Proe. Indian Acad. Sci. (Anim. Sci.), Vol. 89, Number 6, November 1980, pp. 551-556. (~ Printed in India.

Tergal gland and its probable role in sex attraction in the termite , Postelectrotermes na.vari

R V VARMA* Department of Zoology. University of Kerala, Kadavattam, Trivaadrum 695581, India * Present address: Division of Entomology, Korala Forest Research Institute, Peechi 680 653, Kerala, India

MS received 30 November 1979; revised 17 May 1980

Abstract. In Postelectrotermes nayari, a tergal gland is located on each of the 9th and 10th abdominal tergite of the female reproductives. The two glands do not differ much in size and histology. The most significant behavioural pattern of the reproductives is tandem running. Evidence for the release of an excitatory substance is obtained mainly by studying the post-flight-behaviour of the reproductives. Experiments with ether extracts of the different parts of the body show that males are attracted to the extract of tile 9th and 10th abdominal tergites of the female.

Keywords. Tergal gland ; Postelectrotermes nayari.

1. Introduction

In many insects sex attractants play an important role in mating and mprodu~ion. In majority of eases females produce the sex pheromone to which males respond. Recently many investigators have reported the phenomenon of attra~ion between sexes of termites (Noirot 1969; Pasteels 1972; Stuart 1975), but compared to other orders of insects, the role of sex pheromone in determining sexual behaviour of termites is minor. Quennedey (1975) reviewed the morphology of the exogrine glands producing pheromones in cockroaches and termites. However, it is note- worthy that tergal glands are the least known of all the exoerine glands of ter- mites. The present paper embodies the histological studies of the tergal gland and its probable role in sexual behaviour of the reproduetives of P. nayari.

2. Materials and methods

Small colonies of P. nayari Roonwal and Vernm were reared in the laboratory which consisted of pseudergates, soldiers and winged reproductives (elates). Alates collected from field were also used for the study.

551

552 R V Varma

For histological studies, the last abdominal tergites or the whole abdomen of the male and female of P. nayari were cut and fixed in Bouin's fluid. The fixed tissues were processed in the routine manner and 8/~ seations were cut and stained in Heidenhains' haematoxylin or Ehrlich's haematoxylin and eosin. Fat was studied histoohemically by Baker's Sudan Black B method with acetone treated controls; glycogen by PAS te0hnique of Me Menus with control sections treated with saliva and protein by mercury bromphenol blue method of Bonhag (Pearse 1968).

Ether extracts of head region, tergites 1-7 and tergites 8-10 of both male and female dealated reproduotives were prepared. A piece of filter paper was soaked in each of the extracts and placed in a petridish having 5 males and 5 females. The number of times the female and the male touched or were attracted to the filter paper aontaining the extract within 5 rain and the sex of the animal were recorded. Filter paper soaked in ether alone served as control.

The post-flight behaviour of the reproduotives of P. nayari was also studied.

3. Observations

In P. nayari a tergal gland is present on each of the 9th and 10th abdominal t~rgite of the female reproduetives (figure 1). The glands have not been observed in the male reproductives, soldiers or pseud~rgates.

Each crescent-shaped gland is 180-300ix long. The two glands in the adjacent tergites do not show much difference in size and cellular details (figure 2). Each gland consists of two types of cells, which differ only in size and are dlstributed almost equally. Very small e~ntraUy placed nuclei and vacuoles are seen in all these cells.

Histochemical studies of the tergal gland reveal presence of very little fat in the area which appears vacuolated in histological preparations. Carbohydrates and proteins have not been detected in the gland.

Evidence for the release of a sex attraetant or excitatory substance has mainly Gome from the post-flight behaviour of P. nayari. The reproductives fly about only for a short while. As soon as they alight, they move about for sometime and then shed their wings. During their search for a suitable nesting site, they usually try to congeal under a piece of wood or under any moistened surface with soil particles.

The most significant behavioural pattern in post-flight is tandem framing (figure 3). After dealation, both males and females move around excitedly. They often show circling movements. As soon as the males come in contact with the females, they closely follow the female, frequently contacting with arttennae and mouth-parts (figure 4). Oe0asionally it is found that when a pair moves in tandem, a third one ,~ntrudes and follows it for a few centimeters. The calling posture characteristic of females of many species of termites has not been noticed in the female imago of P. nayari. In P. nayari males follow the females and not vice versa. Members of the same sex do not pair or move in tandem. One~ the link between the male and female is established, then they move in pairs. When the goata0t is lost, the female stops and waits until the contact is re-established. When the male from such a moving pair is forcibly removed, and when 1he

Sex attraction in termite 553

'i rER.GL

f !

i

Figures 1-4. 1. Sagittal section of the tergal glands of female reproductive of P. nayari :< 100. TER. GL--tergal gland. 2. Sagittal section of the tergal gland on the 9th sternite of the female reproductive of P. nayari × 400. N--nucleus. 3. Photograplx showing tandem running by the reproductives of P. nayari (length of the animal approximately 7 ram). 4, Photograph showing the female being followed by the mate (length of the animal approximately 7 tam). (M--male; F--female.)

Sex attraction in termite 555

Table 1. Showing the number of times the males and the females responded to the various body axtracts of the roproductives of P. nayarL

Sex of animal Number of touches Control Source of from which extract extract is M F M F

prepared

Torgitos (1-7) F 5 3 3 1 Tergitos (8-10) F 32 2 1 0 Head region F 2 4 4 1 Tergitos (1--7) IV[ 6 0 5 3 Tergites (8-10) M 9 11 2 1 Head region M 4 2 0 4

famal~ is mechanically stimulated, sh~ moves only for a short distance and fails to exhibit the normal behavioral patterns. The mechanical stimulus induces only very little moving activity on the part of the female.

Experiments with diffemrtt body extracts in ether show that the males are attracted towards the extract of the last (8-10) abdominal tergites of the females. The attracted males are quite exdited and are drawn close to the filter paper with the extract. They inspect the filter paper with the antennae, move back for a short while and then again touch the paper. Table 1 shows the number of contacts per male and female of P. nayari, to various extracts of male and female of the species. Extracts of the different parts of the body are touched casually by both sexes, but the characteristic behavioural responses in males are aroused only by the extract of the last (8-10) abdominal tergites of the females.

4. Discussion

Although sex pheromones play a relatively less important role in termites there is no doubt that chemical communication is involved in their sexual behaviour (Noirot 1969; Stuart 1970, 1975; Wall 1969). Barth (1955) had shown earlier that in Syntermes dirus tergal gland secrÙtions seemingly have some effect on pair- ing of reproduatives. The post-flight behaviour of P. nayari indicates that some kind of sex attraatant is involved in the process of tandem behaviour and pair formation. It is also possible that sex attraction in these is the result of a short term interaction between the opposite sexes. Stuart (1970) suggests that since termites are poor flyers, they do not require highly volatile pheromones to perform elaborate sexual behaviour.

In Reticulitermes it has been shown that the tandem behaviour of the reproduc- fives is due to an excitatory pheromone (Stuart 1969, 1975). From the way in which the males repeatedly touch the secretion-soaked filter paper, it seems likely that in P. nayari also the odour produced by the tergal gland secretion acts as an excitatory pheromone, rather than as a true sex attractant. Leuthold and Ltischer (1974) have shown that in Trinervitermes bettonianus the sternal gland is

556 R V Varma

used in trail marking during tandem behaviour as well as (in the case of female) a sex pheromone. The adults of Zootermopsis nevadensis do not possess the tergal ~l~nd (P&steels 1972).

Acknowledgments

The author is indebted to the late Prof. K K Nayar, Department of Zoology, University of Kerala, Trivandrum, for providing faoilities and guidance. The fmanaiat assistance from the University of Kerala is also acknowledged.

References

Baxth R, 1955 Ubcr die tergitalen Drussenfelder von Syntermes dirus (Isoptera); Rev. Brasil Biol. 15 257-263

Noirot C 1969 Glands and secretions ; in Biology of termites, (eds) K Krishna and F M Weesner (New York: Academic Press Inc.) 1 89-123

Pasteels J M 1972 Sex-specific pheromones in a termite ; Experientia 28 105 Pearse A G E 1968 Histochemistry, theoreticaland applied, 3rd edition (London : Churchill Ltd.)

1 VII q- 759 pp. Quennedey A 1975 Morphology of exocrine glands producing pheromones and defensive substances

in subsocial and social insects ; Prec. IUSSI Symposium, Dijon, (eds.)Noirot Ch, P E Howse and G Le Masne pp. 34-38

Stuart A M 1969 Social behaviour and communication ; in Biology of termites (eds)K Krishna and F M Weesner (New York : Academic Press Inc.) 1 193-229

Stuart A M 1970 Kole of chemicals ia termite communication; in Communication by chemical signals (¢ds.) J W Johnston, D G Moulton and A Turk (New York : Appleton--Centuary-- Crafts) 1 79-106

Stuart A M 1975 Chemoreception, behaviour and polyethism in termites (Isoptera) ; in OIfaction and Taste V (eds.) D Denton and J Coghlan (New York : Academic Press) pp. 343-348

Leuthold R H and Liischer M 1974 An unusual caste polymorphism of the sternal gland and its trvil pheromone production in the termite, Trinervitermes bettonianus ; Ins. Sociaux 21 335-341

Wall M 1969 Untersuchungen uber die tergaldrnse der termite Kalotermes flavicollis (Fabr.) (Isoptera) ; Proc. VL Int. Congr. IUSSI, Bern. pp. 295-297