. 1. Hypotheses about declining populations of container-inhabiting Aedes mosquitoes following the invasion by additional species were tested.



2. The larval competition hypothesis was studied experimentally in pure and mixed cultures of Aedes aegypti (L.), A.albopictus (Skuse) and A.triseriatus (Say). The experiments used decomposing leaf litter in the laboratory, as opposed to most previous research which used non-natural food.



3. Resistance to starvation is introduced as a new measure of larval performance and competitiveness. The hypothesis is that more successful larvae store larger energy reserves and resist the lack of food longer.



4. Contrary to previous research showing better performance of A.aegypti in mixed cultures, A.albopictus developed faster and had greater survival when natural food was used.



5. Resistance to starvation was greater in the better performing species (i.e. A.aegypti with non-natural food and A.albopictus with leaf litter). Oxygen consumption by starved larvae was similar in the three container species, and in the ground-water mosquito, A.taeniorhynchus (Wied.), whose resistance to starvation was comparatively very low.

Competition and resistance to starvation in larvae of container-inhabiting Aedes mosquitoes.

Aedes albopictus (Skuse) was detected for the first time in Italy in 1990. Thanks to its high biological adaptability, it spread rapidly to colonize various urban areas in central and northern Italy. The purpose of this study was to examine the ecological niche occupied by Ae. albopictus and the role of competition with Culex pipiens L., which is a widespread indigenous species, in urban areas. The larval development cycle and competition for food between the two species was also studied under laboratory conditions. The study showed that both species can colonize any type of artificial water container. Ae. albopictus mainly occupies saucers under flower pots and other, usually smaller-sized, containers, whereas Cx. pipiens tends to develop more in large tanks (100–200 liters) used in residential gardens and other larger-sized containers. It would seem that the two species interact mainly in medium-sized containers (10–50 liters) such as manholes and tires. Laboratory studies showed that, at 25°C,...

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On the competition occurring between Aedes albopictus and Culex pipiens (Diptera: Culicidae) in Italy

Public health aspects of dirofilariasis in the United States.

Publisher Summary Filarial nematodes are arthropod-borne parasites, which sometimes cause serious disease in man and animals. The most important filarial worms of man are Onchocerca volvulus, the cause of river-blindness and severe skin disease, and Wuchereria bancrofti, the cause of tropical elephantiasis and hydrocoel. Another serious pathogen of man is Brugia malayi (B. malayi), and its distribution is limited to Asia. There are two well-defined strains of B. malayi, which differ in their microfilarial periodicity patterns. The nocturnally subperiodic strain is found in the dense swamp forest where its mosquito vectors prefer to feed at night but also bite during the day. The nocturnally periodic strain of B. malayi is found in the open plains where the vectors feed only at night. The correlation between peak peripheral microfilaraemia and peak biting time suggests that filarial nematodes have adapted their periodicity patterns to vector periodicity patterns for facilitating their transmission by mosquitoes. Nocturnally subperiodic B. malayi is common in wild monkeys, and this led to the assumption that it is zoonotic. Mansonia mosquitoes, the vectors of subperiodic B. malayi, feed on a variety of animal hosts, including man. The chapter presents the vector-parasite and definitive host–parasite relationships.

Brugian filariasis: epidemiological and experimental studies.

Mathematical models of transmission dynamics of infectious diseases provide a useful tool for investigating the impact of community based control measures. Previously, we used a dynamic (constant force-of-infection) model for lymphatic filariasis to describe observed patterns of infection and disease in endemic communities. In this paper, we expand the model to examine the effects of control options against filariasis by incorporating the impact of age structure of the human community and by addressing explicitly the dynamics of parasite transmission from and to the vector population. This model is tested using data for Wuchereria bancrofti transmitted by Culex quinquefasciatus in Pondicherry, South India. The results show that chemotherapy has a larger short-term impact than vector control but that the effects of vector control can last beyond the treatment period. In addition we compare rates of recrudescence for drugs with different macrofilaricidal effects.

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EPIFIL: the development of an age-structured model for describing the transmission dynamics and control of lymphatic filariasis.

A method is described whereby the fate of infective filarial larvae after feeding by vector mosquitoes may be estimated. In this investigation, Aedes togoi with a 77% rate of infection and an average of 7·5 infective Brugia pahangi larvae per mosquito, were permitted to feed on mice. The following observations were made: 1. 1. 22·3% of the expected number of infective larvae were transmitted to the tissues of mice. 2. 2. 32·3% of larvae remained in the mosquito. 3. 3. 45·4% of larvae were estimated to have been lost on the surface of the skin. 4. 4. A relatively heavy (20 larvae) infection from a single mosquito was observed in one instance; however, in approximately one half of the mice exposed to mosquitoes harbouring infective larvae, no larvae were transmitted to the tissues of the mice.

The fate of Brugia pahangi larvae immediately after feeding by infective vector mosquitoes

Experiments were designed to determine the normal route of infection in mosquito-transmitted filariae. Evidence is presented to show that the puncture wound made by the mosquito is the usual route of entrance and that this penetration of infective larvae takes place after the mouthparts of the mosquito have been withdrawn from the skin.

Studies on the transfer of infective Brugia pahangi larvae from vector mosquitoes to the mammalian host.

Observations were made on experimental transmission of infective Brugia pahangi larvae by Aedes togoi requiring varying periods of time for feeding and ingesting varying amounts of blood. Significantly more larvae were transmitted by mosquitoes which fed to repletion and required a longer feeding period than by those which failed to ingest any blood on short feeding attempts. This difference is attributed to the difference in probing time rather than lack of engorgement. No significant difference in transmission was found between mosquitoes which had fed to repletion and those which were partially engorged. Limited observations on infective mosquitoes probing several times in rapid succession for short periods, suggest that transmission and loss of larvae on the skin surface are very similar in mosquitoes feeding for a longer period.

Experimental transmission of filarial larvae in relation to feeding behaviour of the mosquito vectors.

Frequency of the labral brush movements of first, second, and fourth instars of Aedes aegypti (L.) and Aedes albopictus (Skuse) was studied comparatively in the laboratory. A frequency of 197 strokes per min for the first and second instars was observed in the former species compared to 118 strokes per min in the latter species. A faster ingestion rate of algal cells also was observed in first and second instars of Ae. aegypti (mean 57.5 cells per s) compared with first and second instars of Ae. albopictus (mean 22.4 cells per s). The digestive enzymes chymotrypsin (EC 3.4.21.1) and trypsin (EC 3.4.21.4) were more active in the peritrophic membrane (including food contents) than in the midgut epithelium of both species. Chymotrypsin activity in 11-d-old third and fourth instars of Ae. albopictus was 28 times higher than in the corresponding stadia of Ae. aegypti, indicating that the former species may have a superior enzymatic process for digesting food proteins.

Food ingestion and digestive enzymes in larval Aedes aegypti and Ae. albopictus (Diptera: Culicidae).

The use of artificially produced puncture wounds as a route whereby Brugia pahangi larvae could be administered to a vertebrate host was tested in mice. Approximately 50% of the larvae administered were recovered in the tissues. This method of infection was then compared with that commonly used in experimental infections, namely inoculation with a syringe and needle. The differences in infections produced by these two procedures are too small and the number of observations too few to make any generalizations on the relative effectiveness of the two methods, but it is evident that patent infections can be produced in a natural host by using artificial puncture wounds, and this method of infection, perhaps with certain modifications, will probably be of value in subsequent studies on development and distribution of filarial nematodes in the vertebrate host.

Adam Ewert

Papers

The fate of Brugia pahangi larvae immediately after feeding by infective vector mosquitoes

Studies on the transfer of infective Brugia pahangi larvae from vector mosquitoes to the mammalian host.

Experimental transmission of filarial larvae in relation to feeding behaviour of the mosquito vectors.

Food ingestion and digestive enzymes in larval Aedes aegypti and Ae. albopictus (Diptera: Culicidae).

Microfilarial levels in cats infected with Brugia pahangi by two alternative routes.