Biochemistry of mosquito infection: preliminary studies of biochemical change in Culex pipiens quinquefasciatus following infection with Lagenidium giganteum

Effects of culture medium and formulation on the larvicidal activity of the mosquito pathogen Lagenidium giganteum (Oomycetes: Lagenidiales) against Aedes aegypti

In this work, we examined the production of infective zoospores of Lagenidium giganteum in four culture media, and the larvicidal activity of the cultures was determined against Aedes aegypti larvae, as well as the effect of polymer encapsulation. Medium containing sunflower seed extract showed the greatest production of zoospores, 5.92×10(6) zoospores/ml after six days of fermentation at 25±2°C and 150rpm shaking. This culture tested against A. aegypti 1st stage larvae caused different mortality rates at 24, 48 and 72h posttreatment. The LC(50) obtained was 43.9, 41.1 and 42.9μl of total culture/ml, at 24, 48 and 72h posttreatment respectively, while the culture grown in medium with soybean meal showed 3-5 times higher LC(50) values. Finally, the total culture including mycelium, zoospores and presporangia formulated with 2.5% pectin showed significantly higher mortality rates, around 100% more than the unformulated culture, whose values were from 40 to 1% at 3, 6, 9, and 12d posttreatment in the bioassays carried out in the laboratory to determine residual activity.

Biochemical activities of entomophagous fungi

This review is directed toward the study of the physiology and biochemistry of parasitic fungi on insects and stresses the usefulness and utility of these organisms from the standpoint of applied research and biotechnology. The review covers the principal contributions made by investigators toward elucidation of the infective mechanisms of the entomogenous fungi, and the various biochemical attributes of these organisms. The interplay of the various enzymes and associated biochemical substances which are involved in the infective process is discussed as well as the important studies of the peculiar physiology frequently associated with these microorganisms.

The extracellular acid phosphatase of the mosquito-parasitizing fungus Lagenidium giganteum

The mosquito-parasitizing fungus Lagenidium giganteum secreted a soluble acid phosphatase and beta-D-glucosidase into the growth medium. The acid phosphatase was isolated and purified to single component, and some of its physicochemical properties were determined. The enzyme exhibited a pH optimum of 5.6 in phthalate buffer with p-nitrophenyl phosphate and was temperature-inactivated at 55 degrees C. Enzyme activity seems to be limited to phenyl-phosphate substrates. A molecular weight of 42,800 was found and the amino acid content was also determined. A Km for p-nitrophenyl phosphate of 1.6 x 10(-7) M was found. The possible involvement of the enzyme in the infective process was discussed.

Functional relationships between free amino acids in the hemolymph of fourth instar larvae of the mosquito Aedes aegypti (Diptera, Culicidae) as a basis for toxicological studies

Characteristic correlations reflecting particular metabolic interactions between free amino acids have been pointed out and used as a sensitive test for the detection of biochemical intoxication symptoms in fourth instar larvae of the mosquito Aedes aegypti exposed for 0-8, 12, 24, and 36 hr to various doses of Bacillus thuringiensis delta-endotoxin ranging from 0.01 to 1 mg liter-1. In a first pool, serine was negatively correlated with glycine while cystine and alanine were positively correlated with serine and proline. A second pool was characterized by strong positive correlations between leucine, valine, isoleucine, and threonine. These two groups were linked by a negative (hyperbolic) correlation between cystine and threonine. Preliminary data then gave evidence that the slopes of the linear regressions of Gly on Ser and Ala on Ser increased and those of Ile on Thr and Val on Leu decreased with increasing doses of B. thuringiensis israelensis delta-endotoxin. Functional relationships thus exhibited a high semiological value in metabolic stress studies.

Defense reactions by larvae of Aedes aegypti during infection by the aquatic fungus Lagenidium giganteum (Oomycete)

The adherence of zoospores of Lagenidium giganteum to the cuticle of mosquito larvae is the initial step in the infection process. Subsequently, a germ tube penetrates the integument, inducing a rapid melanization of the injured cuticle and epidermis. After entering the hemocoel the developing hyphae are occasionally encapsulated locally. This process is slow (6 to 12 h postincubation) and most frequently cell-free, although it can be mediated by circulating hemocytes. Sporadic hemocyte mediation of the humoral encapsulation process in larval stages of Culicidae adds a previously unreported dimension to this unusual type of defense reaction. The defense reactions of larvae of Aedes aegypti were ineffective against observed infection by Lagenidium giganteum.