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Scanning electron microscopic studies of antennalsensilla of adult worker Apis florea F (Hymenoptera:

Apidae)M Gupta

To cite this version:M Gupta. Scanning electron microscopic studies of antennal sensilla of adult worker Apis florea F(Hymenoptera: Apidae). Apidologie, Springer Verlag, 1992, 23 (1), pp.47-56. �hal-00890969�

Original article

Scanning electron microscopic studiesof antennal sensilla of adult worker Apis florea F

(Hymenoptera: Apidae)

M Gupta

Haryana Agricultural University, Department of Zoology,Laboratory of Animal Behaviour and Simulated Ecology, Hisar- 125 004, Haryana, India

(Received 10 January 1989; accepted 25 October 1991)

Summary — The micromorphology of the antennae of the honey bee Apis florea F was studied.The number and distribution of the various types of sensilla were examined. Sensilla observed weresensilla placodea, basiconica, trichodea, ampullacea, coeloconica and campaniformia. Sensilla tri-chodea were found most frequently and were present on all the antennal segments. Sensilla placo-dea and sensilla basiconica were present on 8 distal segments. Sensilla ampullacea and sensilla co-eloconica were present on 5 distal segments while sensilla campaniformia were confined to 7 distalsegments. The highest density of sensillae was found on the distal antennel segment. The distribu-tion of different types of sensilla on the antenna resembled that described for other Apis species.

Apis florea / antenna / sensilla / morphology / SEM

INTRODUCTION

The honey bee, Apis florea F acts as apollinating agent of some crops in the hotclimates of the Indian sub-continent (Rah-man, 1940; Rauala, 1972). This paperpresents an initial study of the olfactorysystem of this insect.

The antennae are the main sites of ol-

factory receptors in most insects (Wiggles-worth, 1965). Scanning electron micro-

scopic (SEM) studies of worker honeybees, Apis mellifera, have been carriedout earlier (Slifer and Sekhon, 1960; Sli-

fer, 1970; Dietz and Humphreys, 1971)and also on many other Hymenopterans

(Norton and Vinson, 1974; Argen, 1977,1978).

This study describes the types and dis-tribution of sensilla on the antennae of

Apis florea F workers as revealed by SEM(the first being undertaken by Gupta,1986) and compares these results withother studies in the literature. The majorobjective of this work was to examine theexternal aspects of various sensilla andtheir distribution pattern. This informationwill be useful at a later stage in conduct-ing physiological studies associated withbehaviour to determine whether morpho-logically similar structures have been ho-mologized within different taxa.

MATERIALS AND METHODS

Specimens were collected from fields locatednear Haryana Agricultural University duringMarch 1981.

The antennae of A florea worker bees were

ctipped, air-dried over silica gel and mounted onaluminium stubs with adhesive tape and silverglue. The preparations were coated under vacu-um with a 35-mm layer of pure gold in a sputtercoating unit. The antennae were viewed and

photographed using a Phillips PSEM 501 B atan accelerating voltage of 7.2 kV.

Counts of sensilla were made directly fromthe SEM video monitor. The side of the antenna

against the head was defined as the upper andthe side away from the head as the under side.

The segments starting from the proximal to dis-tal end of the antenna were designated as Se1,Se2 and so on.

RESULTS

The antenna of worker bees of A floreahad 10 segments. Its length varied from3.0-3.5 mm. The last segment had a bluntroundish end. The distribution of different

types of sensilla along the antenna is illus-trated in figs 1, 2 and table I.

Most of the sensory structures found onthe antenna of worker bees are situatedon the 8 distal segments. The remaining 2segments of the flagellum are exclusivelycovered with sensilla placodea. Sensilla

placodea and setae occupy distinct zoneson the segments with very little overlap-ping. Scape and pedicel only have hairsand are completely devoid of setae andsensilla (fig 3). The surface is rough in thesetae-rich zone and smooth in the sensilla

placodea-rich zone.Setae are found on all the segments of

the flagellum. The first 2 segments aredominated by setae 2-33 μm long (mean15 μm) 0.68-2.3 μm width (mean 1.3 μm).Proximally in Se1, they appear needle-like(fig 4) and incline close to the surface but

gradually become knife- or sabre-like anderect on reaching the sensilla placodeafield. The setae are larger on the inner sideof the antenna (fig 5). The outer side ofSe10 has smooth and curved setae. A fewbifid and trifid setae are present on the fla-gellum. Some setae are patterned (fig 6).More sensilla trichodea were found than

any other type. Other sensilla occurredwith decreasing frequency: sensilla placo-dea > sensilla coeloconica/sensilla ampul-lacea > sensilla basiconica > sensilla cam-

paniformia.Sensilla placodea were distributed from

the proximal end of Se3 to the last seg-ment, Se10. There were 3 times as manyon the upper side (dorsal side) as on theunder side (ventral side). They occurred asoval pore plates with a thick, slightly raisedrim and indistinct furrows all around (fig 7).Sensilla trichodea were most abundant.

These were found on all the segments ofthe antenna. These were 0.83 times as

many on the upper side as on the underside. This type of sensillum was ultrastruc-turally segregated into types A, B and CD(figs 7-9). Sensilla trichodea A had a blunttip (fig 9, inset). Sensilla trichodea B oc-curred in sharply bent forms. Sensilla tri-chodea CD type were curved. Sensillabasiconica were less visible at the apex.They were lodged in a distinct socket andwere thick with blunt depressed tips, prob-ably indicating a pore (fig 10).

Sensilla campaniformia occurred on the7 distal segments of the antenna. The wallaround the bulb had a button-like knob (fig11). Sensilla ampullacea and sensilla coel-oconica occurred on the 5 distal segmentson the antenna. Sensilla ampulacea hadsmaller pores whereas sensilla coeloconi-ca showed wide pores (figs 11, 12).

DISCUSSION

The location of different types of sensillaon antenna of A florea is similar to those ofA mellifera. But the population of the typesof olfactory sensilla was comparativelymuch less on the antenna of A florea

(Bhardwaj, 1974; Gupta, 1982) than on Amellifera (Dietz et al, 1974). The distribu-tion of various types of sensillae along theantenna is similar to that found in other

Apis species.Sensilla trichodea type A are the most

common structures on the antenna. The

morphology of this sensillum indicates anolfactory function (Slifer and Sekhon,1961). The olfactory function of sensilla tri-chodea over the year was also hypothe-

sized by various workers (Vogel, 1921;Frisch, 1967; Schneider, 1968; Dietz and

Humphreys, 1971). However, Lacher

(1964) reported that sensilla trichodea typeA did not respond to any chemical stimulibut sensilla trichodea type B responded tomechanical stimuli in A mellifera. In Apis,Martin and Lindauer (1966) found some ofthese sensilla on the distal antennal seg-ment of A mellifera and suggested that

they may be used to decipher wax smooth-ness. This type of arrangement of sensillawas neither observed in this study nor is it

frequently encountered in other bees. Ess-len and Kaissling (1976) suggested a gus-tatory function of sensilla trichodea typeCD. It has also been reported that the sen-silla trichodea are the sex pheromone re-ceptors on the male spruce budworm Cho-

ristoneura fumigarana (Albert et al, 1974)and the male red banded leaf roller Aroyro-taenia velutinana (O’Connell, 1972, 1975).

The sensilla placodea have been shownto be odour receptors in A mellifera (Lach-er and Schneider, 1963; Kaissling and

Renner, 1968). Sensillum basiconicum hasan apical pore at its tip. Although there isno evidence from the present morphologi-cal investigation to indicate the presenceof a closing - opening mechanism of theapical pores, such a process is known forthe terminal pores of gustatory sensilla in

Schistocerca gregaria (Blaney and Chap-man, 1969), Locusta migratoria (Blaney etal, 1971) and the blowflies Phormia reginaand Calliphora vicinia (Sturchow et al,1973). Slifer et al (1959) and Schneider etal (1964) thought that sensilla basiconicaparticipated in chemoreception in grass-hoppers and moths, and the pores presentin their walls are much suited for the per-ception of olfactant molecules.

In sensilla ampullacea and sensilla coel-oconica the surface around the pore is

smooth in A florea (figs 11, 12) in contrastto A mellifera in which it was patterned (Ar-gen, 1975). These have been shown to re-spond to carbon dioxide in A mellifera

(Lacher, 1964), temperature in Aedes ae-

gypti (Davis and Sokolove, 1975) and Peri-planta americana (Altner et al, 1977) andhumidity in P americana (Yokohari and Ta-neda, 1976; Altner et al, 1977; Yokohari,1978). Sensilla campaniformia are prob-ably mechanoreceptors (Pringle, 1938;Esslen and Kaissling, 1976; Yokohari andTaneda, 1976; Yokohari, (1978) reportedthe presence of campaniform sensilla oncockroach legs which are mechanorecep-tors and responded to the stresses of thecuticle. Campaniform sensilla are found tooccur in association with ampullaceousand coeloconic sense organs and hencethese may be considered sensitive to tem-

perature, carbon dioxide and humidity or a

combination of these factors. This specula-tion is based on the electrophysiologicalfindings of Lacher (1964) for A mellifera.

All Apis species studied so far possesssimilar types of sensilla on their antennae.It is the distribution of these sensilla alongthe antenna that differs among species.The similarities in distribution among the

Apis species are pronounced. Less similar-ity occurs in distribution if one comparesA florea with less closely related Hymenop-tera.

ACKNOWLEDGMENTS

The valuable assistance of the late RP Kapiland the technical aid of V Sethi and SCP Shar-ma are gratefully acknowledged. The study wassupported by Haryana Agricultural University,Hisar, India. I am grateful to RC Sihag for help-ful discussion.

Résumé — Étude en microscopie élec-tronique à balayage des sensilles del’antenne chez l’ouvrière adulte d’Apisflorea (Hymenoptera, Apidae). Les ré-

cepteurs sensoriels du flagelle des ouvriè-res d’Apis florea ont été étudiés en micro-scopie optique et en microscopieélectronique à balayage (MEB). L’antennecomprend le scape, le pédicelle et le fla-

gelle constitué de 10 segments. Le scapeet le pédicelle n’ont que des poils en formede plumes mais aucune structure sembla-ble aux soies ou aux sensilles du flagelle.Les soies prédominent sur les 2 premierssegments du flagelle. On n’observe pas deséparation nette entre les sensilles et leszones de soies. La distribution et le nom-bre des divers types de sensilles (tricho-dea, placodea, basiconica, ampullacea,coelonica et campaniformia) ont été déter-minés. Les sensilla trichodea sont les plusnombreuses et présentes sur tous les seg-ments du flagelle. Les sensilla placodea et

basiconica sont présentes sur les 8 seg-ments terminaux. Les sensilla ampullacea/coelonica sont présentes sur les 5 seg-ments terminaux et les sensilla campani-formia sur les 7 derniers. Certaines sen-silla basiconia présentent une dépressionmontrant un pore à l’apex. Trois types desensilla trichodea sont présents; les sen-silla trichodea A sont fines et droites, les Bsont courbées. Les types C ou D sont in-curvés mais difficiles à distinguer l’un de

l’autre. Les sensilla ampullacea/coelonicaet les campaniformia se présentent pargroupes dans la même région. Les sen-silla ampullacea sont plus petites que lescoelonica, elles-mêmes plus petites queles campaniformia. Ces dernières sont lesmoins nombreuses.

Apis florea / antenne / sensille / mor-

phologie / MEB

Zusammenfassung — Rasterelektro-

nenmikroskopisches Studium von denFühlerssensillen der Arbeitsbiene Apisflorea (Hym, Apidae). Die sensorischen

Rezeptoren am Flagellum der Arbeiterin-nen von Apis florea wurden mittels Licht -und REM-Mikroskopie untersucht. Die An-tenne besteht aus Schaft, Pedicel (Sockel)und 10-gliedriger Geißel (Flagellum).Schaft und Sockel tragen nur gefiederteHaare und keine Strukturen ähnlich den

Borsten und Sensillen der Geißel. Die

ersten beiden Segmente der Geißel sindvor allem mit Borsten besetzt. Zwischenden Arealen der Sensillen und der Borstenist keine klare Abgrenzung zu erkennen.Es wurden Verteilung und Populationenvon Sensilla trichodea, Sensilla placodea,Sensilla basiconica, Sensilla ampulacea,Sensilla coeloconica und Sensilla campa-niformia bestimmt. Die Sensilla trichodeawaren am häufigsten und wurden auf allenGeißelsegmenten gefunden. Sensilla pla-codea und S basiconica waren an den

acht distalen Segmenten vorhanden. Sen-silla ampulacea und S coeloconica warenauf fünf, S campaniformia auf sieben dista-le Segmente beschränkt. Die größte Sen-sillendichte wurde auf dem letzten Geißel-

segment gefunden. Einige S basiconicawaren in die Oberfläche eingesunken, sodaß sie den Eindruck einer Pore erweck-ten. Es gab drei Typen von S trichodea:Sensilla trichodea A waren schlank und

gerade; S trichodea B waren gebogen; Strichodea vom Typ C oder D waren kurven-förmig, aber in der gegenwärtigen Studiesehr schwer voneinander zu unterschei-den. S ampullacea, S coeloconica und Scampaniformis traten in Gruppen in dem-selben Feld auf. S ampullacea waren klei-ner als S coeloconica, die ihrerseits kleinerwaren als S campaniformia. In geringsterHäufigkeit traten S campaniformia auf.

Apis florea / Antenne / Sensille / Mor-

phologie / REM

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