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Innervation of cibarial sensilla of Aedes aegypti (L.) (Diptera: Culicidae)
hr. J. Inserr Morjdol. & Dnbr.vol.. Vol. IO, No.4. pp. 355 10159. 1981. Primed in Greal Brimin.
ooze-7322/81/ou)355-045020.00/0 0 1981 Pcrgamon Press Ltd.
SCIENTIFIC INNERVATION
NOTE
OF CIBARIAL SENSILLA OF AEDES AEGYPTI (L.) (DIPTERA: CULICIDAE) SUSAN MCIVER and ROMAN SIEMICKI
Department of Zoology, University of Toronto, Toronto, Ontario, Canada MSS IA1 (Accepfed
14 April
1981)
IN MOSQUITOES. as well as other blood-feeding nematocerous Diptera, a blood-meal goes directly to the midgut, while a sugar-meal is sent to the crop. Owing to their location, the cibarial sensilla have been generally considered to play a major role in determining the acceptability and destination of a meal, although as indicated by Friend and Smith (1977), there is little direct evidence for this. The external morphology of the cibarial sensilla of a number of mosquito species has been described by light or scanning electron microscopic techniques (Day, 1954; von Cernet and Buerger, 1966; Lee, 1974; Lee and Davies, 1978; Uchida, 1979). In the cibaria of both sexes of Aedes aegypfi (L), are S types of sensilla: 2 pairs of palatal papillae located on the anterior dorsal hard palate of the cibarium; a pair of campaniform sensilla, one sensillum on either side of the dorsal hard palate; one pair of dorsal papillae behind the campaniform sensilla; trichoid sensilla in the anterior dorsal wall lateral to the campaniform sensilla; and 4 ventral papillae in 2 groups in the posteroventral wall of cibarium. The number and location of all these sensilla, except the trichoid ones, are the same in both sexes (Lee, 1974). The purpose of this study was to determine the innervation of the cibarial sensilla of both sexesof A. uegypti (L.). The results aid in understanding feeding behavior, and facilitate experimental investigations of these sensilla in mosquitoes. The specimens were obtained from a laboratory colony that originated from a collection made near Orlando, Florida. The techniques employed for transmission electron microscopy have been described in detail by Mclver
(1974).
We did not observe any differences in the innervation of male and female sensilla. The palatal, dorsal and ventral papillae all have thick walls and arise from membraneous sockets. Each papilla in the anterior pair of palatal papillae is innervated by 3 neurons (Fig. 1) and each in the posterior pair by 4 (Fig. 2). In all palatal papillae the dendrites extend to near the tips of the papillae and with few exceptions are unbranched. Each dorsal papilla is innervated by 2 neurons (Fig. 3) and each ventral one by 3 (Fig. 4). In both the dorsal and ventral papillae the unbranched dendrites terminate at the papillar tips. All the cibarial papillae of A. aegypri have morphological characteristics of known contact chemosensilla. namely, thick walls and unbranched dendrites which extend to the peg tip and lack tubular bodies. In Toxorhynchites mosquitoes probably homologous papillae have terminal pores (Lee and Davies, 1978). ATP and other adenine nucleotides act as phagostimulants for A. aegypri (Galun et al., 1963; Galun, 1967). Detection of these stimuli plus others, which may be involved in determination of destination of a meal, is most likely a function of the cibarial chemosensilla. Elucidation of a more precise function of each type of papilla awaits experimental investigation. Each campaniform and trichoid sensillum is innervated by one neuron, whose dendrite distally terminates as a tubular body, a parallel arrangement of microtubules in an electron-dense material and a characteristic of the cuticular mechanosensilla (Mclver, 1975). The distal portion of the dendrite, including the tubular body, is encased within a sturdy cuticular sheath (Figs. 5,6). In the campaniform sensillum, the cuticular sheath merges with the cuticle in the center of the peg-like cap. In the trichoid sensillum, the dendrite extends some distance into the hair where it is attached by the cuticular sheath (Fig. 6). Campaniform sensilla act as propioceptors, detecting strains in the cuticle (Pringle, 1938). The ones herein may detect strains resulting from expansion of the cibarium during feeding or as suggested by Rice (1973) for cibarial campaniform sensilla of Culliphora eryfhrocephalu may monitor the viscosity of the materials in the pump. The trichoid sensilla are quite similar to the LC2 sensilla in the labrocibarium of the tsetse fly (Rice ef ol., 1973) and probably act as fluid-flow meters. It is unknown whether the determination of destination of a meal is a function solely of the peripheral sensilla or involves central nervous system factors as well. Our finding that sensilla in both sexes of A. aegypti have the 355
356
SCIENTIFIC
NOTE
FIGS. 1 -4 Sections through dendrites (D) of cibarial papillae. (I) palatal, one of the anterior pair, male. (2) palatal. one of posterior pair, female. (3) dorsal, female. (4) ventral, male. Scale = 0.5um. FIG. 5. Oblique section through campaniform sensillum, male. C = peg-like cap; S = cuticular sheath; T = tubular body. Scale = 0.5 urn. FIG. 6 Oblique section through trichoid sensillum, male. H = hair; S = cuticular sheath encasing tubular body. Scale = 0.5um. same number of neurons indicates that determination of destination is not related to presence of neurons. Involvement of the peripheral sensilla is most likely at the level of the sensitivity of specific receptor sites in the dendritic membrane. Interestingly, in some adult Toxorhynchires mosquitoes, which are non-biting and feed on nectar, Lee and Davies (1978) found a reduction in size and number of certain papillae.
Acknowledgemenfs-This
study
was supported
by the Medical
Research
Council
(Canada),
grant
MT2909.
SCIENTIFIC
357
NOTE
REFERENCES DAY. M. F. 1954. The mechanism
of food
distribution
to midgut
or diverticula
in the mosquito.
Ausr. J. Biol.
Sri. 1: 515-24. W. G. and J. J. B. SMITH. 1977. Factors affecting feeding by bloodsucking insects. Annu. Rev. Enromol. 22: 309-31. GALUN. R. 1967. Feeding stimuli and artificial feeding. Bull. W/d. Hlth. Org. 36: 590-93 GALUN. R., Y. AVI-DOR and M. BAR-ZEEV. 1963. Feeding response in Aedes uegyp/i: stimulation by adenosine triphosphate. Science, ( Wush.) D.C. 142: 1674 - 75. GERNET. G. VON and G. BUERGER. 1966. Labral and cibarial sense organs of some mosquitoes. Quoesr. FRIEND.
Enromol. 2: 259 - 70. LEE, R. 1974. Structure and funclion of the fascicular stylets, and the labral and cibarial sense organs of male and female Aedes oegypri (L.) (Diptera, Culicidae).Quuesr. Eniomol. 10: 187 -215 LEE, R. M. K. W. and D. M. DAVIES. 1978. Cibarial sensilla of Toxorhynchires mosquitos (Diptera: Culicidae). In!. J. Insect Morphol. Embryo/. 7: 189 - 94. MCIVER. S. B. 1974. Fine structure of antenna1 grooved pegs of the mosquito, Aedes uegypti. Cell Tissue Res. 153: 327 - 37. MCIVER. S. B. 1975. Structure of cuticular mechanoreceptors of arthropods. Annu. Rev. Enfomol. 20: 381 -97. PRINGLE. J. W. S. 1938. Proprioception in insects. II. The action of the campaniform sensilla on the legs. J. Exp. Biol. 15: 114-31. RICE. M. J. 1973. Cibarial sense organs of the blow fly, Culliphoru erythrocephulu (Meigen) (Diptera: Calliphoridae). Inl. J. lnsecr Morphol. Embryo/. 2: 109 - 16. RICE, M. J., R. GALUN and J. MARCALIT. 1973. Mouthpart sensilla of the tsetse fly and their function. III. Labrocibarial sensilla. Ann. Trap. Med. Purisitol. 67: 109- 16. UCHIDA. K. 1979. Cibarial sensilla and pharyngeal valves in Aedes ulbopicrus (Skuse) and CulexpipienspuNens Coquillett (Diptera: Culicidae). Inr. J. Insecr Morphol. Embryo/. 8: 159 - 67.
ooze-7322/81/ou)355-045020.00/0 0 1981 Pcrgamon Press Ltd.
SCIENTIFIC INNERVATION
NOTE
OF CIBARIAL SENSILLA OF AEDES AEGYPTI (L.) (DIPTERA: CULICIDAE) SUSAN MCIVER and ROMAN SIEMICKI
Department of Zoology, University of Toronto, Toronto, Ontario, Canada MSS IA1 (Accepfed
14 April
1981)
IN MOSQUITOES. as well as other blood-feeding nematocerous Diptera, a blood-meal goes directly to the midgut, while a sugar-meal is sent to the crop. Owing to their location, the cibarial sensilla have been generally considered to play a major role in determining the acceptability and destination of a meal, although as indicated by Friend and Smith (1977), there is little direct evidence for this. The external morphology of the cibarial sensilla of a number of mosquito species has been described by light or scanning electron microscopic techniques (Day, 1954; von Cernet and Buerger, 1966; Lee, 1974; Lee and Davies, 1978; Uchida, 1979). In the cibaria of both sexes of Aedes aegypfi (L), are S types of sensilla: 2 pairs of palatal papillae located on the anterior dorsal hard palate of the cibarium; a pair of campaniform sensilla, one sensillum on either side of the dorsal hard palate; one pair of dorsal papillae behind the campaniform sensilla; trichoid sensilla in the anterior dorsal wall lateral to the campaniform sensilla; and 4 ventral papillae in 2 groups in the posteroventral wall of cibarium. The number and location of all these sensilla, except the trichoid ones, are the same in both sexes (Lee, 1974). The purpose of this study was to determine the innervation of the cibarial sensilla of both sexesof A. uegypti (L.). The results aid in understanding feeding behavior, and facilitate experimental investigations of these sensilla in mosquitoes. The specimens were obtained from a laboratory colony that originated from a collection made near Orlando, Florida. The techniques employed for transmission electron microscopy have been described in detail by Mclver
(1974).
We did not observe any differences in the innervation of male and female sensilla. The palatal, dorsal and ventral papillae all have thick walls and arise from membraneous sockets. Each papilla in the anterior pair of palatal papillae is innervated by 3 neurons (Fig. 1) and each in the posterior pair by 4 (Fig. 2). In all palatal papillae the dendrites extend to near the tips of the papillae and with few exceptions are unbranched. Each dorsal papilla is innervated by 2 neurons (Fig. 3) and each ventral one by 3 (Fig. 4). In both the dorsal and ventral papillae the unbranched dendrites terminate at the papillar tips. All the cibarial papillae of A. aegypri have morphological characteristics of known contact chemosensilla. namely, thick walls and unbranched dendrites which extend to the peg tip and lack tubular bodies. In Toxorhynchites mosquitoes probably homologous papillae have terminal pores (Lee and Davies, 1978). ATP and other adenine nucleotides act as phagostimulants for A. aegypri (Galun et al., 1963; Galun, 1967). Detection of these stimuli plus others, which may be involved in determination of destination of a meal, is most likely a function of the cibarial chemosensilla. Elucidation of a more precise function of each type of papilla awaits experimental investigation. Each campaniform and trichoid sensillum is innervated by one neuron, whose dendrite distally terminates as a tubular body, a parallel arrangement of microtubules in an electron-dense material and a characteristic of the cuticular mechanosensilla (Mclver, 1975). The distal portion of the dendrite, including the tubular body, is encased within a sturdy cuticular sheath (Figs. 5,6). In the campaniform sensillum, the cuticular sheath merges with the cuticle in the center of the peg-like cap. In the trichoid sensillum, the dendrite extends some distance into the hair where it is attached by the cuticular sheath (Fig. 6). Campaniform sensilla act as propioceptors, detecting strains in the cuticle (Pringle, 1938). The ones herein may detect strains resulting from expansion of the cibarium during feeding or as suggested by Rice (1973) for cibarial campaniform sensilla of Culliphora eryfhrocephalu may monitor the viscosity of the materials in the pump. The trichoid sensilla are quite similar to the LC2 sensilla in the labrocibarium of the tsetse fly (Rice ef ol., 1973) and probably act as fluid-flow meters. It is unknown whether the determination of destination of a meal is a function solely of the peripheral sensilla or involves central nervous system factors as well. Our finding that sensilla in both sexes of A. aegypti have the 355
356
SCIENTIFIC
NOTE
FIGS. 1 -4 Sections through dendrites (D) of cibarial papillae. (I) palatal, one of the anterior pair, male. (2) palatal. one of posterior pair, female. (3) dorsal, female. (4) ventral, male. Scale = 0.5um. FIG. 5. Oblique section through campaniform sensillum, male. C = peg-like cap; S = cuticular sheath; T = tubular body. Scale = 0.5 urn. FIG. 6 Oblique section through trichoid sensillum, male. H = hair; S = cuticular sheath encasing tubular body. Scale = 0.5um. same number of neurons indicates that determination of destination is not related to presence of neurons. Involvement of the peripheral sensilla is most likely at the level of the sensitivity of specific receptor sites in the dendritic membrane. Interestingly, in some adult Toxorhynchires mosquitoes, which are non-biting and feed on nectar, Lee and Davies (1978) found a reduction in size and number of certain papillae.
Acknowledgemenfs-This
study
was supported
by the Medical
Research
Council
(Canada),
grant
MT2909.
SCIENTIFIC
357
NOTE
REFERENCES DAY. M. F. 1954. The mechanism
of food
distribution
to midgut
or diverticula
in the mosquito.
Ausr. J. Biol.
Sri. 1: 515-24. W. G. and J. J. B. SMITH. 1977. Factors affecting feeding by bloodsucking insects. Annu. Rev. Enromol. 22: 309-31. GALUN. R. 1967. Feeding stimuli and artificial feeding. Bull. W/d. Hlth. Org. 36: 590-93 GALUN. R., Y. AVI-DOR and M. BAR-ZEEV. 1963. Feeding response in Aedes uegyp/i: stimulation by adenosine triphosphate. Science, ( Wush.) D.C. 142: 1674 - 75. GERNET. G. VON and G. BUERGER. 1966. Labral and cibarial sense organs of some mosquitoes. Quoesr. FRIEND.
Enromol. 2: 259 - 70. LEE, R. 1974. Structure and funclion of the fascicular stylets, and the labral and cibarial sense organs of male and female Aedes oegypri (L.) (Diptera, Culicidae).Quuesr. Eniomol. 10: 187 -215 LEE, R. M. K. W. and D. M. DAVIES. 1978. Cibarial sensilla of Toxorhynchires mosquitos (Diptera: Culicidae). In!. J. Insect Morphol. Embryo/. 7: 189 - 94. MCIVER. S. B. 1974. Fine structure of antenna1 grooved pegs of the mosquito, Aedes uegypti. Cell Tissue Res. 153: 327 - 37. MCIVER. S. B. 1975. Structure of cuticular mechanoreceptors of arthropods. Annu. Rev. Enfomol. 20: 381 -97. PRINGLE. J. W. S. 1938. Proprioception in insects. II. The action of the campaniform sensilla on the legs. J. Exp. Biol. 15: 114-31. RICE. M. J. 1973. Cibarial sense organs of the blow fly, Culliphoru erythrocephulu (Meigen) (Diptera: Calliphoridae). Inl. J. lnsecr Morphol. Embryo/. 2: 109 - 16. RICE, M. J., R. GALUN and J. MARCALIT. 1973. Mouthpart sensilla of the tsetse fly and their function. III. Labrocibarial sensilla. Ann. Trap. Med. Purisitol. 67: 109- 16. UCHIDA. K. 1979. Cibarial sensilla and pharyngeal valves in Aedes ulbopicrus (Skuse) and CulexpipienspuNens Coquillett (Diptera: Culicidae). Inr. J. Insecr Morphol. Embryo/. 8: 159 - 67.