Mating-regulated atrial proteases control reinsemination rates in Anopheles gambiae females

Anopheles gambiae mosquitoes are the most important vectors of human malaria. The reproductive success of these mosquitoes relies on a single copulation event after which the majority of females become permanently refractory to further mating. This refractory behavior is at least partially mediated by the male-synthetized steroid hormone 20-hydroxyecdysone (20E), which is packaged together with other seminal secretions into a gelatinous mating plug and transferred to the female atrium during mating. In this study, we show that two 20E-regulated chymotrypsin-like serine proteases specifically expressed in the reproductive tract of An. gambiae females play an important role in modulating the female susceptibility to mating. Silencing these proteases by RNA interference impairs correct plug processing and slows down the release of the steroid hormone 20E from the mating plug. In turn, depleting one of these proteases, the Mating Regulated Atrial Protease 1 (MatRAP1), reduces female refractoriness to further copulation, so that a significant proportion of females mate again. Microscopy analysis reveals that MatRAP1 is localized on a previously undetected peritrophic matrix-like structure surrounding the mating plug. These data provide novel insight into the molecular mechanisms shaping the post-mating biology of these important malaria vectors.

Microanatomy of the American Malaria Vector Anopheles aquasalis (Diptera: Culicidae: Anophelinae) Midgut: Ultrastructural and Histochemical Observations

The mosquito gut is divided into foregut, midgut, and hindgut. The midgut functions in storage and digestion of the bloodmeal. This study used light, scanning (SEM), and transmission (TEM) electron microscopy to analyze in detail the microanatomy and morphology of the midgut of nonblood-fed Anopheles aquasalis females. The midgut epithelium is a monolayer of columnar epithelial cells that is composed of two populations: microvillar epithelial cells and basal cells. The microvillar epithelial cells can be further subdivided into light and dark cells, based on their affinities to toluidine blue and their electron density. FITC-labeling of the anterior midgut and posterior midgut with lectins resulted in different fluorescence intensities, indicating differences in carbohydrate residues. SEM revealed a complex muscle network composed of circular and longitudinal fibers that surround the entire midgut. In summary, the use of a diverse set of morphological methods revealed the general microanatomy of the midgut and associated tissues of An. aquasalis, which is a major vector of Plasmodium spp. (Haemosporida: Plasmodiidae) in America.

The Midgut Muscle Network of Anopheles aquasalis (Culicidae, Anophelinae): Microanatomy and Structural Modification After Blood Meal and Plasmodium vivax (Haemosporida, Plasmodiidae) Infection

The mosquito midgut is divided into two regions named anterior midgut (AMG) and posterior midgut (PMG). The midgut expands intensely after the blood ingestion to accommodate a large amount of ingested food. To efficiently support the bloodmeal-induced changes, the organization of the visceral muscle fibers has significant adjustments. This study describes the spatial organization of the Anopheles aquasalis (Culicidae, Anophelinae) midgut muscle network and morphological changes after bloodmeal ingestion and infection with Plasmodium vivax (Haemosporida, Plasmodiidae). The midgut muscle network is composed of two types of fibers: longitudinal and circular. The two types of muscle fibers are composed of thick and thin filaments, similar to myosin and actin, respectively. Invagination of sarcoplasm membrane forms the T-system tubules. Sarcoplasmic reticulum cisternae have been observed in association with these invaginations. At different times after the bloodmeal, the fibers in the AMG are not modified. A remarkable dilation characterizes the transitional area between the AMG and the PMG. In the PMG surface, after the completion of bloodmeal ingestion, the stretched muscle fibers became discontinued. At 72 h after bloodmeal digestion, it is possible to observe the presence of disorganized muscle fibers in the midgut regions. The Plasmodium oocyst development along the basal layer of the midgut does not have a significant role in the visceral musculature distribution. This study provides features of the visceral musculature at different blood feeding times of An. aquasalis and shows important changes in midgut topography including when the mosquitoes are infected with P. vivax.

Detection of Plasmodium berghei infected Anopheles stephensi using near-infrared spectroscopy

BACKGROUND

The proportion of mosquitoes infected with malaria is an important entomological metric used to assess the intensity of transmission and the impact of vector control interventions. Currently, the prevalence of mosquitoes with salivary gland sporozoites is estimated by dissecting mosquitoes under a microscope or using molecular methods. These techniques are laborious, subjective, and require either expensive equipment or training. This study evaluates the potential of near-infrared spectroscopy (NIRS) to identify laboratory reared mosquitoes infected with rodent malaria.

METHODS

Anopheles stephensi mosquitoes were reared in the laboratory and fed on Plasmodium berghei infected blood. After 12 and 21 days post-feeding mosquitoes were killed, scanned and analysed using NIRS and immediately dissected by microscopy to determine the number of oocysts on the midgut wall or sporozoites in the salivary glands. A predictive classification model was used to determine parasite prevalence and intensity status from spectra.

RESULTS

The predictive model correctly classifies infectious and uninfectious mosquitoes with an overall accuracy of 72%. The false negative and false positive rates were 30 and 26%, respectively. While NIRS was able to differentiate between uninfectious and highly infectious mosquitoes, differentiating between mid-range infectious groups was less accurate. Multiple scans of the same specimen, with repositioning the mosquito between scans, is shown to improve accuracy. On a smaller dataset NIRS was unable to predict whether mosquitoes harboured oocysts.

CONCLUSIONS

To our knowledge, we provide the first evidence that NIRS can differentiate between infectious and uninfectious mosquitoes. Currently, distinguishing between different intensities of infection is challenging. The classification model provides a flexible framework and allows for different error rates to be optimised, enabling the sensitivity and specificity of the technique to be varied according to requirements.

Morphometric and morphological appraisal of the eggs of Anopheles stephensi (Diptera: Culicidae) from India

BACKGROUND & OBJECTIVES

Anopheles stephensi is one of the most important urban malaria vectors in India and contribute about 12% of total malaria cases. An. stephensi has three ecological variants; type, intermediate and mysorensis that can be differentiated on the basis of differences in number of ridges on egg float and on the basis of spiracular indices. Because of its anthropophilic nature the 'type' form is an efficient malaria vector. In the present study, the egg surface morphometry and morphology of An. stephensi 'type' form was studied and detail distinguish- ing characters were recorded for its correct identification.

METHODS

Eggs of An. stephensi 'type' form were studied by scanning electron microscopy (SEM) after sputter- coating with gold. In total 23 egg characters were analysed morphologically and morphometrically, which included egg attributes, deck attributes, ventral tubercles, micropyle and float attributes.

RESULTS

The dorsal surface of the egg of 'type' form was curved while the ventral surface was concave and both anterior and posterior ends were blunt. The average length and width of egg was 473.94 + 11.18 and 154.69 + 2.66 μm respectively. The number of float ribs observed was 20.33 ± 0.33. The maximum length of float was found to be 246.57 + 15.27 μm, whereas maximum width was 87.16 + 3.83 μm.

INTERPRETATION & CONCLUSION

The present study has generated some important data which is specific to An. Stephensi 'type' form and provided significant morphological and morphometric standards for its correct identification. This information could be useful in differentiation of An. stephensi 'type' form from other ecological forms of the same species as well as other species of Anopheles.

"Super e-noses": Multi-layer perceptron classification of volatile odorants from the firing rates of cross-species olfactory receptor arrays

Current electronic noses, or e-noses, that employ insect odorant receptors (Ors) as their sensory front end are potentially limited by the fact that the Ors come from a single species. In addition, a realistic e-nose also demands low numbers of Ors at its sensory front end due to the difficulties of receptor/sensor integration and functionalisation. In this work, we report the first investigations of a `Super E-Nose' that incorporates Ors from both the model organism Drosophila melanogaster fruit fly (DmOr) and the mosquito, Anopheles gambiae (AgOr). Furthermore, we report how an Artificial Neural Network (ANN), in the form of a hybrid double hidden layer Multi-Layer Perceptron (MLP), can be used to determine the optimal Ors that provide the best prediction performance in the classification of unknown odorants into their respective chemical class. Our findings demonstrate how 3-Or arrays consisting of DmOr only, AgOr only, or cross-species DmOr-AgOr combinations correctly classified all unknown odorants of the validation set. In addition, we report that all 3-Or combinations perform equally well as the complete 74 DmOr-AgOr array. Thus, the results of this work support further investigation into cross-species `Super E-noses' coupled with hybrid MLPs for the classification of unknown odorants.

Reproductive biology in Anophelinae mosquitoes (Diptera, Culicidae): Fine structure of the female accessory gland

The morphology and ultrastructure of female accessory reproductive glands of Anopheles maculipennis s.s., Anopheles labranchiae and Anopheles stephensi were investigated by light and electron microscopy. The reproductive system in these species is characterized by two ovaries, two lateral oviducts, a single spermatheca and a single accessory gland. The gland is globular and has a thin duct which empties into the vagina, near the opening of the spermathecal duct. Significant growth of the accessory reproductive gland is observed immediately after blood meal, but not at subsequent digestion steps. At ultrastructural level, the gland consists of functional glandular units belonging to type 3 ectodermal glands. The secretory cells are elongated and goblet shaped, with most of their cytoplasm and large nucleus in the basal part, close to the basement lamella. Finely fibrous electron-transparent material occupies the secretory cavity that is in contact with the end of a short efferent duct (ductule) emerging from the gland duct. The present study is the first detailed description of female accessory gland ultrastructure in Anophelinae and provides insights into the gland's functional role in the reproductive biology of these insects.

An overview of malaria transmission from the perspective of Amazon Anopheles vectors

In the Americas, areas with a high risk of malaria transmission are mainly located in the Amazon Forest, which extends across nine countries. One keystone step to understanding the Plasmodium life cycle in Anopheles species from the Amazon Region is to obtain experimentally infected mosquito vectors. Several attempts to colonise Anopheles species have been conducted, but with only short-lived success or no success at all. In this review, we review the literature on malaria transmission from the perspective of its Amazon vectors. Currently, it is possible to develop experimental Plasmodium vivax infection of the colonised and field-captured vectors in laboratories located close to Amazonian endemic areas. We are also reviewing studies related to the immune response to P. vivax infection of Anopheles aquasalis, a coastal mosquito species. Finally, we discuss the importance of the modulation of Plasmodium infection by the vector microbiota and also consider the anopheline genomes. The establishment of experimental mosquito infections with Plasmodium falciparum, Plasmodium yoelii and Plasmodium berghei parasites that could provide interesting models for studying malaria in the Amazonian scenario is important. Understanding the molecular mechanisms involved in the development of the parasites in New World vectors is crucial in order to better determine the interaction process and vectorial competence.

[Analysis of the spatial organization of the XL chromosome attachment site in nurse cell nuclei of the malaria mosquito Anopheles atroparvus]

The spatial position of the site of XL chromosome attachment to the nuclear envelope of ovarian nurse cells relative to the oocyte has been analyzed in the malaria mosquito Anopheles atroparvus. The XL chromosome attachment sites in the oocyte-nurse cell system of this species have been demonstrated to be orderly arranged, with the attachment sites in two out of three nurse cells in the same layer identically oriented relative to the oocyte.

[Comparison of PCR, ELISA-CSP and direct microscopic observation methods for the detection of Plasmodium falciparum sporozoites in Anopheles gambiae M in Senegal]

A comparative study between the Enzyme-Linked Immuno Sorbent Assay (ELISA-CSP) for circumsporozoitic antigen detection method, the direct observation after dissection and the polymerase chain reaction (PCR) technique used to identify Plasmodium falciparum genomic DNA markers was carried out. This to evaluate the sensibility and the specificity of the PCR, for the determination of both sporozoitic index (ICSP) and the entomological inoculation rate (EIR). The study is conducted in laboratory on eighty six specimens of Anopheles gambiae M infected after being fed with the blood of a gametocytes carrier from Dielmo (Senegal). Salivary glands of forty-eight specimens randomly selected (test A) among the infected eighty six are microscopically observed after manual dissection for the sporozoites detection. The content of these salivary glands and the crushed head/thorax of the remaining 38 specimens (test B) are tested in ELISA-CSP and PCR. The positive and negative results obtained were recorded and summarized for each method. A pair-comparison of the results obtained with each method generally revealed a good sensibility and an excellent specificity The kappa coefficient (K) of test A indicated a "moderate" to "excellent" concordance between the three different methods performed. By using the crushed head/thorax sample, generally used to determine the transmission parameters (ICSP and EIR), the PCR/ELISA-CSP concordance was excellent. In the light of the values of sensibility and specificity obtained, this PCR is comparable to the other methods for the assessment of sporozoitic index and entomological inoculation rate.

Scanning electron microscopy of the cibarial armature of species in the Anopheles dirus complex (Diptera: Culicidae)

The structure of the cibarial armature of mosquitoes has been found to be useful for taxonomic identification. We used a scanning electron micrograph to examine the cibarial armature of 4 of 5 species in the Anopheles dirus complex existing in Thailand: Anopheles dirus Peyton & Harrison, and An. cracens Sallum & Peyton, An. scanloni Sallum & Peyton, and An. baimaii Sallum & Peyton. In all species examined, there was only 1 row of large teeth or cones (modes = 12) characteristic of the Neomyzomyia series. The cones usually have anterior spines and a fimbriated or deeply cleft tip. No significant differences were observed among the 4 species examined, thus the cibarial armature has little value for taxonomic differentiation among these species. However, they appear different from closely related species in the Leucosphyrus complex reported previously.

Morphological method for sexing anopheline larvae

BACKGROUND & OBJECTIVES

Most of autocidal control of malaria vectors relies on the rearing and release of large numbers of sterile male into a wild population and it would be crucial to separate the males from females before release. This could result in enormous economic benefits in the mass rearing and raise the efficiency of the field operations. The development of genetic sexing of mosquitoes, enabling the release of males only, but impairing the overall fitness of the released insect has been considered greatly. Here we report on a morphological sexing method for the preferential diagnosis and separation of males in late III and IV instar larvae for the mosquitoes Anopheles stephensi Liston and An. culicifacies s.l. (Diptera: Culicidae), the principal vectors of human malaria in Asia and Indian subcontinent.

METHODS

Male mosquitoes are identified by their tube like organ at the 9th abdomen segment which originates from segment parallel to the spiracles. Length and width of this organ is measured as 66.66 +/- 9.5 and 14.3 +/- 1.5 microm respectively. The whole length of the organ is 201.63 +/- 23.4 microm. Two fried eggs in the anterior portion of the segment are apparent in males. The length of tube in female is shorter than the male (almost half of the length--37.95 +/- 4.0 microm), its width is slightly stout and wider than the male (16.72 +/- 1.4 microm). Two fried eggs in the anterior portion of the segment are absent. After separation of live male larvae by those characteristics, they were transferred into the trays and emerged adults were identified to ascertain correct identification of sex.

RESULTS

All the larvae with male organs developed into male adults with hairy antennae and club shaped palpi, whereas all the female larvae developed into adult females.

INTERPRETATION & CONCLUSION

The sex separation at the larval stage will provide a clue for embryonic origin of sex organs, insecticide selection at the larval stage, sex related genes, male sterility and other measures.

Odor coding in the maxillary palp of the malaria vector mosquito Anopheles gambiae

BACKGROUND

Many species of mosquitoes, including the major malaria vector Anopheles gambiae, utilize carbon dioxide (CO(2)) and 1-octen-3-ol as olfactory cues in host-seeking behaviors that underlie their vectorial capacity. However, the molecular and cellular basis of such olfactory responses remains largely unknown.

RESULTS

Here, we use molecular and physiological approaches coupled with systematic functional analyses to define the complete olfactory sensory map of the An. gambiae maxillary palp, an olfactory appendage that mediates the detection of these compounds. In doing so, we identify three olfactory receptor neurons (ORNs) that are organized in stereotyped triads within the maxillary-palp capitate-peg-sensillum population. One ORN is CO(2)-responsive and characterized by the coexpression of three receptors that confer CO(2) responses, whereas the other ORNs express characteristic odorant receptors (AgORs) that are responsible for their in vivo olfactory responses.

CONCLUSIONS

Our results describe a complete and highly concordant map of both the molecular and cellular olfactory components on the maxillary palp of the adult female An. gambiae mosquito. These results also facilitate the understanding of how An. gambiae mosquitoes sense olfactory cues that might be exploited to compromise their ability to transmit malaria.

Plasmodium vivax: Impaired escape of Vk210 phenotype ookinetes from the midgut blood bolus of Anopheles pseudopunctipennis

The site in the midguts of Anopheles pseudopunctipennis where the development of Plasmodium vivax circumsporozoite protein Vk210 phenotype is blocked was investigated, and compared to its development in An. albimanus. Ookinete development was similar in time and numbers within the blood meal bolus of both mosquito species. But, compared to An. pseudopunctipennis, a higher proportion of An. albimanus were infected (P=0.0001) with higher ookinete (P=0.0001) and oocyst numbers (P=0.0001) on their internal and external midgut surfaces, respectively. Ookinetes were located in the peritrophic matrix (PM), but neither inside epithelial cells nor on the haemocoelic midgut surface by transmission electron microscopy in 24h p.i.-An. pseudopunctipennis mosquito samples. In contrast, no parasites were detected in the PM of An. albimanus at this time point. These results suggest that P. vivax Vk210 ookinetes cannot escape from and are destroyed within the midgut lumen of An. pseudopunctipennis.

Preliminary characterization of hemolymph coagulation in Anopheles gambiae larvae

Hemolymph coagulation is a first response to injury, impeding infection, and ending bleeding. Little is known about its molecular basis in insects, but clotting factors have been identified in the fruit fly Drosophila melanogaster. Here, we have begun to study coagulation in the aquatic larvae of the malaria vector mosquito Anopheles gambiae using methods developed for Drosophila. A delicate clot was seen by light microscopy, and pullout and proteomic analysis identified phenoloxidase and apolipophorin-I as major candidate clotting factors. Electron microscopic analysis confirmed clot formation and revealed it contains fine molecular sheets, most likely a result of lipophorin assembly. Phenoloxidase appears to be more critical in clot formation in Anopheles than in Drosophila. The Anopheles larval clot thus differs in formation, structure, and composition from the clot in Drosophila, confirming the need to study coagulation in different insect species to learn more about its evolution and adaptation to different lifestyles.

High levels of human chitotriosidase hinder the formation of peritrophic membrane in anopheline vectors

In the Anopheles midgut, Plasmodium falciparum produces a specific chitinase able to penetrate the blood meal surrounding the chitin-containing peritrophic membrane (PM). High levels of an analogous chitinase, chitotriosidase (CHIT), may be found in human blood, being the markers of macrophage activation. To verify the hypothesis that CHIT present in malaria patient blood could help parasite to overcome PM, we carried out a bioassay by feeding Anopheles stephensi females on an artificial apparatus that contained human blood from four different sources and with different chitinase concentrations: (1) healthy donors, as negative controls; (2) patients with malaria; (3) patients with Gaucher disease; and (4) whole blood enriched with commercial P. falciparum chitinase, as positive controls. After 16, 20 and 24 h of bloodfeeding, mosquitoes were dissected to extract the midgut and assess the effect of the different chitinases on membrane structure. Optical microscopy showed that formation of PM was clearly complete after 16 h in the posterior midgut from Anopheles already fed with healthy donor bloods. By contrast, PM formation was visible after 16 h in the posterior midgut of mosquitoes fed with malaria and Gaucher patient bloods but appeared clearly damaged at 20 and 24 h. At the same time, the PM formation was almost completely inhibited in the midgut of Anopheles fed with P. falciparum chitinase-enriched bloods. These alterations were clearly confirmed by transmission electronic microscopy. In the present paper, we demonstrate that human CHIT from different sources is active on anophelines' PM.

Effects of a neem extract on blood feeding, oviposition and oocyte ultrastructure in Anopheles stephensi Liston (Diptera: Culicidae)

Secondary metabolites of the neem tree (Azadirachta indica A. Juss., Meliaceae) exhibit a wide range of biological activities in insects. However, few studies have addressed the effects of neem extracts or compounds in arthropods of medical importance. In this study, a laboratory strain of Anopheles stephensi was used to assess the effects of a commercial formulation (Neem Azal) (NA)), containing azadirachtin A at 34%, on blood feeding, oviposition and oocyte ultrastructure. Oral administration of Neem Azal) to A. stephensi females through artificial blood meals did impair blood intake and oviposition in a concentration dependent manner. Similar results were obtained on females, which had consumed Neem Azal) in sucrose solution before taking a blood meal of plain blood. Neem treated females displayed a delay in oocyte development in both the phase of vitellogenesis and the phase of choriogenesis. The ultrastructural studies on ovaries from Neem Azal) treated females revealed distinct structural modifications indicative of: (i) a complete block of oogenesis, (ii) impairment of vitellogenesis and vitelline envelope formation, (iii) a severe degeneration of follicle cells. In agreement with results obtained in other insects, this study indicates that Neem Azal) impairs hormone control of oogenesis and exerts a cytotoxic effect on both follicular cells and oocytes of the Asian malaria vector A. stephensi.

[Localization of repetitive DNA sequences in the pericentromeric heterochromatin of malarial mosquitoes of the "Anopheles maculipennis" complex]

Distribution of eight fragments of conserved repetitive DNA from pericentromeric heterochromatin of chromosome 2 of Anopheles atroparvus has been investigated by in situ hybridization on polytene chromosomes of An. atroparvus and An. messeae. We have shown that heterochromatic regions of all chromosomes both in An. atroparvus and An. messeae vary in combinations of, at least, conserved repeats. Some repeats have been found only in pericentromeric heterochromatic regions of chromosomes 2 (clones Atr2R-46a, Atr2R-73, Atr2R-85a in An. atroparvus and Atr2R-25 in An. messeae). Others have been found in two (clones Atr2R-25a and Atr2R-90 in An. atroparvus, Atr2R-25a in An. messeae) and more (clones Atr2R-118, Atr2R-136 in An. atroparvus, Atr2R-73 in An. messeae) pericentromeric heterochromatic regions of chromosomes. DNA comparison of pericentromeric heterochromatic regions of chromosomes in species of the "Anopheles maculipennis" complex is species- and chromosome-specific, due, in particular, to different maintenance of conserved repeates.

Unusual sensilla on the antennae of female Anopheles barbirostris

The 1st scanning electron microscopic study of the antennae of female Anopheles barbirostris van der Wulp revealed the presence of a sunken patch of 7-10 sensilla in well-developed sockets borne in an unusual location. Such sensilla have not been reported in any species of Anopheles, Culex, or Aedes. The position and arrangement of these sensilla are reported in this communication.

mtDNA inheritance in the mosquitoes of Anopheles stephensi

The inheritance of mtDNA was tested in malaria vector mosquitoes of Anopheles stephensi strains using PCR-RFLP analysis for its utility in addressing epidemiological questions related to the transmission and spread of malaria. Reciprocal crosses were made between two haplotypes with distinct mtDNA restriction fragment length polymorphism (RFLP) profiles through 20 consecutive generations. All of the progenies produced by these crosses had the mtDNA haplotype of the female parent suggesting that, if it occurs, paternal inheritance of mtDNA in An. stephensi is rare.

Comparative morphometry and morphology of Anopheles aconitus Form B and C eggs under scanning electron microscope

Comparative morphometric and morphological studies of eggs under scanning electron microscope (SEM) were undertaken in the three strains of two karyotypic forms of Anopheles aconitus, i.e., Form B (Chiang Mai and Phet Buri strains) and Form C (Chiang Mai and Mae Hong Son strains). Morphometric examination revealed the intraspecific variation with respect to the float width [36.77 +/- 2.30 microm (Form C: Chiang Mai strain) = 38.49 +/- 2.78 microm (Form B: Chiang Mai strain) = 39.06 +/- 2.37 microm (Form B: Phet Buri strain) > 32.40 +/- 3.52 microm (Form C: Mae Hong Son strain)] and number of posterior tubercles on deck [2.40 +/- 0.52 (Form B: Phet Buri strain) = 2.70 +/- 0.82 (Form B: Chiang Mai strain) < 3.10 +/- 0.32 (Form C: Chiang Mai strain) = 3.20 +/- 0.42 (Form C: Mae Hong Son strain)], whereas the surface topography of eggs among the three strains of two karyotypic forms were morphologically similar.

The role of reactive oxygen species on Plasmodium melanotic encapsulation in Anopheles gambiae

Malaria transmission depends on the competence of some Anopheles mosquitoes to sustain Plasmodium development (susceptibility). A genetically selected refractory strain of Anopheles gambiae blocks Plasmodium development, melanizing, and encapsulating the parasite in a reaction that begins with tyrosine oxidation, and involves three quantitative trait loci. Morphological and microarray mRNA expression analysis suggest that the refractory and susceptible strains have broad physiological differences, which are related to the production and detoxification of reactive oxygen species. Physiological studies corroborate that the refractory strain is in a chronic state of oxidative stress, which is exacerbated by blood feeding, resulting in increased steady-state levels of reactive oxygen species, which favor melanization of parasites as well as Sephadex beads.

Interaction of insect trypanosomatids with mosquitoes, sand fly and the respective insect cell lines

Interaction experiments between hematophagous insects and monoxenous trypanosomatids have become relevant, once cases of human infection involving these protozoa have been reported. Moreover, investigations related to the interaction of insects with trypanosomatids that harbour an endosymbiotic bacterium and thereby lack the paraflagellar rod structure are important to elucidate the role of this structure in the adhesion process. In this work, we compared the interaction of endosymbiont-bearing trypanosomatids and their aposymbiotic counterpart strains (without endosymbionts) with cell lines of Anopheles gambiae, Aedes albopictus and Lutzomyia longipalpis and with explanted guts of the respective insects. Endosymbiont-bearing strains interacted better with insect cells and guts when compared with aposymbiotic strains. In vitro binding assays revealed that the trypanosomatids interacted with the gut epithelial cells via flagellum and cell body. Flagella attached to the insect gut were enlarged, containing electrondense filaments between the axoneme and flagellar membrane at the point of adhesion. Interactions involving the flagellum lacking paraflagellar rod structure were mainly observed close to tight junctions, between epithelial cells. Endosymbiont-bearing trypanosomatids were able to colonise Aedes aegypti guts after protozoa feeding.

Laboratory evaluation of Bacillus sphaericus recycling in mosquito larvae

After ingestion by Culex pipiens and Anopheles pharoensis 4th instar larvae, spores of Bacillus sphaericus strain faiyoum rapidly germinated inside live mosquito midgut. Bacterial counts and electron microscopic observations on intoxicated larvae revealed that the number of viable spores rapidly decreased during the first 12 h, with a maximum between 12 and 24 h. In cadavers, the number of heat-resistant spores quickly increased between the first and second day post-feeding. After one week, the number of spores inside dead larvae reached approximately 20 times the number of ingested spores for both mosquito species (4 x 16(5) spores/larva). Ultrathin sections of recycled spores showed the presence of a crystalline inclusion identical to that initially present in spores before ingestion. Bioassay on Cx pipiens 4th instar larvae showed a similar toxicity between in vivo recycled spores (LC50 = 1.1 +/- 0.3 x 10(5) spores/ml after 24h exposure) and culture-medium-grown spores of B. sphaericus strain faiyoum (LC50 = 1.7 +/- 10(5) spores/ml).

Immuno-electron microscopic observation of Plasmodium berghei CTRP localization in the midgut of the vector mosquito Anopheles stephensi

The subcellular localization of Plasmodium berghei circumsporozoite protein and thrombospondin-related adhesive protein (PbCTRP) in the invasive stage ookinete of P. berghei was studied in the midgut of Anopheles stephensi by immuno-electron microscopic observations using polyclonal antibodies and immuno-gold labeling. PbCTRP was found to be associated with the micronemes of a mature ookinete throughout the movement from the endoperitrophic space to the basal lamina of the midgut epithelium. PbCTRP was also observed in the electron-dense area outside the ookinete, which might have been secreted from the apical pore. PbCTRP is found most abundantly at the site of contact between the apical end of an ookinete and the basal lamina of an epithelial cell. These results suggest that PbCTRP functions as an adhesion molecule for ookinete movement into the midgut lumen and epithelial cell and for ookinete association with the midgut basal lamina and transformation into an oocyst.

Anopheles albitarsis embryogenesis: morphological identification of major events

Anopheles albitarsis embryogenesis was analyzed through confocal microscopy of clarified eggs. Using Drosophila melanogaster as reference system, the major morphogenetic events (blastoderm, gastrulation, germ band extension, germ band retraction, dorsal closure) were identified. The kinetics of early events is proportionally similar in both systems, but late movements (from germ band retraction on) progress slower in An. albitarsis. Major differences in An. albitarsis related to D. melanogaster were: (1) pole cells do not protrude from the blastoderm; (2) the mosquito embryo undergoes a 180 degrees rotation movement, along its longitudinal axis; (3) the head remains individualized throughout embryogenesis; (4) extraembryonary membranes surround the whole embryo. A novel kind of malaria control is under development and is based on the use of genetically modified mosquitoes. Phenotypic analysis of the embryonic development of mutants will be imposed as part of the evaluation of effectiveness and risk of employment of this strategy in the field. In order to accomplish this, knowledge of the wild type embryo is a prerequisite. Morphological studies will also serve as basis for subsequent development biology approaches.

Fine structure of the eggs of Anopheles (Anopheles) punctimacula

The egg of Anopheles (Anopheles) punctimacula is described from scanning electron micrographs. Eggs of An. punctimacula are boat shaped, with lateral floats extending 70% of the length of the egg. Plastronlike polyhedral chorionic cells with distinctive boundaries and round tubercles in the cell field cover the dorsal, lateral, and ventral surfaces. Narrow decks enclosing a field of irregular jagged tubercles and 2-4 lobed tubercles are present at both egg poles.

The eggs of Anopheles galvaoi and Anopheles evansae, two species of the subgenus Nyssorhynchus

The ultrastructure of the eggs of Anopheles (Nyssorhynchus) galvaoi Causey, Deane, and Deane and Anopheles (Nyssorhynchus) evansae (Brethes) are described and illustrated with scanning electron micrographs. The eggs of these species are similar to those of Anopheles (Nyssorhynchus) aquasalis Curry, Anopheles (Nyssorhynchus) oswaldoi (Peryassu), and Anopheles (Nyssorhynchus) konderi Galvão and Damasceno in having floats long, widely joined posteriorly on the dorsal surface, the frill encircling the anterior end of the egg, and the crown absent. A few distinctive characters to distinguish An. evansae from An. galvaoi are given.

Cellular-mediated reactions to foreign organisms inoculated into the hemocoel of Anopheles albimanus (Diptera: Culicidae)

The immune response against different organisms and particles inoculated in the hemocoel of female Anopheles albimanus Wiedemann was investigated. Histological and ultrastructural observations indicated that melanization and hemocyte type participation varied according to the particles inoculated. The initial responses against heat-killed Microccocus lysodeikticus and Escherichia coli included hemocyte lysis and melanization whereas the response to heat-killed Saccharomyces cerevisiae was only cellular, and an initial melanization of Sephadex G-25 (neutral charged) beads was followed by the formation of cellular aggregates. After 24 h, hemocytes were involved in all terminal encapsulation events. Plasmodium vivax Grassi and Feletti formalin-fixed sporozoites induced a weak response. Cellular aggregates were observed 1 h postinoculation, but participating hemocytes could not be identified because of the extensive cellular damage and lysis. Sporozoites were also observed in the core of these aggregates, mixed with cell debris and free in the hemolymph. The effect on the inoculated particles was also different-S. cerevisiae was encapsulated only by hemocytes, whereas M. lysodeikticus was lysed and E. coli was phagocytosed by plasmatocytes. These results indicate that hemocytes are important components in the immune response in An. albimanus.

Evidence for a new sibling species of Anopheles minimus from the Ryukyu Archipelago, Japan

The Anopheles minimus complex is known to comprise at least 2 sibling species (A and C) in Thailand and Vietnam. This study investigated the specific status of An. minimus on Ishigaki Island, the Ryukyu Archipelago, Japan using morphological and genetic analyses. Morphological studies revealed that almost all (99.5%) of the adult mosquitoes are characterized by the humeral pale spot on the costa of their wings, a character that partially differentiates species A and C elsewhere. A high frequency (81.4%) have a pale fringe spot at the tip of vein 1A, a character rarely observed in other An. minimus populations. Significant seasonal variation in the size of wild An. minimus mosquitoes on the island was observed, with the largest size in the winter. Scanning micrographs of the cibarial armature of females from Ishigaki Island revealed that over 90% had cone filaments clearly differing in shape from those of species A or C. The Giemsa-stained metaphase karyotypes of larval brain cells were somewhat similar to those of species A, with a few exceptions, but were very different from those reported for species C. Crossing experiments between species A (CM strain) from Thailand and the progeny of An. minimus from Ishigaki Island (ISG strain) revealed postzygotic genetic incompatibility, although no prezygotic isolation. Hybrid progeny were only obtained from CM female x ISG male. F2 hybrid progeny were not obtained, since the hybrid males were sterile or almost sterile with atrophied testes or abnormal spermatozoa, although the polytene chromosomes of hybrid larvae showed synapsis. The hybrid females backcrossed with either CM or ISG males laid eggs with significantly lowered fertility and viability. The sequence for the D3 region of the 28S gene of ribosomal DNA of the ISG strain differed from those of species A and C. In addition, sequence data from Vietnamese mosquitoes suggest that the An. minimus complex may contain additional species. The morphological, cytogenetic, molecular, and hybridization evidence together suggest the existence of another sibling species of the An. minimus complex on Ishigaki Island, which is provisionally designated An. minimus species E.

Evidence of the specific status of Anopheles flavirostris (Diptera: Culicidae)

Anophelesflavirostris (Ludlow) from Lombok Island, Indonesia, was crossed with An. minimus species A (CM strain) from Thailand and species E (ISG strain), a new sibling species, from Japan, to determine genetic compatibility. We also compare the scanning micrographs of female cibarial armature of these three species. Both An. minimus CM and ISG females crossed with An. flavirostris males produced eggs without embryos. One An. flavirostris female crossed with an An. minimus CM male deposited unhatchable eggs with an 18% embryonation rate. The scanning micrographs of the cibarial armature clearly show significant differences among An. flavirostris and the two sibling species of the An. minimus complex. These results support the specific status of An. flavirostris. Previous records of An. minimus Theobald in this country are also discussed.

[Polymorphism of pericentromeric heterochromatin in natural populations of Anopheles maculipennis Mg]

Variations in pericentromeric heterochromatin quantity was found in polytene chromosomes X and 3 (in 3L arm) in the ovarian trophocytes in two natural populations of Anopheles meculipennis Mg. (Moscow, Sochi). The existence of block and non-block variants and of heterozygotes between them was shown. Northern population have more variants of blocks than the southern populations do.

Morphological and biochemical analyses of the salivary glands of the malaria vector, Anopheles darlingi

Adult Anopheles darlingi salivary glands are paired organs located on either side of the esophagus. The male glands consist of a single small lobe. The female gland is composed of two lateral lobes, with distinct proximal and distal portions, and a medial lobe. The lobes are acinar structures, organized as a unicellular epithelium that surrounds a salivary canal. The general cellular architecture is similar among the lobes, with secretory material appearing as large masses that push the cellular structures to the periphery of the organ. Cells of the proximal-lateral lobes show asynchronous cycles of secretory activity and contain secretory masses with finely filamentous aspect. In the distal-lateral lobes, cells display synchronous cycles of activity, and have a dense secretory product with mottled pattern. Cells of the medial lobe have secretory masses uniformly stained and highly electrondense. Biochemical analysis of the adult female salivary glands revealed apyrase, alpha-glucosidase and lysozyme activities. Alpha-glucosidase and lysozyme activities are detected mostly in the proximal lobes while apyrase is mainly accumulated in the distal lobes. This differential distribution of the analyzed enzymes reflects a specialization of different regions for sugar and blood feeding. Thus, the morphological differences observed in the lobes correlate with functional ones.

Taxonomic study of species formerly identified as Anopheles mediopunctatus and resurrection of An. costai (Diptera: Culicidae)

Anopheles (Anopheles) mediopunctatus (Lutz) and Anopheles (Anopheles) costai Fonseca & Ramos are redescribed with illustrations of the male genitalia and larval and pupal stages. The pupa of An. costai has paired lateral projections on the wing case, a feature also known in members of the Umbrosus Group from Southeast Asia. An. costai is resurrected from the synonymy of An. mediopunctatus based on features of the male genitalia, larva, and pupa, and An. bonneorum Fonseca & Ramos (emended from bonnei) is considered to be a new synonym of An. costai. It is noted that the author of An. mediopunctatus is Lutz, not Theobald, as cited in most literature references.

Ultrastructure of eggs of Anopheles rondoni, Anopheles lutzii, and Anopheles parvus, three species of the subgenus Nyssorhynchus

The ultrastructures of the eggs of Anopheles (Nyssorhynchus) rondoni (Neiva & Pinto), Anopheles (Nyssorhynchus) lutzii Cruz, and Anopheles (Nyssorhynchus) parvus (Chagas) are described and illustrated with scanning electron micrographs. The egg of Anopheles rondoni is similar in several respects to those of other species of the Argyritarsis Section. The egg of An. lutzii is similar to that of Anopheles antunesi Galvão and Amaral in having floats widely joined anteriorly on the ventral side, and the anterior end barely visible beyond the floats. The egg of An. parvus is remarkable in possessing an anterior fingerlike structure that bears several lobed tubercles at the apex. The fingerlike structure and the micropyle are within the prominent anterior crown formed by the frill. The egg of An. parvus has floats with the anterior pole uppermost, which is an unusual position for Anopheles.

Formation of basement membrane-like structure terminates the cellular encapsulation of microfilariae in the haemocoel of Anopheles quadrimaculatus

The encapsulation of microfilariae in the haemocoels of mosquitoes combines both humoral and cellular reactions: the microfilariae are first encased in an acellular layer of melanin, followed by a cellular encapsulation by plasmatocytes. In this study, we demonstrated that cellular encapsulation of Brugia pahangi microfilariae in the haemocoel of the mosquito Anopheles quadrimaculatus was terminated by the formation of a basement membrane-like structure on the outermost surface of the cellular capsule. This structure occurred in the early stage of cellular encapsulation and was evident on the exterior surface of the plasmatocyte, when the active haemocytes were attaching to the already melanized microfilariae. The termination structure appears to be laid down by releasing the vesicle inclusions of haemocytes and has similarities in ultrastructure and cationic colloidal gold staining properties with that of mosquito basement membranes.

Multiple blood feeding by Anopheles freeborni and Culex tarsalis (Diptera:Culicidae): spatial and temporal variation

Multiple blood feeding in field populations of Anopheles freeborni Aitken and Culex tarsalis Coquillet was detected using a histologic technique. Examination of 333 blood engorged An. freeborni and 41 Cx. tarsalis females revealed that 13 and 10% of these females imbibed multiple blood meals, respectively. Spatial and temporal distribution of multiple blood feeding events was evaluated against the percentage of blood fed females and the abundance of female mosquitoes. The percentage of blood fed An. freeborni females was higher among those collected in pasture and riparian habitats than those collected in rice field and mixed habitats. Conversely, spatial variation of multiple blood feeding in An. freeborni was not significantly associated with rice field, pasture, riparian, or mixed habitats. The decrease of multiple blood feeding for An. freeborni through the season was correlated inversely with the increase of the abundance of adult females; but not with the percentage of blood fed females. These results confirmed that multiple blood meals in An. freeborni, and perhaps in Cx. tarsalis, are a frequent phenomenon, and that the histologic procedure is an appropriate tool for longitudinal and region-wide detection of multiple blood feeding necessary in epidemiologic studies.

Spermatogenesis in mosquitoes (Diptera: Culicidae)

An ultrastructural study of spermatogenesis has been carried out on 18 species of mosquitoes of the Anophelinae, Culicinae and Toxorhynchitinae sub-families. In this spermatogenesis, which follows a classical way, primordial cells, primary and secondary spermatogonia, as well as primary and secondary spermatocysts are considered. We have identified 9 stages of development all along the spermiogenesis. This process ends up with the formation of a needle-like spermatozoon showing head and tail regions. After a treatment with tannic acid, the protofilaments of the axoneme of Culex tigripes are counted. For the first time we have carried out a complete study of spermatogenesis in mosquitoes.

Larval rearing temperature affects morphology of Anopheles albimanus (Diptera:Culicidae) male genitalia

The structure of the male genitalia of Anopheles albimanus Wied. is affected by larval rearing temperature. Morphometric analyses of 50 specimens revealed significant variation of 5 genitalic characters. The gonocoxa, dorsal claspette lobes, and aedeagus were longer for males reared at 22 degrees C. The parabasal seta was longer and the aedeagus was wider for males reared at 30 degrees C. Extra parabasal setae and lateral projections of the aedeagus were seen on some specimens.

Characterization of the modes of action of anti-Pbs21 malaria transmission-blocking immunity: ookinete to oocyst differentiation in vivo

The impact of immune sera, and peripheral blood cells (PBC) from mice immunized with Plasmodium berghei ookinetes; and of purified immunoglobulin or Fab fragments from anti-Pbs21 monoclonal antibody 13.1, upon establishment of oocyst infections in the mosquito was studied. Infections were initiated either from gametocyte-infected mice, or membrane feeders which contained either gametocytes or mature ookinetes. PBC from ookinete-immunized mice presented with non-immune serum failed to show any transmission-blocking activity. Anti-ookinete serum, intact anti-Pbs21 monoclonal antibody 13.1 or its Fab fragments, all inhibited oocyst formation significantly. When gametocyte-infected mice or gametocytes in membrane feeds were used, inhibition did not directly correlate with antibody concentration. In membrane feeders that contained ookinetes and antibody, concentration-dependent inhibition usually occurred. The efficacy of purified 13.1 IgG was dependent upon the ookinete concentration. The ookinete plasmalemma and cytoplasm were significantly disturbed after 12 h in bloodmeals that contained antibody 13.1, but not in the isotype controls. These changes may have caused the observed failure of the ookinete to migrate as rapidly as the controls from the destructive environment of the bloodmeal.

A technique for nucleic acid in situ hybridization to polytene chromosomes of mosquitoes in the Anopheles gambiae complex

A sensitive, simple, and reproducible in situ hybridization technique for the detection and precise localization of specific nucleic acid sequences on chromosomes of members of the Anopheles gambiae complex is described. Modifications of the in situ hybridization technique are described that allow simultaneous hybridization of several probes with the chromosomes on a single slide and the multiple use of a single chromosome preparation for several different probes hybridized successively on the same slide. Examples are shown that illustrate the utility of the technique for localization of both single copy and repeated sequences in both polytenized euchromatin and centromeric heterochromatin.

Variation of larval susceptibility to Lagenidium giganteum in three mosquito species

A significantly greater number of Lagenidium giganteum zoospores were found encysting on the dorsal thoracic surface of Anopheles gambiae larvae than on the larvae of Aedes aegypti and Culex pipiens. However, germ tube penetration in the cuticle of A. gambiae provoked an intense and diffuse melanization which encapsulated the fungus and protected 56% from death. Although a small number of zoospores attach to and penetrate the cuticular surface of A. aegypti and C. pipiens approximately 99% of both species succumb to fungal infection. Melanization in A. aegypti is slower, weaker, more localized, and generally ineffective against L. giganteum infection compared to A. gambiae. Upward migration of L. giganteum zoospores to the water surface favored encounters with mosquito larvae and was speculated to be due to negative geotaxis rather than positive aerotaxis and phototaxis. Otherwise, initial contact between larva and zoospore was random.

The role of the mosquito peritrophic membrane in bloodmeal digestion and infectivity of Plasmodium species

Secretion and luminal formation of the peritrophic membrane (PM) were induced in female Anopheles stephensi and Aedes aegypti by feeding the mosquitoes on a warmed suspension of latex particles in Ringer's solution. The PM in A. stephensi was produced from apical secretion vesicles stored in the midgut epithelial cells and secreted into the lumen during feeding. In A. aegypti, the PM was formed de novo. When the latex feeding was followed 24 hr later by a meal of lyophilized pig blood, the 2 mosquito species exhibited very different modifications to their PM structure; in A. stephensi no PM was formed around the blood meal, whereas de novo synthesis of the PM in A. aegypti continued during the blood meal, with the resulting PM greatly thickened compared to the normal feeding. This artificial induction of PM formation was used as the basis to study the role of the PM in blood meal digestion and in infectivity of mosquitoes by the appropriate species of Plasmodium. The feeding of a latex suspension alone had no stimulatory effect on the 2 major midgut proteases, trypsin and aminopeptidase, in either species. After a blood meal alone, proteases rose to maximum activity at 30 hr and 24 hr after feeding in A. stephensi and A. aegypti, respectively. After double feeding, protease activities in both species were almost identical to those in blood-fed mosquitoes. Neither the absence of a PM (in A. stephensi) nor the presence of a thickened PM (in A. aegypti), therefore, has any effect on the ability of mosquitoes to digest a blood meal. Malaria infectivity, measured by oocyst counts, also was compared after normal and double feeding using infective blood meals. Infectivity of A. stephensi by Plasmodium berghei was unaffected by the presence or absence of the PM. The thickened PM produced by double feeding in A. aegypti caused a reduction of midgut infectivity by Plasmodium gallinaceum. These results suggest that the PM may act as a partial, but not an absolute, barrier to invasion of the midgut by the ookinete.

A scanning electron microscopic study of the sporogonic development of Plasmodium falciparum in Anopheles stephensi

The full development of Plasmodium falciparum in Anopheles stephensi mosquitoes was studied by scanning electron microscopy. Ookinetic development was described from in vitro cultures. Growing oocysts beneath the basal lamina of the midgut wall mechanically stretch this lamina until it is torn and displaced by day 7. In young oocysts the wall appears smooth. In older oocysts wrinkles in the wall are visible after routine fixation. Osmium tetroxide postfixation greatly reduced the occurrence of these wrinkles. Intracapsular development of sporozoites was visualized after mechanical manipulation of the oocysts during sample preparation. In contrast to P. berghei, no ectopic development was seen in P. falciparum in the mosquito midgut. The mechanism of sporozoite escape from the oocyst appears to be similar to that described for rodent malaria. Fracturing of salivary glands provided the first view by scanning electron microscopy of sporozoites located in proximal and distal gland cells and in the draining duct.

Penetration of the mosquito midgut wall by the ookinetes of Plasmodium yoelii nigeriensis

The penetration route of ookinetes of Plasmodium yoelii nigeriensis in the midgut of a mosquito, Anopheles omorii, was investigated by electron microscopy. Within 15-18 h after an infective blood meal, ookinetes could be seen in the midgut lumen, in the process of entering the midgut wall, or lodged between the basement membrane and the basal lamina. The morphology of the ookinetes and their transformation into early oocysts were found to be similar to those previously reported. Ookinetes penetrated the midgut wall by the intercellular route; however, the intracellular occurrence of the parasite was also observed. Vacuoles appeared around the penetrating ookinetes during the penetration process, but no change in the electron density of the rhoptry-microneme complex was noted.

Ultrastructural localization of phenoloxidase in the midgut of refractory Anopheles gambiae and association of the enzyme with encapsulated Plasmodium cynomolgi

A melanogenic enzyme, phenoloxidase, was localized ultrastructurally in the midgut epithelia of 2 strains of Anopheles gambiae, a refractory strain that melanotically encapsulates Plasmodium cynomolgi ookinetes on the midgut, and a susceptible strain that does not. Midguts were incubated with either dopa or dopamine, and the resultant electron-dense product of phenoloxidase activity was localized on the basal lamina (BL) and cellular basal membrane labyrinth (BML) in uninfected mosquitoes of both strains. In infected refractory mosquitoes, the reaction products still were observed on the BL and BML but were especially dense in the BML of midgut cells near encapsulated ookinetes and in the capsule itself. In infected susceptible mosquitoes, phenoloxidase localization was reduced or absent in the BL and BML and was not observed near parasites. Phenylthiourea (PTU) inhibited the phenoloxidase reaction, indicating that the reaction product deposited in the absence of PTU resulted from enzyme activity and not autooxidation of the substrates. It is concluded that higher levels of phenoloxidase in the refractory strain following a blood meal may contribute to the ability to encapsulate ookinetes.

Plasmodium falciparum ookinetes migrate intercellularly through Anopheles stephensi midgut epithelium

The migration of Plasmodium falciparum and P. berghei ookinetes through the midgut epithelium in Anopheles stephensi was studied by transmission electron microscopy. With ruthenium red (RR) staining, the results of previous studies were confirmed: P. falciparum ookinetes take an intercellular route through the midgut epithelium. In the same mosquito species, the rodent parasite P. berghei appeared to take an intracellular position, as previously suggested by other authors. The intra- or intercellular ookinete migration of P. berghei or P. falciparum, respectively, can perhaps be related to the higher mortality of P. berghei-infected mosquitoes within the first 2 days of infection. Evidence is presented that oocyst capsule formation begins as early as during the migration of the ookinete. After localization between the epithelial cells and the midgut basal lamina, the rapidly expanding oocyst stretches the overlying layer of the latter at the haemocoelic surface while a new basal lamina is generated between the oocyst and epithelial cell.

Lectin-binding sites in the midgut of the mosquitoes Anopheles stephensi Liston and Aedes aegypti L. (Diptera: Culicidae)

The presence and distribution of binding sites for eight different lectins, Con A, DBA, HPL, LFA, RCA I, SBA, UEA I, and WGA, were compared in the midguts of Plasmodium gallinaceum-infected Aedes aegypti and Plasmodium berghei-infected Anopheles stephensi. Lectins with high specificity for N-acetyl-D-glucosamine (GlcNAc) exhibited high binding preference for the peritrophic membrane and microvillar glycocalyx of Ae. aegypti; the same structures were preferentially labeled by N-Acetyl-D-galactosamine (GalNAc)-specific lectins in An. stephensi. No differences could be observed in the lectin-binding patterns of the intercellular spaces or cellular organelles and structures. The Plasmodium ookinete surface did not react with any of the lectins tested. It appears that sugars are involved in vector recognition by the parasite and that the peritrophic membrane and/or glycocalyx may be crucial structures for the penetration of the gut epithelium by the ookinete.

Ultrastructure of the encapsulation of Plasmodium cynomolgi (B strain) on the midgut of a refractory strain of Anopheles gambiae

Using transmission electron microscopy, we investigated the encapsulation of the simian malaria parasite, Plasmodium cynomolgi, in a refractory strain of the mosquito, Anopheles gambiae. After the ookinete penetrates the mosquito midgut epithelium and lodges between the basal membrane and the basal lamina, an electron-dense, melanin-like substance begins to coalesce around the parasite. Completely encapsulated parasites were found as early as 16 hr after the blood meal. Granules of the melanin-like substance often appeared to condense onto the parasite from the fluid in the extracellular spaces of the basal membrane labyrinth. Melanin granules also appeared to condense from the hemolymph onto the basal lamina underlying the parasite. In addition, groups of tubules, vesicles, and membranous whorls often were found in midgut cells that were located next to or were enclosing parasites. These structures were unusually electron-dense, and may have been associated with melanization. Hemocytes rarely were observed near completed capsules and neither hemocytes nor their remnants were components of the capsules. During later stages of encapsulation, parasites appeared abnormal and often were infiltrated with melanin. Although late-stage capsules were usually located basally, completed capsules enclosed by membranes were occasionally observed near the apical border of the midgut. Other capsules associated with cellular debris, were found in the lumen of the midgut from 1 to 6 days after the blood meal.