Our paper presents an assessment of research and operational development in relation to medically important mosquito-borne disease, mainly the arboviruses Ross River, Barmah Forest, Murray Valley encephalitis, Japanese encephalitis, Kunjin and dengue, but also with respect to malaria. Since 1972, there have been considerable gains in research output, organisational structure, communication, surveillance including quarantine inspection and operational control. This has been due to the 1974 epidemic of Murray Valley encephalitis virus extending into temperate Australia, increasing occurrence of Ross River and the dengue viruses, the discovery of Barmah Forest virus as a disease entity in 1988, and the introduction of Japanese encephalitis in 1995. Because many of the outputs involve methodologies of global import, this has resulted in an unprecedented upsurge in publications of international standard.

Medical entomology: changes in the spectrum of mosquito‐borne disease in Australia and other vector threats and risks, 1972–2004

Our review outlines changes in insecticide usage for mosquito control against Australian mosquitoes, with a focus on biologically based insecticides. The most widely used microbial insecticide is Bacillus thuringiensis var. israelensis de Barjac (Bti) and it is regularly used in estuaries and freshwater. In comparison, the use of Bacillus sphaericus (Neide) is limited to freshwater. The only insect growth regulator registered for mosquito control in Australia is s-methoprene, and it is used in both estuaries and freshwater. Although biologically based insecticides have been used for more than 10 years, there remains knowledge gaps surrounding the use of specific formulations in specific habitats: for example, VectoBac WG (Bti) and VectoBac G (Bti) in containers containing freshwater, or Altosid pellets (s-methoprene) in ground-pool freshwater habitats. Where broad-scale mosquito control programs have been implemented in Australia, a reduction in the incidence of mosquito-borne disease, mainly Ross River virus, has been recorded. Therefore, the future application of these products is supported. The use of insecticides should be integrated with public education, biological control, physical habitat modification and coupled with spatial risk assessment.

Biologically based insecticides for the control of immature Australian mosquitoes: a review

Resistance of the dengue vector to temephos stimulated its substitution for Bacillus thuringiensis var. israelensis (Bti) since 2001 in Brazil. The persistence of the two Bti formulations employed at that time by the Health Ministry, Vectobac G and Aquabac G, was assayed under laboratory and outdoor conditions. Both formulations were tested at 0.2 g/10 liters of water, the same concentration applied in the field for vector control. The tests were done against Ae. aegypti third instar larvae (Rockefeller strain). In the laboratory, Vectobac G and Aquabac G caused at least 95% mortality until 101 and 45 days after treatment, respectively. In the outdoor assays, test containers of different materials were treated with either formulation and placed in a shaded area. Larvae were introduced each 3-6 days and mortality was recorded 24 and 48 hours later. In the first set of assays, performed in June 2001, mortality levels of 70% or more were attained for 2-5 weeks for both formulations in all containers. The exception was for the iron one that rusted, resulting in low mortality after seven days. In the second set of assays (August 2001), 70% mortality was attained for just 1-2 weeks for all the containers and both formulations.

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Residual effect of two Bacillus thuringiensis var. israelensis products assayed against Aedes aegypti (Diptera: Culicidae) in laboratory and outdoors at Rio de Janeiro, Brazil.

Laboratory bioassays were conducted on the efÞcacy of a water-dispersible granule (WG) formulation of Bacillus thuringiensis variety israelensis (VectoBac WG; active ingredient (AI): 3,000 Bti international toxic units (ITU)/mg) against third instars of six common Australian mosquito species, Aedes aegypti (L.), Ochlerotatus vigilax (Skuse), Ochlerotatus notoscriptus (Skuse), Culex sitiens Wiedemann, Culex annulirostris Skuse, and Culex quinquefasciatus Say. The normal model for log-linear mortality data was used to determine laboratory 48-h LC50 and LC95 values. The target mosquito species tested were extremely sensitive to the VectoBac WG formulation, with the most sensitive species (Cx. annulirostris and Cx. quinquefasciatus ,L C 95 value of 0.019 ppm) being twice as susceptible as the most tolerant (Oc. notoscriptus ,L C 95 value of 0.037 ppm). Cx. annulirostris was selected as a target species for a small-plot evaluation of VectoBac WG and VectoBac 12 aqueous solution (AS) ((AI): 1,200 Bti ITU/mg) efÞcacy over time, in freshwater in southeastern Queensland, Australia. Replicated cohorts of caged third instars were exposed weekly to six concentrations of WG formulation (0.004 Ð 0.13 ppm) and three concentrations of the 12AS formulation (0.04 Ð 0.13 ppm). In water with high organic content, treatment concentrations of 0.008 ppm WG and 0.04 ppm 12AS and above produced signiÞcant larval control (96%) at 48 h posttreatment, with no residual control at week 1. Water quality was not affected by treatment with either formulation.

https://bioone.org/journals/Journal-of-Economic-Entomology/volume-96/issue-6/0022-0493-96.6.1786/Efficacy-of-VectoBac-Bacillus-thuringiensis-variety-israelensis-Formulations-for-Mosquito/10.1603/0022-0493-96.6.1786.pdf

Efficacy of VectoBac (Bacillus thuringiensis variety israelensis) Formulations for Mosquito Control in Australia

Background & objective Vector control, using agents of chemical origin, continues to be practiced in the control of vector borne diseases. However, due to some drawbacks including lack of selectivity, environmental contamination, and emergence and spread of vector resistance, development of natural products for vector control has been a priority in this area. In the present study we evaluated the larvicidal and emergence inhibitory activities of a neem based formulation Neem Azal T/S 1.2 per cent EC against the vectors of malaria, filariasis and dengue. Methods Larvicidal and emergence inhibition (EI) activity of a neem formulation, NeemAzal T/S 1.2 per cent EC, was studied in the laboratory respectively against early 4(th) and early 3(rd) instar larvae of Anopheles stephensi, Culex quinquefasciatus and Aedes aegypti following standard procedures. Results Among the three vector species studied, An. stephensi was highly susceptible to NeemAzal T/S as revealed by the LC(50) and LC(90) values (1.92 and 2.76 ppm). The formulation produced an overall mortality or inhibition of emergence of 90 per cent (EI(90), when 3(rd) instar larvae were treated) at 0.046, 0.208 and 0.866 ppm in An. stephensi, Cx. quinquefasciatus and Ae. aegypti, respectively. The corresponding EI(50) values were 0.006, 0.048 and 0.249 ppm. On treatment, NeemAzal T/S induced certain morphogenetic abnormalities, broadly characterized in five types, in larvae, pupae and adults of all the three vector species. The percentage of dead specimens of any stage showing morphogenetic abnormalities was the maximum in Cx. quinquefasciatus (14.4%; n=2113) followed by Ae. aegypti. Interpretation & conclusion Our results indicated that because of its emergence inhibition activity, NeemAzal T/S 1.2 per cent EC could be a promising candidate for the use in integrated vector management programme and replace chemical insecticides.

Larvicidal & emergence inhibitory activities of NeemAzal T/S 1.2 per cent EC against vectors of malaria, filariasis & dengue.

Laboratory bioassay studies of the efficacy of VectoBac 12AS (active ingredient: 1,200 International Toxic Units [ITU]/mg Bacillus thuringiensis var. israelensis) against field-collected late 3rd/early 4th-instar larvae of Culex sitiens indicated excellent control potential. A 95% lethal concentration (LC95) value of 1.381 x 10(7) ITU was calculated, which equated to a dosage of 0.011 liters/ha. This dosage represented 1.8% of the recommended lowest dosage rate for the product. A field trial of VectoBac 12AS against late 3rd/early 4th-instar field specimens of Cx. sitiens in floating mesh cylinders was then conducted in salt-marsh pools near Coomera Marina, southeast Queensland, Australia. At a rate of 0.5 liters/ha, 100% mortality of Cx. sitiens larvae was recorded at 24 h posttreatment.

K Watson

Papers

Laboratory and field evaluation of efficacy of VectoBac 12AS against Culex sitiens (Diptera: Culicidae) larvae.