Fine structure of the antenna and its sensory cone in larvae of Aedes aegypti (L.)

Abstract

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...

The molecular and cellular basis of olfactory-driven behavior inAnopheles gambiaelarvae

“…Not surprisingly, the number and morphology of larval antennal terminal structures were consistent among individuals and throughout larval instars, as well as similar to those described for Ae. aegypti (9).…”

“…Vacuoles were observed near the base of the cone, similar to those found in Ae. aegypti, that may function in lipid-soluble odor detection (9). The An.…”

A highly conserved candidate chemoreceptor expressed in both olfactory and gustatory tissues in the malaria vector Anopheles gambiae

“…6 B and D, which is published as supporting information on the PNAS web site). Both organs house terminal sensilla in mosquitoes that are thought to be chemosensory in function on the basis of their fine structures (27,36). In the case of the maxillary palpus, labeling was clear in a small number of cell bodies and in projections into the sensillar cone (Fig.…”

“…2 and 6) is in agreement with Vosshall et al (14), who observed that DOr83b was expressed in D. melanogaster larvae. The distal end of the larval antenna and maxillary palpus of mosquitoes contain several innervated, sensory-type structures that potentially function in both olfaction and gustation (27,36). Specific expression of the AgOR7 protein in these tissues is consistent with their having a chemosensory function, although it remains unclear whether that role may be olfactory, gustatory, or both.…”

Fine structure of the cuticle, epidermis, and fat body of larval Elateridae (Coleoptera) and changes associated with molting

“…Zacharuk 1970), the effects of the molting process on infection by microbial pathogens, and the structural nature of the cuticular apparatus of insect sense organs and its role in sensillar function (e.g. Scott and Zacharuk 1971 ;Zacharuk 1971b;Zacharuk et al 1971).…”