Tropidacris collaris (Orthoptera: Romaleidae) is a large and voracious grasshopper, which, in recent years, has become a recurrent pest in increasingly extensive areas of Argentina's northern provinces. In the present work chitinase activity was measured in 59 entomopathogenic fungal isolates native to Argentina, and the relationship between enzymatic activity and fungal virulence was assessed. Isolate LPSC 1067 caused the highest mortality on T. collaris nymphs (97.7 ± 1.22%). Nine isolates caused no mortality, while the remaining 49 caused mortalities ranging from 6.6 ± 0.3% (LPSC 770) to 91.06 ± 1.51% (LPSC 906). Several isolates revealed chitinolytic capabilities on test plates, although the activities differed with respect to the ratio of the chitin-decay-halo and fungal-colony diameters. A principal component analysis indicated that isolate LPSC 1067, obtained from a long-horned grasshopper (Orthoptera: Tettigoniidae), would be a potential candidate for T. collaris biocontrol because the strain exhibited the highest mortality, a shorter median lethal time, and a high enzymatic activity and growth rate.
The South American locust Schistocerca cancellata (Serville) was the most serious agricultural pest in Argentina during the first half of the last century and remains as a threat when preventive control measures are relaxed in the outbreak area. In this study, we analysed in the laboratory, the effectiveness of 26 fungal strains (isolated from both insects and soil collected in Argentina) for S. cancellata control and determined the relationship between the chitinase, protease and lipase levels in these fungi and their insecticidal activities. We observed that Beauveria bassiana (isolate LPSC 1067) caused the highest mortality (9091.03%), the highest values of chitinolytic, proteolytic and lipolytic activity were 6.1390.05, 2.5690.11 and 2.3390.47, respectively, and the lowest median lethal time was 5.96 days. This is the first time that a wide variability in chitinase, protease and lipase activity as well as in virulence has been reported in a representative sample of different entomopathogenic fungal strains from Argentina.
Tolypocladium cylindrosporum is an entomopathogenic fungi that has been studied as a biological control agent against insects of several orders. The fungus has been isolated from the soil as well as from insects of the orders Coleoptera, Lepidoptera, Diptera and Hymenoptera. In this study, we analyzed the ability of a strain of T. cylindrosporum, isolated from soil samples taken in Tierra del Fuego, Argentina, to produce hydrolytic enzymes, and to study the relationship of those activities to the fungus pathogenicity against pest aphids. We have made the traditional and molecular characterization of this strain of T. cylindrosporum. The expression of hydrolase activity in the fungal strain was estimated at three incubation temperatures (4ºC, 12ºC and 24ºC), on different agar media supplemented with the following specific substrates: chitin azure, Tween ® 20, casein, and urea for chitinase, lipase, protease, and urease activity, respectively. The hydrolytic-enzyme activity was estimated qualitatively according to the presence of a halo of clarification through hydrolase action, besides was expressed semi-quantitatively as the ratio between the hydrolytic-halo and colony diameters. The pathogenicity of the fungus was tested on adults of the aphid Rhopalosiphum padi at three temperatures of incubation (4ºC, 12ºC and 24ºC). The suspension was adjusted to a concentration of 1x10 7
A screening was carried out on 69 fungal strains isolated from alkaline-calcareous, neutral and alkaline-sodic soils, as well as from their associated plant material, to determine their ability to grow at alkaline pH. A total of 32 fungi were selected for their ability to produce alkaline keratinase activity in submerged shaken cultures supplemented with soybean meal (SM) and tryptone and on cow hair (CH) under solid state fermentation conditions. Although several fungal strains produced keratinolytic activity on both SM and CH, they differed in the levels detected. Among them, Aspergillus niger, Cladosporium cladosporioides, Metarrhizium anisopliae, Neurospora tetrasperma and Westerdikella dispersa were the best producers, with levels higher than 1.2 U ml -1 . Different fungal species are here reported for the first time for their ability to produce keratinolytic activity at alkaline pH.
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