Sérgio Batista Alves

Beauveria bassiana yeast phase on agar medium and its pathogenicity against Diatraea saccharalis (Lepidoptera: Crambidae) and Tetranychus urticae (Acari: Tetranychidae).

Beauveria bassiana colonizes insect hosts initially through a yeast phase, which is common in some artificial liquid cultures, but not reported on artificial solid media. We describe a yeast-like phase for B. bassiana isolate 447 (ATCC 20872) on MacConkey agar and its virulence toward Diatraea saccharalis and Tetranychus urticae. The yeast-like cells of B. bassiana developed by budding from germinating conidia after 24-h incubation. Cells were typically 5-10 microm and fungal colonies were initially circular and mucoid, but later were covered with mycelia and conidia. Ability to produce yeast-like cells on MacConkey medium was relatively common among different B. bassiana isolates, but growth rate and timing of yeast-like cell production also varied. Metarhizium anisopliae and Paecilomyces spp. isolates did not grow as yeast-like cells on MacConkey medium. Yeast-like cells of B. bassiana 447 were more virulent against D. saccharalis than conidia when 10(7)cells/ml were used. At 10(8)cells/ml, the estimated mean survival time was 5.4 days for the yeast suspension and 7.7 days for the conidial suspension, perhaps due to faster germination. The LC(50) was also lower for yeast than conidial suspensions. Yeast-like cells and conidia had similar virulence against T. urticae; the average mortalities with yeast-like cells and conidia were, respectively, 42.8 and 45.0%, with 10(7)cells/ml, and 77.8 and 74.4%, with 10(8)cells/ml. The estimated mean survival times were 3.6 and 3.9 for yeast and conidial suspensions, respectively. The bioassay results demonstrate the yeast-like structures produced on MacConkey agar are effective as inoculum for B. bassiana applications against arthropod pests, and possibly superior to conidia against some species. Obtaining well-defined yeast phase cultures of entomopathogenic hyphomycetes may be an important step in studies of the biology and nutrition, pathogenesis, and the genetic manipulation of these fungi.

Use of Entomopathogenic Fungi in Latin America

Microbial control of insects, and the use of entomopathogenic fungi for this purpose, has been researched and used in small scale in Latin American countries since the early 1900’s. However, the large scale commercial production of these organisms is a recent phenomenon, the use of entomopathogens in pest control is still in its infancy in Latin America, just as in world. Although, commercial products can be found in most, if not all, countries in the region, the market share for these products is still minimum, with some notable exceptions for certain crops in some countries.Despite its small share in the pesticide market, microbial control in general and the use of entomopathogenic fungi has received much attention from some research institutions throughout Latin America. The factors that have stimulated the development of entomopathogenic fungi as pesticides in Latin America are as variable as the economies in the region, their crops and pest problems, and technological expertise. However, some common trends can be identified as described in this chapter.

External development of the entomopathogenic fungi Beauveria bassiana and Metarhizium anisopliae in the subterranean termite Heterotermes tenuis

The subterranean termite Heterotermes tenuis is one of the main pests of sugarcane and eucalyptus in Brazil, and the use of entomopathogenic fungi, alone or associated to chemicals, is an efficient and environmentally favorable method for its control. Studies related to the fungal development on these insects are important due to the effect of insect behavior on entomopathogens. The objective of this work was to describe the external development of Beauveria bassiana and Metarhizium anisopliae on H. tenuis using Scanning Electron Microscopy (SEM), determining the duration of the different phases of fungal infection. Two fixation techniques for preparing SEM samples were also evaluated. Worker specimens of H. tenuis were inoculated with a 1 x 109 conidia mL -1 suspension of the fungi and maintained at 25±1 o C and 70±10% relative humidity. Insects were collected from 0 to 144 hours after inoculation and prepared on SEM stubs for each of the two fixation techniques. The results obtained with the two techniques were compared and duration of the different phases of the infection process were estimated from SEM observations and compared for three fungal isolates. B. bassiana and M. anisopliae have similar development cycles on the termite, but some important differences exist. The penetration, colonization and conidiogenesis phases are relatively faster for M. anisopliae than for B. bassiana, which results in a faster rate of insect mortality. The fixation technique with OsO 4 vapor is suitable for preparation of insects to be used in SEM observation of the developmental stages

External events related to the infection process of Cornitermes cumulans (Kollar) (Isoptera: Termitidae) by the entomopathogenic fungi Beauveria bassiana and Metarhizium anisopliae

The objectives of this study were to observe the external development of Metarhizium anisopliae and Beauveria bassiana on workers and soldiers of Cornitermes cumulans (Kollar) and to establish comparisons between the insect fixation techniques known as critical point and desiccator. Termite workers and soldiers inoculated with B. bassiana (447) and M. anisopliae (1037) were utilized. After inoculation, the insects were left at 25±0.5°C. In order to make observations, samples from both castes were removed at 0, 6, 12, 24, 48, 72, 96, 120, 144, and 168h after inoculation. The external development of M. anisopliae and B. bassiana conidia on the termite C. cumulans showed that M. anisopliae and B. bassiana conidial germination occurred on several regions of the termites body mainly between 6h and 12h and penetration mainly between 12h and 24h after fungal application. Several penetration points were observed originating from the same germ tube. Colonization of the host by M. anisopliae occurred between 24h and 72h, and most insects died between 72h and 96h. Conidiogenesis began between 96h and 120h with the peak between 144h and 166h for M. anisopliae and between 120h and 144h for B. bassiana. Thus, only conidiogenesis for B. bassiana started earlier, probably because this fungus/isolate shows a higher insect colonization speed. This factor, in addition to multiple penetration points for the same germination tube, could explain the higher virulence of the isolates. The critical point fixation technique provided the best preservation of structures in both the pathogen and the insect.