Roman Siemicki

Fine structure of antennal putative thermo‐/hygrosensilla of adult Rhodnius prolixus Stål (Hemiptera: Reduviidae)

At least five nonporous sensilla with inflexible sockets (npsensilla) occur on each antenna of both sexes of adult Rhodnius prolixus. Externally the sensillum appears as a short, rounded peg set into a pit surrounded by a depression. A very electron‐dense material occurs in the peg lumen and the inner aspect of the pit. Filamentous extensions of this material radiate into the overlying outlets.

Fine structure of the antennal tip of the crabhole mosquito, Deinocerites cancer Theobald (Diptera : Culicidae)

Abstract The antennal tips of both sexes of Deinocerites cancer Theobald bear sensilla coeloconica (pegs in pits) and internal sensilla with bipolar neurons that lack any connection with the cuticle. Each sensillum coeloconicum is innervated by 3 neurons. The dendrites of 2 neurons extend unbranched into the peg, whereas that of the third terminates below the peg base and is divided into numerous lamellae and microvilli. In males, the lamellated dendrite is much larger and more complex in organization than in females, a feature which is probably related to the unusual pupal finding and attendance phases of the mating behavior of the male. The 2 neurons with unbranched dendrites probably respond to heat transferred by convection. Possibly, the lamellated dendrite may be sensitive to infrared radiation or mechanical stimuli. Each internal sensillum in male D. cancer has one bipolar neuron with a dendrite divided into lamellae and microvilli. Females have similar internal sensilla plus a type with 2 bipolar neurons, the dendrite of one is unbranched and that of the other is lamellate in structure. The internal sensilla represent an intermediate form between the usually accepted Type I and Type II arthropod sensilla. Based on similarity in fine structure it is suggested that the internal sensilla have the same proposed functions as the sensilla coeloconica.

Fine structure of antennal sensilla of male Aedes aegypti (L.)

Abstract The terminal two antennal segments of male Aedes aegypti bear the same variety of sensillar types as the females antenna, namely, sensilla chaetica, sensilla coeloconica, sensilla ampullacea, grooved pegs, and four types of sensilla trichodea: long and short, pointed-tipped trichodea and blunt-tipped types I and II. Each type of sensillum has a similar fine structure in both sexes. Of the 514 neurones which innervate these sensilla in the male, 91% are olfactory receptors, 7% mechanoreceptors, and 2% thermoreceptors. The total number of neurones in the male is about four times fewer than in the female, but the ratio of those responding to the various stimuli is similar. The sensilla studied herein probably mediate stimuli involved in location of suitable resting sites and nectar meals. In addition they are apparently involved in location of vertebrates as recent studies indicate that certain male mosquitoes are attracted to hosts to bring them into the proximity of the females for mating. This host finding behaviour of males would explain why they have the same sprectrum of sensillar types as do females.

Fine structure of tarsal sensilla of Aedes aegypti (L.) (Diptera: Culicidae)†

The tarsi of all three pairs of legs of both sexes of Aedes aegypti (L.) bear spine sensilla, five types of hair sensilla, which are designated A, B, C1, C2 and C3, and campaniform sensilla. Type A and B hairs, spines, and cam‐paniform sensilla are innervated by one neuron with a tubular body, a characteristic of cuticular mechanoreceptors. In particular the hairs and spines are tactile receptors and the campaniform sensilla are proprioceptors. The C1, C2, and C3 hair sensilla have the morphological features of contact chemoreceptors. Type C1 and C3 hairs are innervated by five and four neurons, respectively, which extend to the tip of the hair. Type C2 is innervated by five neurons, one of which terminates at the base of the hair in a tubular body while the remaining four extend to the tip of the hair. The role of the type C hairs in oviposition behavior, nectar feeding, and recognition of conspecific females is discussed. Presumed efferent neurosecretory fibers occur near the spine and hair sensilla.

Palpal sensilla of selected anopheline mosquitoes.

Palps of both sexes of Anopheles stephensi, A. albimanus, A. quadrimaculatus, and female A. gambiae were examined and found to be equipped to perceive both mechanical and olfactory stimuli. Present on the palps are sensilla chaetica, tactile and/or air current receptors, campaniform sensilla, proprioceptors, and thin-walled capitate pegs, olfactory receptors probably sensitive to carbon dioxide. The fine structure of each type of sensillum is described. Mosquitoes have various types of antennal and palpal sensilla which are responsible for the reception of external stimuli, including those involved in host finding and selection. Several investigators have reported on the detailed structure (Elizarov and Chaika, 1972; McIver, 1971, 1972; McIver and Charlton, 1970; McIver and Hudson, 1972) and function (Bassler, 1958; Kellogg, 1970) of palpal sensilla of culicine mosquitoes, but information about those on anopheline mosquitoes has been lacking. This work was conducted to (a) determine the types of palpal sensilla on both sexes of Anopheles stephensi Liston, Anopheles albimanus Wiedemann, and Anopheles quadrimaculatus Say, and female Anopheles gambiae Giles and (b) describe the fine structure of the sensilla on female A. stephensi. MATERIALS AND METHODS Specimens of A. stephensi, A. gambiae, A. albimanus, and A. quadrimaculatus were obtained from laboratory colonies maintained, respectively, at the Department of Parasitology, Department of Botany, University of Toronto, Central American Malaria Research Station, San Salvador, and the Center for Disease Control, Atlanta, Georgia. For transmission electron microscopy, palps were removed from mosquitoes immersed in Karnovskys fixative (Karnovsky, 1965) at pH 7 and 4 C and left in the fixative for 18 hr. After rinsing in 0.05 M Sorensens 10% sucrose buffer, pH 7, the tissue was postfixed in 1% Os04 in veronal acetate buffer at pH 5 and at room temperature for 2 hr. Dehydration through ethanol was followed by embedding in Spurrs low viscosity epoxy medium (Spurr, 1969). For scanning electron microscopy specimens were fixed in 5% formalin and dehydrated through a graded series of ethanols to xylene (Slifer, 1972), attached to the stubs with silver conductive paint, Received for publication 9 December 1974. coated with gold during spin rotation, and examined in a Cambridge Stereoscan microscope. For counting the sensilla, double coverslip mounts of heads were prepared as described by McIver (1969). All numerical results are means of at least 10 counts or measurements. Statistical significance was determined using Students t test at the 5% level and adjustment for multiple comparison effect was made. Permeable areas in the cuticle were demonstrated by staining whole specimens with crystal violet (Slifer, 1960) from 30 min to 2 hr.

Fine structure of antennal mechanosensilla of adult Rhodnius prolixus stål (Hemiptera: Reduviidae)

Each antenna of both sexes of adult Rhodnius prolixus has approximately 570 mechanosensitive neurons that innervate five morphologic types of cuticular mechanosensilla: campaniform sensilla, tapered hairs, trichobothria, and type I and type II bristle sensilla. Each campaniform sensillum and tapered hair is presumably innervated by one mechanosensitive bipolar neuron and probably functions in proprioception. The campaniform sensilla being located at the base of the scape could monitor the position of the antenna. Tapered hairs are found at the distal margin of flagellar segment I and projecting laterally from the bases of the pedicel and scape. They probably provide information about the relative positions of the antennal segments. Seven trichobothrium are located on the pedicel and three on flagellar segment I. Each trichobothrium has a long filamentous hair inserted into the base of a socket that extends inwardly as a cuticular tube and is innervated by one bipolar neuron with a tublar body, a parallel arrangement of microtubules associated with electron‐dense material. The trichobothria may respond to small variations in air currents.

Bifurcate sensilla on the tarsi of female black flies, Simulium venustum (Diptera: Simuliidae): Contact chemosensilla adapted for olfaction?

The ventral surface of the most proximal tarsomere of each mesothoracic leg of the female black fly, Simulium venustum Say, bears approximately 60 bifurcate sensilla. Externally, a sensillum appears as a hair set into an asymmetric socket and with the distal tip flattened into two flared lobes. A single pore opens into a short groove at the base of the lobes. The hair shaft is divided into two lumina, one of which contains the dendrites. Each sensillum is innervated by four neurons, the dendrites of which extend unbranched to the pore. Sensillum liquor bathes the dendritic tips and extends through the pore into the adjacent groove and across part of the lobes. A sieve‐like structure exists in the pore region of many if not all sensilla. At least two sheath cells are associated with each sensillum.

Fine structure of pegs on the maxillary palps of adult Toxorhynchites brevipalpis theobald (Diptera : Culicidae)

Abstract Each peg sensillum on the palps of female Toxorhynchites brevipalpis (Diptera : Culicidae) consists of a thin-walled, porous, digitiform peg set into a shallow cuticular depression, with at least 3 sheath cells and 3, sometimes 2 neurons. These sensilla have the structural features of olfactory chemosensilla, and similar pegs on the palps of other mosquitoes are known, from behavioral and electrophysiological studies, to be sensitive to air-borne stimuli. In T. brevipalpis the neurons probably respond to odors associated with nectar and oviposition sites. The dendrites of all the neurons extend the length of the peg lumen and divide into approximately 30 digitiform branches. These results, when compared with those from blood-feeding female mosquitoes, suggest that the lamellated dendrite, present in the latter and absent in T. brevipalpis , is associated with carbon dioxide sensitivity in hematophagous insects. The sensory sinus is extensively developed in the peg sensilla. Large sinuses occur in both the intermediate and outer sheath cells and join to form a common sinus beneath the peg. The intermediate and outer sheath cells are apparently metabolically active, as indicated by the occurrence of high numbers of large mitochondria and closely spaced lamellae and microvilli. In 1 3 of the pegs examined, large mitochondria were observed within the projections of the intermediate cell in the peg lumen. Peg sensilla were not found on the palps of male T. brevipalpis

Campaniform sensilla on the palps of Anopheles stephensi Liston (Diptera: Culicidae)

Abstract The terminal portion of the dendrite and cuticular aspects of the campaniform sensilla on the palps of the mosquito, Anopheles stephensi, are described. The domed cap, which is hinged to a surrounding ring of raised cuticle, is composed of 3 layers: an outer exocuticular layer, a middle spongy layer, and an inner fibrous layer. A single dendrite is attached by the cuticular sheath to the outer layer of the cap.

Fine structure of maxillary sensilla of larval Toxorhynchites brevipalpis (Diptera: Culicidae) with comments on the role of sensilla in behavior

Each maxilla of fourth instar Toxorhynchites brevipalpis bears nine sensilla: Four are located at the tip of the maxillary palp and five on the maxillary body. At the palp tip are three tapered pegs on bulbous bases (MS1, MS2, MS6) that are innervated by four, two, and two neurons, respectively, and probably function in chemoreception. Also at the palp tip is a sturdy, cuticular rod with a lumen (MS5) that opens distally to the exterior. The proximal end of the rod is closed by a cuticular base to which a single unbranched dendrite containing only a few microtubules is attached. The function of MS5 is enigmatic; possibilities include mechanoreception and detection of infrared radiation.