Among Oriental anopheline mosquitoes (Diptera: Culicidae), several major vectors of forest malaria belong to the group of Anopheles (Cellia) leucosphyrus Dönitz. We have morphologically examined representative material (> 8000 specimens from seven countries) for taxonomic revision of the Leucosphyrus Group. Six new species are here described from adult, pupal and larval stages (with illustrations of immature stages) and formally named as follows: An. latens n. sp. (= An. leucosphyrus species A of Baimai et al., 1988b), An. cracens n. sp., An. scanloni n. sp., An. baimaii n. sp. (formerly An. dirus species B, C, D, respectively), An. mirans n. sp. and An. recens n. sp. Additionally, An. elegans (James) is redescribed and placed in the complex of An. dirus Peyton & Harrison (comprising An. baimaii, An. cracens, An. dirus, An. elegans, An. nemophilous Peyton and Ramalingam, An. scanloni and An. takasagoensis Morishita) of the Leucosphyrus Subgroup, together with An. baisasi Colless and the An. leucosphyrus complex (comprising An. balabacensis Baisas, An. introlatus Baisas, An. latens and An. leucosphyrus). Hence, the former Elegans Subgroup is renamed the Hackeri Subgroup (comprising An. hackeri Edwards, An. pujutensis Colless, An. recens and An. sulawesi Waktoedi). Distribution data and bionomics of the newly defined species are given, based on new material and published records, with discussion of morphological characters for species distinction and implications for ecology and vector roles of such species. Now these and other members of the Leucosphyrus Group are identifiable, it should be possible to clarify the medical importance and distribution of each species. Those already regarded as vectors of human malaria are: An. baimaii[Bangladesh, China (Yunnan), India (Andamans, Assam, Meghalaya, West Bengal), Myanmar, Thailand]; An. latens[Borneo (where it also transmits Bancroftian filariasis), peninsular Malaysia, Thailand]; probably An. cracens (Sumatra, peninsular Malaysia, Thailand); presumably An. scanloni (Thailand); perhaps An. elegans (the Western Ghat form of An. dirus, restricted to peninsular India); but apparently not An. recens (Sumatra) nor An. mirans[Sri Lanka and south-west India (Karnataka, Kerala, Tamil Nadu)], which is a natural vector of simian malarias. Together with typical An. balabacensis, An. dirus and An. leucosphyrus, therefore, the Leucosphyrus Group includes about seven important vectors of forest malaria, plus at least a dozen species of no known medical importance, with differential specific distributions collectively spanning > 5000 km from India to the Philippines.
In a coastal village in northwest Malaysia, 3231 fed Anopheles females of eight to 10 species were collected, marked with fluorescent dust, and released on three consecutive nights. In collections made on the 10 nights after the first release, 58 mosquitoes of three species, An. lesteri paraliae, An. subpictus and An. vagus, were recaptured; the recapture rates were 3.42%, 1.19% and 0.97%, respectively. The data for An. subpictus and An. vagus were insufficient for further analysis. Those for An. l. paraliae were plotted against time of recapture and, from the regression coefficient, an estimate of 0.68 was obtained for the daily survival rate. An independent estimate based on the parous rate during the previous year was 0.55. The temporal distribution of the recaptures strongly suggested a gonotrophic cycle and oviposition cycle of two days.
Mark-release-recapture experiments were carried out in Sabah, East Malaysia on the malaria and filariasis vector, Anopheles balabacensis. Samples of wild females were marked with different colours of fluorescent pigments, released in man-baited huts fitted with exit traps. Simultaneous collections and releases were also made in night-biting catches on a water buffalo and on four men. All subsequent recaptures were made in the same situation in which the mosquitoes were marked. The same individual mosquitoes were caught biting men and buffalo on different occasions and the numbers caught showed a strong preference for man over buffalo. The length of the oviposition cycle in the field was found to be 3.0 days. After blood-feeding on man in a hut, An. balabacensis were found to exit on the night or early morning. The same individual mosquitoes were found resting in the hut or exit trap on different occasions. The results indicate that there is strong evidence for the existence of genetic variability in the tendency of An. balabacensis to rest in houses and to bite man and buffalo. The obvious existence of this phenomenon is considered discouraging for the prospects of interruption of malaria transmitted by An. balabacensis in nature.
Some species of the Anopheles dirus species complex are considered to be highly competent malaria vectors in Southeast Asia. Anopheles dirus is the primary vector of Plasmodium falciparum and P. vivax while An. cracens is the main vector of P. knowlesi. However, these two species are difficult to distinguish and identify based on morphological characters. Hence, the aim of this study was to investigate the potential use of antennal sensilla to distinguish them. Large sensilla coeloconica borne on the antennae of adult females were counted under a compound light microscope and the different types of antennal sensilla were examined in a scanning electron microscope. The antennae of both species bear five types of sensilla: ampullacea, basiconica, chaetica, coeloconica and trichodea. Observations revealed that the mean numbers of large sensilla coeloconica on antennal flagellomeres 2, 3, 7, 10 and 12 on both antennae of both species were significantly different. This study is the first to describe the types of antennal sensilla and to discover the usefulness of the large coeloconic sensilla for distinguishing the two species. The discovery provides a simple, reliable and inexpensive method for distinguishing them.
Anopheles (Cellia) litoralis King and Anopheles (Cellia) sundaicus Rodenwaldt, vectors of malaria, were collected from the same brackis and sea-water habitats in six localities in Sabah. They share the same breeding habitats with predominance of one species over the other. The two species although distinct have small morphological differences and are taxonomically separated by certain wing characters. Hybridization between the two species was successful. Reciprocal crosses produced viable progeny which appeared to develop normally to adults. Hybridized females laid fewer viable eggs in comparison with the parents. The F1 hybrids resembled the litoralis parent in most characters. Backcrosses of both litoralis and sundaicus parents with the F1 hybrids yielded no eggs. F1 male hybrids were thus assumed to be sterile. The results obtained from cross matings between the two species suggested something more than subspecific status.
The relationship among body size (as indicated by wing length), age (as indicated by parity dissections), and malaria infection were observed in host-seeking Anopheles maculatus Theobald females collected in aboriginal villages of peninsular Malaysia. Both ELISA and salivary gland dissections were used to determine malaria infection. The wings of parous females were significantly longer than those of nulliparous females, suggesting that larger females live longer than smaller ones, and thus have a higher vectorial capacity. Body size differences were not detected between infected parous and uninfected parous females. Females infected with only oocysts were significantly larger than females infected with sporozoites. No correlation was found between the number of oocysts or sporozoites and body size in this small sample.
A 14-months survey was carried out to identify the species composition of Anopheles mosquitoes from Kampung Bongor, Grik, Perak. Adding to that, a preliminary one month mosquito population screening was done at Kampung Tepin, Serian, Sarawak. Consequently, the insecticide susceptibility status of a pyrethroid was tested against two selected species of Anopheles collected from these two locations in Malaysia. A total of 4,497 Anopheles from 11 species were identified from collections in Kampung Bongor, whereas 2,654 An. letifer were collected from Kampung Tepin. The An. maculatus of Kampung Bongor and An. letifer of Kampung Tepin were then selected and tested using WHO standard diagnostic test kits and impregnated papers with 0.75% permethrin. The response values of KT50 and KT95 for An. maculatus were recorded at 28.09 minutes and 62.98 minutes respectively. Anopheles letifer recorded much slower response values of KT50 and KT95, which was at 35.09 minutes and 73.03 minutes respectively. Both An. maculatus and An. letifer showed 100% mortality after 24 hours holding period. The results indicate that both species were still susceptible to the tested pyrethroid. For effective vector control and resistance management, accurate and periodic insecticide resistance monitoring should be undertaken especially in rural areas with agricultural usage of insecticides.