Campaniform Sensilla Research Articles

Morphology and sensilla of the enigmatic Bhutan pine aphid Pseudessigella brachychaeta Hille Ris Lambers (Hemiptera: Aphididae) – A SEM study

The aphid tribe Eulachnini is unusual in being both diverse in species number and specializing on conifer hosts. The Bhutan pine aphid Pseudessigella brachychaeta Hille Ris Lambers, 1966; the only known species of its genus and native of the Himalayan region, displays characteristics of both the Palearctic genus Eulachnus and the Nearctic Essigella. Species of all three genera, as well as eulachnine Cinara subgenus Schizolachnus, share the same ecological niche, feeding almost exclusively on the needles of true pines. To obtain a better understanding of this enigmatic aphid and its biological context within the Eulachnini, we conducted a scanning electron microscopy study of the fine morphology and sensilla of the live-bearing and egg-laying forms of the species. The general morphology most resembles that of species of the genus Eulachnus but in detail Pseudessigella also displays unique features. Many types of sensilla, including coeloconic, campaniform, placoid and trichoid sensilla occur at different locations on the antennae, mouthparts, and legs. The rhinariolum on the second antennal segment is described and illustrated for the first time in Lachninae and a second rhinariolum-like sensillum, hitherto unknown in aphids, is also described on the second antennal segment. We discuss the morphological features of Pseudessigella and the distribution of antennal and labial sensilla with respect of their possible taxonomic and functional significance.

Antennal sensilla and their nerve innervation in first‐instar nymphs of Porphyrophora sophorae Arch. (Hemiptera: Coccomorpha: Margarodidae)

Porphyrophora (Hemiptera: Coccomorpha: Margarodidae) is a genus of soil-inhabiting scale insects. The antennal sensilla and their innervation in the first-instar nymphs of Porphyrophora sophorae were studied using light microscopy and scanning and transmission electron microscopy to understand the function of these sensilla and determine the sensillar innervation feature on these small antennae. The results show that the six-segmented antennae of these nymphs have 20-23 sensilla which can be morphologically classified into seven types, for example, one Böhm's bristle (Bb), one campaniform sensillum (Ca), one Johnston's organ (Jo), 13-16 aporous sensilla trichodea (St), two coeloconic sensilla (Co), one straight multiporous peg (Mp1), and one curvy multiporous peg (Mp2). According to their function, these sensilla can be categorized into three categories: mechanoreceptors, that is, Bb, Ca, Jo, and St; thermo/hygroreceptors, that is, Co only; and chemoreceptors, that is, Mp1 and Mp2. The dendrites that innervate the Mp1, Mp2, and Co sensilla combine to form a large nerve tract (NT1) in the antennal lumen. Because NT1 extends through and out of the antenna, the somata of these neurons are present in the lymph cavity of the insect's head. The dendrites that innervate the mechanoreceptors form another nerve tract (NT2). The somata of these neurons are located inside the scape and pedicel. J. Morphol. 277:1631-1647, 2016. © 2016 Wiley Periodicals, Inc.

Fine structure of antennal sensilla of the spittlebug Philaenus spumarius L. (Insecta: Hemiptera: Aphrophoridae). I. Chemoreceptors and thermo-/hygroreceptors

The meadow spittlebug, Philaenus spumarius (L.) (Hemiptera: Cercopoidea: Aphrophoridae), is a polyphagous species that transmits Xylella fastidiosa, a bacterium associated with “Olive Quick Decline Syndrome” in Southern Italy. In this study, the morphology and the ultrastructure of the antennal sensilla of P. spumarius were investigated. The antennae consist of three segments: a basal scape, a pedicel and a flagellum composed of a basal enlargement (ampulla) and a long segment (filament). The pedicel bears a single campaniform sensillum while the ampulla houses twelve coeloconic sensilla and three large basiconic sensilla. These latter sensilla show a smooth multiporous external cuticular wall and a total number of 27 sensory neurons per sensillum. The coeloconic sensilla belong to two morphologically distinct types: double-walled and single-walled sensilla. The sensory peg of the double-walled sensilla is smooth at the base and distally has a grooved cuticular surface with pores organized in spoke channels between each ridge. Three sensory neurons enter the lumen while at the basal level, before entering the peg, a fourth sensory neuron is found. The single-walled sensilla show an aporous thick cuticular wall and two sensory neurons entering the sensillar lumen, with a third neuron ending at the sensillum base.

Common mechanisms of force detection and control in insects.

Information from sense organs that detect forces may be particularly important in neural control of muscles as modular groups (synergists). We have performed comparative studies to characterize force detection in insects using physiological studies in stick insects and cockroaches to gain insight into comparable mechanisms in fruit flies (Drosophila), in which new and powerful genetic tools have been developed. Campaniform sensilla are mechanoreceptors that encode forces as cuticular strains. Previous studies have shown they can reinforce muscle synergies. Receptors fulfill similar functions in different species but the effects of individual groups are determined by the specific forces they encode. Whole mount and dissected preparations were studied using confocal and light microscopy. Sense organs and leg muscles were labeled using diI diffusion from the thorax. Activities in peripheral nerves and muscles were recorded extracellularly. Many receptors are homologous but the structure and responses of the femoral group (fCS) and mobility of the trochanter-femur joint are species specific. In cockroaches and stick insects, sensitivities to forces in the joint plane are correlated with effects on muscle synergies. In Drosophila, the fCS are located on the ventral femur, suggesting that they should be sensitive to forces in the joint plane. We are currently testing motor effects using neurophysiological recordings from larger Calliphorid flies. There are clear homologies in some groups of force receptors. Legs of flies combine elements found in cockroaches and stick insects. Sensory feedback can have similar effects in activation of muscle synergies in flies.

Reinvestigation of the antennal morphology of the white-backed planthopper Sogatella furcifera (Horváth) (Hemiptera: Delphacidae)

Reinvestigation of the antennal morphology of the white-backed planthopper Sogatella furcifera (Horváth), a major pest of rice in Asia, revealed the presence of sensilla and other structures not reported in previous studies of this species. Scanning electron microscopic examination of antennae of males and females confirmed that the antennae of S. furcifera are similar to those of other recently studied species, consisting of scape, pedicel, and flagellum composed of a basal bulb and an apical segmented arista. In contrast to previous studies that only described four types of sensilla, twelve types of sensilla were observed. The scape and pedicel have dispersed sensilla which contain a Böhm bristle, single dome-shaped campaniform sensilla, several sensilla trichodea I and papillae-like sensilla I. A sensilla basoconicum II, several sensilla basiconica I, single sensillum campaniformium II, sensilla trichodea I, sensilla trichodea II, plaque organs, and papillae-like sensilla II occurred on the pedicel. A single sensillum coeloconicum and three sensilla basiconica III are located apically on the posterior surface of the bulb. Sensilla trichodea I were the most abundant and plaque organs were the most conspicuous sensilla, distributed on the pedicel. No differences were observed in antenna shape and basic structure in the males and females. The possible functions of the sensilla are discussed in relation to their morphology and compared to those found in other Fulgoroidea, especially Delphacidae. The external morphology, distribution, and abundance of sensilla located on the antennae of S. furcifera are illustrated, with a brief discussion of their taxonomic, phylogenetic, and putative functional significance.

Sexual dimorphism in antennal morphology and sensilla ultrastructure of a pupal endoparasitoid Tetrastichus howardi (Olliff) (Hymenoptera: Eulophidae).

Tetrastichus howardi (Olliff) (Hymenoptera: Eulophidae), a pupal parasitoid of a great number of Lepidoptera pests, has a great potential for biological control. To investigate the olfactory system of this parasitoid, we examined the morphology and ultrastructure of the antennal sensilla of both male and female T. howardi using scanning and transmission electron microscopic techniques. Antennae of male and female T. howardi were geniculate in shape, which consisted of scape, pedicel and flagellum with 5 and 4 flagellomeres, respectively. The sexual differences were recorded in the types, structure, distribution and abundance of antennal sensilla of T. howardi. Fourteen morphologically distinct types of antennal sensilla were found on the female antennae, while seventeen on the male antennae. They were: multiporous plate sensilla (MPS1-4), chaetica sensilla (CH1-3), multiporous trichodea sensilla (MTS), aporous trichodea sensilla (ATS1-5), multiporous grooved peg sensilla (MGPS), coeloconic sensilla (COS), campaniform sensilla (CAS), terminal finger-like hairy sensilla (TFI), cuticular pore (CP), and ventral sensory plaque (VSP). MPS4, ATS (3-5), and VSP only occurred on the male antennae, while MPS2 and MPS3 only on the female antennae. The MPSs, MTS, MGPS, TFI, and CP may function as olfactory sensilla involving in detecting odor stimuli whereas the ATSs, CHs, and CAS may serve as mechanoreceptors. COS were presumed to play a role as chemo-, thermo- or hygro-receptor. The results could facilitate future studies on the biology of olfaction in T. howardi.

The structure and morphogenic changes of antennae of Matsucoccus matsumurae (Hemiptera: Coccoidea: Matsucoccidae) in different instars

To better understand the functioning and morphogenic changes of the antennae of Matsucoccus matsumurae (Kuwana) in different instars, the antennae are examined using light microscopy, scanning and transmission electron microscopy. The results show that the antennae of M. matsumurae display three different styles in morphology and sensillar distribution in different instars. The antennae of first instar nymphs are relatively simple, including one campaniform sensillum (Ca), four smooth aporous trichoid sensilla (SAt), two intersegmental sensilla (Ins), two coeloconic sensilla (Co), three multiporous pegs (Mp) and four uniporous pegs (Up). The antennae of adult females and third instar male nymphs both possess similar antennae, and exhibit seven types of sensilla. Adult female antennae have in total 82–108 sensilla, including 9–16 Böhm's bristle (Bb), 3–7 Ca, 50–75 SAt, 0–3 Ins, 3–10 Co, 8 Mp and 5 Up, whereas third instar male nymph antennae possess approximately 62–79 sensilla. Adult male antennae are the most developed, possessing 259–312 sensilla, including 7–15 Bb, 2–5 Ca, 7–11 grooved aporous trichoid sensilla, 4–9 SAt, 0–3 Ins, 2–7 Co, 23–29 knobbed seta sensilla, 179–230 multiporous trichoid sensilla and 8 Mp. Based on these results, the main functions and morphogenic changes of antennae M. matsumurae in different instars are discussed.

How many mechanosensory organs in the bushcricket leg? Neuroanatomy of the scolopidial accessory organ in Tettigoniidae (Insecta: Orthoptera)

The subgenual organ and associated scolopidial organs are well studied in Orthoptera and related taxa. In some insects, a small accessory organ or Nebenorgan is described posterior to the subgenual organ. In Tettigoniidae (Ensifera), the accessory organ has only been noted in one species though tibial sensory organs are well studied for neuroanatomy and physiology. Here, we use axonal tracing to analyse the posterior subgenual organ innervated by the main motor nerve. Investigating seven species from different groups of Tettigoniidae, we describe a small group of scolopidial sensilla (5–9 sensory neurons) which has features characteristic of the accessory organ: posterior tibial position, innervation by the main leg nerve rather than by the tympanal nerve, orientation of dendrites in proximal or ventro-proximal direction in the leg, and commonly association with a single campaniform sensillum. The neuroanatomy is highly similar between leg pairs. We show differences in the innervation in two species of the genus Poecilimon as compared to the other species. In Poecilimon, the sensilla of the accessory organ are innervated by one nerve branch together with the subgenual organ. The results suggest that the accessory organ is part of the sensory bauplan in the leg of Tettigoniidae and probably Ensifera.

Gyroscopic sensing in the wings of the hawkmoth Manduca sexta: the role of sensor location and directional sensitivity

The wings of the hawkmoth Manduca sexta are lined with mechanoreceptors called campaniform sensilla that encode wing deformations. During flight, the wings deform in response to a variety of stimuli, including inertial-elastic loads due to the wing flapping motion, aerodynamic loads, and exogenous inertial loads transmitted by disturbances. Because the wings are actuated, flexible structures, the strain-sensitive campaniform sensilla are capable of detecting inertial rotations and accelerations, allowing the wings to serve not only as a primary actuator, but also as a gyroscopic sensor for flight control. We study the gyroscopic sensing of the hawkmoth wings from a control theoretic perspective. Through the development of a low-order model of flexible wing flapping dynamics, and the use of nonlinear observability analysis, we show that the rotational acceleration inherent in wing flapping enables the wings to serve as gyroscopic sensors. We compute a measure of sensor fitness as a function of sensor location and directional sensitivity by using the simulation-based empirical observability Gramian. Our results indicate that gyroscopic information is encoded primarily through shear strain due to wing twisting, where inertial rotations cause detectable changes in pronation and supination timing and magnitude. We solve an observability-based optimal sensor placement problem to find the optimal configuration of strain sensor locations and directional sensitivities for detecting inertial rotations. The optimal sensor configuration shows parallels to the campaniform sensilla found on hawkmoth wings, with clusters of sensors near the wing root and wing tip. The optimal spatial distribution of strain directional sensitivity provides a hypothesis for how heterogeneity of campaniform sensilla may be distributed.

New Species of the Genus Eryngyothrips (Thysanoptera, Thripidae) from Iran

A new thrips species, Eryngyothrips veisii sp. n. (Thripidae, Thripinae) is described and illustrated based on individual specimens collected from Choqasabz Forest Park (Ilam Province), western Iran. This new species is most similar to E. discolor Bhatti, but is readily distinguished from the latter by divided ferna, prothorax color yellowish brown, absence of metanotal campaniform sensilla, and the longest postocular setae pair III.

Sensilla on different organs of female and male Telenomus dendrolimusi Chu (Hymenoptera: Scelionidae).

Telenomus dendrolimusi Chu is a dominant egg parasitoid of Dendrolimus, which is the most serious conifer defoliator in China. However, the host locating mechanism of T. dendrolimusi is unclear. To take better advantage of this kind of parasitoid, it is necessary to clarify the basic knowledge of the organization of the wasp's sensory system. In this study, the external morphologies of the sensilla on the entire female and male T. dendrolimusi body were described using scanning electron microscopy. Antennae shape and sensilla types were sexually dimorphic. Ten segments and nine types of sensilla were found on the female antenna, including basiconic sensillum (BS), chaeticum sensillum (ChS), trichoid sensillum type 1 (TS1), trichoid sensillum type 2 (TS2), trichoid curvata sensillum (TCS), sickle-shaped sensillum (SSS), multiporous gustatory sensillum (MGS), campaniform sensillum (CS), and styloconica sensillum (STS). The distribution of the sensilla was directional on female antenna. The male antenna consisted of 12 segments, and 1-3 segments were similar to those of the female. Five types of sensilla were found on male antenna, including BS, ChS, TS1, TCS, and STS. The mouthparts, thoracic legs, eyes, mesonotum, and wings were all covered with longitudinally fluted TSs without hole. A tympana structure appeared on the thoracic legs. Special crevice-shaped structures were found on the abdomens of both T. dendrolimusi sexes. Possible sensilla functions are discussed according to their morphology. These results provide a solid basis for further researches about the parasitic mechanisms of T. dendrolimusi.

Force feedback reinforces muscle synergies in insect legs

The nervous system solves complex biomechanical problems by activating muscles in modular, synergist groups. We have studied how force feedback in substrate grip is integrated with effects of sense organs that monitor support and propulsion in insects. Campaniform sensilla are mechanoreceptors that encode forces as cuticular strains. We tested the hypothesis that integration of force feedback from receptors of different leg segments during grip occurs through activation of specific muscle synergies. We characterized the effects of campaniform sensilla of the feet (tarsi) and proximal segments (trochanter and femur) on activities of leg muscles in stick insects and cockroaches. In both species, mechanical stimulation of tarsal sensilla activated the leg muscle that generates substrate grip (retractor unguis), as well as proximal leg muscles that produce inward pull (tibial flexor) and support/propulsion (trochanteral depressor). Stimulation of campaniform sensilla on proximal leg segments activated the same synergistic group of muscles. In stick insects, the effects of proximal receptors on distal leg muscles changed and were greatly enhanced when animals made active searching movements. In insects, the task-specific reinforcement of muscle synergies can ensure that substrate adhesion is rapidly established after substrate contact to provide a stable point for force generation.

The effect of different host plants on the antennal and mouthparts sensilla of the larvae of Spodoptera littoralis; (Lepidoptera; Noctuidae)

The distribution and mor phology of various sensory organs (sensilla) on the antenna and mouthparts of Spodoptera littoralis larvae were investigated using scanning electron microscopy. In this study we focused on the morphological alterations of the antennal and mouthparts sensilla of Spodoptera littoralis last instar larvae reared on different hos t plants; alfalfa, cotton, and soybean leaves. Based on our results, we found that sensillum chaeticum on the antenna was morphologically affected by shifting the host plan t since it became longer in those larvae reared on soybean and alfalfa leaves when compared with those reared on cotton leaves. Furthermore, several morphological variations were observed in sensilla trichodea on the labium, mandibles, and labrum by shifting the host plant. In addition, clear morphological changes were observed in sensillum digitiformium on the maxillary palps due to changing the host plant. On the other hand, no morphological changes in ante nnal basiconic, trichodium and styloconic galeal sensilla styloconica, maxillary campaniform and placodeum sensilla were observed. Taken together, these results showed that shifting host plants of Spodoptera littoralis larvae induced plasticity and morphological changes of th e antennal and mouthparts sensilla.

The role of leg touchdown for the control of locomotor activity in the walking stick insect.

Much is known on how select sensory feedback contributes to the activation of different motoneuron pools in the locomotor control system of stick insects. However, even though activation of the stance phase muscles depressor trochanteris, retractor unguis, flexor tibiae and retractor coxae is correlated with the touchdown of the leg, the potential sensory basis of this correlation or its connection to burst intensity remains unknown. In our experiments, we are using a trap door setup to investigate how ground contact contributes to stance phase muscle activation and burst intensity in different stick insect species, and which afferent input is involved in the respective changes. While the magnitude of activation is changed in all of the above stance phase muscles, only the timing of the flexor tibiae muscle is changed if the animal unexpectedly steps into a hole. Individual and combined ablation of different force sensors on the leg demonstrated influence from femoral campaniform sensilla on flexor muscle timing, causing a significant increase in the latencies during control and air steps. Our results show that specific load feedback signals determine the timing of flexor tibiae activation at the swing-to-stance transition in stepping stick insects, but that additional feedback may also be involved in flexor muscle activation during stick insect locomotion. With respect to timing, all other investigated stance phase muscles appear to be under sensory control other than that elicited through touchdown.

Lehr's fields of campaniform sensilla in beetles (Coleoptera): Functional morphology. III. Modification of elytral mobility or shape in flying beetles

Some flying beetles have peculiar functional properties of their elytra, if compared with the vast majority of beetles. A “typical” beetle covers its pterothorax and the abdomen from above with closed elytra and links closed elytra together along the sutural edges. In the open state during flight, the sutural edges diverge much more than by 90°. Several beetles of unrelated taxa spread wings through lateral incisions on the elytra and turn the elytron during opening about 10–12° (Cetoniini, Scarabaeus, Gymnopleurus) or elevate their elytra without partition (Sisyphus, Tragocerus). The number of campaniform sensilla in their elytral sensory field is diminished in comparison with beetles of closely related taxa lacking that incision. Elytra are very short in rove beetles and in long-horn beetles Necydalini. The abundance of sensilla in brachyelytrous long-horn beetles Necydalini does not decrease in comparison with macroelytrous Cerambycinae. Strong reduction of the sensory field was found in brachyelytrous Staphylinidae. Lastly, there are beetles lacking the linkage of the elytra down the sutural edge (stenoelytry). Effects of stenoelytry were also not uniform: Oedemera and flying Meloidae have the normal amount of sensilla with respect to their body size, whereas the sensory field in the stenoelytrous Eulosia bombyliformis is 5–6 times less than in chafers of the same size but with normally linking broad elytra.

Dopaminergic modulation of phase reversal in desert locusts.

Phenotypic plasticity allows animals to modify their behavior, physiology, and morphology to adapt to environmental change. The global pest, the desert locust, shows two extreme phenotypes; a solitarious phase that is relatively harmless and a gregarious phase that forms swarms and causes extensive agricultural and economic damage. In the field, environmental conditions can drive isolated animals into crowded populations and previous studies have identified the biogenic amine serotonin as a key determinant of this transition. Here we take an integrated approach to investigate the neurochemical, physiological, and behavioral correlates defined by a laboratory based paradigm that mimics facets of swarm break down as gregarious locusts become isolated. Following isolation there was an increased propensity of locusts to avoid conspecifics, and show a reduced locomotion. Changes in choice behavior occurred within 1 h of isolation although isolation-related changes progressed with increased isolation time. Isolation was accompanied by changes in the levels of the biogenic amines dopamine, octopamine, and serotonin within the CNS within 1 h. Dopamine levels were higher in isolated animals and we focused on the role played by this transmitter in synaptic changes that may underpin solitarization. Dopamine reduced synaptic efficacy at a key central synapse between campaniform sensilla (CS) and a fast extensor tibiae motor neuron that is involved in limb movement. We also show that dopamine injection into the haemocoel was sufficient to induce solitarious-like behavior in otherwise gregarious locusts. Further, injection of a dopamine antagonist, fluphenazine, into isolated locusts induced gregarious-like behavior. This highlights that dopaminergic modulation plays an important role in the plasticity underpinning phase transition and sets a context to deepen the understanding of the complementary role that distinct neuromodulators play in polyphenism in locusts.

A new species of Forcipomyia Meigen (Diptera: Ceratopogonidae) described with immature stages from India.

Life stages of Forcipomyia parasecuris sp. n. is described, illustrated and photomicrograph based on examination with scanning electron microscope and binocular microscope. The larvae were collected from rotting banana stump of a banana garden at lower Gangetic plain area in India. Absence of ocular sensillum and campaniform sensillum in ocular area of pupa, a synapomorphic character of this proposed new species exhibits its uniqueness in genus Forcipomyia. This is also the first life stage of any Forcipomyia described from India.

Lehr's fields of campaniform sensilla in beetles (Coleoptera): Functional morphology. II. Wing reduction and the sensory field

Loss of the flight ability and wing reduction has been reported for many taxa of Coleoptera. If elytra are closed, their roots are clenched between the tergum and the pleuron, forces applied to the elytra can not be transmitted to the field of campaniform sensilla situated on the root. That is why it is plausible to assume that the field becomes redundant in non-flying beetles. We examined the relationships between the hind wing reduction and characters of this mechanosensory field in beetles of six families. We measured the size of the elytron, that of the hind wing and counted the number of sensilla in the sensory field. Mesopterous non-flying beetles retain one half to one third of sensilla present in macropterous species of the same body size. Further reduction of the sensory field in brachypterous species is obvious, but sensilla are still present in insects with strongly reduced wings, as long as their elytra are separable and mesothoracic axillaries are present. Complete loss of sensilla coincides with the existence of a permanent sutural lock. However, some beetles with permanently locked elytra and absence of axillaries still retain few campaniform sensilla. A very special case of an extreme wing modification in feather-wing beetles is considered. No sensilla were revealed either on the root of the elytron or on the basal segment of such fringed wings in flying ptiliid species.

Sexual dimorphism of adult labial palps of the peach fruit moth Carposina sasakii Matsumura (Lepidoptera: Carposinidae) with notes on their sensilla

AbstractThe labial palps and their sensilla of the peach fruit moth Carposina sasakii Matsumura, a serious pest of pome fruits in eastern Asia, were investigated using light microscopy and scanning and transmission electron microscopy. The labial palps are three‐segmented and exhibit distinct sexual dimorphism in length: much longer in the female than in the male. Four types of sensilla were found on the labial palps: campaniform, squamiform, chaetic and flattened sensilla. The campaniform sensilla are present on the first segment alone. The squamiform sensilla are located on all the three segments. The chaetic sensilla are mainly present on the third segment. The flattened sensilla are grooved with wall pores and situated in a labial palp‐pit organ, which is located at the apex of the distal segment of the labial palp. The sexual dimorphism of the labial palp and the labial palp‐pit organ was briefly discussed.

Lehr's fields of campaniform sensilla in beetles (Coleoptera): Functional morphology. I. General part and allometry

In this first of three articles we show the construction of the articular part of the elytron, the root. The root bears a conspicuous field of campaniform sensilla. This field was studied using light and scanning electron microscopes. The diversity of shape of the field among beetles, types of orientation of elongated sensilla within the field, individual variability of their number among conspecifics are demonstrated. Elongated sensilla point to the junction of the elytron with the second axillary plate. Presumably, they monitor twist movement in this junction, which is possible if the elytron is open. The goal of the whole project is to reveal the effect of both structure and function of the hind wings and elytra on the morphology of this mechanosensory field. Our data on allometric relationships between the animal size and quantitative characteristics of the field in normally flying beetles provide an important background for further functional analysis of this sensory organ.We selected 14 series of several species belonging to the same taxon but differing in size from big to small. It is revealed that the area of the sensory field is directly proportional to the elytral area, whereas the number of sensilla is proportional to the square root of the elytral area. Despite the great range in the elytral area (1500 times) in series of selected species the area of an external pit or cap of a single sensillum varies only 25-fold. The density of sensilla per unit area of the sensory field increases with decrease of the elytral area.