Fecundity, parity, and adult feeding relationships among Nyssorhynchus malaria vectors from Venezuela

Relative to their pre-engorgement weights, nulliparous Anopheles nuneztovari consumed significantly smaller blood meals than A. marajoara, A. triannulatus or A. aquasalis. When females were deprived of sugar before blood feeding, only one-quarter of A. nuneztovari, but more than two-thirds of A. marajoara, A. triannulatus and A. aquasalis matured eggs. Sugar feeding before blood, or two sucessive blood meals by sugar-deprived females, increased the proportion of nulliparous a. nuneztovari which developed eggs, but not significantly so. Nearly all individuals of nulliparous, sugar-fed A. marajoara, A. triannulatus and A. aquasalis matured eggs after one blood feeding. Among A. nuneztovari, A. marajoara and A. aquasalis that matured some eggs in the laboratory, there were no positive correlations between the number of eggs developed and relative vlood mealsize. However, blood meals larger than the mean size significantly increased the chance that A. nuneztovari would develop some eggs. Mean fecundities of gravid A. nuneztovari and A. marajoara reared in the laboratory were significantly lower than those of the same species captured at human bait in nature. Post-engorgement access to sugar by A. nuneztovari (captured at human bait) did not influence fecundity, but significantly enhanced survivorship and the proporticon of individuals which retained eggs. Release-recapture experiments revealed that relatively small blood meals are typical of A. nuneztovari only during the first gonotrophic cycle. We suggest that multiple blood feeding, seemingly necessary for most A. nuneztovari to develop a first clutch of eggs, may increase the probability of infection with Plasmodium vivax where this mosquito species is a primary vector.

Molecular biological approaches to the study of vectors in relation to malaria control

To a large extent, control of malaria vectors relies on the elimination of breeding sites and the application of chemical agents. There are increasing problems associated with the use of synthetic insecticides for vector control, including the evolution of resistance, the high cost of developing and registering new insecticides and an awareness of pollution from insecticide residues. These factors have stimulated interest in the application of molecular biology to the study of mosquito vectors of malaria; focussing primarily on two aspects. First, the improvement of existing control measures through the development of simplified DNA probe systems suitable for identification of vectors of malaria. The development of synthetic, non-radioactive DNA probes suitable for identification of species in the Anopheles gambiae complex is described with the aim of defining a simplified methodology wich is suitable for entomologist in the field. The second aspect to be considered is the development of completely novel strategies through the development of completely novel strategies through the genetic manipulation of insect vectors of malaria in order to alter their ability to transmit the disease. The major requirements for producing transgenic mosquitoes are outlined together with the progress wich has been made to date and discussed in relation to the prospects which this type of approach has for the future control of malaria.

Ecology of malaria vectors in the Americas and future direction

The resurgence of malaria in the Americas has renewed interest in Anopheles biology. Anopheles darlingi, An. albimanus, An. nuneztovai and An aquasalis are reconfirmed as major malaria vectors and other species are playing important roles in regional malaria transmission. Adultbiting activity and larval ecology are discussed in detail. Seasonal abundance and daily biting activity of Anopheles vary considerably among species and geographically for the same species. Anopheles albimanus has the least amount of variation in biting activity over its range and An. darlingi has the greatest. All species studied are more exophilic and exophagic than endophilic and endophagic. Anopheles darling is more antropophilic, endophilic and endophagic than other Anophelines. Larval studies remain more descriptive than comprehensive. Research on Anophelines is becoming more integrated and biologists are using new biochemical techniques and ecological principles to answer critical questions. This "pluralization" will help us understand species complexes, population dynamics and malaria transmission. integrated control programs will require more regional, in-depth ecological studies.

Vectors control importance on leishmaniasis transmission

We reviewed the control of transmission of leishmaniasis regarding chemotherapy, reservoirs elimination, vaccination and insect control through the use of chemical insecticides. We also discussed complementary measures like monitoring traps, impregnated bednets and curtains, repelents, pheromones, biological control, etc. A cost comparison of insecticide interventions through the use of products belonging to the four main chemical groups was also alone, comparing together conventional formulations versus a slow-release insecticide developed by the Núcleo de Pesquisas de Produtos Naturais, Universidade Federal do Rio de Janeiro. We finally did recommendations on the situation that would justify an insecticide intervention to control sandflies.

Early sporogonic development in local vectors of Plasmodium falciparum in rural Cameroon

In ongoing studies on experimental transmission of Plasmodium falciparum in the city of Yaounde gametocyte carriers are daily being identified among dispensary patients with malaria-like complaints. This species comprises 93 of all parasitemias and because of the selection criteria most patients have it as a recent infection. 17 of all P. falciparum-positives carry detectable gametocytes with little difference between youngsters and adults. Blood of adult carriers is taken and infection of Anopheles gambiae mosquitoes is attempted by membrane feeding; the establishment of infection is judged by the presence of oocysts.

Interactions between parasites and insects vectors

This review stresses the importance of studies that will provide a basic understanding of the pathology of parasite-infected vector insects. This knowledge should be a vital component of the very focussed initiatives currently being funded in the areas of vector control. Vector fecundity reduction is discussed as an example of such pathology. Underlying mechanisms are being investigated in a model system, Hymenolepis diminuta-infected Tenebrio molitor and in Onchocerca-infected blackflies and Plasmodium-infected Anopheles stephensi. In all cases, host vitellogenesis is disrupted by the parasite and, in the tapeworm/beetle model, interaction between the parasite and the endocrine control of the insect's reproductive physiology has been demonstrated.

Molluscicide control of snail vectors of schistosomiasis

A review of the methodology recommended by the World Health Organization for the use of molluscicides for the control of snail vectors of schistosomiasis is presented. Discussion of the principle molluscicides used, their advantages and disadvantages, the techniques and equipment required for their application and evaluation of effect as well as the biological control of snails is included.

Genetic variability and differentiation between populations of Rhodnius prolixus and R. pallescens, vectors of Chagas' Disease in Colombia

Enzyme polymorphism in Rhodnius prolixus and R. pallescens (Hemiptera, Reduviidae), principal vectors of Chagas' disease in Colombia, was analyzed using starch gel electrophoresis. Three geographic locations were sampled in order to determine gene flow between populations and to characterize intra- and interspecific differences. Of 25 enzymes assayed 10 were successfully resolved and then used to score the genetic variation. The enzymes PEPD, GPI, PGM and ICD were useful to differentiate these species and PGD, PGM and MDH distinguished between sylvatic and domiciliary populations of R. prolixus. Both polymorphism and heterozygosity indicated greater genetic variability in sylvatic habitats (H = 0.021) compared to domiciliary habitats (H = 0.006) in both species. Gene flow between sylvatic and domiciliary populations in R. prolixus was found to be minimal. This fact and the genetic distance between them suggest a process of genetic isolation in the domiciliary population.

A two years study on vectors of cutaneous leishmaniasis: Evidence for sylvatic transmission cycle in the State of Campeche, Mexico

Vectors of cutaneous leishmaniasis in the State of Campeche were studied in relation to the transmission cycle of Leishmania (Le.) mexicana. To determine how transmission of leishmaniasis occurs, we collected phlebotomine sand flies for two years. In the first year (October 1990 to November 1991) the collections were made with CDC light traps, Shannon traps and direct captures at natural shelters around the village (<200 m) of La Libertad. In the second year (February 1993 to January 1994) the catches were performed at 8 km southeast of La Libertad in the forest. Female sand flies were examined for Leishmania. During the first year, 347 sand flies of nine species were collected, most of which were Lutzomyia deleoni (61.3%). When all nine species were considered, more females than males were captured. Low densities of anthropophillic species of sand flies around the village indicated that sylvatic transmission was taking place. For the second year, 1484 sand flies of 16 species were caught. The most common were L. olmeca olmeca (21.7%), L. cruciata (19.2%) and L. ovallesi (14.1%). Similarly, more females were caught than males. Thirty-five females of five species were found infected with flagellates believed to be Leishmania sp. The highest infection rate was found in L. olmeca olmeca (7.1%) followed by L. cruciata (4.5%) and L. ovallesi (1.1%). These data plus other evidence on the epidemiology of human cases and results from reservoir studies are discussed in relation to the sylvatic transmission cycle.

Potential Vectors of Dirofilaria immitis (Leidy, 1856) in Itacoatiara, Oceanic Region of Niterói Municipality, State of Rio de Janeiro, Brazil

Dirofilaria immitis is a widespread mosquito-borne parasite that causes dirofilariasis, a commonly diagnosed disease of dogs that is rarely reported in cats and humans. A mosquito survey was conducted in Itacoatiara in the State of Rio de Janeiro, from March 1995 to February 1996, using canine, feline and human baits. A total of 3,667 mosquitoes were dissected for D. immitis larvae, representing 19 species and 10 genera. From those, Ae. scapularis, Ae taeniorhynchus, Cx. quinquefasciatus, Cx. declarator, Cx. saltanensis and Wy. bourrouli were found infected with D. immitis parasites, and among those, only the first three harbored infective larvae. The majority of larvae were found in the Malpighian tubules (889/936), and larval melanization was observed in the two Aedes species. In descending order, the best vectors were Ae. scapularis, Ae. taeniorhynchus, and Cx. quinquefasciatus which alternate seasonally in importance. Cx. quinquefasciatus is suggested to be a vector to cats. The potential transmission of D. immitis parasites by these three vectors to man is discussed.

Comparison of some behavioral and physiological feeding parameters of Triatoma infestans klug, 1834 and Mepraia spinolai porter, 1934, vectors of chagas disease in Chile

There are two vectors of Chagas disease in Chile: Triatoma infestans and Mepraia spinolai. We studied the feeding behavior of these species, looking for differences which could possibly explain the low impact of the latter species on Chagas disease. Both species used thermal cues to locate their feeding source and consumed a similar volume of blood which was inversely related to the body weight before the meal and directly related to the time between meals. The average time between bites were 6.24 and 10.74 days. The average bite of M. spinolai lasted 9.68 min, significantly shorter than the 19.46 min for T. infestans. Furthermore, while T. infestans always defecated on the host, this behavior was observed in M. spinolai in only one case of 27 (3.7%). The delay between the bites and defecation was very long in M. spinolai and short in T. infestans. These differences may affect the reduced efficiency of transmission of Chagas infection by M. spinolai.