The distribution of immature Culicoides spp. in the intertidal zone was investigated at Moogurrapum Creek, SE Queensland. The aims of this study were (1) to determine the distribution of Culicoides immatures; (2) to attempt to determine some of the environmental factors influencing these distributions; and (3) to express these relationships in qualitative and quantitative terms.
Light trapping indicated that five Culicoides spp., - C. subimmaculatus, C. marmoratus, C.longior, C. henryi, C.cordiger - may have been breeding in the study site.
Soil sampling on six transects traversing mangrove and saltmarsh revealed the breeding habitats of four species but not of C. cordiger.
The transects were surveyed for elevation, vegetation and soil type. This information is presented in profile diagrams together with the distribution of Culicoides immatures.
The distribution of intertidal vegetation (mangroves and saltmarsh plants) was compared to a system of mangrove zonation listed for eastern Australia. Although not well defined, the vegetation exhibited some zonation. The distribution of immature Culicoides did not correspond with the mangrove zones, but was related to the presence or absence of intertidal vegetation and the nature of the intertidal soil.
Four habitat zones were recognized as supporting populations of immature Culicoides - open mangrove forest, closed mangrove forest, the Ceriops zone (creek levee) and salt-marsh.
An experiment to quantify the environmental factors - site (elevation), vegetation, and substrate - associated with the distribution of Culicoides immatures was conducted. It involved introducing a range of substrates into the zones for colonization by immatures through oviposition or larval invasion.
To test the feasibility of a full experiment, a pilot study was carried out involving three of the habitat zones (salt-marsh was excluded). Four sites, each of two subsites, were selected to assess the effects of elevation and vegetational cover. Four substrate types were introduced in two types of receptacles for colonization by Culicoides.
Recommendations are given for handling and processing large amounts of material.
A total of 1,121 Culicoides larvae were recovered from the receptacles of which 1,103 were identified. C. marmoratus was the most common species followed by C. longior and C. subimmaculatus. Too few C. henryi were taken for statistical analyses.
Site was the most significant factor affecting the distribution of the three species. Vegetation was significant for C. longior but this was related to topographical variations within a site. Substrate type was significant in influencing the distribution of C. subimmaculatus.
The distribution of Culicoides was found to be a response to a system of inter-related factors. Vegetation and soil are related to elevation and to each other, and form the main components of the environment at each site.
During the experiment, adult Culicoides were collected to determine the size of the ovipositing population. Few females were collected but meteorological conditions may not have been favourable.
Larval populations were monitored to determine the stage and rate of development of the three Culicoides species. The populations in the sites were similar to those in the receptacles suggesting that larvae dispersed into the substrates from the surrounding soils. Alterations to the substrates (deposition of silt, algal mats) provided dispersing larvae with a means of entry.
The study indicated that C. marmoratus was associated with algae of the genus Enteromorpha.
Descriptions of the immatures of C. henryi have been published and a new species, C. longior, has been described in all stages together with additional taxonomic information on C. ornatus, a closely related species.