Production, longevity and infectivity of zoospores of an Argentinean isolate of the mosquito pathogen Leptolegnia chapmanii Seymour (Oomycota: Peronosporomycetes)

PELIZZA SEBASTIAN ALBERTO; LÓPEZ LASTRA C.C; BECNEL J. J.; HUMBER R. A.; GARCÍA, J.J.

Brasília-DF. Brasil. Del 30/6/07 al 4/7/07

Simposio; X Simpósio de Controle Biológico (Sicombiol); 2007

Sociedad entomologica brasilera, y EMBRAPA

Some oomycetous fungi from the Saprolegniales, classified in the Oomycetes but now in the Straminopiles (Peronosporomycetes), have potential as biocontrol agents for medically important Diptera, especially mosquitoes. The major entomopathogen from this group, Leptolegnia chapmanii, has been isolated from several mosquito species and found to have a number of desirable attributes. An Argentinean isolate of L. chapmanii, which was the first report of this pathogen from the Southern Hemisphere, is under study in order to determine its potential as a biocontrol agent of mosquitoes. The effect of temperature on the production, survival and infectivity of zoospores of L. chapmanii was determined under laboratory conditions. Production of zoospores of L. chapmanii in vitro and in vivo upon 1st and 4th instars larvae of the mosquito Aedes aegypti was studied at three different temperatures. Zoospores from infected larvae were infective to mosquito larvae for 51, 12, and 5 consecutive days when maintained at 25, 35, and 10ºC, respectively. Maximum zoospore production by infected 4th instar larvae was 9.6 ± 1.4 x 104 zoosp/larva (61,000 encysted and 35,000 swimming zoospores) at 48 h at 25ºC. The average zoospores (encysted + flagellated) produced by individual 4th instar Ae. aegypti larvae infected with L. chapmanii was 3.57±0.46 x 105 zoospores over a total of 6 consecutive days at 25ºC. Zoospore production in vitro was also affected by temperature with a maximum number of zoospores (47,666/ml) produced at 25ºC. When zoospores produced in vitro were used as inoculum against A. aegypti larvae at 25ºC, larval mortality was recorded for 5 consecutive weeks. The encystment process for zoospores took 17–20 minutes; the germination of cysts (excystment) occurred 5 minutes after exposure in water to mosquito larvae. The minimum time of contact between zoospores and mosquito larvae to develop infection was two minutes. Infection took place by zoospore attachment onto and then penetration through the larval cuticle and, by ingestion of cysts as was demonstrated by histological studies. Temperature directly affected infectivity and production of zoospores in vivo and in vitro although L. chapmanii zoospores have demonstrated tolerance to a wide range of temperatures. Apoio financeiro: ANPCyT PICT Nº11118/02, CONICET, CICPBA, UNLLeptolegnia chapmanii, has been isolated from several mosquito species and found to have a number of desirable attributes. An Argentinean isolate of L. chapmanii, which was the first report of this pathogen from the Southern Hemisphere, is under study in order to determine its potential as a biocontrol agent of mosquitoes. The effect of temperature on the production, survival and infectivity of zoospores of L. chapmanii was determined under laboratory conditions. Production of zoospores of L. chapmanii in vitro and in vivo upon 1st and 4th instars larvae of the mosquito Aedes aegypti was studied at three different temperatures. Zoospores from infected larvae were infective to mosquito larvae for 51, 12, and 5 consecutive days when maintained at 25, 35, and 10ºC, respectively. Maximum zoospore production by infected 4th instar larvae was 9.6 ± 1.4 x 104 zoosp/larva (61,000 encysted and 35,000 swimming zoospores) at 48 h at 25ºC. The average zoospores (encysted + flagellated) produced by individual 4th instar Ae. aegypti larvae infected with L. chapmanii was 3.57±0.46 x 105 zoospores over a total of 6 consecutive days at 25ºC. Zoospore production in vitro was also affected by temperature with a maximum number of zoospores (47,666/ml) produced at 25ºC. When zoospores produced in vitro were used as inoculum against A. aegypti larvae at 25ºC, larval mortality was recorded for 5 consecutive weeks. The encystment process for zoospores took 17–20 minutes; the germination of cysts (excystment) occurred 5 minutes after exposure in water to mosquito larvae. The minimum time of contact between zoospores and mosquito larvae to develop infection was two minutes. Infection took place by zoospore attachment onto and then penetration through the larval cuticle and, by ingestion of cysts as was demonstrated by histological studies. Temperature directly affected infectivity and production of zoospores in vivo and in vitro although L. chapmanii zoospores have demonstrated tolerance to a wide range of temperatures. Apoio financeiro: ANPCyT PICT Nº11118/02, CONICET, CICPBA, UNL