Sérgio B. Alves

Efficacy of Beauveria bassiana (Balsamo) Vuillemin isolates for control of stored-grain pests

Abstract: Seventy two isolates of Beauveria bassiana or Metarhizium anisopliae were screened for control of Sitophilus oryzae, S. zeamais (Col., Curculionidae), and Rhyzopertha dominica (Col., Bostrychidae). Beauveria bassiana isolates produced highest mortalities against all three hosts. Ten isolates (all B. bassiana) were selected for further experimentation in the second phase of selection process. Bioassays were conducted by inoculating 50 adult insects of each species, maintained at 26 ± 0.5°C, 70 ± 10% RH, 12 h photophase, for 10 days. The cumulative mortalities after 10 days exposure and lethal time for 50% of the population (LT50) were calculated and compared. S. oryzae and S. zeamais were less susceptible to B. bassiana isolates than R. dominica, which was completely killed by several isolates. Isolate 476 was the most virulent to S. oryzae, and isolate 604 was the most virulent to S. zeamais. Isolate 604 was best overall, but isolates 476 and 643 should also be considered as control agents for stored‐grain pests. A combination of isolates may be advantageous if mixed pest infestations occur.

Selection of Beauveria spp. isolates for control of the termite Heterotermes tenuis (Hagen, 1858)

Heterotermes tenuis is an important pest in sugarcane in Brazil, where alternative control methods are necessary due to cancellations of chemical pesticide registrations. Experiments were conducted to determine the pathogenicity, virulence and mass production yields of Beauveria spp. isolates as potential microbial control candidates for H. tenuis. Results demonstrated that the average virulence of the B. brongniartii isolates was comparable to that of B. bassiana isolates. Isolates obtained from soil were as effective as microbial control agents as those obtained directly from insect hosts. However, no B. brongniartii or soil isolate was among those best isolates selected, which included two of the three termite isolates tested. LT50 for 15 selected isolates varied between 2.91 and 4.91 days, and termite mortalities caused by these isolates were between 78.7 and 98.7% after 8 days. Significant differences were observed among these selected isolates. Conidial productions on artificial media (PDA and cooked rice) correlated well for the selected isolates. However, spore production on the termite cadavers did not correlate with production on these artificial media. The most productive isolate on cadavers (634) was 21% more productive than the second best isolate (447), and was also a good conidial producer on artificial media with 25% lower conidial yield than the best producer (756). The least productive isolate on cadavers or artificial medium (760) produced only 3% of production by isolate 756 on cooked rice and 45% of production on termite cadavers. Because high conidial production on cadavers is a desirable characteristic to facilitate transmission of the disease in the nest, isolate 634 was selected for further development as microbial agent for H. tenuis control.

Potential of some Metarhizium anisopliae isolates for control of Culex quinquefasciatus (Dipt., Culicidae)

Abstract: The potential of some isolates of Metarhizium anisopliae and Beauveria bassiana for use in the integrated management of Culex quinquefasciatus was evaluated. Metarhizium anisopliae isolate 1037 was selected in initial bioassays with a 50% lethal concentration (LC50) of 1.97 × 104 conidia/ml. This fungus caused higher mosquito larva mortality when applied as a conidial suspension to the surface of the water than as dry conidia, with a time to 50% lethal (LT50) of 1 day compared with 3.6 days for the dry conidial application. However, results with UV‐ and heat‐inactivated conidia did not confirm a possible role of fungal toxins in causing mortality when ingested by C. quinquefasciatus larvae. Metarhizium anisopliae did not remain active for as long as the bacterium Bacillus sphaericus isolate 2362. At 24 h after application, the fungus‐induced mortality on mosquito larvae was significantly lower than the mortality caused by the bacterium. By the second day, almost no activity by the fungus was observed. Results suggest that M. anisopliae isolate 1037 has potential for use in mosquito control programmes.

Seleção de isolados de Beauveria bassiana (Bals.) Vuill. e Metarhizium anisopliae (Metsch.) Sorok. contra o cascudinho Alphitobius diaperinus (Panzer) (Coleoptera: Tenebrionidae)

This study was carried out to evaluate entomopathogenic fungi isolates as microbial control agents of the lesser mealworm, Alphitobius diaperinus (Panzer). Larvae and adults were inoculated with conidial suspension of 99 isolates of Beauveria bassiana (Bals.) Vuill. and Metarhizium anisopliae (Metsch.) Sorok. (105 to 109 conidia/ml). Vegetative growth on culture media and sporulation on culture media, cooked rice and lesser mealworm cadavers were also evaluated. Isolates of B. bassiana were more effective than the M. anisopliae isolates and larvae were more susceptible than adults. The isolates UNIOESTE 04 and UNIOESTE 02 were originally obtained from adults of the lesser mealworm and were the most efficient isolates. In addition, UNIOESTE 04 showed high level of sporulation on different culture media and is considered a potential useful tool to lesser mealworm control.

Efeito de imidacloprid e fipronil sobre Beauveria bassiana (Bals.) Vuill. e Metarhizium anisopliae (Metsch.) Sorok. e no comportamento de limpeza de Heterotermes tenuis (Hagen)

The fungitoxic effects of imidacloprid and fipronil on the entomopathogenic fungi Beauveria bassiana (Bals.) Vuill. and Metarhizium anisopliae (Metsch.) Sorok. were evaluated. The colony radial growth and conidial production were measured in the presence of the insecticides added to the culture medium. Imidacloprid was less toxic to the fungi than fipronil, and M. anisopliae was less affected by either insecticide than B. bassiana. The changes in the grooming behavior of Heterotermes tenuis (Hagen) under the action of the insecticides was also evaluated. Using scanning electron microscopy, conidia of B. bassiana and M. anisopliae were observed on the surface of the insect tegument at different times after inoculation. Imidacloprid at sublethal concentrations affected the grooming behavior of H. tenuis, while fipronil did not alter this behavior.

Potential of Bacillus thuringiensis israelensis Berliner for controlling Aedes aegypti

The importance of the entomopathogenic bacterium Bacillus thuringiensis israelensis in the control of Aedes aegypti is presented. The use and potential of B. thuringiensis israelensis against the mosquito vector of dengue fever is described. Other aspects such as insects resistance development against chemicals and advantages and constraints of using microbial control are discussed. Emphasis is given to the importance of the use of this bacterium in Brazil, which could contribute significantly to solving the mosquito problem without affecting the environment, humans and others invertebrate organisms in critical regions.

Epizootia de Aschersonia cf. goldiana em Bemisia tabaci (Homoptera: Aleyrodidae) biótipo B no estado de São Paulo

The first observations on the presence of Bemisia tabaci biotype B (=B. argentifolii) in Brazil were made in the beginning of the 1990s in the State of Sao Paulo. from then on, that whitefly has spread out to other States. In the summer of 1997/98, B. tabaci biotype B reached Guaira-Miguelopolis, an area of the State of Sao Paulo not yet infested, with high populations of the insect, mainly in soybean, cotton and vegetable crops. In the the first week of February 1998, during a survey in an abandoned field of soybean, an epizootic of Aschersonia cf. goldiana was verified on that whitefly in the whole area, with total infection of nymphs in the lower surface of the leaves. At the same date, in two other soybean fields of the region, the incidence of this entomopathogen was low, but it increased in the following two weeks, reaching high control levels of the insect, which was similar to the previously observed field. This occurrence indicates A. cf. goldiana as a potential agent for biological control of B. tabaci biotype B.

Differential susceptibility of adults and nymphs of Blattella germanica (L.) (Blattodea: Blattellidae) to infection by Metarhizium anisopliae and assessment of delivery strategies

Microbial insecticides for cockroach control, such as those containing entomopathogenic fungi, may be an alternative to reduce contamination by chemicals in housing and food storage environments. Virulence of isolate ESALQ1037 belonging to the Metarhizium anisopliae complex against nymphs and adults of Blattella germanica (L.), and its infectivity following exposure of insects to a contaminated surface or to M. anisopliae-bait were determined under laboratory conditions. Estimated LD50 15 d following topical inoculation was 2.69 x 10(5) conidia per adult, whereas for nymphs the maximum mortality was lower than 50%. Baits amended with M. anisopliae conidia had no repellent effect on targets; adult mortality was inferior to 25%, and nymphs were not susceptible. All conidia found in the digestive tract of M. anisopliae-bait fed cockroaches were unviable, and bait-treated insects that succumbed to fungal infection showed a typical mycelial growth on mouthparts and front legs, but not on the hind body parts. As opposed to baits, the use of a M. anisopliae powdery formulation for surface treatment was effective in attaining high mortality rates of B. germanica. Both nymphs and adults were infected when this delivery strategy was used, and mycelia growth occurred all over the body surface. Our results suggest that the development of powders or similar formulations of M. anisopliae to control B. germanica may provide faster and better results than some of the strategies based on baits currently available.

Ocorrência natural de Beauveria bassiana (Bals.) Vuilleman (Moniliales: Moniliaceae) sobre o cascudinho, Alphitobius diaperinus (Panzer) (Coleoptera: Tenebrionidae), em aviário comercial de Cascavel, PR

One of the main problems in poultry houses in Brazil is the lesser mealworm, Alphitobius diaperinus Panzer. This insect inhabits the litter, manure and soil of poultry houses, feeding on bird manure, cadavers and spilt feed. The lesser mealworm serves as a reservoir of many animal pathogens. Chickens also feed readily on the beetles in infested litter and this sometimes causes nutritional problems and affects weight gain. Current control measures are generally unsatisfactory and microbial control may be a promising strategy to control A. diaperinus. Natural occurrence of entomopathogens is very important for the natural control of insect pests and this paper records the occurrence of Beauveria bassiana (Bals.) Vuill. on the lesser mealworm in commercial poultry houses, in Brazil. The evaluation was carried out weekly for six months (September/2002 to February/2003). The soil around the poultry house was collected and transferred to Zoology Laboratory from Unioeste, at Cascavel, PR. Infected larvae and adults were always present, but infected pupae were registered twice. Larvae were more susceptible than pupae and adults (incidence ranging from 49% to 100%, mean 74%, 33% to 50%, mean 6.9%; 0.9% to 100%, mean 40.7%, respectively). The pathogenicity of the fungus was confirmed under laboratory conditions following procedures outlined in Kochs postulates.

Culture media selection for mass production of Isaria fumosorosea and Isaria farinosa

This work investigated the production of the fungi Isaria fumosorosea and Isaria farinosa in biphasic fermentation using agro-industrial products and residues. Combinations of natural liquid substrates, alternative to the complete medium and potato dextrose medium, were evaluated. The best liquid media were sugarcane molasses + rice broth, rice broth + yeast and sugarcane molasses + yeast + rice broth, which resulted in the highest viable propagule concentration. The molasses + rice broth medium was selected for the next phase of the study in which the production of both fungal isolates was evaluated in solid grain substrates. In solid-state fermentation, the best conidia production was achieved with the soybean meal and broken corn for I. farinosa, and whole rice and broken rice for I. fumosorosea. Results demonstrated that the two fungal species could be rapidly produced with higher yield of conidia on agro-industrial resources by using biphasic fermentation techniques.