The mosquitocidal activity of conidia of Tolypocladium tundrense and Tolypocladium terricola.

Tolypocladium tundrense and T. terricola UV-irradiated conidia exhibited acute toxicity to Aedes aegypti larvae in concentrations of 5 x 10(5) and 5 x 10(6) ml-1, respectively. Substances deposited on the surface of conidia following sporulation appear to be responsible for rapid intoxication and killing of mosquito larvae. Treatment of larvae with dried methanolic extract of the spores also induced a high level of mortality accompanied by the same histological changes, including vacuolization and subsequent destruction of mitochondria of the midgut cells. Cyclosporin A was identified as a predominant metabolite forming the spore surface layer.

Coelomomyces psorophorae var tasmaniensis Couch + Laird (1988) (Coelomomycetaeceae: Blastocladiales), a fungal pathogen of the mosquito Aedes australis. I: Structural changes in the outer walls of sporangia during germination.

The germination of sporangia in Coelomomyces psorophorae var tasmaniensis (C. p. tas.) is uncoordinated and thus there is a mixture of developmental stages in any given population. Continuous urografin gradients separated out the critical stages of germinating sporangia giving four bands, each band representing a consecutive stage of germination. These stages were investigated for changes in the sporangial wall using Transmission Electron Microscopy (TEM). The sporangia have a typical two-layered wall, an electron dense outer layer which can be divided into three distinct sub-layers D1, D2, and D3 and an inner electron transparent secondary wall. Stage 3 sporangia have an intact D1 layer on their outer wall. In the subsequent stages (4 & 4b) there is a progressive breakdown of this layer.

Coelomomyces psorophorae var tasmaniensis Couch + Laird (1988) (Coelomomycetaeceae: Blastocladiales), a fungal pathogen of the mosquito Aedes australis. II: Nuclear changes during meiospore formation.

The presence of synaptonemal complexes were checked in dividing chromosomes as evidence for meiotic division in germinating sporangia. Continuous urografin gradients were used to separate out the various phases of germinating sporangia, the nuclei were removed and embedded for ultrastructural studies. Meiotic inhibitors were applied to germinating sporangia to retard meiotic division to highlight the synaptonemal complexes. At an early phase of sporangial differentiation dividing nuclei developed with synaptonemal complexes. Meiotic inhibitors and stimulators may be used to control sporangial germination for an induction of a high meiospore count. This may be of crucial importance in the utilization of Coelomomyces spp. as a biological control agent of mosquito species.

Tolypocladium cylindrosporum (Deuteromycotina: Moniliales), a fungal pathogen of the mosquito Aedes australis. II. Methods of spore propagation and storage.

A laboratory fermenter was used to produce up to 12 l of infective Tolypocladium cylindrosporum blastoconidia in Sabouraud dextrose broth. Two media derived from coconuts were also demonstrated as suitable alternative systems for the production of viable blastoconidia. T. cylindrosporum conidia when dried at 37 degrees C and stored at 4 degrees C retained their viability for 10 months, but, when stored at 25 degrees C, the conidia lost viability after 2 months and blastoconidia did not survive the drying process. Distilled water suspensions were a simple, economic technique for the long-term storage of spores at both 4 and 25 degrees C. The adsorption of conidia onto silica gel crystals was a very suitable technique for the storage of stock culture material at 4 degrees C. The virulence, production and storage capabilities of both spore types were examined.

Tolypocladium cylindrosporum (Deuteromycotina: Moniliales), a fungal pathogen of the mosquito Aedes australis. III. Field trials against two mosquito species.

A blastoconidial preparation of the New Zealand isolate of T. cylindrosporum was tested in two field trials against larvae of the freshwater mosquito Aedes subalbirostris and the brackish water species Ae. australis. There was some reduction in the population of the Ae. subalbirostris larvae and larvae collected from the test pools exhibited signs of fungal infection when reared in the laboratory. In the brackish pools there was no observable decrease in the larval populations even though Ae. australis is the natural host of T. cylindrosporum [NZ]. Water volume fluctuations in the test pools were a major difficulty experienced when monitoring the results. Tests against field-collected non-target fauna indicated that T. cylindrosporum is non-specific in action. Species of daphnid, dixid larvae and copepods were all susceptible to infection at varying degrees.

Tolypocladium cylindrosporum (Deuteromycotina: Moniliales), a fungal pathogen of the mosquito Aedes australis. I. Influence of temperature, pH and salinity on the growth and sporulation of the fungus in the laboratory.

The New Zealand strain of Tolypocladium cylindrosporum was cultured on Sabouraud dextrose agar medium under varying regimes of growth conditions. The isolate exhibited good tolerances to temperature (4-35 degrees C), pH (3-10) and salinity (0-7% NaCl). Optimal vegetative growth and sporulation were recorded between a temperature range of 20-30 degrees C, pH of 5-6 and a salinity level of 0-2% NaCl. The North American isolate of the fungus showed similar tolerances, while the European isolate was less tolerant.

Field trials of Tolypocladium cylindrosporum against larvae of Aedes polynesiensis breeding in crab holes in Fiji.

The New Zealand isolate of the entomopathogenic fungus Tolypocladium cylindrosporum was field-tested against larvae of the crab hole breeding mosquito Aedes polynesiensis. A reduction of approximately 87% was achieved in the larval populations of all crab holes treated with T. cylindrosporum by day 21 of spore application. However, the mosquito populations recovered to the pretreatment level within two months indicating that any residual activity of this pathogen was insignificant.

The urban mosquitoes of Suva, Fiji: seasonal incidence and evaluation of environmental sanitation and ULV spraying for their control.

Larval surveys and oviposition traps were used to monitor urban mosquito populations in two adjacent transects in Suva, Fiji between May 1978 and August 1979. Populations of Aedes aegypti and Ae. pseudoscutellaris fluctuated seasonally with changes in rainfall, the latter species being most prevalent throughout the year. Populations of these two species were highest between December and July and lowest between August and October. Larval populations of Culex quinquefasciatus did not show a seasonal variation and larval populations of Cx. annulirostris were too low for any conclusions to be made. All species were found breeding most often in miscellaneous containers, with tyres, plant containers and flower vases also being important sources for Ae. aegypti breeding. Through environmental sanitation the Breteau Index for all species was reduced by 88%; Premise Index by 72% and the Container Index by 83%, when compared to a control area. ULV applied malathion was effective in temporarily reducing Ae. pseudoscutellaris populations from 50--100%. Effects on Ae. aegypti were inconclusive. It is concluded that through enforcement of the existing laws and strict monthly surveillance during the periods of highest seasonal density, urban Aedes and Culex populations can be maintained at an acceptable level.