Morphometric differences in midgut epithelial cells between strains of female Aedes aegypti (L.) (Insecta,Diptera)

Midgut epithelial cells of female Aedes aegypti deriving from 2 different mosquito strains were compared morphometrically. One of the 2 strains was recently isolated from nature (East Africa). The other strain is an old laboratory strain, reared under laboratory conditions for about 30 years. The quantitative morphological comparison demonstrates, that the ultrastructural composition of the midqut epithelial cells corresponds generally in both strains. It can be shown, however, that in the old strain, compared to the new strain, the organelle amount of midgut epithelial cells is significantly reduced during the first 53 days of the mosquito's life. Parallel to decreased relative volumes of organelles and reduced surface densities of membrane systems an increase in lysosome-like structures is observed. These observations are interpreted as deterioration processes, possibly due to the long rearing in the laboratory. Therefore, care should be taken in the selection of an A.aegypti strain for any quantitative morphological or physiological investigation.     

Isolation of trypsin isozymes from the mosquito Aedes aegypti (L.)

Trypsin has been isolated from midgut homogenates of blood-fed females of Aedes aegypti by a simple two-step purification procedure: ion-exchange chromatography followed by affinity chromatography. The resulting mosquito trypsin contains a number of isozymes, among which 5 major SDS-PAGE bands are recognized with molecular weights of 26.7, 28.5, 29.7, 31.0 and 32.0 kdaltons, as are some minor bands above and below this range. The isozymic pattern is comparable to that in crude homogenates. Isoelectric focussing of purified trypsin however, revealed over 20 tryptic isozymes, demonstrating that several isozymes segregate into subforms. A high correlation between TAME-active fractions and their DFP equivalent was demonstrated by using ³H-labelled DFP as a marker for trypsin on native acrylamide gels.The purification factor and the specific activities are discussed with respect to the unusual amounts of protein of dietary origin present in the midgut homogenates. Interference of blood-borne coagulation factors of a tryptic nature is unlikely.     

Secretion in the male accessory glands of Aedes aegypti (L.) (Diptera : Culicidae)

The objective of this work is to determine the nature, the mode of synthesis, and release of the secretion of accessory glands of the male mosquito, Aedes aegypti (Diptera : Culicidae). Cytological studies revealed that each of the 2 glands has 2 morphological types of regionally specialized secretory cells, each type differing in the nature, and the release of its products. The anterior region (AR) cells secrete small (0.3–1.3 μm) electron-lucent granules, which during the peak period of synthesis seemed to transport the flocculent and fibrous granular substance to the apical cytoplasm of the cell by means of binary fusions. This cytoplasm, when filled with secretory granules, pinches off and falls freely into the lumen of the gland, thus, exhibiting a macroapocrine mode of secretion. The posterior region (PR) cells, however, elaborate large (mean diameter 2 μm) electron-dense granules, which are released into the lumen essentially by rupture of the cell membrane at the apical end. In males mated to depletion, the volume of the gland is reduced by 67%; there is no subsequent recovery of secretory capacity.     

A cytogenetic analysis of meiotic drive in the mosquito,Aedes aegypti (L.)

Meiotic drive in Aedes aegypti (L.) is shown by a Giemsa C-banding technique to be associated with preferential isochromatid breakage of the X chromosome during male meiosis. These breaks remain open at least until anaphase-I and, since the range of cells affected is proportional to the sensitivity of the X chromosome to the Distorter gene, it is argued that they are directly related to the decreased number of spermatozoa found in distorting males. This reduction is considered to be attributable to the degeneration of more X- than Y-bearing spermatids but it is probable that some non-functional X-bearing spermatozoa are also produced. Chromosome breakage is almost completely confined to four sites, two adjacent to the centromere, one just proximal to the intercalary band and another about the centre of the unbanded arm. Although the first three of these lie within a region in which crossing-over does not take place, fragmentation occurs more frequently in a chiasmate arm than in one devoid of chromatid exchange.     

The mosquito Aedes aegypti (L.): evidence for three new proteinases

The effect of inhibitors was studied on the proteolytic activity of crude extracts of the mosquito Aedes aegypti (L.), prepared 25 h after blood intake. This activity is only partially inhibited by the lima bean trypsin inhibitor (LBTI) or by EDTA. Experiments with mixed inhibitors are used to indicate that, apart from the well characterized trypsin-like enzymes, at least three other proteinases are present. These are an LBTI-resistant serine proteinase, a metal chelator-sensitive proteinase, and a proteinase which can only be inhibited by the ovomucoid inhibitor. These newly described proteinases are inactive against several model substrates developed for mammalian enzymes. They are partially separable by ion-exchange chromatography.     

Potential of crude seed extract of celery, Apium graveolens L., against the mosquito Aedes aegypti (L.) (Diptera: Culicidae).

Crude seed extract of celery, Apium graveolens, was investigated for anti-mosquito potential, including larvicidal, adulticidal, and repellent activities against Aedes aegypti, the vector of dengue haemorrhagic fever. The ethanol-extracted A. graveolens possessed larvicidal activity against fourth instar larvae of Ae. aegypti with LD50 and LD95 values of 81.0 and 176.8 mg/L, respectively. The abnormal movement observed in treated larvae indicated that the toxic effect of A. graveolens extract was probably on the nervous system. In testing for adulticidal activity, this plant extract exhibited a slightly adulticidal potency with LD50 and LD95 values of 6.6 and 66.4 mg/cm2, respectively. It showed repellency against Ae. aegypti adult females with ED50 and ED95 values of 2.03 and 28.12 mg/cm2, respectively. It also provided biting protection time of 3 h when applied at a concentration of 25 g%. Topical application of the ethanol-extracted A. graveolens did not induce dermal irritation. No adverse effects on the skin or other parts of the body of human volunteers were observed during 3 mo of the study period or in the following 3 mo, after which time observations ceased. A. graveolens, therefore, can be considered as a probable source of some biologically active compounds used in the development of mosquito control agents, particularly repellent products.     

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.     

Dynamics and Characterization of Aedes aegypti (L.) (Diptera: Culicidae) Key Breeding Sites

The present study aimed to analyze the dynamics of containers used as breeding sites by Aedes aegypti (L.) in the city of Aracaju, SE, one of the Northeast Brazilian states. A total of three entomological surveys were performed during different precipitation levels. Breeding sites were categorized according to their function into storage, disposable containers, and reusable containers. “Mean number of pupae” and “frequency of each type of breeding site” were the criteria considered to identify key breeding sites. House index and Breteau index were calculated in each survey. A total of 3,647 water reservoirs were found, of which 220 were breeding sites, where 22,880 immature forms were identified. There were no differences in the mean number of larvae of several types of breeding sites and in the number of larvae among surveys. Larval indices showed a reduction in the second visit, but with no effect on adult occurrence when the number of pupae was considered. Key breeding sites resulted from containers used for water storage. The area studied showed conditions favorable to a new epidemic of dengue fever.     

Cytological mapping of the M and D loci in the mosquito,Aedes aegypti (L.)

The separate identities of the male-determining factor, M, and the sex-linked Distorter gene, D, are established in an Accra strain of Aedes aegypti. Their to each other and to Giemsa C-bands. Thus, M is invariably inherited with the centromere, whereas D lies towards the intercalary band. Approximately 1.2% recombination occurs between M and D but, in a chromosome known for its distal localization of chiasmata, it is argued that he two are not necessarily as closely linked cytologically as this might imply. Evidence on the genetic effects of recombination in the region of M and D is also considered.The work was supported by a grant from the Science Research Council.     

Calibration and evaluation of field cage for oviposition study with Aedes (Stegomyia) aegypti female (L.) (Diptera: Culicidae)

Differences among results gathered from insect behavior studies conducted in laboratory and field situations are due to ambient variables that differ greatly between both environments. In laboratory studies the environmental conditions can be controlled whereas in field temperature, humidity and air velocity vary uncontrollably. The objective of this study was to calibrate and evaluate an experimental area (field cage) (14 x 7 x 3.5 m) subdivided into eight test cages (2.5 x 2.5 x 2 m) for use in behavioral oviposition tests of Aedes aegypti (L.) mosquitoes for developing a new methodology to assess attractants and oviposition traps. Test cage calibration involved: (1) minimal experiment duration tests; (2) optimal female release number per traps test and (3) trap placement tests. All tests used gravid A. aegypti females; 3-4 days post blood meal and the sticky trap MosquiTRAP to catch adults. Ninety percent of the females released were recaptured 2h after the beginning of the experiment, and this allowed up to 32 test repetitions/day to be conducted in the field cage. The minimum number of females necessary to conduct statistical analyses was 20 females/trap/test per cage. No significant difference was found in the behavioral response of gravid females to four different trap positions within test cages. Field trapping results with attractant were similar to those in the field cage. Therefore, the field cage could replace field trapping for evaluating at least mosquito traps and oviposition attractants for A. aegypti.     

Structural organization of the brain and subesophageal ganglion of male Aedes aegypti (L.) (Diptera : Culicidae)

The brain and subesophageal ganglion of male Aedes aegypti (L.) (Diptera : Culicidae) are described from cryofractures and silver-stained, semithin (0.5 μm) serial sections of whole heads observed in the scanning and light microscopes. The brain and subesophageal ganglion of male A. aegypti are fused. The major structures of the brain include the protocerebral lobes and bridge, the mushroom bodies, central complex of the protocerebrum, the mechanosensory regions and olfactory loves of the deutocerebrum, and the tritocerebrum. Major commissures of the brain are the anterior optic tract, central commissure, posterior dorsal commissure, and subesophageal commissure. The structural associations of brain components with each other and the subesophageal ganglion, as well as the paths of the major nerve tracts in male A. aegypti are described and compared with those in other Diptera.