After several decades of intensive research in salt marshes, both community structure and basic ecological processes are reasonably well understood (44, 50, 78, 88). Further up the estuary, however, the often extensive tracts of tidal freshwater wetlands (Figure 1) are not so well researched (52, 99, 113). Historically, tidal freshwater environments have been ignored by limnologists because of the presence of oceanic tidal influence, and neglected by marine ecologists because they are bathed by freshwater and inhabited primarily by freshwater organisms.

Comparative ecology of tidal freshwater and salt marshes

This paper addresses three major issues. Firstly, molecular taxonomy and its application to elucidate the biodiversity and biogeography of entomopathogenic nematodes is considered. Accurate identification is fundamental for understanding biodiversity, and because these nematodes are morphologically conservative, molecular techniques will provide the insights necessary to develop a robust, morphologically based taxonomy. Secondly, a review of the knowledge on their biogeography and habitat specificity, including a consideration of the limitations to the available data is given. Much of the information is presented in two tables which summarize the distributions of recognized species at continental and national levels. Thirdly, this paper provides a brief consideration of the Convention on Biological Diversity and its implications for future work with entomopathogenic nematodes and biological control.

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Entomopathogenic Nematodes: Biodiversity, Geographical Distribution and the Convention on Biological Diversity

Entomopathogenic nematodes (EPNs) of the families Steinernematidae and Heterorhabditidae are lethal pathogens of insects. These pathogens contribute to the regulation of natural populations of insects, but the main interest in them is as an inundatively applied biocontrol agent. Their success in this role can be attributed to the unique partnership between a host-seeking nematode and a lethal insect-pathogenic bacterium. Because of their biocontrol potential, considerable attention has been directed over the past few decades to Heterorhabditis and Steinernema and their respective bacterial partners, Photorhabdus and Xenorhabdus.

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Biology and behaviour.

http://manoa.hawaii.edu/ctahr/termite/aboutcontact/grace/pdfs/268.pdf

Fifty years of attempted biological control of termites - Analysis of a failure

Antagonistic factors, broadly identified as antibiosis, competition and natural enemies, impact on entomopathogenic nematodes. Antibiosis can occur through the release of plant chemicals from the roots into the soil, which may adversely affect the host-finding behavior of the infective stage nematode, or the presence of these chemicals in the host insect may negatively affect nematode reproduction. In laboratory studies, intra-specific and inter-specific competition reduces nematode fitness, and inter-specific competition can cause local extinction of a nematode species. For example, after concomitant infection of a host, a steinernematid species usually excludes a heterorhabditid species. The mechanism for the steinernematid superiority has been postulated to be a bacteriocin(s) produced by Xenorhabdus, the symbiotic bacterium of the steinernematid, which prevents Photorhabdus, the symbiotic bacterium of the heterorhabditid, from multiplying. Inter-specific competition between two steinernematid species ...

Effects of microbial and other antagonistic organism and competition on entomopathogenic nematodes

Entomopathogenic nematodes (Heterorhabditidae and Steinernematidae) were isolated from Sri Lankan soils using the Galleria baiting technique. Samples collected from different agro-ecological regions and different habitat types revealed that the presence of nematodes was restricted to sandy coastal soils. Two heterorhabditid and three steinernematid RFLP types were discovered within 5–100 m of the sea. Members of both families were equally prevalent. However, no parasitized insects were found although insect species were encountered which are potentially natural hosts. These nematodes were present at high temperatures (some above 30°C) and neither the monsoon rain nor the drought had any effect on their prevalence.

Occurrence and distribution of entomopathogenic nematodes in Sri Lanka

Larval diet quality and rearing conditions have a direct and irreversible effect on adult traits. Therefore, the current study was carried out to optimize the larval diet for mass rearing of Aedes aegypti, for Sterile Insect Technique (SIT)-based applications in Sri Lanka. Five batches of 750 first instar larvae (L1) of Ae. aegypti were exposed to five different concentrations (2-10%) of International Atomic Energy Agency (IAEA) recommended the larval diet. Morphological development parameters of larva, pupa, and adult were detected at 24 h intervals along with selected growth parameters. Each experiment was replicated five times. General Linear Modeling along with Pearson's correlation analysis were used for statistical treatments. Significant differences (P < 0.05) among the larvae treated with different concentrations were found using General Linear Modeling in all the stages namely: total body length and the thoracic length of larvae; cephalothoracic length and width of pupae; thoracic length, thoracic width, abdominal length and the wing length of adults; along with pupation rate and success, sex ratio, adult success, fecundity and hatching rate of Ae. aegypti. The best quality adults can be produced at larval diet concentration of 10%. However, the 8% larval diet concentration was most suitable for adult male survival.

Determination of the efficiency of diets for larval development in mass rearing Aedes aegypti (Diptera: Culicidae).

(1) The ecology of a saltmarsh system on a small islet on the north-west coast of Sri Lanka was investigated, using association-analysis and reciprocal averaging to order the floristic and edaphic data. (2) Six chief plant communities-thorn scrub, dry saltmarsh pasture, an Arthrocnemum consociation, Suaeda communities, damp saltmarsh pasture and depressions-were tentatively recognized, and their ecological and floristic distinctiveness and interrelationships were further elucidated by the multivariate analyses. (3) The distribution within the saltmarsh system of some selected edaphic factors such as moisture regime, water-retaining capacity, textural properties, organicmatter content, pH, and calcium, carbonate and chloride concentrations was established. (4) The zonation of the saltmarsh vegetation is discussed in relation to the individual and integrated effects of several ecological factors, of which topography, textural variations of the soil, and exposure to floods, tides and winds, appear to be of particular importance.

The ecology of a saltmarsh in sri lanka

Immature mosquitoes are aquatic, and their distribution, abundance, and individual fitness in a particular breeding habitat are known to be dependent on mainly three factors: biotic factors, abiotic factors, and their interaction between each other and with other associated taxa. Mosquito breeding habitats harbor a diversified naturally occurring microbiota assemblage, and the biota have different types of interactions with mosquito larvae in those habitats. Those interactions may include parasitism, pathogenism, predation, and competition which cause the mortality of larvae, natural reduction of larval abundance, or alterations in their growth. Many microbiota species serve as food items for mosquito larvae, and there are also some indigestible or toxic phytoplanktons to larvae. However, when there is coexistence or mutualism of different mosquito species along with associated microbiota, they form a community sharing the habitat requirements. With the available literature, it is evident that the abundance of mosquito larvae is related to the densities of associated microbiota and their composition in that particular breeding habitat. Potential antagonist microbiota which are naturally occurring in mosquito breeding habitats could be used in integrated vector control approaches, and this method rises as an ecofriendly approach in controlling larvae in natural habitats themselves. To date, this aspect has received less attention; only a limited number of species of microbiota inhabiting mosquito breeding habitats have been recorded, and detailed studies on microbiota assemblage in relation to diverse vector mosquito breeding habitats and their association with mosquito larvae are few. Therefore, future studies on this important ecological aspect are encouraged. Such studies may help to identify field characteristic agents that can serve as mosquito controlling candidates in their natural habitats themselves.

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L. D. Amarasinghe

Papers

Occurrence and distribution of entomopathogenic nematodes in Sri Lanka

Determination of the efficiency of diets for larval development in mass rearing Aedes aegypti (Diptera: Culicidae).

The ecology of a saltmarsh in sri lanka

Naturally Occurring Microbiota Associated with Mosquito Breeding Habitats and Their Effects on Mosquito Larvae.

Geographic, economic and socio-cultural factors which defining the risk of dengue transmission in Kelaniya, Sri Lanka.