Antennal sensilla of the ground beetle Bembidion properans Steph. (Coleoptera, Carabidae)

PERGAMON

Micron 33 (2002) 429±440

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Antennal sensilla of the ground beetle Bembidion properans Steph. (Coleoptera, Carabidae) Enno Merivee a,*, Angela Ploomi a, MaÈrt Rahi b, Jose Bresciani c, Hans Peter Ravn d, Anne Luik a, VaÈino Sammelselg e a

Institute of Plant Protection, Estonian Agricultural University, 64 Kreutzwaldi Street, 51014 Tartu, Estonia b Institute of Zoology and Botany, Estonian Agricultural University, 181 Riia Street, 51014 Tartu, Estonia c Royal Veterinary and Agricultural University, BuÈlowsvej 13, DK 1870 Frederiksberg C, Denmark d Danish Forest and Landscape Research Institute, Hoersholm Kongevej 11, DK 2970 Hoersholm, Denmark e Institute of Physics, University of Tartu, 142 Riia Street, 51014 Tartu, Estonia Received 17 August 2001; revised 12 December 2001; accepted 14 December 2001

Abstract The arrangement of antennal sensilla was studied in female and male ground beetles Bembidion properans Steph. (Coleoptera, Carabidae) using scanning electron microscopy. The ®liform antennae, 1.8±1.9 mm in length, consist of the scape, pedicel and nine ¯agellomeres. In both sexes, three types of sensilla chaetica, two types of sensilla trichodea, six types of sensilla basiconica, one type of sensilla coeloconica and one type of sensilla campaniformia were distinguished. The possible function of the sensilla is discussed and three types of sensilla are considered olfactory, sensilla trichodea type 2 and sensilla basiconica types 1 and 2. Olfactory sensilla form dorsal and/or ventral sensillar ®elds on the ¯agellomeres and occur sparsely or not at all outside these areas. No sexual differences in the types, number and distribution of antennal sensilla were found. q 2002 Elsevier Science Ltd. All rights reserved. Keywords: Antennae; Typology; Number; Distribution pattern; SEM

1. Introduction The ground beetle Bembidion properans is one of the most abundant carabids in agricultural habitats and may have importance as a biological control agent (Edwards and George, 1981; Ekbom and Wiktelius, 1985; Desender, 1986; Pollet and Desender, 1988, 1989). Although some literature data on the feeding ecology of this polyphagous predator are available (Pollet and Desender, 1986, 1987a,b, 1988, 1989), there is no information on the prey searching behaviour of this carabid beetle. B. properans is active during the daytime, and is believed to ®nd its prey by sight (Ekbom and Wiktelius, 1985; Pollet and Desender, 1986; Morwinsky and Bauer, 1997). However, abundant trichoid and basiconic olfactory sensilla found on the antennae in some ground beetles (Daly and Ryan, 1979; Kim and Yamasaki, 1996; Merivee et al., 2000) indicate that chemical cues are probably more commonly used in prey detection and habitat selection in Carabidae than the few reported cases would suggest. * Corresponding author. Fax: 1372-7-313351. E-mail address: [email protected] (E. Merivee).

Here we describe the typology, numbers and location of antennal sensilla in both male and female beetles of B. properans to form a ®rm base for future electrophysiological and behavioural experiments.

2. Material and methods The beetles were collected in Denmark (Lyngby) in 1996, and in Estonia in 1998. Air-dried antennae, together with half of the head, of freshly killed beetles were fastened with either silver paint or carbon paste to aluminium stubs in a vertical position and coated with gold in a sputter coater. Three antennae of both sexes were observed and micrographs were taken from four sidesÐdorsal, ventral, anterior, and posterior, using scanning electron microscopes BS-301 (Tesla Brno, Czech Republic), JSM-840A (JEOL, Japan) or JSM-35 CF (JEOL, Japan). The types, numbers and location of sensilla were identi®ed from SEM montage micrographs. Four large-scale views, dorsal, ventral, anterior, and posterior, were reconstructed of the whole surface of each antennomere by exact ®tting of micrographs alongside each other. On the mounted pictures, borderlines were drawn in

0968±4328/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved. PII: S 0968-432 8(02)00003-3

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E. Merivee et al. / Micron 33 (2002) 429±440

the middle, from the tip to the base, of the antennomeres. These borderlines divided the surface of the antenna into four, dorso-anterior, dorso-posterior, ventro-anterior, and ventro-posterior areas. Each of these areas is observable in two respective mounted pictures. In the middle parts of these overlapping areas, a row of the same sensilla was identi®ed and marked with coloured pen in both respective mounted pictures. The coloured rows served as borders to avoid double counting of sensilla. In classifying sensilla, the terminology of Schneider (1964) and Zacharuk (1985) was used.

3. Results 3.1. General structure of the antennae B. properans has ®liform ¯agellar antennae, 1.8±1.9 mm in length. The antennae consist of the scape (Fig. 1A), pedicel (Fig. 1B) and nine ¯agellomeres of similar shape (Figs. 1C±E and 2A±C). However, the antennomeres vary markedly in size (Table 1). Segments of the antenna are almost round in their cross-section, except for the tip of the terminal ¯agellomere, which is laterally ¯at in shape (Fig. 2D and E). The ball-joints between the scape and the head and between the scape and the pedicel provide the antennae with a remarkable mobility in every direction (Figs. 1A and 3A). The small dorsal and ventral incisions at the scape tip, however suggest that the up-and-down movements of the ¯agellum have a special role in the beetles' behaviour. The antennae of male and female beetles are similar in their general structure and size. Table 1 Mean length (mm) of antennal segments of B. properans. Sc, scape; Pe, pedicel. N ˆ 6 (3 males and 3 females) Sc

0.23

Pe

0.13

Flagellomeres 1

2

3

4

5

6

7

8

9

0.17

0.17

0.16

0.16

0.16

0.15

0.15

0.15

0.24

3.2. Typology of antennal sensilla Three types of chaetoid sensilla (s.ch.1±3), two types of trichoid sensilla (s.t.1 and s.t.2), six types of basiconic sensilla (s.b.1±6), one type of coeloconic sensilla (s.co) and one type of campaniform sensilla (s.ca) were differentiated according to their size and shape on the antennae of

both male and female beetles. Characteristic morphological features of B. properans' antennal sensilla are summarized in Table 2. Long hair-like sensilla were divided into chaetoid and trichoid sensilla according to their way of attachment to the antennal surface. The hairs standing in a wide articulary socket were classi®ed as sensilla chaetica, but long hairs, which sit tightly and immovably in their sockets were classi®ed as trichoid sensilla. Short pegs and cones, which reach above the socket, were classi®ed as basiconic sensilla irrespective of whether they sit in a wide or tight socket. Tiny s.b.4 cones, however, may be sunken into the cuticle to a higher or lower degree (Figs. 2D and 5D). If the cone lies deeply in its socket so that the tip of the cone only barely reaches above the antennal surface, s.b.4 resemble coeloconic sensilla (Fig. 3D). S.b.6 have also been referred to as BoÈhm sensilla (B.s.). Coeloconic sensilla are small pit organs. Deep in the pit ori®ce, the tip of a tiny peg can be seen (Figs. 3D, E and 4D). Campaniform sensilla vary in their shape. As a rule, on the distal ¯agellomeres, the domes are more rounded, larger and surrounded by a lower or higher cuticular collar (Figs. 2D and 4F). On the proximal ¯agellomeres, on the other hand, the domes are smaller, often with an irregular shape and without a clear cuticular collar (Fig. 4E). In the middle of the dome, a tiny central cap is situated (Fig. 4E and F). 3.3. Number and distribution pattern of antennal sensilla Each type of sensilla has a speci®c number, location on the antennomeres, and distribution pattern along the antenna. The total numbers and distribution patterns of sensilla on the antennomeres are summarized in Tables 3 and 4. In total, over 800 s.ch.1 were found on the antenna of B. properans. The number varies considerably in different beetles. The bristles are located on the antennomeres with an almost even density (Figs. 1B±E and 2A, B), except for the scape, where they can be found only near the distal margin (Fig. 1A), and distal part of the ninth ¯agellomere, where they are sparse (Fig. 2C±E). The number of s.ch.1 on the antennomeres increases signi®cantly towards the tip of the antenna. The number of s.ch.2 is stable, 66 bristles per antenna. They stand in a whorl of 6 or 7 around the tips of all ¯agellomeres (Figs. 1C±E and 2A, B, D, E). Around the central part of the terminal ¯agellomere is a second whorl, which consists of six bristles (Fig. 2C). The distribution of s.ch.3 is restricted to the two most

Fig. 1. Antennal segments and sensilla in female B. properans. D and V indicate the dorsal and ventral faces of the antennomeres, respectively; ch.1, ch.2 and ch.3 show sensilla chaetica types 1, 2 and 3, respectively; b.3 and b.5 indicate sensilla basiconica types 3 and 5, respectively; Bs, location of BoÈhm sensilla. Bar ˆ 10 mm. (A) Frontal side of the scape. SHJ and SPJ show joints between the scape and head, and between the scape and pedicel, respectively; ACP, appendages of cuticular plates; DS, large cuticular depression at the scape base; asterisks show the locations of tiny cuticular pores; arrowheads show two large pores in the cuticular depression of the scape base; arrows indicate the location of stout sensilla basiconica type 5. (B) Ventral face of the pedicel. (C) Frontal side of the ®rst ¯agellomere. (D) Frontal side of the second ¯agellomere. (E) The fourth ¯agellomere.

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Table 2 Morphological types of antennal sensilla in the ground beetle B. properans. N ˆ 6 Types of sensilla

Morphological characteristics of sensilla Length (mm)

Diameter (mm)

Tip

Wall

Shape

Socket

Figures

S.ch.1 S.ch.2 S.ch.3 S.t.1 S.t.2 S.b.1

23±75 35±80 90±190 21±35 12±21 5±15

Sharp Blunt Sharp Sharp Blunt Blunt

Grooved Grooved Grooved Grooved Grooved Smooth

Curved Straight Curved Curved Straight or slightly curved Curved

Wide Wide Wide Tight Tight Tight

1C±E, 2A, 3C, F, 4C 1C±E, 2A±E, 3C,E, 4C, 5E 1A,B, 3B 2A, 3C, 4C 2B±E, 4A,B,F 2A, 3E,F

S.b.2

9±16

Blunt

Smooth

Curved

Tight

3E

S.b.3 S.b.4 S.b.5 S.b.6 (B.s.) S.co. S.ca.

2±3 1±2 3.5±23 3±8 ± ±

1.5±2.8, Bristle base 1.9±3.1, Bristle base 2.9±4.6, Bristle base 1.6±2.2, Hair base 1.5±2.1, Hair base 1.3±2.2, Peg base 1.0±1.9, Peg middle 2.0±2.7, Peg base 2.4±3.1, Peg middle 1.1±1.3, Peg base 0.9±1.2, Peg base 1.5±2.4, Peg base 1.0±1.4, Peg base 1.2±1.4, Pit ori®ce 1.2±3.5, Dome 0.4±0.7, Central cap

Sharp Sharp Sharp Sharp ± ± ±

Smooth Smooth Smooth Smooth ± ± ±

Straight Straight Straight Straight ± ± ±

Tight Tight or wide Wide Wide ± ± ±

1A, 5B 2D, 3D, 5D 1A, 5A,C 1A, 3A, 5F 3D±F, 4D 2D, 3E 4E,F

s.t.1 can be found. On the average, 120±122 hairs of this type occurred on one antenna in B. properans. S.t.2 are concentrated at the tip of the antenna (Fig. 2B and C). Their number, 206 and 220 hairs per antenna in female and male beetles, respectively, increases signi®cantly towards the tip of the ¯agellum and in the distal part of the terminal ¯agellomere they are the prevailing type of sensilla (Figs. 2D, E and 4A). They form two separate, ventral and dorsal, sensillar ®elds on the ¯agellomeres, which only in the distal area of the terminal ¯agellomere

basal antennal segments only. The bristles occur in groups of 2±3 distally on the dorso-anterior area of the scape (Figs. 1A and 3B) and on the ventral side of the pedicel (Fig. 1B). S.t.1 can be found on all ¯agellomeres, except for the ®rst one. They stand in a row around the ¯agellomeres, proximally to s.ch.2 sensilla (Figs. 2A and 4C). Close to every s.ch.2, usually two s.t.1 occur so that their number on the ¯agellomeres is nearly twice as large as the number of s.ch.2. However, on the terminal ¯agellomere, some more

Table 3 Mean numbers ^ SD and distribution of sensilla on the antenna of male B. properans. Sc, scape; Pe, pedicel. N ˆ 3 Type

S.ch.1 S.ch.2 S.ch.3 S.t.1 S.t.2 S.b.1 S.b.2 S.b.3 S.b.4 S.b.5 S.b.6 S.co S.ca

Sc

11 ^ 2:5 ± 2 ^ 0:0 ± ± ± ± 4 ^ 0:0 ± 8 ^ 1:2 35 ^ 1:5 ± ±

Pe

23 ^ 4:2 ± 3 ^ 0:6 ± ± ± ± ± ± ± 21 ^ 0:6 ± ±

Flagellomeres

Total

1

2

3

4

5

6

7

8

9

36 ^ 7:0 6 ^ 0:0 ± ± ± ± ± ± ± ± ± ± 1 ^ 1:2

52 ^ 6:0 6 ^ 0:0 ± 12 ^ 0:0 ± 1 ^ 0:6 ± ± ± ± ± 1 ^ 1:2 1 ^ 1:2

72 ^ 12:4 7 ^ 0:0 ± 14 ^ 0:6 ± 22 ^ 4:0 ± ± ± ± ± 1 ^ 1:2 2 ^ 0:0

91 ^ 14:7 7 ^ 0:0 ± 14 ^ 0:6 ± 38 ^ 3:1 ± ± ± ± ± 1 ^ 1:2 2 ^ 0:0

93 ^ 15:5 7 ^ 0:0 ± 14 ^ 0:0 ± 44 ^ 10:8 3 ^ 2:3 ± ± ± ± 2 ^ 0:0 2 ^ 0:0

95 ^ 9:0 7 ^ 0:0 ± 14 ^ 0:0 4 ^ 3:2 60 ^ 9:3 11 ^ 1:2 ± ± ± ± 2 ^ 0:0 2 ^ 0:0

92 ^ 9:6 7 ^ 0:0 ± 14 ^ 0:0 10 ^ 4:0 61 ^ 2:9 12 ^ 4:6 ± ± ± ± 2 ^ 0:0 2 ^ 0:0

111 ^ 12:9 7 ^ 0:0 ± 14 ^ 0:0 27 ^ 10:4 83 ^ 5:0 10 ^ 1:7 ± ± ± ± 2 ^ 0:0 2 ^ 0:0

138 ^ 18:7 12 ^ 0:0 ± 24 ^ 2:5 179 ^ 9:6 104 ^ 8:9 15 ^ 0:6 ± 3 ^ 1:0 ± ± 6 ^ 0:6 5 ^ 1:7

814 ^ 96:5 66 ^ 0:0 5 ^ 0:6 120 ^ 2:5 220 ^ 24:9 413 ^ 29:9 51 ^ 4:7 4 ^ 0:0 3 ^ 1:0 8 ^ 1:2 56 ^ 2:1 17 ^ 3:8 16 ^ 2:9

Fig. 2. Flagellomeres and antennal sensilla in female B. properans. D and V, dorsal and ventral faces of the antenna, respectively; ch.1 and ch.2, sensilla chaetica types 1 and 2, respectively; t.1 and t.2, sensilla trichodea types 1 and 2, respectively; b.1, sensilla basiconica type 1. Bar ˆ 10 mm. (A) Posterior side of the sixth ¯agellomere. Arrowheads indicate sparse tiny cuticular pores; arrow shows single large pore in the dorso-posterior area of the ¯agellomere. (B) Frontal view of the eighth ¯agellomere. Arrowheads show sensilla trichodea type 2. (C) Frontal side of the ninth ¯agellomere. Arrowheads show sensilla trichodea type 2. (D) Tip of the posterior side of the ninth ¯agellomere. Arrows show a group of sensilla campaniformia; arrowhead shows sensillum basiconicum type 4. (E) Dorsal view of the tip of the ninth ¯agellomere.

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433

434

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Fig. 3. Antennal sensilla in B. properans. Bar ˆ 10 mm. (A) Scape base. Bs, BoÈhm sensilla; ACP, appendages of cuticular plates; DS, cuticular depression; arrowheads show two large pores in the cuticular depression. (B) Distal area of the scape. Ch.1 and ch.3 show sensilla chaetica types 1 and 3, respectively. (C) Distal area of the sixth ¯agellomere. Ch.1 and ch.2, sensilla chaetica types 1 and 2, respectively; t.1, sensillum trichodeum type 1; arrow shows a large pore close to ch.2. (D) A group of sensilla coeloconica and sensillum basiconicum type 4 in the middle part of the ninth ¯agellomere. (E) Ventro-posterior area of the seventh ¯agellomere. B.1 and b.2, sensilla basiconica types 1 and 2, respectively; ch.1 and ch.2, sensilla chaetica types 1 and 2, respectively; t.1, sensillum trichodeum type 1; co, sensillum coeloconicum; asterisks show the location of two sensilla campaniformia; arrow shows a tiny pore; arrowhead shows a pore associated with sensilla chaetica type 2. (F) Dorsal area of the seventh ¯agellomere. Ch.1, sensilla chaetica type 1; b.1, sensilla basiconica type 1; co, sensillum coeloconicum.

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435

Fig. 4. Antennal sensilla in B. properans. Bar ˆ 10 mm (A and C) or 1 mm (B and D±F). (A) Distal part of the ninth ¯agellomere. T.2, sensilla trichodea type 2; arrowheads show tiny cuticular pores. (B) Sensilla trichodea type 2 (t.2). (C) Distal part of the third ¯agellomere. Ch.1 and ch.2, sensilla chaetica types 1 and 2, respectively; t.1, sensilla trichodea type 1; arrow shows a pore associated with sensilla chaetica type 2; arrowheads show tiny cuticular pores at the distal margin of the ¯agellomere. (D) Sensillum coeloconicum (co). Ch.1, middle part of the sensillum chaeticum type 1. (E) Sensillum campaniformium. (F) A group of sensilla campaniformia at the tip of the ninth ¯agellomere. t.2 show the tips of sensilla trichodea type 2; arrowhead shows the base of sensillum chaeticum type 1.

436

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Fig. 5. Antennal sensilla in B. properans. Bar ˆ 10 mm (A and F) or 1 mm (B±E). (A) Sensilla basiconica type 5. (B) Basiconic sensillum type 3. (C) Stout basiconic sensilla type 5. (D) Basiconic sensillum type 4. (E) Base of the sensillum chaeticum type 2 (ch.2). Arrow shows a large pore associated with ch.2. (F) BoÈhm sensilla (Bs). ACP, appendages of cuticular plates.

fuse. S.t.2 are located predominantly on the dorsal side of the ¯agellum, 72 and 70% in male and female beetles, respectively. In the dorsal ®elds of sensilla their number is slightly larger on the antenna's frontal side. In the ventral sensillar ®elds, on the contrary, they are a little more numerous on the posterior side of the antenna (Table 5).

S.b.1 can be found abundantly on the ¯agellomeres 3±9, but in some specimens a few also on the second ¯agellomere; in total, 406 and 413 pegs on one antenna in female and male beetles, respectively. Their number increases towards the tip of the antenna. S.b.1 also form two separate, dorsal and ventral, sensillar ®elds on the ¯agellomeres

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437

Table 4 Mean numbers ^ SD and distribution of sensilla on the antenna of female B. properans. Sc, scape; Pe, pedicel. N ˆ 3 Type

S.ch.1 S.ch.2 S.ch.3 S.t.1 S.t.2 S.b.1 S.b.2 S.b.3 S.b.4 S.b.5 S.b.6 S.co S.ca

Sc

8 ^ 0:6 ± 2 ^ 0:0 ± ± ± ± 9 ^ 1:2 ± 13 ^ 3:6 37 ^ 0:6 ± ±

Pe

Flagellomeres

23 ^ 1:2 ± 3 ^ 0:0 ± ± ± ± ± ± 1 ^ 0:6 22 ^ 0:6 ± ±

Total

1

2

3

4

5

6

7

8

9

44 ^ 2:6 6 ^ 0:0 ± ± ± ± ± ± ± ± ± ± 2 ^ 0:6

53 ^ 5:6 6 ^ 0:0 ± 12 ^ 0:6 ± 1 ^ 0:6 ± ± ± ± ± 2 ^ 0:6 1 ^ 1:0

71 ^ 1:5 7 ^ 0:0 ± 14 ^ 0:0 ± 22 ^ 0:6 ± ± ± ± ± 2 ^ 0:0 2 ^ 0:0

91 ^ 3:6 7 ^ 0:0 ± 14 ^ 0:6 1 ^ 1:2 35 ^ 4:9 ± ± ± ± ± 2 ^ 0:0 2 ^ 0:0

99 ^ 2:1 7 ^ 0:0 ± 14 ^ 0:0 2 ^ 2:1 53 ^ 4:2 1 ^ 0:6 ± ± ± ± 2 ^ 0:0 2 ^ 0:0

94 ^ 5:0 7 ^ 0:0 ± 13 ^ 0:6 3 ^ 3:1 54 ^ 9:2 7 ^ 1:5 ± ± ± ± 2 ^ 0:0 2 ^ 0:0

98 ^ 5:7 7 ^ 0:0 ± 14 ^ 0:0 6 ^ 1:2 61 ^ 4:0 11 ^ 1:2 ± ± ± ± 2 ^ 0:0 2 ^ 0:0

110 ^ 3:8 7 ^ 0:0 ± 14 ^ 0:0 17 ^ 5:2 85 ^ 2:3 9 ^ 0:6 ± ± ± ± 2 ^ 0:0 2 ^ 0:0

147 ^ 4:2 12 ^ 0:0 ± 27 ^ 0:6 177 ^ 11:4 95 ^ 5:9 14 ^ 2:1 ± 3 ^ 0:6 ± ± 7 ^ 0:6 5 ^ 1:0

838 ^ 23:6 66 ^ 0:0 5 ^ 0:0 122 ^ 1:2 206 ^ 13:5 406 ^ 18:9 42 ^ 0:6 9 ^ 1:2 3 ^ 0:6 14 ^ 3:2 58 ^ 1:5 21 ^ 0:6 20 ^ 0:6

(Fig. 3F). Only some s.b.1 stand outside of these sensillar ®elds, especially at the distal margin of the ¯agellomeres. Unlike s.t.2, most of s.b.1 sensilla are located on the ventral side of the antenna, 58 and 56% in male and female beetles, respectively. In the dorsal sensillar ®elds, the number of s.b.1 is considerably larger on the frontal side of the antenna. In the ventral sensillar ®elds, in contrast, they are more numerous on the posterior side of the ¯agellomeres (Table 6). S.b.2 are markedly less numerous than s.b.1, 51 pegs were found on the antennal ¯agellum in males, and 42 pegs in females. They form a rather compact group in the ventro-posterior area of the ¯agellomeres 5±9 (Fig. 3E). In addition to these, some long s.b.2 lie in a row around the terminal ¯agellomere, at a distance of about 1/3 from its tip. The two following types of basiconic sensilla found on the antennae of B. properans, are very tiny and rare, sharptipped pegs, s.b.3 and s.b.4 (Tables 3 and 4). In contrast to the s.b.4, s.b.3 have a small longitudinal furrow or depression at its tip, faced to the antenna base. S.b.3 were observed

on the scape only, mostly on its frontal and ventral faces (Figs. 1A and 5B). On the other hand, s.b.4, usually 3 pegs per antenna, are restricted to the terminal ¯agellomere. One of them is situated near the group of dome-shaped sensilla, s.ca., at the very tip of the posterior side of the ¯agellomere (Fig. 2D), the second lies also at the tip of the ¯agellomere, but on its anterior side, close to the group of coeloconic sensilla. The third s.b.4 can be found in the middle of the posterior side of the ¯agellomere, near the second group of coeloconic sensilla (Fig. 3D). In some specimens, one or two s.b.4 may occur also in other areas of the terminal ¯agellomere. S.b.5, which vary remarkably in shape and size, are usually located sparsely on the scape (Figs. 1A and 5A). However, in some females, single s.b.5 were observed at the pedicel base, too. In some cases, a group of very short and stout cones were found posteriorly at the scape base (Fig. 5C). S.b.6 (BoÈhm sensilla), as a dense group, occupy the bases of the scape and pedicel at the joints between the scape and the head and between the scape and the pedicel (Figs. 1A

Table 5 Placement of sensilla trichodea type 2 on the antenna of B. properans. DA, DP, VA and VP, dorso-anterior, dorso-posterior, ventro-anterior and ventro-posterior areas of the ¯agellomeres, respectively. N ˆ 3

Table 6 Placement of sensilla basiconica type 1 on the antenna of B. properans. DA, DP, VA and VP, dorso-anterior, dorso-posterior, ventro-anterior and ventro-posterior areas of the ¯agellomeres, respectively. N ˆ 3

Sex

Sex

Area

Flagellomeres 1

2

3

4

5

6

7

8

9

Area

Flagellomeres

1

2

3

4

5

6

7

8

9

Male

Total DA DP VA VP

± ± ± ± ±

± ± ± ± ±

± ± ± ± ±

± ± ± ± ±

± ± ± ± ±

4 3 1 ± ±

10 5 3 1 1

27 14 10 1 2

179 65 58 24 32

Male

Total DA DP VA VP

± ± ± ± ±

1 ± ± ± 1

22 2 1 5 14

38 7 4 6 21

44 11 6 9 18

60 15 9 15 21

61 16 12 13 20

83 19 15 22 27

104 30 25 18 31

Female

Total DA DP VA VP

± ± ± ± ±

± ± ± ± ±

± ± ± ± ±

1 ± ± ± 1

2 ± ± ± 2

3 2 ± ± 1

6 6 ± ± ±

17 10 5 ± 2

177 74 48 25 30

Female

Total DA DP VA VP

± ± ± ± ±

1 ± ± ± 1

22 3 2 7 10

35 6 6 10 13

53 13 8 15 17

54 13 11 13 17

61 13 14 13 21

85 24 14 18 29

95 28 22 14 31

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and 3A). Although their numbers vary a little in different beetles, on the average, 56 s.b.5 were counted on the antenna, both in males as well in females. S.co. occur mostly in pairs on the ¯agellomeres 2±8, one on the dorsal, the other on the ventral side (Fig. 3E, F). In some specimens, on the proximal ¯agellomeres, they were found also singly. However, there are more of them on the apical ¯agellomereÐusually three are located frontally at the very tip of the ¯agellum, three in the middle of the back side (Fig. 3D). S.ca. usually lie on the ¯agellomeres in pairs next to each other. On the apical ¯agellomere, they are a little more numerousÐtwo to four posteriorly at the tip of the ¯agellomere (Figs. 2D and 4F), two or three dorsally in the middle of the frontal side. 3.4. Cuticular pores Abundant cuticular pores, various in their size and location, can be found on all surfaces of the antenna. Two large pores may be noticed in the cuticular depression at the scape base (Fig. 3A). Single large pores also occur dorsoposteriorly at the base of all ¯agellomeres (Fig. 2A). One medium-sized cuticular pore is associated with every s.ch.2 sensillum, lying proximally close to the bristle base (Figs. 3C, E and 5E). Abundant tiny pores were found scatteredly on the whole surface of the antenna (Figs. 1A, 2A, 3E and 4A, C). Appendages of cuticular plates (ACP) are abundant at the bases of all antennomeres, close to the intersegmental joints (Figs. 1A, 3A and 5F). 4. Discussion The wide articular socket and the pointed tip of the large bristles of s.ch.1 and s.ch.3 as well as the ultrastructural evidence of similar antennal sense organs, classi®ed as `trichoid sensilla type 1', in the ground beetle Nebria brevicollis (Fab.) (Daly and Ryan, 1979) suggest that mechanoreception is the most probable function for these sensilla. Although s.t.1 differs from s.ch.1 most conspicuously by the absence of the wide socket at the hair base, these large sharp-tipped hairs also seem to function as mechanoreceptors. These three types of large bristles and hairs have striking differences in their numbers and distribution pattern indicating that they probably have different sensory function in the beetles' behaviour. Electrophysiological and ultrastructural studies are needed to explain to which kind of mechanical stimuli these sensilla respond. S.ch.2 also have a wide articular socket, but in contrast to the s.ch.1 and s.ch.3, these large bristles are blunt-tipped, characteristic of chemoreceptors (Keil and Steinbrecht, 1984; Zacharuk, 1985). By their shape, number and distribution pattern, the s.ch.2 are similar to the `sensilla trichodea type 3' found on the antennae of N. brevicollis. The internal structure of these sensilla in the latter showed that

they probably function as mechano- and contact chemoreceptors (Daly and Ryan, 1979). Abundant blunt-tipped, immovable hairs which resemble s.t.2 of B. properans are common on the antennal ¯agellum of insects. They resemble `sensilla trichodea type 2' and `sensilla trichodea' on the antennae of the ground beetles Bembidion lampros Hbst (Merivee et al., 2000) and Platynus dorsalis (Pont.) (Merivee et al., 2001), respectively. Although adequate blunt-tipped hairs are absent in the ground beetle Carabus ®duciarius saishutoicus Csiki (Kim and Yamasaki, 1996), the similarities in length, grooved base and distribution pattern along the ¯agellum indicate that abundant conical `sensilla basiconica type 1' on their antennae may functionally correspond to the s.t.2 of B. properans. In male moths, trichoid sensilla respond to female sex pheromone related compounds (Keil and Steinbrecht, 1984; Zacharuk, 1985; Hansson et al., 1986; Hallberg et al., 1994). Striking differences in the number of these trichoid sensilla, for example, in click beetles (Merivee, 1992; Merivee et al., 1999) suggest that they probably function as sex pheromone receptors in males of some beetles, too. In contrast, no striking sexual differences in the number of the blunt-tipped trichoid sensilla were found in the ground beetles B. properans, B. lampros (Merivee et al., 2000) and P. dorsalis (Merivee et al., 2001), indicating that these sensilla probably respond to aggregation pheromone to be produced by some ground beetles (Moore and Wallbank, 1968; Wautier, 1970, 1971). Various subtypes of blunt-tipped, non-articulated pegs with a smooth wall, analogous to the s.b.1 and s.b.2 in B. properans, are plentiful on the ground beetles' antennae, although some minor differences may be noted in their external morphological details (Daly and Ryan, 1979; Kim and Yamasaki, 1996; Merivee et al., 2000). In other insects, these basiconic sensilla are known to be olfactory receptors responding to food and habitat related compounds (Schneider, 1964; Zacharuk, 1985). Ultrastructural evidences of the sensilla basiconica type 1 in N. brevicollis support olfactory function of these sensory organs in ground beetles (Daly and Ryan, 1979). On the other hand, the presence of a wide articular socket, pointed tip, and the location of the basiconic sensilla s.b.5 and s.b.6 (BoÈhm sensilla) on the scape and pedicel only suggests that these are mechanoreceptors although histological as well as electrophysiological evidence is absent in beetles (Schneider, 1964; Keil and Steinbrecht, 1984; McIver, 1985; Zacharuk, 1985). In the honeybee, BoÈhm sensilla are shown to be phasic±tonic mechanoreceptors (Schneider, 1964). Concentration of BoÈhm sensilla at the intersegmental joints between the scape and the head as well as between the scape and the pedicel, in many insects, suggests that these sensilla probably perceive the antennal position and movements. We suppose that these intersegmental sensilla in combination with the antennal shaft may perceive both wind direction and strength in anemotactic reactions, not only in the ground beetles but also in many other beetles

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searching on the ground. Electrophysiological and behavioural experiments are needed to con®rm their function. Rare, sharp-tipped s.b.3 are the third type of basiconic sensilla found on the antennal scape of B. properans. In contrast to s.b.5 and s.b.6, s.b.3 seem to have no large articulary socket at their base. A small groove or depression, not characteristic for mechanoreceptive pegs, at the tip of tiny s.b.3 indicate that they are probably identical in function to `sensilla basiconica type 3' on the scape of B. lampros (Merivee et al., 2000), and ear-shaped `sensilla auricillica' in the proximal part of the antennae of P. dorsalis (Merivee et al., 2001). Though no other sensilla but mechanoreceptors have been described on the antennal scape of beetles, the function of s.b.3 sensilla still needs to be clari®ed. Very small and rare s.b.4 on the apical ¯agellomere in B. properans resemble the `sensilla basiconica type 4' and sensilla basiconica type 3 in the same area of the antennae of the ground beetles B. lampros (Merivee et al., 2000) and P. dorsalis (Merivee et al., 2001), respectively. However, similar sensilla are missing in the ground beetle Carabus ®duciarius saishutoicus Csiki (Kim and Yamasaki, 1996). The data about their function are not available. Pit-organs, similar to s.co. of B. properans have been described also in other ground beetles (Kim and Yamasaki, 1996; Merivee et al., 2000), but they are missing, for instance, in click beetles (Merivee, 1992; Merivee et al., 1998, 1999) and in bark beetles (Hallberg, 1982; Faucheux, 1989, 1994). In the ground beetle C. ®duciarius saishutoicus, these pit-organs are classi®ed as sensilla ampullacea, however (Kim and Yamasaki, 1996). Chemo-, thermo-, or hygroreception are the most probable functions for these sensilla (Zacharuk, 1985). Campaniform sensilla are common on the antennae of ground beetles and click beetles (Merivee, 1992; Kim and Yamasaki, 1996; Merivee et al., 1998, 1999, 2000). In some other insects, they are often located close to the certain articulations on the wings, legs, and halteres, perceiving stress in the cuticle resulting from mechanical deformation (McIver, 1985; Zacharuk, 1985). Which kind of stimuli they respond on insect antennae, still needs to be clari®ed. The most numerous, presumably olfactory sensilla, s.t.2 and s.b.1, form two, dorsal and ventral, sensillar ®elds on the ¯agellomeres. Their numbers on the ¯agellomeres, growing towards the tip of the antenna, are unevenly distributed between the two ®elds of sensilla. On the average, 70±72% of all s.t.2 stand in dorsal sensillar ®elds. On the contrary, a majority of s.b.1, 56±58% on the average, was counted in the ventral sides of the ¯agellomeres. In addition, certain lateral asymmetry occurs in the location of these sensilla (Tables 5 and 6). Similar asymmetry in the distribution of antennal olfactory sensilla has also been observed in the ground beetle B. lampros (Merivee et al., 2000) and in some click beetles (Merivee et al., 1997, 1999). It has been suggested (Merivee et al., 1997) that asymmetries in the distribution pattern of olfactory sensilla on insects' antennae may be due to the peculiarities

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of their search behaviour (waiting, walking, ¯ying, antennal movements), which causes certain areas of the antennal surface to catch the wind-borne odour molecules more effectively than the others. Besides the sensory organs abundant cuticular pores, obviously openings of the antennal glands, penetrate the surface of the antennae of B. properans. Differences in size and placement of these pores suggest differences in the function of respective cuticular glands. In some other insects, antennal glands may have enzymatic activity, degrading molecules of pheromones (Taylor et al., 1981; Vogt and Riddiford, 1981; Prestwich, 1987) or plant±host volatiles (Dickens et al., 1992) to prevent them overloading the antennal chemosensilla. In Chrysomelidae, antennal glands may produce pheromone (Medvedev and Pavlov, 1988; Bartlet et al., 1994). Further investigations are needed to clarify the function of the antennal cuticular glands in Carabidae. Acknowledgements We thank Mrs Jelena Asari for producing the high-quality micrograph illustrations. We gratefully acknowledge that the essential part of SEM studies was carried out using the equipment JSM-35 CF donated to University of Tartu by Studsvik AB (Sweden). This research was partly supported by grant no. 4092 from the Estonian Science Foundation. References Bartlet, E., Isidoro, N., Williams, I.H., 1994. Antennal glands in Psylliodes chrysocephala, and their possible role in reproductive behaviour. Physiol. Entomol. 19, 241±250. Daly, P.J., Ryan, M.F., 1979. Ultrastructure of antennal sensilla of Nebria brevicollis (Fab.) (Coleoptera: Carabidae). Int. J. Insect Morphol. Embryol. 8, 169±181. Desender, K., 1986. On the relation between abundance and ¯ight activity in carabid beetles from a heavily grazed pasture. J. Appl. Entomol. 102, 225±231. Dickens, J.C., Visser, J.H., Van den Pers, J.N.C., 1992. Detection and deactivation of pheromone and plant odor components by the Beet Armyworm, Spodoptera exigua (Hubner) (Lepidoptera: Noctuidae). J. Insect Physiol. 39, 503±516. Edwards, C.A., George, K.S., 1981. Carabid beetles as predators of cereal aphids. Proceedings, 1981 Brighton Crop Protection ConferenceÐ Pests and Diseases. Lavenham Press, Lavenham, UK, pp. 191±199. Ekbom, B.S., Wiktelius, S., 1985. Polyphagous arthropod predators in cereal crops in central Sweden. Z. Angew. Entomol. 99, 433±442. Faucheux, M.J., 1989. Morphology of the antennal club in the male and female bark beetles Ips sexdentatus Boern. and I. typographus (L.) (Coleoptera: Scolytidae). Ann. Sci. Nat., Zool. Paris 10, 231±243. Faucheux, M.J., 1994. Distribution and abundance of antennal sensilla from two populations of the pine engraver beetle, Ips pini (Say) (Coleoptera, Scolytidae). Ann. Sci. Nat., Zool. Paris 15, 15±31. Hallberg, E., 1982. Sensory organs in Ips typographus (Insecta: Coleoptera)Юne structure of antennal sensilla. Protoplasma 111, 206±214. Hallberg, E., Hansson, B.S., Steinbrecht, R.A., 1994. Morphological characteristics of antennal sensilla in the European cornborer Ostrinia nubilalis (Lepidoptera: Pyralidae). Tissue Cell 26, 489±502.

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