Studies on the mosquito-killing watermolds in Taiwan
Date Issued
2004
Date
2004
Author(s)
Chen, Chi-Min
DOI
zh-TW
Abstract
The first-instar larvae of Aedes aegypti and Aedes albopcitus were used as baits for isolation of mosquito-parasitic fungi from soil and water samples collected from different locations in Taiwan. Totally, 453 soil samples and 18 water samples collected from Taipei, Ilan, Hualien, Hsinchu, Miaoli, Taichung, Tainan, Nanto, Chiayi, Yunlin, Kaohsiung, and Pintung, respectively were tested. Mosquito-parasitic fungi were isolated from 5 soil samples, all from cultivated sites (cultivated fields, managed grasslands, gardens). Four isolates of Pythium spp. and one isolate of Saprolegnia ( Saprolegnia megasperma ) were isolated from the soil samples collected from the farm in Hualien. In the pathogenicity test on Amaranthus mangostanus and Brassica chinensis seedlings and seeds, it showed brown roots on seedlings and 0% germination rate on seeds when Saprolegnia megasperma were inoculated. The four Pythium spp. won’t cause brown root on seedlings and showed 80%~100% germination rate on seeds.
Optimum temperature range for mycelial growth of the four Pythium spp. was 24-32℃and the Saprolegnia megasperma was 16-32℃. In the dark, the four Pythium spp. won’t growing when temperature below 4℃ and above 40℃. The Saprolegnia megasperma grows better in the light. Treating the four Pythium spp. agar blocks with different kinds of solution, we had maximum zoospore production with tap water that has been put into a fish tank for 7 days. The zoospore production were increase with the period of hyphae growing but the zoospore production of 90028 was reverse.
The LC50 of the four Pythium spp. were 7.8 -36. 5 zoospores/μl of Aedes aegypti and 11.9-35.6 zoospores /μl of Aedes albopictus. Using zoospores of Pythium spp. as inocula to infect the first-instar larvae, scanning electron micrographs shows cyst attaching to the anal gill and few between head and thorax in 4 hours. Photomicrograph of inoculation Pythium sp. zoospores on first-instar larvae in 24 hours, hyphae growth from the anal gill and some cyst aggregate either. Some infected larvae were surrounded by hyphae and some formed sporangia. It shows potential to introduce Pythium spp. as biocontrol agents against larvae of Aedes aegypti and Aedes albopcitus.
Subjects
水生菌
斑蚊幼蟲
生物防治
watermolds
biocontrol
Type
other
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