Temporal activity of biting midges (Diptera: Ceratopogonidae) on cattle near Darwin, Northern Territory, Australia.

The activity of nine species of biting midges aspirated from cattle was recorded in the late afternoon, evening and early morning at a site near Darwin, Northern Territory, between March and June in 1999 and 2001. There were no significant differences between the temporal activity patterns for nulliparous and parous females of any species. Nulliparous females dominated collections of all species except Culicoides marksi. C. actoni and Forcipomyia (Lasiohelea) sp., were mostly active during daylight hours while C. peregrinus, C. bundyensis and C. brevipalpis, were nocturnal. Differences in the peak activity of C. brevitarsis were noted between years and occurred slightly earlier than that observed at other sites. C. fulvus, C. marksi and C. oxystoma were generally crepuscular but differed in the length and peak period of activity. C. actoni was four times more active in the evening than in the morning while C. marksi and C. peregrinus, were respectively 2.6 and 3.4 times more active in the morning than in the evening. Numbers of the other six species were not significantly different in the evening and morning. All nine species were collected at least once from cattle shortly after dawn.

Laboratory evaluation of two native fishes from tropical North Queensland as biological control agents of subterranean Aedes aegypti.

The ability of 2 freshwater fishes, eastern rainbow fish Melanotaenia splendida splendida and fly-specked hardyhead Craterocephalus stercusmuscarum stercusmuscarum, native to North Queensland to prey on immature Aedes aegypti was evaluated under laboratory conditions. The predation efficiency of the 2 species was compared to the exotic guppy, Poecilia reticulata, which is commonly used as a biological control agent of mosquito larvae. Of the 3 fish species tested, M. s. splendida was shown to be the most promising agent for the biological control of Ae. aegypti that breed in wells. Melanotaenia s. splendida consumed significantly greater numbers of immature Ae. aegypti than P. reticulata, irrespective of developmental stage or light conditions. Unlike C s. stercusmuscarum, M. s. splendida could be handled, transported, and kept in captivity for extended periods with negligible mortality. However, M. s. splendida was also an efficient predator of Litoria caerulea tadpoles, a species of native frog found in wells during the dry season. This result may limit the usefulness of M. s. splendida as a biological control agent of well-breeding Ae. aegypti and suggests that predacious copepods, Mesocyclops spp., are more suitable. However, the use of M. s. splendida as a mosquito control agent in containers that are unlikely to support frog populations (e.g., aquaculture tanks and drinking troughs) should be given serious consideration.

Comparative immunogenicity of two bivalent botulinum vaccines.

OBJECTIVE: To compare the ability of a new single-dose botulinum vaccine containing a non-mineral oil adjuvant with a single dose of a conventional botulinum vaccine product to produce antibody to Clostridium botulinum types C and D in cattle in Northern Australia. DESIGN AND PROCEDURE: One hundred and fifty Brahman steer weaners were randomly divided into two groups receiving either a single dose of CSL Bivalent Botulinum vaccine or Websters Singvac. Blood samples were collected at 0, 8 and 24 weeks and tested by antibody ELISA. The final samples were also tested by the toxin neutralisation test, to test titres of neutralising antibody. RESULTS: Six months after inoculation, cattle vaccinated with Websters Singvac had ELISA antibody response twice that of CSL conventional product. However, this difference was only evident for neutralising antibody to type C botulinum toxin. Both products produced similar titres of type D neutralising antibody after a single dose. CONCLUSION: Websters' Singvac produces a greater neutralising antibody response to type C botulism upon single inoculation than a conventional vaccine. The product produces an equivalent neutralising antibody response to type D.

Importance of Hydrilla verticillata (hydrocharitaceae) as habitat for immature mosquitoes at the Ross River reservoir, Australia.

From November 1990 to November 1992, immature mosquitoes were sampled from the shoreline and from emergent beds of the submerged aquatic plant Hydrilla verticillata at the Ross River reservoir, northern Australia. Aerial mapping of Hydrilla beds was done in conjunction with sampling to estimate total immature mosquito numbers. Larvae of 7 species were found. Culex annulirostris. Anopheles annulipes s.l., and Anopheles amictus comprised 80.4% of the total. Peak larval densities occurred in the late wet season period in both habitat types (March to May) but Hydrilla generally supported higher densities, particularly of An. annulipes s.l. (43.7% of the total sample), than the shoreline habitats. Anopheles annulipes replaced Cx. annulirostris as the predominant taxon when 1990-92 data were compared with data for 1985-86. The Hydrilla beds supported on the order of 5.6 x 10(9) immatures during the period of peak density. This suggests that where human exposure is of concern, mosquito control in habitats such as Hydrilla is warranted.

Alphavirus infection in mosquitoes at the Ross River reservoir, north Queensland, 1990-1993.

This study addresses the potential problem of alphavirus infection associated with recreational use of the Ross River reservoir in north Queensland, Australia. From 1990 to 1993, 51,497 adult female mosquitoes were collected mainly by CO2-supplemented light traps. Four localities within the reservoir were considered and compared with mosquitoes collected during 1991 from 2 public localities around Townsville City. Ten isolates of Ross River virus, one of Barmah Forest virus, and 2 of Sindbis virus were recovered from Aedes normanensis, Anopheles amictus, and Culex annulirostris. All isolates were collected during the wet seasons of 1991 and 1992 using an enzyme immunoassay and cross-checked using a polymerase chain reaction assay Estimation of relative hazard was based on total mosquito abundance, prevalence of vector species, and on mosquito infection rates. Based on 1990-93 data, it was concluded that the Big Bay area of the Ross River dam, currently being considered as a primary recreational locality, was relatively safer than Antill Creek, Ross River, and Toonpan and presented no greater hazard than localities around urban Townsville, away from the reservoir. However, because of the changing ecology of the reservoir and lack of a full understanding of annual alphavirus activity, periodic surveillance is recommended.

Changes in mosquito populations with expansion of the Ross River Reservoir, Australia, from stage 1 to stage 2A.

Female mosquitoes were collected at 4 sites around the Ross River reservoir (Stage 2A) from 484 carbon dioxide-supplemented light traps. The seasonal abundance from these collections during 1991-93 was compared statistically with that for similar collections done for the Stage 1 reservoir in 1984-85. Principally due to clearing of the forest prior to the inundation of the Stage 2A, several tree hole/plant axil and shaded pool species are no longer present or are rare. Due to extensive loss of marginal emergent vegetation and creation of expanses of shallow muddy pools, mean number per trap of Anopheles amictus and Aedes normanensis increased up to 36- and 282-fold, respectively, from Stage 1 to 2A. For Culex annulirostris, mean abundance did not exceed densities recorded for Stage 1. However, from examination of trends from 1991 to 1993, mean catches of Culex, Anopheles spp., and Mansonia uniformis were increasing despite the progressive reduction of the inundated area of the reservoir. Cluster analysis of species abundance indicated broad similarities with Stage 1 data, and differences in faunal composition of the reservoir area compared with that around Townsville. In view of the continuing stabilization of the Stage 2A reservoir area, continued surveillance of major vector species is recommended.

Habitat partitioning among the mayfly species (Ephemeroptera) of Yuccabine Creek, a tropical Australian stream.

This study examines the distributions among microhabitats of 12 detritivorous species of mayfly in Yuccabine Creek, an upland tropical rainforest stream. Analysis of data from regular benthic sampling and from in situ experiments using implanted substrata showed that although all species occurred in all the microhabitats examined, different species had significantly different peaks of abundance in different microhabitats, leading to distinct partitioning of the available habitat. The observed patterns of distribution were closely associated with the distribution of fine detritus deposits (FPOM). In the absence of FPOM in fast-flowing regions of the stream, leaf litter was the prime determinant of species distribution. Current velocity and substratum particle size influenced the distribution of the detritus and leaf litter. Abundance of mayflies was greatest in the pool habitat for all except two of the species.