AbstractCulicoides ornatus is the main pest species of biting midge in coastal northern Australia. As the control of biting midges is usually not practical after they have dispersed from their larval habitat, and as little was known about the larval biology of C. ornatus, this study was undertaken to identify and characterise the location of larval habitats within mangroves near Darwin. Emergence trapping was used to identify larval habitats. Three types of larval habitat were found, each associated with a particular mangrove vegetation zone. The highest densities of emerging midges were recorded at the edge of the vegetation line on creekbanks of the upper reaches of small tidal creeks (around Mean High Water Neap), while low to moderate emergence was found in both the transitional zone of Bruguiera and Ceriops at the landward edge of the creekbank forest (just below Mean High Water Spring), and in the Sonneratia zone at the seaward edge of mangrove lined foreshores (between Mean Low Water Neap and Mean Sea Level). Creekbanks were a dry season only habitat, the transitional zone was a wet season only habitat, and the seasonal pattern of emergence was not determined in the Sonneratia zone, sampling only being undertaken in the late dry season.
Peak emergence within each fortnightly tidal cycle occurred around the day of the neap tide, with a variation of three to four days through the year. Emergence occurred later at higher tidal elevations, with a four day difference between the time of emergence in the Sonneratia zone and at creekbank sites. Emergence was also greater on pre-full moon cycles than on pre-new moon cycles, after allowing for seasonal changes in numbers. Synchronised emergence appeared to be the result of the synchronisation of pupation. Field data indicated that there was a tidal cue for pupation, that it coincided with exposure of the habitat by an ebb tide, and that there was a circadian basis to its perception by larvae. Emerging females were autogenous, moving out of the mangroves and into the adjacent hinterland in search of blood meals immediately after their first oviposition.
The extensive distribution of larval habitats within the mangroves near Darwin indicated that, using current technology, control methods aimed at the larval habitat such as insecticidal spraying or habitat modification, are unlikely to be either effective or environmentally acceptable. Consequently, control must continue to rely on methods such as the use of buffer zones between mangroves and residential communities, and personal protection and avoidance.
|Date of Award
|Charles Webb (Supervisor)