The fine structure of the antenna and of the antennal sensory cone, the largest of the eight antennal sensilla, of fourth instar larvae of the mosquito Aedes aegypti are described and discussed. The antennal integument supports and encloses only sensillar elements. The antennal sensory cone seems to be a chemoreceptor of a modified composite basiconic type. It is innervated by about 12 neurons grouped into six units. Each neuronal unit has a trichogen and tormogen cell, but no neurilemma or other accessory cells, associated with it. Stimulating molecules may diffuse directly through the non-perforate conical cuticular covering to the dendritic branches, and through six vacuoles between the dendrites and the epicuticle at the base of the cone. Peripheral vesicles in the cone, their probable formation from secretions produced in the junction body region, and their possible function in the stimulating mechanism of the sense organ are described and discussed. Dendritic neurotubules originate from ciliary tubules in the junction body region, in the dendritic plasma, or by branching. Tight junctions provide possible electrotonic coupling between all the dendritic branches of the sensillum, and between dendrites in each unit. The neuronal perikaryons and portions of the axons and proximal dendrites are not ensheathed, but extend naked in close proximity through the antennal hemo-sinus into an ensheathed nerve at the base of the antenna.The cephalic sensilla of fourth instar larvae of the mosquito Aedes aegypti were described by Yin ('70) within the limits of resolution of the light microscope. Some of the sensilla she noted appeared to be new types that could not be related to any sensilla of other insects for which descriptions are available. While several ultrastructural studies on selected sensilla of adult mosquitoes are available, none are known to us on sensilla of larval forms of this group, even though some of the species are of medical importance. In fact, little is known about the fine structure of sensilla of larval insect forms in general, and particularly of those from aquatic habitats.A series of studies were therefore undertaken to describe the fine structure of the cephalic sensilla of larval Aedes aegypti. This report details the fine structure of the antenna and of the largest and most complex of the antennal sensilla. This sensillum, referred to by Yin ('70) as the "tube J. MORPH., 135: 273-298.organ," is termed the antennal sensory cone in the present study.
MATERIALS AND METHODSEggs from a stock laboratory colony of the yellow fever mosquito Aedes aegypti were hatched in deoxygenated water at about 33°C (Burgess, '59). The larvae were reared to the fourth (last) instar in distilled water on a diet of 9: 1 by weight of brewer's yeast and fine ground oat cereal. Under these conditions the first three instars occupy about one day and the fourth instar about three days. To avoid undue cellular changes connected with moulting in our ultrastructural studies of the sensilla, we observed the third...
In Manitoba, Saskatchewan, and Alberta, Ctenicera destructor (Brown) occurs in the brown and black soils of the Grassland Formation, and C. aeripennis (Kby.) occurs in the grey soils of the Forest Formation.The incubation period of the eggs of C. destructor varied inversely with temperature. It averaged 20 days at 68° F and 11.5 days at 86° F. The duration of the larval stage varied from about 1 to more than 2 years at 68° F. The male larvae completed their development in 9 or 10 stadia, and the female larvae in 10 or 11 stadia. The female larvae usually fed more, but completed their development sooner than did the male, and both sexes fed most during the ninth stadium. The pupal period varied from 2–3 weeks at 68° F. In the field, male beetles emerged 1 or more days before the females. The ratio of males: females was about 1.5. Each female laid an average of about 200 eggs. The adults were not observed to fly.
There are typically six elongate pegs positioned in longitudinal grooves in the outer walls of the distal segment of the labial palps of larvae of Ctenicera destructor (Brown). They are termed digitiform sensilla on the basis of their form and function. Each has a subapical pore typical of a contact chemoreceptor in surface scan, and a terminally branched dendrite but not the cuticular pores typical of a chemoreceptive porous hair. The dendritic terminations are encased by the dendritic sheath, the subapical pore is plugged in the wall of the peg, and there is only one innervating neuron, all of which are typical of a tactile mechanoreceptor. These pegs respond electrophysiologically to contact and vibratory stimuli, but not to the amino acids, sugars, salts, and water tested, nor to a changed pressure in the cephalic hemocoel.
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