INFORMATIONAL ITEM

Mosquito larvae (Culex tarsalis)) infected by the parasite (left),

Zoospores being released from dying larvae (right) J. Kerwin, both

Lagenidium giganteum

A Useful Biological Control Agent against Immature Mosquitoes

· Lagenidium giganteum is a watermold that parasitizes the larval stage of mosquitoes. This group, although they look like fungi and have a "fungal lifestyle", nonetheless are related to diatoms and brown algae. The infective stage is a motile spore that goes on a search-and-destroy mission selectively seeking mosquito larvae.

· L. giganteum is not an obligate parasite and can grow on rotting vegetation or dead insects. In the absence of its hosts, it grows much faster and is easier to isolate from mosquito larvae. Infected mosquito larvae are covered by a characteristic grey-white appearance found either in the larval head capsule or the breathing apparatus at the tail end of the larva.

· This parasite can be found in freshwater habitats supporting mosquito populations in the southern U.S., but has also been found in California, Cuba, Colombia and England. It will become dormant at temperatures below 60°F or above 90°F. Moderate levels of salinity or organic load prevent it from sporulating, which is necessary for mosquito infection.

· Infection of a larval host is initiated by motile zoospores that selectively recognize chemical signals on the outer exoskeleton of mosquito larvae. After attaching, the zoospores inject themselves into the larva. There, they consume body tissues and the larva dies of starvation within 1-4 days. At that time, each cell of the parasite can form an exit tube and release ~ 30 asexual spores, which in turn seek out a new host and/or dormant sexual oospores that can remain viable in a dehydrated state for at least seven years.

· Zoospores do not have a cell wall, so they are much too fragile to be applied directly in a breeding habitat; therefore, either presporangia, oospores, or a mixture of both are applied. Sporulation then occurs in the treated site to initiate infection. This parasite is registered with the U.S. Environmental Protection Agency and several states, including California, for use as an operational mosquito control agent. Besides being host specific, L. giganteum has the ability to recycle for weeks, months, or even years in a given breeding habitat after a single application.