Antennal sensory system of the cockroach, Periplaneta americana: Postembryonic development and morphology of the sense organs

Antennal Sensory System of the Cockroach, Periplanetaamericana: Postembryonic Development andMorphology of the Sense OrgansROLLIE SCHAFER and THOMAS V. SANCHEZDepartment of Biology, NMIMT, Socorro, New Mexico 87801ABSTRACT Antennal growth in the cockroach, Periplaneta americana, takesplace by division of the meriston (third antennal segment) and the meristalsegments at the base of the antennal flagellum. Olfactory and contact chemo-receptive sense organs are the most numerous receptor organs on the antennaat all stages of postembryonic development. The sensory complement of maleand female antennae is identical during the nymphal period, but a large differ-ence between sexes appears at the adult stage. The adult male has nearly twiceas many olfactory sensilla as the female, and more than half of these sensillaappear at the adult stage. These morphological data are consistent with thehypothesis that sensory receptors specific to the female sex attractant appearin the male only at the adult stage.

The antennal sense organs of cock-roaches mediate a variety of functions in-cluding olfaction (Yamada, 71), phero-mone reception (Roth and Barth, 67),contact chemoreception or taste (Roth andWillis, 52a), and hygro- and thermorecep-tion (Gunn and Cosway 38; Roth andWillis, 52b; Loftus, 68). Morphologicalstudies of the antennal sense organs of sev-eral species of cockroaches have been pub-lished: Blattella germanica (Roth andWillis, 52b; Ishii, 71), Gromphadorhinaportentosa (Slifer, 68), and Leucophaeamaderae (Schafer, 71a). However, theantennal sense organs of Periplaneta amer-icana have not been described, despite thewidespread use of this species in behavioraland physiological studies.The postembryonic development and re-generation of roach antennae have beenstudied in several species including Blat-tella germanica (Campbell and Priestley,70), Leucophaea maderae (Schafer, 73),Blabera craniifer (Urvoy, 63), and Peri-planeta americana (Campbell, 28; Haas,55). The present study describes the post-embryonic development of the antenna ofPeriplaneta, the morphology of the anten-nal sense organs, and the development ofthe adult pattern of sense organs. Thechordotonal organs of the scape and pedi-cel are not described here but have beencovered by Urvoy (63) in Blaberacraniifer.MATERIALS, METHODS ANDNOMENCLATUREThe cockroaches used in this study camefrom six oothecae (families) of Periplanetaamericana L. (Dictyoptera, Blattaria). Anaverage of 24 siblings emerged from eachootheca. During the course of development,a few animals were added to the originalgroup and their stage of development de-termined by examining several differentmorphological features. Of the features ex-amined, tibial length (Gier, 47) and thenumber of cercal segments (Nigam, 33)proved to be the most accurate in deter-mining the stage of development.For the preparation of whole mounts,several animals were selected and their an-tennae fixed within 30 minutes after molt-ing. It is possible to anticipate molting inPeriplaneta by noting certain changes ineye color which take place just prior to themolt (Flint and Patton, 59). The prepara-tive procedure has been fully describedelsewhere (Schafer, 73). The wholemounts of newly-molted antennae result-ing from this procedure are nearly trans-parent. Absolute counts of all the sensilla

on a single segment can be made by mov-ing the microscopes plane of focus throughthe preparation and counting sensilla atsuccessive levels. The total number ofeach type of sensillum was extrapolatedfrom absolute counts of all the sensilla on20-25% of the segments in each antenna.Growth and segment addition werestudied by counting segments and mea-suring their sizes. Previous experienceusing microdissection of pre-molt antennae(Schafer, 73) has shown that segmentcounts and measurements are a reason-ably accurate method of following the pat-tern of segment addition during postem-bryonic development (cf. Campbell andPriestley, 70).Antennae were fixed, sectioned, andstained using the method of Schafer (71a)to determine the subcuticular structure andinnervation of the antennal sense organs.The method of Slifer (60) was used todemonstrate porous areas of sensillarcuticle. Prior to examination in the scan-ning electron microscope (JEOL JSM-U2),antennae were dessicated and coated withgold.The nomenclature used in this paper isas follows:1. Segment is used to denote any sub-division of the antenna including thescape, pedicel, and the many divisions ofthe antennal flagellum.2. The meriston (after Campbell andPriestley, 70) is the third antennal seg-ment. This elongated segment has previ-ously been found to be largely responsiblefor the addition of new antennal segmentsduring nymphal development (Campbelland Priestley, 70; Schafer, 71a, 73).3. The meristal segments are the newsegments which emerge from the meristonat each molt and undergo binary divisionat the following molt. This term is syn-onymous with the primary zone (Primar-zone) of Haas (55) and the meristalannuli of Campbell and Priestley (70).4. The antennal flagellum consists ofall antennal segments distal to the meris-ton, including the meristal segments.5. The terminal molt is defined as themolt from which the adult emerges. Anymphal molt is a molt from which an im-mature insect or nymph emerges.RESULTS AND DISCUSSIONNormal development of the insectThe American cockroach, Periplanetaamericana, passes through eleven nymphalinstars under normal conditions in ourcultures. Variations in the number ofnymphal stadia are almost nonexistentunless the animals are subjected to signi-ficant trauma such as amputation of an-tennae or legs (cf. Ishii, 71; Schafer, 73).Normal development under the conditionsof this study took approximately 47 weeksat an average temperature of 25C.Growth of the antennaThe filiform antenna of cockroaches con-sists of a whip-like flagellum (composed ofmany similar-appearing segments) andthree enlarged basal segments (the scape,pedicel, and meriston). The gross mor-phology and postembryonic developmentof the Periplaneta antenna is similar to thatobserved in other species of cockroaches(Urvoy, 63; Campbell and Priestley, 70;Schafer, 73). The total number of anten-nal segments increases during postembry-onic development by about 3.1 times, or byapproximately 95 segments. At hatching,female Periplaneta antennae average 47 2 segments and males 45 2 segments(table 1). The average number of seg-ments increases at an accelerating paceduring succeeding nymphal instars andreaches a total of 135 33 segments inthe male and 139 26 segments in thefemale at the adult stage (table 1). Theaverage length of adult antennae is 4.2 cm.Addition of new segments during normalgrowth of the Periplaneta antenna occursin two ways: (1) The third antennal seg-ment, or meriston, divides at each nymphalmolt to produce from 4 to 14 new seg-ments plus a new meriston adjoining thepedicel. (2) These new segments, termedmeristal segments, then undergo a binarydivision at the next nymphal molt to pro-duce from 4 to 28 additional segments, thenumber depending on the stage of devel-opment (table 1). Meristal segments areeasily recognized because they lack thedense covering of small, thin-walled senseorgans which is seen on more distal an-tennal segments. Normal antennal growththrough the addition of new segments

occurs entirely by division of the meristonand the adjacent meristal segments. How-ever, if the antenna is severed near thebase during nymphal development, thescape and pedicel will aid in regenerationof a new antenna by dividing. A new an-tenna can also be regenerated after totalantennectomy, but usually only after theformation of a regeneration blastema atthe site of amputation in the subsequentinstar (Schafer, 73, and unpublished dataon Periplaneta).As noted in a previous paper (Schafer,73), the considerable growth potential ofthe cockroach antenna is continually off-set by a mechanical loss of segments fromthe tip of the antenna. It can be calculatedthat without segment losses the Periplanetaantenna would reach a length of over 260segments at the adult stage. However, noadult antennae have been observed to havemore than 168 segments. Some loss ofdistal segments takes place during themolting process when great stress is placedon the antenna. Loss of segments alsooccurs immediately prior to the molt whenthe old, outer cuticle has become brittle,and the newly-formed inner cuticle has notacquired the strength later attained aftertanning. Segment losses are incurred pri-marily when the antennae contact othercockroaches or objects in the culture con-tainer. On occasion, only the outer cuticlehas been observed to break off, leavingseveral white, newly-formed segments pro-truding from the broken tip. It is probablethat segment losses also occur during theprocess of cleaning the antenna with themouthparts (cf. Campbell and Priestley,70). These processes are of importance be-cause the overall lengthening of the an-tenna during postembryonic developmentis the net result of segment addition in thebasal antenna and losses at the distal tip.Any future studies using this attractivepreparation as a model developmental sys-tem should take account of this fact.No sexual dimorphism is apparent inthe gross morphology of nymphal seg-ments, but sexual dimorphism does existin the meriston and meristal segments ofthe adult stage. The adult females meris-ton is longer than the male's (averagefemale length 0.53 mm versus 0.28 mm inthe male). The total length of the first tenmeristal segments in adults is 1.92 mm inmales and 1.56 mm in females. These dif-ferences may be related to the sexual di-morphism of olfactory organs on adultantennae which is discussed later.Types of sense organsThe organs of the Periplaneta antennamay be divided into at least eight differ-ent morphological types (table 2). An at-tempt has been made to keep the nomen-clature consistent with the designationsused in a previous paper on the antennalsensilla of the African woodroach, Leuco-phaea maderae (Schafer, 71a) and the

Type of senseorganProbablemodalityTotal no. unitsin adult antennaPostembryonicincreaseLocation and distribution

S. Chaetica A(Hair platesensilla )Joint proprio-ception 13 X 1022.7 XOccur as hair plate sensilla athead-scape and scape-pediceljoints.

S. Chaetica B(Thick-walledchemoreceptors )(a) Contact chemo-reception and(b) Tactile sense 1(a) 2 X 10(b) 6.5 X 1036.7 XOccur on all segments as orderlyperipheral rings. Especiallydense on flagellum.

S. Trichodea( Thin-walledchemoreceptors )Olfaction 2Male: 8.6 X 104Female: 4.8 x 10414 X8 XOccur primarily on antennalflagellum distal to meristalsegments.

S. Basiconica(Thin-walledchemoreceptors )Olfaction1 X 1026.4 XOccur distal to first ring ofS. Chaetica B on flagellarsegments.

Cold ReceptorSensillumThermoreception 31 X 1023 XOccur on ventral side of alter-nating segments in distal one-third of antenna, distal to firstring of S. Chaetica B.

S. Campaniformia(Sensory domes )Detection ofstressin cuticle 42 X 1022.9 XOccur singly on scape and pedicel,some in association with hairplates; also concentrated at distalmargin of pedicel, and dorsally inflagellum with one sensillum/segment.

Marginal sensillaJoint proprio-ception2 X 1022.2 XOccur in threes at distal marginof each meristal segment, also inthrees on alternating segments ofrest of flagellum.

Johnstons organProprioceptionIn pedicel.

TABLE 2Sense organs of Periplaneta antenna1 Schafer (71b).2 R. Schafer, unpublished electrophysiological data.3 Loftus (68).4 Pringle (38).338 ROLLIE SCHAFER AND THOMAS V. SANCHEZnomenclature used by Roth and Willis(52b) in their study of Blattella germanica.1. Sensilla chaetica A. Plain tactilehairs, hair plate sensilla, proprioceptivesensilla (figs. 2, 5). These thick-walledtactile sensilla occur only on the scape andpedicel. They are distributed in four groupson the proximal scape adjacent to the head-scape articulation and in three groups onthe proximal pedicel next to the scape-pedicel articulation (fig. 5). During move-ment of these joints the shafts of thesensilla chaetica A are deflected by con-tact with the cuticle of the proximal mem-ber of the articulation. Electrophysiologicalrecording from this type of sensillum inLeucophaea has shown that the senseorgan is a proprioceptor which is sensitiveto rate and angle of joint movement(Schafer, 71b). The sensillum itself con-sists of a shaft 6-75 in length seated ina roughly circular base adapted to allowfree movement of the hair. Each hair isinnervated by a single neuron. Duringpostembryonic development, the size of theshaft and its base increases considerably.In general, shaft lengths are short in thepedicel hair plates where the articulationis somewhat restricted in its range ofmovement, while shaft lengths are longerin the scape hair plates where the articula-tion is capable of considerable movement.2. Sensilla chaetica B. Thick-walledchemoreceptors or taste hairs (figs. 1, 3, 6).Thick-walled chemoreceptors occur on allsegments of the Periplaneta antenna.Within each segment the chaetica B arearranged in rings around the circumfer-ence of the segment. Long and short sen-silla alternate in each ring, with the longersensilla having differentiated at an earlierstage than the short ones. During postem-bryonic development, each molt adds an-other ring of sensilla chaetica B to each ofthe flagellar segments up to a maximumof eight rings on any single segment.The sensillum itself consists of a long,tapering shaft (35-250 n in length)seated in a flexible base (10-25 ^ in diam-eter) which is adapted to allow movementof the hair shaft (fig. 6). The shaft of thesensillum is always slanted distally andthe tip of the shaft is recurved outward, sothat objects touched by the antenna con-tact only the tips of thick-walled chemo-

INSTARADULTDEVELOPMENTAL STAGEFig. 1 Increase in olfactory sensilla, contactchemoreceptor organs, and other types of anten-nal sensilla during the postembryonic develop-ment of Periplaneta americana. Olfactory sensilla(sensilla trichodea) undergo the greatest increaseduring postembryonic development. At the termi-nal molt the male nearly doubles his complementof olfactory sensilla. Males and females have beencombined in the nymphal ins tars; no difference inthe total number of antennal sensilla is observ-able until the adult stage is reached.receptors. The surface of the hair shaft isheavily fluted, unlike the thin-walledchemoreceptors which have nearly smoothsurfaces (figs. 4, 10, 11). As in other cock-roaches (Slifer, 68; Schafer, 71a), thehair has a lumen containing a cuticularsheath in its proximal half. This cuticularsheath extends down to the level of thesensory cell bodies located below thesensillum in the hypodermis. Sensillachaetica B are innervated by three to fivesensory cells which have dendrites pro-jecting up to the hair tip through the cutic-ular sheath. The tip of the sensillum ispermeable to crystal violet using Slifers(60) technique. This indicates that ex-posure of the dendrites to the external en-vironment occurs at or near the tip. Scan-ning electron micrographs of the sensillumtip (figs. 7-9) show considerable structure,but it is not clear whether the tip has asingle pore, or is composed of an area ofpermeable cuticle with many smaller pores,

or has regulatory structures such as thosein chemoreceptor hairs of locusts (Blaneyand Chapman 69; Bemays, Blaney andChapman, 72) and blow flies (Stiirckow,Holbert and Adams, 67).It is reasonable to assume that the pri-mary function of sensilla chaetica type B iscontact chemoreception. Single unit record-ings from sensilla chaetica B on the Leu-cophaea antenna indicate the presence ofa single mechanoreceptor (Schafer, 71b).The remaining two to four neurons areprobably the site of contact chemorecep-tion (Roth and Willis, 52a) in the cock-roach antenna. Since there are approxi-mately 6.5 x 103 sensilla chaetica B in theadult Periplaneta antenna (table 3), bothtactile sensation and contact chemorecep-tion are well represented.3. Sensilla trichodea. Thin-walledchemoreceptors or sensory hairs with finetips (figs. 1, 4, 11). Except for the adultstage, thin-walled chemoreceptors onlyoccur in large numbers distal to the meri-stal segments, and never occur on thescape and pedicel at any stage. The lackof thin-walled sensilla on the scape andpedicel and their relative scarcity on themeriston and meristal segments may re-flect the activity of a differential inhibitoryprocess at work in the basal antenna whichprevents the differentiation of thin-walledsensilla in this region. The sparse distribu-tion of thin-walled chemoreceptors is notshared by the thick-walled chemoreceptorswhich are relatively numerous on the basalsegments of the antenna. Although thethin-walled sensilla trichodea are, by andlarge, confined to the distal flagellum, theyare the most numerous type of sensillumon the antenna at all stages of develop-ment (table 3, fig. 3). For example, theadult male antenna has 3.9 X 104 sensillatrichodea per antenna as compared with acombined total of 7.3 X 103 for all othertypes of sensilla on the antenna.The sensilla trichodea occur in a varietyof forms with many intermediate types.Shaft lengths vary considerably (6-56 ^),while the base diameter is relatively con-sistent within each developmental stage(4-7 ju,). Male adult sensilla trichodeaappear to be longer on the average thanadult female sensilla trichodea whenviewed in the scanning electron micro-scope (not illustrated). Shaft tips varyfrom relatively blunt to very fine (fig. 4).The hair shaft is permeable to crystal vio-let using the Slifer (60) technique, but thepore-tubule system (Ernst, 69) is beyondthe resolving power of the scanning elec-tron microscope (fig. 11). Sensilla tri-chodea contain an inner cuticular sheathwhich arises at the base of the hair shaftand contains sensory dendrites which pro-ject upward from the neuron cell bodieslocated in the hypodermis. Innervation bytwo neurons is most common.A minute type of trichodea (sensillatrichodea type B) which was found on thescape and pedicel in Leucophaea (Schafer,71a) was not observed in Periplaneta.4. Sensilla basiconica. Basiconic sen-sory pegs or cones (figs. 2, 4, 10). Sensillabasiconica in Periplaneta are noticeablylarger than similar sensilla in other speciesof cockroaches. The Periplaneta sensorycone is readily identifiable by the distinc-tive broad shaft ending in a very blunt tip(fig. 10). In the adult antenna, thebasiconic sensillum is about 13 ju. high witha base 8-9 p wide. The distribution of thesesensilla is very limited. They are alwaysfound distal to the first row of sensillachaetica B on a segment. On the average,fewer than one sensillum per segment wasfound (fig. 2). No definite pattern of dis-tribution was noted, but there seemed tobe a tendency to concentrate most of thebasiconic sensilla on the most distal seg-ments of the flagellum and at the base ofthe flagellum near the meristal segments.Although few sections were obtained withthis type of sensillum, innervation appearsto be by 2-3 neurons.Cold receptor sensilla. This type ofsensilla trichodea containing a thermore-ceptor was first described by Loftus (68).It is usually found distal to the first rowof sensilla chaetica B on the ventral sideof every other segment in the distal thirdof the antenna. Adults have an average of33 of these sensilla per antenna, and nonewas observed on antennae of first andsecond instar nymphs (fig. 2). The shaft,which is about 6.5 ^ long in the adult, hasa very fine tip and always curves distally.The most easily recognized characteristic isthe well defined circular base 8-10 /x in di-ameter which stands out among the many

Fig. 2 Increase in mechanoreceptive andother types of antennal sensilla during the post-embryonic development of Periplaneta americana.The increase in mechanoreceptive and other typesof sensilla is relatively regular throughout devel-opment in comparison with olfactory sensilla(fig. 1).other sensilla trichodea which have some-what smaller bases, around 6.5 p. in diam-eter. The distribution of this type of sensil-lum is analogous to that of the coeloconicsensilla of the Leucophaea antenna(Schafer, 71a). Innervation is unknown.5. Sensilla campaniformia. Sensorydomes (figs. 12, 13). The campaniformsensilla of the Periplaneta antenna areprimarily oval cuticular domes whose longaxis is always aligned parallel to the longaxis of the antenna. Campaniform organsare found in three regions of the antenna:(1) on the scape, occurring as scatteredsingle sensilla and in association with thegroups of sensilla chaetica A (hair platesensilla); (2) on the pedicel, occurring asisolated single examples and concentratedin a ring around the distal margin of thesegment; and (3) on the dorsal surface ofthe meristal and flagellar segments whereone campaniform organ is usually foundon each segment at its midpoint. As withBlabera craniifer (Urvoy, 63) and Leuco-phaea maderae (Schafer, 71a), it is prob-able that some of the more circularcampaniform sensilla on the distalmargin of the pedicel are associated withthe connective chordotonal organs and theJohnstons organ of the pedicel. All cam-paniform sensilla examined in the presentstudy appeared to be innervated by a singleneuron.6. Marginal sensilla (figs. 14-18).These mechanoreceptive sensilla were firstreported on the antenna of Leucophaea(Schafer, 71a) and designated sensillascolopidia. Campbell (72) described thedistribution of the organ on the antennaeof 44 species of cockroaches and appliedthe name marginal sensillum to it. Camp-bells (72) term is adopted here becausethe structure of the organ, as nearly ashas been determined, is unlike that of ascolopophorous organ.The distribution of this organ, previouslydescribed by Campbell (72), is as follows:(1) Three marginal sensilla are found ineach meristal segment at the distal marginof the segment, arranged around the cir-cumference of the segment approximatelyequidistant from each other. (2) Threemarginal sensilla, similarly arranged, arefound in alternating segments of theflagellum, distal to the meristal segments.The alternating character of the marginalsensilla on the distal flagellum is producedwhen a new sensillum fails to differentiateduring binary division of the meristal seg-ments. The functional significance of thispattern is unknown, but could easily berelated to proprioception in the distalantenna since the sensilla occur in or verynear the flexible cuticle of joints betweenthe segments.The external appearance of the organis similar to that of a pea in a pod (figs.14-18). It consists of a pointed cuticularknob nestled in an indentation at the dis-tal margin of the segment. The knob hasa roughened area on its upper surfacemuch like that made by the insertion of themicrotubule-containing sensory processesof campaniform organs on the cockroachleg (Moran, Chapman and Ellis, 71). Inthe few light microscope sections which

were obtained, a cuticular sheath and sen-sory process could be discerned extendingabove a single nerve cell body, much likethat seen in campaniform organs on thelegs of Blaberus discoidalis (Moran et al.,71) and the antenna of Leucophaeamaderae (Schafer, 71a). The knob-likestructure was, however, broken up or dis-placed by the sectioning process and therelationship of the sensory process and itscuticular apparatus could not be observed.This interesting structure warrants futureinvestigation with the transmission elec-tron microscope and plastic-imbeddingtechniques.7. Johnstons organ. The chordotonalapparatus of the pedicel has been previ-ously described by Urvoy (63) in the an-tenna of Blabera craniifer. There appearsto be no substantial difference between thestructures described in Blabera and that ofPeriplaneta.Developmental patterns in thedistribution of antennalsensillaThe sensillar population of male Peri-planeta antennae increases nearly 12 timesduring postembryonic development (froman average total of 3,900 sensilla in thefirst instar to 46,200 in the adult). Anten-nal sensilla increase in the female 7.5times (from an average of 3,900 in thefirst instar to 29,300 in the adult). Thishigh degree of sexual dimorphism in adultantennae is achieved entirely at the termi-nal molt. Male and female antennae fol-low the same growth curve during all ofnymphal development (fig. 1), but at theadult molt the male experiences a tremen-dous increase in the number of antennalsensilla even though the surface area ofmale antennae is only slightly larger thanthat of females (table 3).An examination of sensilla counts(table 3) indicates that the sexual dimor-phism of the adult is the result of the addi-tion of an average of 22,700 sensillatrichodea in the male compared with anaverage addition of 5,800 sensilla trichodeain the female. There is no sexual dimor-phism in the nymphal and adult popu-lations of the other types of antennalsensilla, including the thick-walled chemo-receptors. Therefore, the sexual dimor-phism apparent in adult antennae islimited solely to an extra complement ofthin-walled olfactory sense organs in themale.The additional sensilla trichodea of themale Periplaneta antenna are evident intwo respects: (1) the density of sensillatrichodea on the male antenna is greaterthan that of the female (950 sensilla/mm2in the male versus 600 sensilla/mm2 inthe female); and (2) the sensilla trichodeaof the male antenna appear in large num-bers (70 or more per segment) immedi-ately distal to the meriston. In the adultfemale antenna the sensilla trichodea donot appear until about the eighth segmentdistal to the meriston, and then only in re-duced numbers in comparison with themale (about 10 sensilla per segment).The extra receptor organs of male Peri-planeta antennae are almost certainly con-nected with pheromone reception. Themorphological data presented here go along way toward explaining the resultsobtained by Boeckh, Sass and Wharton(70), who found that the electrophysio-logical response of the antenna to an ex-tract containing female sex attractant in-creased about four times in male animalsbetween late instar nymphs and the adultstage, but not in females. Based on thesefacts, a resonable assumption is thatpheromone-specific olfactory receptors orspecialist cells (Schneider, 69) sensitiveto the female sex attractant develop at theadult stage. As yet, however, this attrac-tive suggestion remains only a hypothesis.The data of Boeckh et al. (70) wereobtained using the electroantennogrammethod, a method which has been repeat-edly criticized (Adler, 71; Birch, 71).Total number of units inthe antennaThe total numbers of units (sensorycells) in male and female Periplaneta an-tennae were calculated using the data oftable 3 and the average innervation ofeach type of sensillum. The totals are1.1 X 105 units per adult male antennaand 7.5 X 10 units per adult female an-tenna. Of these totals, approximately 77%of the units in male antenna and 64% infemale antennae are devoted to olfaction(table 2). The rest of the total is com-

Normal postembryonic increase in antennal sensilla and surface area in Periplaneta americana listed according to sensory modality 1InstarandsexAveragetotal surface areaof antennaAveragetotal populationof sensillaAv. totalolfactorysensilla 2Average totalmechanoreceptivesensilla 3Average totalthick-walledchemoreceptors *No. ofantennaecounted

mm2%%%%%

1.2.363,90092,7007230351,000157

2.3.694,400103,1008250381,100178

3.4.0104,600103,2008270411,100175

4.6.4165,400123,80010290441,300206

5.7.9195,600123,90010320491,400227

6.8.9227,000154,90013350531,700268

7.15.9399,600216,50017400612,600407

8.20.04915,7003411,70030440673,500546

9.22.35416,1003511,80030520793,800595

10.30.37419,2004214,50037590904,100636

11. M34.28324,0005216,30042640976,9001073

11. F34.28324,0005216,30042640976,9001072

Adult M41.010046,20010039,000 1006601006,5001004

Adult F37.19129,3006322,100576601006,5001004

1 Each column contains a percentage figure which represents the amount of surface area or the total number of sensilla given as a percent fraction ofthe total in the adult male (adult male = 100% ). Male and female data for instars one through ten were averaged together for clarity of presentation.There was no significant difference in the sensillar population at any stage of nymphal development; sexual dimorphism appeared only at the adult stage.2 Olfactory sensilla: Sensilla Trichodea and Basiconica.3 Mechanoreceptive sensilla: Sensilla Chaetica A, S. Caxnpanifonnia, and Marginal Sensilla.4 Thick-walled chemoreceptors: Sensilla Chaetica B.

posed mainly of contact chemoreceptorsand tactile receptors. Approximately one-third of the antennal sensory system of themale is devoted to sensing the female sexattractant, assuming that the extra recep-tor complement of males is composed ofthe appropriate specialist units. An elec-trophysiological study of this problem isunderway in this laboratory.ACKNOWLEDGMENTSWe thank Los Alamos Scientific Labora-tories for making a scanning electron mi-croscope available under their UniversityCooperation Program. We also thankThomas Gregory for technical assistanceand Dr. Eleanor Slifer and Dr. Frank L.Campbell for critical review of the manu-script. Supported in part by NSF grantGB-32008 to R. Schafer and NSF Institu-tional grant GU-3533 to NMIMT.LITERATURE CITEDAdler, V. E. 1971 Physical conditions impor-tant to the reproducibility of electroantenno-grams. Ann. Ent. Soc. Am., 64: 300-302.Bernays, E. A., W. M. Blaney and R. F. Chapman1972 Changes in chemoreceptor sensilla onthe maxillary palps of Locusta migratoria inrelation to feeding. J. Exp. Biol., 57: 745-753.Birch, M. C. 1971 Intrinsic limitation in theuse of electroantennograms to bioassay malepheromones in Lepidoptera. Nature, 233: 5758.Blaney, W. M., and R. F. Chapman 1969 Thefine structure of the terminal sensilla on themaxillary palps of Schistocerca gregaria(Forsk&l) (Orthoptera, Acrididae). Z. Zell-forsch. mikrosk. Anat., 99: 74-97.Boeckh, J., H. Sass and D. R. A. Wharton 1970Antennal receptors: Reactions to female sexattractant in Periplaneta americana. Science,168: 589.Campbell, F. L. 1928 On the postembryonicdevelopment and regeneration of the antennaeof the American cockroach, Periplaneta ameri-cana L. Unpublished manuscript supplied to theauthor by F. L. Campbell.

1972 A new antennal sensillum ofBlattella germanica (Dictyoptera: Blattellidae)and its presence in other Blattaria. Ann. Ent.Soc. Am., 65: 888-892.Campbell, F. L., and J. D. Priestly 1970 Flagel-lar annuli of Blattella germanica (Dictyoptera:Blattellidae). Changes in their numbers anddimensions during postembryonic development.Ann. Ent. Soc. Am., 63: 81-88.Ernst, K. D. 1969 Die Feinstruktur von Riech-sensillen auf der Antenne des Aaskafers Necro-phorus (Coleoptera). Z. Zellforsch., 94: 72-102.Flint, R. A., and R. L. Patton 1959 Relation ofeye color to molting in Periplaneta americana L.Bull. Brooklyn Ent. Soc., 54: 140.Gier, H. T. 1947 Growth rate in the cockroach,Periplaneta americana (Linn). Ann. Ent. Soc.Am., 40: 303-317.Gunn, D. L., and C. A. Cosway 1938 Tempera-ture and humidity responses in Blatta orientalis.J. Exp. Biol., 15: 555-563.Haas, H. 1955 Untersuchungen zur Segment-bildung an der Antenne von Periplaneta ameri-cana L. Roux Archiv. fur Entwicklungsme-chanik, 147: 434-473.Ishii, S. 1971 Structure and function of theantenna of the German cockroach, Blattellagermanica (L.) (Orthoptera: Blattellidae).Appl. Ent. Zool., 6: 192197.Loftus, R. 1968 The response of the antennalcold receptor of Periplaneta americana to rapidtemperature changes and to steady temperature.Z. vergl. Physiol., 59: 413455.Moran, D. T., K. M. Chapman and R. A. Ellis1971 The fine structure of cockroach campani-form sensilla. J. Cell Biol., 48: 155-173.Nigam, L. N. 1933 The life-history of a com-mon cockroach (Periplaneta americana Lin-neus). Indian J. Agricult. Sci., 3: 530-543.Pringle, J. W. S. 1938 Proprioception in insects.II. The action of the campaniform sensilla onthe legs. J. Exp. Biol., 15: 114-131.Roth, L. M., and E. R. Willis 1952a A studyof cockroach behavior. Am. Midland Naturalist,47: 66-129.

1952b Possible hygroreceptors in Aedesaegypti (L.) and Blattella germanica (L.).J. Morph., 91: 1-14.Roth, L. M., and R. H. Barth 1967 The senseorgans employed by cockroaches in mating be-havior. Behavior, 28: 58-94.Schafer, R. 1971a Antennal sense organs of thecockroach, Leucophaea maderae. J. Morph., 134:91-103.

1971b Insect mechanoreceptors: Infor-mation content in responses of antennal sen-silla chaetica. Proc. Int. Union Physiol. Sci., 9:497 (Abstract).

1973 Postembryonic development inthe antenna of the cockroach, Leucophaeamaderae: Growth, regeneration, and the devel-opment of the adult pattern of sense organs.J. Exp. Zool., 183: 353-364.Schneider, D. 1969 Insect olfaction: Decipher-ing system for chemical messages. Science,163: 1031-1037.Slifer, E. H. 1960 A rapid and sensitive methodfor identifying permeable areas in the bodywall of insects. Entomol. News, 71: 179-182.

1968 Sense organs on the antennalflagellum of a giant cockroach, Gromphador-hina portentosa, and a comparison with thoseof several other species (Dictyoptera, Blattaria).J. Morph., 126: 19-29.Stiirckow, B., P. E. Holbert and J. R. Adams1967 Fine structure of the tip of chemosensi-tive hairs in two blow flies and the stable fly.Experientia, 23: 780-782.Urvoy, J. 1963 Etude anatomo-fonctionelle dela patte et de lantenne de la blatte: Blaberacraniifer B. Annls. Sci. nat. Zool., 12: 287414.Yamada, M. 1971 A search for odour encodingin the olfactory lobe. J. Physiol., 214: 127-143.

PLATES

3 Flagellar segment of Periplaneta antenna, X 240. Thick-walled con-tact chemoreceptors (sensilla trichodea B) and thin-walled olfactorysensilla (sensilla trichodea) cover the segment.4 Thin-walled sensilla, X 1,600. Several sensilla trichodea surround asensillum basiconicum (arrow).5 Group of sensilla chaetica A at scape-pedicel articulation, X 240. Thehair plate sensilla on the pedicel (at right) contact the scape (at left)when the joint is flexed. Two large sensilla chaetica B are seen atleft on the scape.6 Base of sensillum chaeticum B, X 2,400. The base of this type ofsensillum is adapted to allow free movement over a restricted rangeof 30-40. The fluted character of the thick-walled shaft is apparent.Two sensilla trichodea are seen in the foreground.

7-9 Distal tips of three sensilla chaetica B, X 8,000. The tips of thesethick-walled contact chemoreceptor organs are the site of exposureof the sensory dendrites within the hair shaft to the external en-vironment. A dark structure is visible, although it is not clearwhether this is a single pore or an area of porous cuticle containingmany smaller pores. Stereographic examination of this structurehas also failed to disclose its exact nature.10 Sensillum basiconicum, x 2,400. The broad and blunt-tipped appear-ance of the sensillum is apparent here, but is even more strikingin light microscope preparations where some of the subcuticularstructure is visible. Fewer than one of these organs per segment isfound on Periplaneta antennae at all stages of development.11 Sensillum trichodeum, X 8,000. A series of longitudinal lines is justbarely visible on the otherwise smooth surface of the hair. Theselines may reflect the organization of the pore-tubule system (Ernst,69) which serves to conduct odorous stimuli to the sensory den-drites within the shaft of the sensillum.

12 Sensilla campaniformia at the distal margin of the pedicel, X 240.The ring of campaniform organs which occurs on the pedicel (atright) is part of the mechanoreceptive system of the pedicel whichincludes the chordotonal apparatus of the Johnstons organ. Themeriston is at left.13 Campaniform organ on the pedicel, x 2,400. A dimple may be seenat the center of the cuticular dome. This is the site of associationbetween the subcuticular sensory process and the campaniform dome.14 Marginal sensillum at the distal margin of a flagellar segment,X 2,400. The joint between the two flagellar segments is at bottom.The pointed nature of the cuticular knob is clearly evident.15 Marginal sensillum at the distal margin of a flagellar segment,X 2,400. This is the same sensillum shown in the stereographic rep-resentation of figures 16-18). The size of the cuticular knob is small(about 2 /j. across the lesser dimension) in comparison with thesensillum trichodeum above it and the campaniform organ of figure13, which is shown at the same magnification. The joint between twoflagellar segments is at bottom.

16 Marginal sensillum, x 10,000. This is the base picture (0 angle)for the stereographic representation of figures 17-18. The indenta-tion in the top of the cuticular knob may represent the site ofassociation between a subcuticular sensory process and the ex-ternal cuticle of the knob. Similar structures are seen in campani-form organs (fig. 13; Moran et al., 71). The material at the rightof the inset area is artifactual. The dimples in the cuticular sur-face surrounding the sensillum may be external openings of thepore canals of the cuticle.17-18 Stereographic representation of marginal sensillum, 2Vz,X 10,000. The three-dimensional structure of the cuticular knoband its inset may be viewed with a stereoscopic viewer (e.g., CF-8Stereoscope, Abrams Instruments, Lansing, Michigan).

335

J. Comp. Neur., 149: 335-354.

TABLE 1

Segment distribution on the developing antenna of the cockroach, Periplaneta americana 1

InstarSexAv. totalnumber ofsegmentsAverage

increase

observedNNo. ofmeristalsegmentsN1.Male452823Female47 25232.Average59 191317663.Average60 10110954.Average63 28313965.Average67 19423966.Average75 23824967.Average100 3025121268.Average109 499171269.Average116 347812610.Average121 2551411611.Average138 201710116AdultMale135 33-315Female139 26+ 1211 Male and female counts in instars 2 through 11 have been averaged for clarity of presentation.There appeared to be no difference in the distribution of segments on male and female antennae atany stage of development.

ANTENNAL SENSES OF PERIPLANETA 343