水环境中的几种物质对大链壶菌灭蚊效率影响的初步研究

1991年1—4月,作者在实验室中观察了水中分别加入肝粉、葵花籽粉、田泥、淤泥、丝藻和人造沙后,对致倦库蚊幼虫的大链壶菌(Lagenidium giganteum)感染率的影响。发现除人造沙外,其他几种物质皆能明显地增加蚊虫的大链壶菌感染率。并且在一定范围内,蚊虫感染率与所加物质的量成正相关关系。据估计,每100ml水中加入6.4mg葵花籽粉或6mg肝粉分别可使蚊虫感染率增加2倍和3倍。作者认为大链壶菌在肝粉和葵花籽粉中弥漫地腐生生长,并释放大量额外的游动孢子,是这两种有机物增加蚊虫感染率的主要原因。 对田泥、淤泥和人造沙的研究表明,土壤肥力与蚊虫感染率的增加有关。丝藻则可能是由于净化水质造成有利于大链壶菌游动孢子活动的环境而增加蚊虫的感染率。

A PRIMARY STUDY ON THE EFFECTS OF SOME ENVIRONMENTAL SUBSTANCES ON THE INFECTION RATE OF MOSQUITOES BY LAGEN IDIUM GIGANTEUM (OOMYCETES: LA-GENIDIALES)

One of the outstanding advantages of using Lagenidium giganteum as a mosquito biocontrol agent is that it can recycle and persist in mosquito breeding sites. This recycling is completed through its host passage and, probably, its sapro-phytic development in the environment. The former has been documented in a wide range of research, but the latter infered only in a few papers. Since the saprophyti-sm of L. giganteum might contribute directly to its efficiency in mosquito control, it's of great significance to confirm if this phenomenon occurs and to evaluate it quantitatively, if possible. The effects of liver powder (LP), sunflower seed powder (SFP), riceland soil, sand, mud from a barrel with stagnant water, and a species of algae (Ulothrix spp.) on the infection rate of Culex quinquefasciatus larvae by L. giganteum were obser- ed. The results showed that all those substances except sand in the water increased the infection rate significantly, and there were more or less positive correlations between their amounts and the infection rates. It was estimated, according to this data, that an increase of two- or threefold of infection rate could be obtained by adding 6.4 mg of SFP or 6 mg of LP respectively into 100 ml of water with L. giganteum mycelia. An extensively saprophytic development of the fungal mycelia and vesicles producing excess zoospores in LP and SFP were found and were thought to account for this increase. Since SFP floats in water, L. giganteum grown in it can release zoospores at different depth in the water so as to provide an even more efficient way to kill surface-preferring mosquito larvae. The results of comparing study about the effects of riceland soil, mud, and sand suggested that the fertility of soil might be a main factor causing the increase of mosquito infection rate. The possibility of saprophytic growth of L. giganteum in soil couldn't be excluded although no confirmative evidence has been found yet. The role of the algae might be a water quality conditioner to provide a favorable environment for the action and active duration of zoospores of L. giganteum.