Comparisons of different types and concentrations of alginates for encapsulation of Lagenidium giganteum (Oomycetes: Lagenidiales), a fungal pathogen of mosquito larvae

Six different types of alginates used to encapsulate Lagenidium giganteum gave similar levels of fungal infection in Culex quinquefasciatus larvae. Initial infection levels when the capsules were immersed in water after 6 days of storage (15 and 25 degrees C) were 100% for all types of alginate and after 42 days of storage was 62-100%, depending on the type of alginate. Infectivity was 24-100% after the encapsulated fungus were left in water for 7 days and after 15 days was 0 to 26%, depending on the alginate. When 2 of the alginates were tested at different concentrations to give high, medium and low viscosity solutions, the fungus encapsulated using lower concentration alginate solutions usually gave the highest level of infectivity.     

Encapsulation of the mosquito fungal pathogen Lagenidium giganteum (Oomycetes:Lagenidiales) in calcium alginate

The asexual stages (presporangial mycelia) of Lagenidium giganteum cultured on sunflower seed extract were encapsulated in calcium alginate and remained infective to mosquito larvae, Culex quinquefasciatus, after storage at 15 degrees C for up to 75 days. Survival and zoospore release from the encapsulated mycelia persisted for up to 24 days after immersion in water. Encapsulated sexual stages (oospores), held at 23-26 degrees C for up to 35 days or frozen for 8-10 days, were infective to mosquito larvae for up to 48 days after immersion in water and during that time over 50% of the oospores germinated. In outdoor pools, encapsulated mycelia gave 100% control of Cx. quinquefasciatus at 6-7 days after treatment while encapsulated oospores gave 100% control at 11 days posttreatment.     

Factors affecting storage of mycelial cultures of the mosquito fungal pathogen Lagenidium giganteum (Oomycetes: Lagenidiales)

Sunflower seed extract (SFE) agar cultures (in petri dishes) of Lagenidium giganteum (California isolate) were evaluated for zoospore production and ability to infect mosquito larvae, Culex quinquefasciatus, after periods of storage up to 93 days at 15 degrees C. Rates of decrease in zoospore production and infectivity were related to soluble protein concentration in the SFE-agar media but at all concentrations (0.7-6.0 mg/ml) about 50% of the initial levels were lost after 40-50 days of storage. Water loss from the SFE-agar did not affect zoospore production or infectivity except at extremely high levels (about 98% water loss).     

Effect of nutrient concentration in culturing three isolates of the mosquito fungal pathogen, Lagenidium giganteum (Oomycetes: Lagenidiales), on sunflower seed extract

The requirements for soluble protein concentration in sunflower seed extract (SFE) cultures were similar for 3 isolates of Lagenidium giganteum from North Carolina, Louisiana and California. Sunflower seed extract agar containing soluble protein in the range of 1.0 to 4.0 mg/ml was satisfactory for high levels of zoospore production. It is recommended that the protein concentration be 2.0 mg/ml for both SFE agar and liquid SFE culturing media, and the protein assay be with the Bradford method using bovine serum albumin as the standard.     

Population dynamics of Culex quinquefasciatus and the fungal pathogen Lagenidium giganteum (Oomycetes: Lagenidiales) in stagnant water pools

The fungal pathogen Lagenidium giganteum (California isolate), cultured on sunflower seed extract (SFE) and agar, was introduced once (May 15) into outdoor caged replicated stagnant water pools containing all instars of larval Culex quinquefasciatus. Subsequently, first-instar larvae were added daily (May 15-September 30) to simulate natural oviposition. The fungus persisted for the entire 138-day study period, which corresponded with the season of Cx. quinquefasciatus breeding in this region of North Carolina, and recycled in the mosquito larvae producing an 82% reduction of adult mosquitoes produced in comparison to untreated pools. The cycles of fungal activity varied among the pools with 2-4 major epizootics occurring during the study period. Data are presented on the cycling of populations of fungal zoospores, mosquito larvae, pupae and adults during the entire mosquito breeding season.     

Compatibility of Bacillus thuringiensis var. Israelensis and Bacillus sphaericus with the fungal pathogen Lagenidium giganteum (Oomycetes: Lagenidiales)

Larvae of Culex quinquefasciatus were exposed to infection by Lagenidium giganteum and various concentrations of B.t.i. or B. sphaericus. The resulting larval mortalities, percentages of infected dead larvae and percentages of larval body regions containing the fungus were compared. Overall, the effectiveness of Lagenidum giganteum against the larvae was not significantly affected by the presence of B.t.i. or B. sphaericus, and the fungal and bacterial agents were compatible. In experiments using 3-day-old larvae, the extent of growth of the fungus in the infected larvae and the percentage of the larvae infected were related to the concentration of B.t.i. in the range of 0.057-0.456 ITU/ml tested but were not related to the concentration of B. sphaericus in the range of 0.6-4.8 x 10(4) spores/ml. With larvae of various ages treated with a low concentration of B.t.i. (0.114 ITU/ml), exposure to the fungus increased the mortality rate in early but not late instars. After single and multiple applications of B.t.i. and B. sphaericus in the presence of the fungus, followed by drying and reflooding, the fungus persisted and reinfected larvae while the B. sphaericus persisted but the B.t.i. did not.     

Spinosad: a new larvicide against insecticide-resistant mosquito larvae

Among the characteristics of spinosad that are worth noting is its environmentally favorable toxicity profile. It is a compound of biological origin, whose insecticide action is highly effective against a great number of insects. Laboratory larval bioassays of spinosad on Aedes aegypti, Culex quinquefasciatus, and Anopheles gambiae (specimens that were either susceptible or resistant to pyrethroids, carbamates, and organophosphates) showed that this product had a lethal action (mortality after 24 h of exposure) regardless of the original status, susceptible or resistant, of the mosquito larvae.     

Temperature and water quality effects in simulated woodland pools on the infection of Culex mosquito larvae by Lagenidium giganteum (Oomycetes: Lagenidiales) in North Carolina

Asexual stages of the California (CA) isolate of Lagenidium giganteum cultured on sunflower seed extract (SFE)-agar, were applied to outdoor pools containing Culex larvae near Raleigh, NC in August and September 1984. Infection rates among the larvae ranged from 19 to 74% at 2-4 days posttreatment and subsequent epizootics eliminated most of the newly hatched larvae for at least 10 days posttreatment. Substantial reductions in numbers of larvae and adult emergence were achieved from a single application of the fungus. Water quality and temperature data are presented. From laboratory assays of organically polluted water, the percent infection of Culex quinquefasciatus by the fungus was correlated with water quality and temperature. A logistic model of water quality (COD and NH3-N) effects on infectivity rates by the CA isolate is described.     

Effects of a brassinosteroid analogue to mosquito larvae

Many plant compounds are able to modulate herbivore growth and reproduction by directly interacting with steroid hormones systems. In insects, several classes of phytochemicals, including brassinosteroids and related substances, interfere with molting and reproduction. The effects of the molting-hormone antagonist pesticide DI-31, a brassinosteroid analogue, on Aedes aegypti mosquito larvae were tested in two different exposure scenarios. After static exposure of first-instar larvae, the calculated NOEC, LOEC, and LC(50) values referenced to 19 d were 0.03, 0.036, and 0.04 mg/mL, respectively. Semistatic exposure of fourth-instar larvae revealed them to be slightly less susceptible than the younger larvae (NOEC 0.03 mg/mL, LOEC 0.036 mg/mL, LC(50) 0.049 mg/mL referenced to 19 days). In both cases mortality was immediate and larval development was retarded. This study suggests that A. aegypti could be a useful model for the detection of hormonally active substances such as DI-31.     

Larvicidal activities of some organotin compounds on mosquito larvae: a QSAR study

Mosquitoes are not only the cause of nuisance by their bites but also transmit deadly diseases like malaria, filariasis, yellow fever, dengue, and Japanese encephalitis. In this paper, nine QSAR models were developed using different series of organotins with respect to their larvicidal activities against Aedes aegypti and Anopheles stephensi mosquito larvae. Internal [cross-validation (LOO-q(2)), quality factor (Q), Fischer statistics (F), and Y-randomization] and external validation tests have validated all these QSAR models. QSAR results suggest that the two most important determinants for the toxicity are the hydrophobic (pi) and Hammett electronic (sigma(+)) parameters of the substituents, and the kill mechanism is different for these two species of mosquito larvae. On the basis of QSAR (6), nine compounds 4a-4i are suggested as potential synthetic targets.     

Laboratory evaluation of Lagenidium giganteum (Oomycetes: Lagenidiales) in water from Contra Costa County, California, mosquito sources

Six bioassays were performed to evaluate the efficacy of the fungus, Lagenidium giganteum, against mosquitoes in water collected from 75 sources. The fungus infected larvae of 4 genera and produced greater than 90% mortality in water from some of the creeks, artificial containers and the wild rice field tested during 4 of the assays. There was no larval mortality due to the fungus in water from irrigated pastures or marshes. Water quality parameters associated with L. giganteum infection varied among the bioassays; low measurements of total dissolved solids (TDS), hardness (CaCO3), conductivity, chemical oxygen demand (COD), ammonium nitrogen (NH3-N), phosphate (PO4) and salinity were significantly (P less than 0.05) correlated with fungal efficacy in one or more of the assays. Regression analyses selected TDS, CaCO3, COD, NH3-N and/or PO4 as the best predictors of larval mortality due to L. giganteum. Turbidity and pH were not correlated with fungal efficacy.     

Ground and aerial application of the sexual and asexual stages of Lagenidium giganteum (Oomycetes: Lagenidiales) for mosquito control

Fermentor-grown cultures of the sexual and asexual stages of Lagenidium giganteum were applied in rice fields in the Central Valley near Sacramento, CA. Both ground and aerial applications of the asexual stage resulted in high levels of immediate control of sentinel Culex tarsalis and indigenous Cx. tarsalis and Anopheles freeborni larvae and provided some degree of control throughout the four-month mosquito breeding season. Oospores which were desiccated in the field following application provided consistently high larval infection levels after reflooding of the fields. Advantages of using the sexual stage of L. giganteum for field larval control are presented.     

Efficacy of encapsulated Lagenidium giganteum (Oomycetes: Lagenidiales) against Culex quinquefasciatus and Aedes aegypti larvae in artificial containers

Presporangial mycelia of Lagenidium giganteum cultured on sunflower seed extract were encapsulated in calcium alginate and added once (July 18) to outdoor (Raleigh, NC) caged tires, wood and concrete containers populated with first instars of Culex quinquefasciatus or Aedes aegypti. First instars were added twice weekly (for 10 wk) to simulate natural oviposition. The fungus persisted for 10 wk and recycled in the mosquito larvae of both species. The overall reductions of Cx. quinquefasciatus and Ae. aegypti immatures were higher in tires (55 and 45%, respectively) and wood (67 and 38%) than in concrete containers (17 and 14%). There were low correlations of the numbers of mosquito immatures with measurements of water quality (chemical oxygen demand, ammonia nitrogen and conductivity) in the containers.     

Mesocyclops brevisetosus (Cyclopoida: Cyclopoidae) as a potential biological control agent against mosquito larvae in Indonesia

Mesocyclops brevisetosus Dussart and Sarnita, an indigenous copepod in Indonesia, was evaluated as a potentially useful biological control agent against larval Aedes (Stegomyia). In the laboratory, female M. brevisetosus were found to readily consume mosquito larvae of species from 3 genera (Aedes aegypti, Culex quinquefaciatus, and Anopheles farauti). Mesocyclops brevisetosus preferentially fed on larvae of Ae. aegypti (mean 95% consumed), followed by Cx. quinquefasciatus (71%) and An. farauti (54%) during a 24-h period. An individual copepod consumed up to 43 1st and 2nd instars of Ae. aegypti within a 24-h period. In the field, a density of 25 adult copepods/400 ml of water in an artificial container prevented the establishment of Aedes mosquitoes by 98% compared to the control container (without copepods). A density of 50 copepods/400 ml of water completely prevented infestation with Aedes. Over a 12-wk period, evaluation of M. brevisetosus-treated ovitraps reduced Ae. aegypti by 38-100% compared to ovitraps without copepods. The introduced gravid copepods increased 2.5-6.7 times over the original cohort. Mesocyclops brevisetosus showed high fecundity in culture, with a mean of 58 nauplii produced per individual gestation cycle.     

Comparison of floating and sinking encapsulated formulations of the fungus Lagenidium giganteum (Oomycetes: Lagenidiales) for control of Anopheles larvae

Floating calcium alginate capsules containing Lagenidium giganteum and 1% ground cork gave higher levels of control of Anopheles quadrimaculatus larvae in a 100-cm column of water than sinking capsules containing no cork. There was no significant difference between the cork capsules and the sinking capsules in the infection of larvae by the encapsulated fungus after storage (15 degrees C) for 57 days, although infectivity declined during that time from an initial infection rate of 100% to 35% and 40% for the cork and sinking capsules, respectively. Floating capsules containing glass bubbles were less effective than the cork capsules in the 100-cm column of water and had a shorter storage life than either sinking capsules or cork capsules.     

双效微生物制剂现场灭蚊幼效果观察

目的 现场观察双效微生物灭蚊幼制剂灭蚊幼效果,探索适合灭蚊幼施药剂量及施药周期.方法 随机确定实验区污水坑塘和对照区污水坑塘,按5 mL/㎡加水稀释10倍,用电动喷雾器均匀喷洒在水面上,观察蚊幼密度.结果 该制剂施药后1-20 d,灭蚊幼效果达100%,施药后30 d灭蚊幼效果仍达72.41%,通过数据分析,投药间隔以...