to the trichoid sensilla type 3.

the base of the sensilla has a slight depression around it. They are positioned within the depression nearer to the joint that is next to them. These sensilla have a smooth surface without pores or grooves. These sensilla are only located at the end of pedicel connecting to the scape and around the end of basal radicle connecting to the head of the insect. Trichoid sensilla type 6. These trichoid sensilla are structurally similar to the trichoid sensilla type 2. They are smaller in size, measured 29.20 ± 1.25 μm in length and 1.56 ± 0.06 μm in diameter at the base and blunted at the tip (Fig. 5G). The surface of these sensilla has numerous cuticular pores of about 0.1 μm in diameter and approximately 1 μm apart (Fig. 5H). There are no grooves present on the cuticular surface of the sensilla. These trichoid sensilla are only present at the tip of the antenna, with one sensillum on the female

Trichoid sensilla type 5. These sensilla are the shortest of all trichoid sensilla, measuring at 2.37 ± 0.18 μm in length and 0.98 ± 0.03 μm in diameter at the base, and taper gradually to a point (Fig. 5E & F). These sensilla are connected directly to the cuticle without socket, but 299

Journal of Asia-Pacific Entomology 22 (2019) 296–307

S.-S. Wong et al.

Fig. 3. Scanning electron micrographs of the distribution of different types of sensilla on the antennal segments of male P. yasumatsui. Figure shows the presence of trichoid sensilla type 6 (Tr. 6), placoid sensillum type 1 (Pl. 1) and basiconic sensillum (Ba) on fourth flagellomere (A); trichoid sensilla type 2 (Tr. 2) and placoid sensillum type 1 on third flagellomere (B); trichoid sensilla type 2, type 3 (Tr. 3), type 4 (Tr. 4) and basiconic sensillum on second flagellomere (C); trichoid sensilla type 3 on funicle (D); basal anellus (BA) (E); trichoid sensilla type 3 on pedicel (F); trichoid sensilla type 3 on scape (G); and trichoid sensilla type 5 (Tr. 5) on basal radicle (H).

Fig. 4. The distal extremeties of the last antennal segment of male and female parasitoids. Figure shows the placoid sensilla type 1 (Pl. 1), trichoid sensilla type 6 (Tr. 6) and basiconic sensillum (Ba) on the tip of male antenna (A); placoid sensilla type 1 and type 2 (Pl. 2), basiconic sensillum, trichoid sensilla type 1 (Tr. 1), type 2 (Tr. 2) and type 6 on the tip of female antenna (B).

300

Journal of Asia-Pacific Entomology 22 (2019) 296–307

S.-S. Wong et al.

Table 1 Abundance and distribution of different sensilla on the antennae of male and female Pseudoligosita yasumatsui. Antennal segment

Number of sensillum (Approximate) Tr.1

Tr. 2

Tr. 3

Tr. 4

Tr. 5

Tr. 6

Ca

Ba

Pl. 1

Pl. 2

M

F

M

F

M

F

M

F

M

F

M

F

M

F

M

F

M

F

M

F

Basal radicle Scape Pedicel Basal anellus Flagellomere 1 (Funicle) Flagellomere 2 Flagellomere 3 Flagellomere 4

– – – – – – – –

– – – – – – – 1

– – – – – 3 6 –

– – – – – 3 5 1

– 9 8 – 4 3 – –

– 9 8 – 3 3 – –

– – – – 2 4 – –

– – – – 3 4 – –

10 – 5 – – – – –

10 – 5 – – – – –

– – – – – – – 3

– – – – – – – 1

– – 1 – – – – –

– – 1 – – – – –

– – – – 1 1 1 1

– – – – 2 2 1 1

– – – – – – 1 2

– – – – – – 1 2

– – – – – – – –

– – – – – – 1 2

Total

–

1

9

9

24

23

6

7

15

15

3

1

1

1

4

6

3

3

–

3

Values show approximate number of different types of sensilla on each antennal segment. Tr. 1: trichoid sensilla type 1; Tr. 2: trichoid sensilla type 2; Tr. 3: trichoid sensilla type 3; Tr. 4: trichoid sensilla type 4; Tr. 5: trichoid sensilla type 5; Tr. 5: trichoid sensilla type 5; Ca: campaniform sensilla; Ba: basiconic sensilla; Pl. 1: placoid sensilla type 1; Pl 2: placoid sensilla type 2; M: male; F: female; −: nil.

(Fig. 6G). There is a distinct stalk of 1.31 ± 0.05 μm in length and 0.79 ± 0.02 μm in diameter, connecting the bulb-like structure to its base. About one to two of these sensilla are present at the distal end of flagellomere 1–4.

antenna and three sensilla on the male antenna. Campaniform sensilla Campaniform sensilla are present only at one end of the pedicel connecting to the scape, next to a trichoid sensilla type 5. Each sensillum consists of a small dome-shaped, smooth cuticular surface, 0.85 ± 0.03 μm in diameter with a slight depression around it in a ring shape (Fig. 5E).

Cuticular pores The cuticular surfaces of the flagellum of the female antenna are covered with pores of approximately 0.1 μm in diameter and 1 μm apart (Fig. 6H). Across the basal anellus, the pedicel and scape of the female antenna are covered with shallow depression dots with a similar pattern (Fig. 2E). These shallow depression dots are also found on the cuticular surface of flagellum, pedicel and scape of the male antenna.

Placoid sensilla Placoid sensilla are elongated plate-like sensory organs with ridged shafts with numerous pores on top of them. They arise from an elevated cuticular rim and taper apically. The placoid sensilla located at the fourth flagellomere are 31.19 ± 0.48 μm in length and 2.98 ± 0.11 μm in diameter (Figs. 2A, B & 3B). At the third flagellomere, the placoid sensilla are 32.55 ± 0.65 μm in length and 2.78 ± 0.06 μm in diameter. The summit of the plate-like structure is covered with numerous pores of about 0.1 μm in diameter and 0.1 μm apart (Fig. 6A & B). Due to the difference in the distribution of the pores on the summit of placoid sensilla, two different types of placoid sensilla are identified.

Sensory organs on ovipositor The ovipositor of P. yasumatsui is located along the ventral part of the abdomen, starting from the opening of oviduct until the abdomen apex (Fig. 7A). The ovipositor consists of a 323.33 ± 1.76 μm long and 6.42 ± 0.30 μm wide ovipositor stylet, which is encased within an ovipositor sheath of similar length and 10.13 ± 0.83 μm in diameter (Fig. 8A & B). The ovipositor sheath has a full-length slit at the ventral side from which the ovipositor stylet can be pulled out or inserted (Fig. 8A). There is no sensory organ found on the ovipositor sheath (Fig. 7B & D). However, approximately eight large trichoid sensilla, which are 27.90 ± 1.88 μm in length, are found at the abdominal end and located in close proximity to the ovipositor (Fig. 7B & C). There are two relatively large depressions on the left and right sides of the cuticular surface of the abdomen apex that contains three trichoid sensilla in each of them (Fig. 7C). The unsheathed ovipositor stylet consists of three valvulae of similar length (Fig. 8C & D). The first valvula makes up for the dorsal half of the whole stylet structure. The second and third valvulae are half the size of the first valvula, and together they make up the ventral half of the stylet structure. There is no sensillum found on the first valvula. However, there are four styloconic sensilla and two campaniform sensilla at the distal extremity of each of the second and third valvulae (Fig. 8C & D). The styloconic sensilla are cone-like structures, 0.51 ± 0.04 μm in length, located in a shallow cuticular depression of 0.81 ± 0.05 μm in diameter around its base on the ovipositor stylet (Fig. 8F). Three of the styloconic sensilla are pointing away from the distal end of the stylet; while another styloconic sensillum is pointing toward the distal end of the stylet. The campaniform sensilla located on the ovipositor stylet are each consisted of a small elongated dome-shaped, smooth cuticular surface, 0.79 ± 0.01 μm in length with slight depression around it in an oval shape (Fig. 8D).

Placoid sensilla type 1. The pores on the cuticular surface on these sensilla cover the top part of the shaft entirely (Fig. 6A & B). On the female antenna, two of the four placoid sensilla located next to each other at the fourth flagellomere are type 1. One of the two placoid sensilla at third flagellomere is type 1. While for the male antenna, there are two placoid sensilla type 1 located at the fourth flagellomere and one placoid sensillum type 1 located at the third flagellomere. Placoid sensilla type 2. This type of placoid sensilla is distinguished from the placoid sensilla type 1 by a clear central region surrounded by pores on the top part of the shaft (Fig. 6C & D). This type of placoid sensilla is only found on the female antennae. Two of the placoid sensilla type 2 are present at the fourth flagellomere, and one of them is present at third flagellomere, located opposite to the placoid sensilla type 1 at each segment. Basiconic sensilla The basiconic sensilla have a more distinguishing external structure as compared to the trichoid sensilla. These sensilla are also known as basiconic capitate peg sensilla. The basiconic sensilla are bulb-like structures, 1.44 ± 0.07 μm in diameter, located in a shallow cuticular depression of 3.95 ± 0.20 μm in diameter around its base on the antenna (Fig. 6E, F & G). The peg has numerous tiny globular structures covering it, and about 12 grooves along the bulb-like region of the shaft 301

Journal of Asia-Pacific Entomology 22 (2019) 296–307

S.-S. Wong et al.

Fig. 5. Different types of antennal sensilla of P. yasumatsui. Figure shows the cuticular grooves (cg) and socket (s) of trichoid sensillum type 1 (Tr. 1) on fourth flagellomere (Fl. 4) (A); pores (p) on trichoid sensilla type 2 (Tr. 2) (B); cuticular grooves (cg) and socket (s) of trichoid sensilla type 3 (Tr. 3) (C); cuticular grooves (cg) on trichoid sensilla type 4 (Tr. 4) (D); depression (d) around campaniform sensillum (Ca) (E) and trichoid sensilla type 5 (Tr. 5) (E and F); trichoid sensilla type 6 (Tr. 6); and pores on the surface of trichoid sensillum type 6 (H).

Discussion

Lancet is located at the distal end of the stylet, has a saw-like structure, which is 21.53 ± 0.69 μm in length. The lancet is composed of six denticulations on the first valvula, and two denticulations on the second and third valvulae each (Fig. 8E & F). The inner surface of the ovipositor sheath is fully covered with hair-like structures of 1.75 ± 0.14 μm in length (Fig. 8E).

Antenna For the first time, we reported an ultrastructural investigation on the antennal sensilla of a member from the genus Pseudoligosita. We have demonstrated that various sensory organs are present on the antennae of P. yasumatsui. Thus far, there are only a few studies done on the external morphology of antennal sensilla of parasitoids from Trichogrammatidae family, such as Trichogramma australicum (see 302

Journal of Asia-Pacific Entomology 22 (2019) 296–307

S.-S. Wong et al.

Fig. 6. Different types of antennal sensilla of P. yasumatsui (continued). Figure shows the placoid sensillum type 1 (Pl. 1) (A) with close-up view of surface cuticular pores (scp) on it (B); and pores (p) on the surface of trichoid sensilla type 2 (Tr. 2). The placoid sensillum type 2 (Pl. 2) has surface cuticular pores (scp) around a central clear region ranging from its proximal end (C) to distal end (D). Basiconic sensillum (Ba) is located at distal end of flagellomeres (E) with cuticular grooves (cg) on its surface and depression (d) around it (F and G). The surface cuticular pores present on the funicle (Fu) (H).

differences are related to their different functions on the antennae. Trichoid sensilla with a flexible socket and without pores, such as trichoid sensilla type 1, 3 and 5 of P. yasumatsui are pure mechanoreceptors (Keil, 1999). While the trichoid sensilla with a highly porous wall, such as trichoid sensilla type 2 and 6 of P. yasumatsui are most likely olfactory receptors (Keil, 1999; Steinbrecht, 1997). The presence of trichoid sensilla type 1 only at the apical part of the female P. yasumatsui antenna suggests that these sensilla are associated with tactile function. The slight curve observed close to the tip of these sensilla may be resulted from the frequent and intense tapping of the

Amornsak et al., 1998), T. evanescens (see Voegelé et al., 1975) and T. nubilale (see Olson and Andow, 1993). In general, antennal sensilla can be involved in the functions of mechanoreception, such as hygroreception and thermoreception, or chemoreception, such as gustation and olfaction (Schneider, 1964). The trichoid sensilla described in this study are the most abundant sensilla type found on the antennal surface of both male and female P. yasumatsui. The six types of trichoid sensilla are characterized by their hair-like structures but differentiated by their size, presence or absence of cuticular pores and sockets. We assumed that their morphological 303

Journal of Asia-Pacific Entomology 22 (2019) 296–307

S.-S. Wong et al.

Fig. 7. Lower abdomen and ovipositor of P. yasumatsui. Figure shows scanning electron micrographs of ventral view of abdomen and ovipositor of female P. yasumatsui (A). Ovipositor has no visible sensillum present on it but trichoid sensilla (Tr) observed at the distal end of abdomen near the ovipositor (B). A depression (d) is present at the side of the distal end of abdomen containing three trichoid sensilla (Tr) with cuticular grooves (cg) and socket (s) (C). The cuticular surface of the ovipositor is clear of sensilla and pores (D).

locating the host eggs. Trichoid sensilla type 3 are only found on the medial side of the first and second flagellomeres in P. yasumatsui. These sensilla were arranged in a similar pattern as reported in T. nubilale, whereby they are linearly arranged along the interior lateral surface but not located on the exterior lateral surface of all the flagellomeres (Olson and Andow, 1993). Based on their location and our observation, it is hypothesized that the trichoid sensilla type 3 serve as a tactile receptor in the perception of mechanosensory stimuli when the parasitoid is using both of the antennae to hold and touch an object. In P. yasumatsui, the trichoid sensilla type 4 are morphologically similar to trichoid sensilla type 1 and type 3 except for the lack of socket at the base of the sensilla. This is the first observation of these kinds of sensilla in Trichogrammatidae. Therefore, it is difficult to speculate on their role in the present study. The absence of the flexible socket at the base of this type of sensilla may indicate that they are unlikely to serve as mechanoreceptor but may have a structural function to protect the antennal segments or for cleaning purposes. The longitudinal grooves on these sensilla are probably to strengthen the structure of the hair-like structure as observed in trichoid sensilla type 1 and 3. The trichoid sensilla type 5 described in this study are similar in morphology and position to the “hair sensilla” on the antennal hair plates of Trichogramma minutum (see Schmidt and Smith, 1987) and “type 4 sensilla trichodea” in P. cerealellae (see Onagbola and Fadamiro, 2008). These authors suggested the involvement of these sensilla in the measurement of the curved antennal surface and act as proprioceptors. These hair-like structures are suspected to monitor the relative position of one cuticular surface to another. They are located in such position near the joints of antennal segments, so that these sensilla bends according to the flexing of one part of the cuticle with respect to another (Chapman, 1998). The whole antenna of P. yasumatsui was observed to move in a circular direction on the socket and only about 180° at the scape-pedicel joint. Numerous trichoid sensilla type 5 are found on the hair plates at both of the joints. The occurrence of the trichoid sensilla type 5 observed only at the scape-pedicel joint and around the basal radicle socket of P. yasumatsui concurs with the observation made by Chapman (1998) on other insect antennae. Trichoid sensilla type 6 are morphologically similar to trichoid

antennal tip on the surface of host and rice plant. Similar sensilla were reported in T. evanescens as “sensilla type d”, which is relatively slender and somewhat curled, located at the antennal apex (Voegelé et al., 1975). These sensilla are also located within the cage/concave area partially covered by four placoid sensilla of P. yasumatsui, which probably function to prevent them from being crushed while tapping the antennal tip onto the host surface. Trichoid sensilla type 2 have also been previously described with different names such as “multiporous type 3 sensilla trichodea” in Pteromalus cerealellae (see Onagbola and Fadamiro, 2008), “thin-walled chemoreceptor” in Nasonia vitripennis (see Wibel et al., 1984), “sensilla trichodea with wall pores” in Cotesia glomerata (see Bleeker et al., 2004), “multiporous pitted sensilla trichodea C” in T. nubilale (see Olson and Andow, 1993) and “sensilla basiconic type I" in Microplitis croceipes (see Ochieng et al., 2000). In T. nubilale, these sensilla are suspected to function as mechanoreceptor and contact chemoreceptor in detecting the host eggs (Olson and Andow, 1993). However, the presence of trichoid sensilla type 2 with multiporous cuticular surface on the flagellomere 2 and 3 of P. yasumatsui antenna but not at its apical tip, indicates that they are more likely to have an olfactory rather than a gustatory function in host detection. Moreover, these large trichoid sensilla probably provide huge surface area of contact with the atmosphere for better odor detection. Trichoid sensilla type 3 are the most abundant sensilla compared to other types of sensilla on the antenna of P. yasumatsui. The presence of these mechano-hair sensilla on most of the antenna indicates their possible role in detecting changes in air movement around the antenna or perceive air-borne vibrations, as proposed by Mciver (1975). These sensilla are morphologically similar to the “aporous type 2 sensilla trichodea” as described on the antenna of P. cerealellae (see Onagbola and Fadamiro, 2008) and to the “aporous sensilla trichodea B" as described on T. nubilale (see Olson and Andow, 1993). It was suggested that these sensilla might be involved in host examination and host discrimination of P. cerealellae, given that the parasitoid exhibits antennal drumming behavior (Isidoro et al., 1996; Onagbola and Fadamiro, 2008). Since these trichoid sensilla are absent on the last two apical antennal segments of P. yasumatsui, they are unlikely to be in direct contact with the host surface when tapping the antenna on the host eggs. Therefore, these trichoid sensilla are probably not used for 304

Journal of Asia-Pacific Entomology 22 (2019) 296–307

S.-S. Wong et al.

Fig. 8. Unsheathed ovipositor of P. yasumatsui. Figure shows the extremity of lower abdomen of P. yasumatsui containing ovipositor sheath and stylet from left view (A) and right view (B); external surface of the distal end of stylet bearing lancet, styloconic sensilla (St) and campaniform sensilla (Ca), left view (C) and right view (D) (Inset: campaniform sensillum); lancet consists of first valvula (V. 1), second valvula (V. 2), third valvula (V. 3) with several denticulations (dt), left view (E) and right view (F) (Inset: styloconic sensillum). Hair-like structures (h) are present on the inner surface of ovipositor sheath.

are mechanoreceptors, reacting to stresses in the cuticle and acting as proprioceptors for the palps and legs of cockroach, Periplaneta america L. (see Pringle, 1938a, 1938b). These campaniform sensilla have also been reported to occur on the distal surface of the pedicel in N. vitripennis and T. australicum (see Amornsak et al., 1998; Wibel et al., 1984). Based on our observation of the structure and location of the campaniform sensilla of P. yasumatsui antenna, these sensilla are probably proprioceptors to detect the flexing of the scape-pedicel joint. Placoid sensilla are commonly reported on the antennae of parasitic wasps (e.g.Barlin et al., 1981; Wibel et al., 1984; Olson and Andow, 1993; Amornsak et al., 1998; Onagbola and Fadamiro, 2008). Generally, the presence of multiple pores on these sensilla indicates olfactory function (Barlin et al., 1981; Bleeker et al., 2004; Ochieng et al., 2000). The placoid sensilla the worker honeybee, Apis mellifera are assumed to be purposely suited for the processing of odorrant mixture (Akers and Getz, 1993). Both male and female P. yasumatsui have three placoid sensilla type 1 at their apical antennal segments, strongly indicate their role in contact chemoreception. Placoid sensilla type 2 are unique in the females of P. yasumatsui and may have olfactory or gustatory functions on the host egg. The greater abundance of placoid sensilla reported in female P. cerealellae may indicate their function in host location, and perhaps in the detection of host-related semiochemicals (Onagbola and Fadamiro, 2008).

sensilla type 2 except for their smaller size. These trichoid sensilla are present at the tips of both male and female P. yasumatsui, and probably function as gustatory chemoreceptor. Isidoro et al. (1996) proposed that the “multiporous gustatory sensilla” on the antenna of Hymenoptera parasitoids have two functional areas, “touch and taste area” and “release and spread area”, indicating their role in gustation. The trichoid sensilla type 6 are morphologically similar to “multiporous type 3 sensilla trichodea” in P. cerealellae. In P. cerealellae, the high number of the “multiporous type 3 sensilla trichodea” on the male antennae in relation to those on the female antennae suggests a plausible role in mate location, or in the detection of sex pheromones (Onagbola and Fadamiro, 2008). However, in Tamarixia radiate, the male antenna has more and larger olfactory “multiporous sensilla trichoidea” for sensitivity toward the female-produced pheromone (Onagbola et al., 2009). Similar to the observation in T. radiate, the male antenna of P. yasumatsui has more trichoid sensilla type 6 of the similar size than the female antenna. Close-range courtship behavior was observed in P. yasumatsui, the male and female parasitoids tapped and connected the tips of their antenna for a few seconds before mating process took place. On the antenna, campaniform sensilla are described as thick-walled, singly innervated, with smooth semispherical formations of the cuticle (Schneider, 1964). Previous studies have speculated that theses sensilla 305

Journal of Asia-Pacific Entomology 22 (2019) 296–307

S.-S. Wong et al.

Basiconic sensilla described in the present study resemble the “basiconic capitates peg sensilla” on the antenna of P. cerealellae (see Onagbola and Fadamiro, 2008), “multiporous peg” in Tetrastichus hagenowii (see Barlin et al., 1981), “basiconic captitate peg” in N. vitripennis (see Wibel et al., 1984), and “multiporous pitted sensilla basiconica C" in T. nubilale (see Olson and Andow, 1993). Olson and Andow (1993) suggested that the pores present in the furrows on the bulbous distal end of the basiconic sensilla play a role in olfaction, while Wibel et al., (1984) suggested that they serve as hygro-, thermoand mechanoreceptors. In contrast, Onagbola and Fadamiro (2008) observed no pores on this type of sensilla on the flagellomeres of P. cerealellae. The scanning electron micrographs of the basiconic sensilla of P. yasumatsui show no sign of visible pores in the furrow at the bulbous distal end, but it is covered with tiny globular structures (Fig. 4G). The lack of flexible socket at the base of these basiconic sensilla may indicate that they are not mechanoreceptors. The bulb-like structure of basiconic sensilla was observed to range from elongated to more globular shape, suggesting the change of its shape due to atmospheric stimuli. The grooves on the bulbous tips of the basiconic sensilla on the antenna of P. yasumatsui that are without punctuations may allow the expansion or compression of the bulbous tips, suggestive of thermo-, hygro- or baroreceptive functions (Onagbola and Fadamiro, 2008). The cuticular pores observed on the flagellum of the female antenna might serve as a type of sensillum or glandular function in P. yasumatsui. They are most probably the ampullaceous sensilla, which are located in deep pits and usually serve as chemoreceptor (Singh, 2007). However, further investigations of the internal structure of these cuticular pores by transmitting electron microscopy and potassium hydroxide treatment are needed for the confirmation of the function of these cuticular pores (Boo and McIver, 1975; Ramirez-Esquivel et al., 2014).

valvulae of the stylet of P. yasumatsui can slide along each other while drilling. This arrangement may reduce damage on the ovipositor and assist in steering the ovipositor as hypothesized by Gussekloo and Van Leeuwen (2017). The hair-like structures covering the inner surface of ovipositor sheath of P. yasumatsui may act as a cushion for the ovipositor stylet. In short, our morphological studies on the antenna of P. yasumatsui suggest that the antennal sensilla may have both mechanoreceptive and chemoreceptive properties. The putative mechanoreceptors, namely trichoid sensilla type 1, 3, 5, and campaniform sensilla could be involved in the host-location, host-searching, tactile reception, detection of air movement and proprioception. While the putative chemoreceptors, including the trichoid sensilla type 2 and 6, cuticular pores on the antennal segments, placoid sensilla type 1 and type 2 could be involved in the olfactory and gustatory function for food, mate, and hostsearching. There are also putative thermo- and hygroreceptors, such as the basiconic sensilla present on the antennae to detect the changes of the surroundings. On the ovipositor of P. yasumatsui, the styloconic sensilla and campaniform sensilla are both putative mechanoreceptors that direct the egg-laying process. The female P. yasumatsui may use both mechanosensory and olfactory cues to locate the embedded host eggs. The study of the morphology and distribution of different sensilla on the female P. yasumatsui provide important background information for our ongoing research of host location mechanisms in this species by using y-tube olfactometer behavioral test. Future studies on the functional morphology of the antennal and ovipositor sensilla using transmission electron microscopy, electrophysiological recordings, and confocal microscopy may verify the functions of the different sensilla identified in this study. Conflict of interest

Ovipositor

All authors declare no conflict of interest. Author contributions

On the ovipositor stylet of female P. yasumatsui, we discovered two types of ovipositor sensilla, which are styloconic sensilla and campaniform sensilla. Le Ralec and Wajnberg (1990) proposed that the styloconic sensilla found on the ovipositor may serve as mechanoreceptor that is stimulated by the movements of ovipositor stylet during oviposition. The styloconic sensilla on the second and third valvulae of P. yasumatsui have cone-like structures that are point toward and away from the distal end of the stylet. This specific arrangement of styloconic sensilla is presumed to sense back and forth motion of the ovipositor while sawing into the host egg. These styloconic sensilla were also reported on the first and second valvulae of Trichogramma maidis, but their pointing directions are not specified by the authors (Le Ralec and Wajnberg, 1990). The campaniform sensilla of P. yasumatsui ovipositor are located on the stylet surface, further away than the styloconic sensilla from the distal end. According to Singh (2007), campaniform sensilla function as compression and stretch receptors to monitor muscular activity at ovipositors. In P. yasumatsui, their location and presumed function as tactile mechanoreceptor sensitive to external pressure suggest their role in measuring the depth of the insertion of the ovipositor stylet into the host egg. These campaniform sensilla are similar to those which are reported on the first valvula of T. maidis (see Le Ralec and Wajnberg, 1990) and to “type II campaniform sensillum” of Venturia canescens (see Shah, 2012). In P. yasumatsui, the denticulations of the lancet at the stylet apex are suspected to act as the teeth of a saw, which are used to cut through the host egg shell. Based on our observation, rocking motion of the abdomen of P. yasumatsui was observed after the insertion of the ovipositor stylet into the host egg. Similar behavior was reported as abdominal vibrations in Anagrus nigriventris but this movement was not observed while the ovipositor was inserted into empty plant tissues (AlWahaibi and Walker, 2000). The three longitudinally connected

WWL designed the study. WSS prepared the insect samples, conducted the majority of the imaging data, measured and counted the sensilla, prepared the figures and observed the host-searching and oviposition behavior. WSS wrote the first draft of the manuscript. WWL and PACO edited and drafted the revised manuscripts. All authors collaborated on data interpretation, manuscript revisions and preparation of the final manuscript. Acknowledgement We gratefully acknowledge the facilities and instruments provided by the Faculty of Science, Universiti Tunku Abdul Rahman, Malaysia. This research was supported by the Fundamental Research Grant Scheme (vote No. 4435/W02) from Ministry of Higher Education, Malaysia, and a postgraduate scholarship, MyBrain15 awarded to Wong S.S. from Ministry of Education, Malaysia. We would like to extend our sincere gratitude to Dr. Andrew Polaszek from the Natural History Museum, United Kingdom for the species confirmation of Pseudoligosita yasumatsui. References Akers, R.P., Getz, W.M., 1993. Response of olfactory receptor neurons in honeybees to odorants and their binary mixtures. J. Comp. Physiol. A. 173, 169–185. Al-Wahaibi, A.K., Walker, G.P., 2000. Oviposition behavior of Anagrus nigriventris, an egg parasitoid of beet leafhopper, Circulifer tenellus. BioControl 45, 139–153. https://doi. org/10.1023/A:1009994405237. Amornsak, W., Cribb, B., Gordh, G., 1998. External morphology of antennal sensilla of Trichogramma australicum girault (Hymenoptera: Trichogrammatidae). Int. J. Insect Morphol. Embryol. 27, 67–82. https://doi.org/10.1016/S0020-7322(98)00003-8. van Baaren, J., Boivin, G., Le Lannic, J., Nenon, J.P., 1999. Comparison of antennal sensilla of Anaphes victus and A. listronoti (Hymenoptera, Mymaridae), egg parasitoids

306

Journal of Asia-Pacific Entomology 22 (2019) 296–307

S.-S. Wong et al.

sensilla of Pteromalus cerealellae (Hymenoptera: Pteromalidae). Micron 39, 526–535. https://doi.org/10.1016/j.micron.2007.08.001. Onagbola, E.O., Meyer, W.L., Boina, D.R., Stelinski, L.L., 2008. Morphological characterization of the antennal sensilla of the Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Psyllidae), with reference to their probable functions. Micron 39, 1184–1191. https://doi.org/10.1016/j.micron.2008.05.002. Onagbola, E.O., Boina, D.R., Hermann, S.L., Stelinski, L.L., 2009. Antennal sensilla of Tamarixia radiata (Hymenoptera: Eulophidae), a parasitoid of Diaphorina citri (Hemiptera: Psyllidae). Ann. Entomol. Soc. Am. 102, 523–531. https://doi.org/10. 1603/008.102.0324. Ooi, P.A.C., 1988. Ecology and Surveillance of Nilaparvata lugens (Stal): Implications for Its Management in Malaysia. (Ph.D. dissertation), University of Malaya; Malaysia. Ooi, P.A.C., Shepard, B.M., 1994. Predators and parasitoids of rice insect pests. In: Heinrichs, E.A. (Ed.), Biology and Management of Rice Insects. Wiley Eastern Limited, New Delhi, pp. 585–612. Pinto, J.D., 2006. A review of the new world genera of Trichogrammatidae (Hymenoptera). J. Hymenopt. Res. 15, 38–163. Pinto, J.D., Viggiani, G., 2004. A review of the genera of Oligositini (Hymenoptera: Trichogrammatidae) with a preliminary hypothesis of phylogenetic relationship. J. Hymenopt. Res. 13, 269–294. Pringle, B.Y.J.W.S., 1938a. Proprioception in insects I. A new types of mechanical receptor from the palps of the cockroach. J. Exp. Biol. 15, 101–113. Pringle, B.Y.J.W.S., 1938b. Proprioception in insects II. The action of the campaniform sensilla on the legs. J. Exp. Biol. 15, 114–130. Ramirez-Esquivel, F., Zeil, J., Narendra, A., 2014. The antennal sensory array of the nocturnal bull ant Myrmecia pyriformis. Arthropod. Struct. Dev. 43, 543–558. https:// doi.org/10.1016/j.asd.2014.07.004. Schmidt, J.M., Smith, J.J.B., 1987. The external sensory morphology of the legs and hairplate system of female Trichogramma minutum Riley (Hymenoptera: Trichogrammatidae). Proc. R. Soc. Lond. B 232, 323–366. Schneider, D., 1964. Insect antennae. Annu. Rev. Entomol. 9, 103–122. https://doi.org/ 10.1146/annurev.en.09.010164.000535. Shah, Z.A., 2012. Morphology, ultrastructure, and probable functions of the sense organs on the ovipositor stylets of the hymenoptran parasitoid, Venturia canescens (Gravenhorst). Microsc. Res. Tech. 75, 876–883. https://doi.org/10.1002/jemt. 22007. Singh, R., 2007. Elements of Entomology, 1st edition. Rastogi Publications, Meerut. Sivapragasam, A., Chua, T.H., 1992. Functional response of the brown planthopper egg parasitoids Anagrus nr flaveolas (Waterhouse) and Oligosita sp. (Walker). MARDI Res. J. 20, 161–165. Steinbrecht, R.A., 1997. Pore structures in insect olfactory sensilla: a review of data and concepts. Int. J. Insect Morphol. Embryol. 26, 229–245. https://doi.org/10.1016/ S0020-7322(97)00024-X. Turlings, T.C.J., Tumlinson, J.H., Lewis, W.J., 1990. Exploitation of herbivore-induced plant odours by host-seeking parasitic wasps. Science 250, 1251–1253. Viggiani, G., Subba Rao, B.R., 1978. Notes on some Trichogrammatid parasites associated with rice pests in Thailand with the description of a new species. Bolletino del Lab. di Entomol. Agrar. “Filippo Silvestri” di Portici 35, 3–7. Voegelé, J., Josette, C.-U., Pihan, J.P., Jeanne, D., 1975. Structure de l'antenne femelle des trichogrammes. Entomophaga 20, 161–169. Wibel, R.G., Cassidy, J.D., Buhse Jr., H.E., Cummings, M.R., Bindokas, V.P., Charlesworth, J., Baumgartner, D.L., 1984. Scanning electron microscopy of antennal sense organs of Nasonia vitripennis (Hymenoptera: Pteromalidae). Trans. Am. Microsc. Soc. 103, 329–340. Wong, W.L., Brennan, G.P., Halton, D.W., Lim, L.H.S., 2006. Fine structure of the anterior adhesive apparatus (head organs) of Bravohollisia gussevi Lim, 1995 (Monogenea: Ancyrocephalidae). Parasitology 132, 427–438. https://doi.org/10.1017/ S0031182005009054. Zakir, A., Bengtsson, M., Sadek, M.M., Hansson, B.S., Witzgall, P., Anderson, P., 2013. Specific response to herbivore-induced de novo synthesized plant volatiles provides reliable information for host plant selection in a moth. J. Exp. Biol. 216, 3257–3263. https://doi.org/10.1242/jeb.083188.

of Curculionidae. Zoomorphology 119, 1–8. https://doi.org/10.1007/ s004350050076. van Baaren, J., Boivin, G., Bourdais, D., Roux, O., 2007. Antennal sensilla of hymenopteran parasitic wasps: variations linked to host exploitation behavior. Mod. Res. Educ. Top. Microsc. 1, 345–352. Barlin, M.R., Vinson, S.B., Piper, G.L., 1981. Ultrastructure of the antennal sensilla of the cockroach-egg parasitoid, Tetrastichus hagenowii (Hymenoptera: Eulophidae). J. Morphol. 108, 97–108. Begum, S., Anis, S.B., 2013. Taxonomic studies on some genera of Indian Trichogrammatidae (Hymenoptera: Chalcidoidea). World J. Appl. Sci. Res. 3, 42–48. Bleeker, M.A.K., Smid, H.M., Van Aelst, A.C., Van Loon, J.J.A., Vet, L.E.M., 2004. Antennal sensilla of two parasitoid wasps: a comparative scanning electron microscopy study. Microsc. Res. Tech. 266–273. Boo, K.S., McIver, S.B., 1975. Fine structure of sunken thick-walled pegs (sensilla ampullacea and coeloconica) on the antennae of mosquitoes. Can. J. Zool. 53, 262–266. https://doi.org/10.1139/z75-033. Chapman, R.F., 1998. The Insects Structure and Function, 4th edition. Cambridge Univ. Press, Cambridge. https://doi.org/10.1046/j.1467-2494.1998.171733.x. Gurr, G.M., Liu, J., Read, D.M.Y., Catindig, J.L.A., Cheng, J.A., Lan, L.P., Heong, K.L., 2011. Parasitoids of Asian rice planthopper (Hemiptera: Delphacidae) pests and prospects for enhancing biological control by ecological engineering. Ann. Appl. Biol. 158, 149–176. https://doi.org/10.1111/j.1744-7348.2010.00455.x. Gussekloo, S.W.S., Van Leeuwen, J.L., 2017. Mechanisms of ovipositor insertion and steering of a parasitic wasp. Proc. Natl. Acad. Sci. U. S. A. 1–10. https://doi.org/10. 1073/pnas.1706162114. Hansson, B.S., Larsson, M.C., Leal, W.S., 1999. Green leaf volatile-detecting olfactory receptor neurones display very high sensitivity and specificity in a scarab beetle. Physiol. Entomol. 24, 121–126. He, X., Xu, H., Gao, G., Zhou, X., Zheng, X., Sun, Y., Yang, Y., Tian, J., Lu, Z., 2014. Virusmediated chemical changes in rice plants impact the relationship between non-vector planthopper Nilaparvata lugens Stal and its egg parasitoid Anagrus nilaparvatae Pang et Wang. PLoS One 9, e105373. https://doi.org/10.1371/journal.pone.0105373. Hubaishan, M.A., Bagwaigo, A.A., 2010. The effect of the egg parasitoid Pseudoligosita babylonica on Dobas Infestation in Doaan, Shichawi and Asid (Hudramout, Yemen). Proc. 4th. Int. Date Palm Conf. 451–456. Isidoro, N., Bin, F., Colazza, S., Vinson, S., 1996. Morphology of antennal gustatory sensilla and glands in some parasitoid Hymenoptera with hypothesis on their role in sex and host recognition. J. Hymenopt. Res. 5, 206–239. Keil, T.A., 1999. Morphology and development of the peripheral olfactory organs. In: Hansson, B.S. (Ed.), Insect Olfaction. Springer-Verlag Berlin Heidelberg, New York, pp. 5–47. Le Ralec, A., Wajnberg, E., 1990. Sensory receptors of the ovipositor of Trichogramma maidis (Hymenoptera: Trichogrammatidae). Entomophaga 35, 293–299. Lou, Y.G., Ma, B., Cheng, J.A., 2005. Attraction of the parasitoid Anagrus nilaparvatae to rice volatiles induced by the rice brown planthopper Nilaparvata lugens. J. Chem. Ecol. 31, 2357–2372. https://doi.org/10.1007/s10886-005-7106-z. Lytle, J.M., Bernal, J.S., Morse, J.G., 2012. Biology of Pseudoligosita plebeia (Hymenoptera: Trichogrammatidae), an egg parasitoid of Homalodisca spp. (Hemiptera: Cicadellidae) collected from Northwestern Mexico as a potential biocontrol agent of H. vitripennis in California. J. Econ. Entomol. 105, 1532–1539. https://doi.org/10.1603/EC12153. Mciver, S.B., 1975. Structure of cuticular mechanoreceptors of antropods. Annu. Rev. Entomol. 20, 381–397. https://doi.org/10.1146/annurev.en.20.010175.002121. Ochieng, S.A., Park, K.C., Zhu, J.W., Baker, T.C., 2000. Functional morphology of antennal chemoreceptors of the parasitoid Microplitis croceipes (Hymenoptera: Braconidae). Arthropod. Struct. Dev. 29, 231–240. https://doi.org/10.1016/S14678039(01)00008-1. Olson, D.M., Andow, D.A., 1993. Antennal sensilla of female Trichogramma nubilale (Ertle and Davis) (Hymenoptera: Trichogrammatidae) and comparisons with other parasitic Hymenoptera. Int. J. Insect Morphol. Embryol. 22, 507–520. https://doi.org/10. 1016/0020-7322(93)90037-2. Onagbola, E.O., Fadamiro, H.Y., 2008. Scanning electron microscopy studies of antennal

307