Controle biológico microbiano: Beauveria bassiana e Trichoderma harzianum em Atta sexdens rubropilosa, e Metarhizium rileyi em Spodoptera litura
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Data
2022-06-08
Autores
Stefanelli, Luis Eduardo Pontes [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
As formigas cortadeiras (gêneros Atta, Acromyrmex e Amoimyrmex) e a lagarta do tabaco (Spodoptera litura), são importantes pragas agrícolas no Brasil e no Japão. O uso de inseticidas sintéticos é o principal método de controle destes insetos pragas. No entanto, com o crescente relato de surgimento de insetos resistentes e a preocupação com o risco de contaminação ambiental impostos por esses produtos químicos, métodos de controle alternativos veem sendo estudados. Dentre esses novos métodos, o controle biológico através da utilização fungos entomopatogênicos pode vir a ser uma alternativa viável ao uso de inseticidas químicos. Diante disso, o objetivo deste estudo foi avaliar a patogenicidade dos fungos B. bassiana e Trichoderma harzianum para formigas cortadeiras e do fungo M. rileyi para S. litura. Além disso, foi investigada a influência do número de indivíduos contaminados dentro de um grupo no controle da disseminação de fungos entre as operárias da formiga cortadeira. O fungo T. harzianum apresentou alta patogenicidade para larvas e pupas de A. sexdens rubropilosa, causando uma mortalidade mais rápida e menores taxas de sobrevivência. Por outro lado, o fungo B. bassiana foi responsável por causar mortalidade mais rápida de operárias e menores taxas de sobrevivência. Adicionalmente, foi possível observar que o aumento de indivíduos contaminados com B. bassiana ou T. harzianum no grupo diminui sua taxa de sobrevivência. Além disso, iscas contendo 10 e 20% (p/p) dos fungos B. bassiana e T. harzianum não foram eficientes no controle de colônias de A. sexdens. Por outro lado, a pulverização de suspensões de 20% (p/p) de B. bassiana e 10% e 20% (p/p) de T. harzianum foi eficiente e resultou em 100% de mortalidade das colônias aos 11, 9 e 7 dias após a aplicação, respectivamente. Isolados de M. rileyi na concentração de 5,2 × 108 conídios ml − 1 apresentaram mortalidade de 65,5–82,5% em 9 dias em larvas de S. litura, por contato e ingestão. Os resultados apoiam a hipótese de que fungos entomopatogênicos são eficientes no controle de formigas cortadeiras quando operárias contaminadas são alocadas em grupos de operárias saudáveis. Os fungos B. bassiana e T. harzianum são promissores como agentes de controle de colônias de formigas cortadeiras, quando pulverizados sobre o jardim de fungos, embora ainda existam alguns desafios quanto ao seu uso relacionados ao desenvolvimento de tecnologias para a aplicação do patógeno. Adicionalmente, pode-se inferir deste estudo que o isolado de M. rileyi possui grande potencial para uso no controle de S. litura na dose recomendada de 5,2 x 108 conídios ml − 1 causando mortalidade em torno de 60-80%.
Leaf-cutting ants (genera Atta, Acromyrmex and Amoimyrmex) and tobacco caterpillar (Spodoptera litura) are important agricultural pests in Brazil and Japan. The use of synthetic insecticides is the main method of controlling these pests. However, with the growing report of the emergence of resistant insects and the concern about the risk of environmental contamination posed by these chemicals, alternative control methods have been studied. Among these new methods, biological control through the use of entomopathogenic fungi may become a viable alternative to the use of chemical insecticides. Therefore, the aim of this study was to evaluate the pathogenicity of the fungi Beauveria bassiana and Trichoderma harzianum for leaf-cutting ants and of the fungus Metharizium rileyi for tobacco caterpillar. Furthermore, we investigated whether the number of infected individuals within a group influences the control of fungal dissemination among leaf-cutting ant workers. We found that the fungus T. harzianum showed high pathogenicity against leaf cutting ant larvae and pupae, leading to faster mortality and lower survival rates. On the other hand, the fungus B. bassiana was responsible for causing faster mortality of workers and lower survival rates. Additionally, it was possible to observe that the increase of infected individuals with B. bassiana or T. harzianum in the group decreases its survival rate. Furthermore, baits containing 10 and 20% (w/w) of the fungi B. bassiana and T. harzianum were not efficient in controlling A. sexdens colonies. On the other hand, spraying suspensions of 20% (w/w) of B. bassiana and 10% and 20% (w/w) of T. harzianum was efficient and resulted in 100% mortality of the colonies at 11, 9 and 7 days after application, respectively. Isolates of M. rileyi at a concentration of 5.2 × 108 conidia ml − 1 showed mortality of 65.5–82.5% in 9 days in S. litura larvae, by contact and ingestion. The results support the hypothesis that entomopathogenic fungi are efficient in controlling leaf-cutting ants when contaminated workers are allocated to groups of healthy workers. The fungi B. bassiana and T. harzianum are promising as control agents for leaf-cutting ant colonies, when sprayed on the fungus garden, although there are still some challenges regarding their use related to the development of technologies for the application of the pathogen. Additionally, it can be inferred from this study that the M. rileyi isolate has great potential for use in the control of S. litura at the recommended dose of 5.2 x 108 conidia ml − 1 causing mortality around 60-80%.
Leaf-cutting ants (genera Atta, Acromyrmex and Amoimyrmex) and tobacco caterpillar (Spodoptera litura) are important agricultural pests in Brazil and Japan. The use of synthetic insecticides is the main method of controlling these pests. However, with the growing report of the emergence of resistant insects and the concern about the risk of environmental contamination posed by these chemicals, alternative control methods have been studied. Among these new methods, biological control through the use of entomopathogenic fungi may become a viable alternative to the use of chemical insecticides. Therefore, the aim of this study was to evaluate the pathogenicity of the fungi Beauveria bassiana and Trichoderma harzianum for leaf-cutting ants and of the fungus Metharizium rileyi for tobacco caterpillar. Furthermore, we investigated whether the number of infected individuals within a group influences the control of fungal dissemination among leaf-cutting ant workers. We found that the fungus T. harzianum showed high pathogenicity against leaf cutting ant larvae and pupae, leading to faster mortality and lower survival rates. On the other hand, the fungus B. bassiana was responsible for causing faster mortality of workers and lower survival rates. Additionally, it was possible to observe that the increase of infected individuals with B. bassiana or T. harzianum in the group decreases its survival rate. Furthermore, baits containing 10 and 20% (w/w) of the fungi B. bassiana and T. harzianum were not efficient in controlling A. sexdens colonies. On the other hand, spraying suspensions of 20% (w/w) of B. bassiana and 10% and 20% (w/w) of T. harzianum was efficient and resulted in 100% mortality of the colonies at 11, 9 and 7 days after application, respectively. Isolates of M. rileyi at a concentration of 5.2 × 108 conidia ml − 1 showed mortality of 65.5–82.5% in 9 days in S. litura larvae, by contact and ingestion. The results support the hypothesis that entomopathogenic fungi are efficient in controlling leaf-cutting ants when contaminated workers are allocated to groups of healthy workers. The fungi B. bassiana and T. harzianum are promising as control agents for leaf-cutting ant colonies, when sprayed on the fungus garden, although there are still some challenges regarding their use related to the development of technologies for the application of the pathogen. Additionally, it can be inferred from this study that the M. rileyi isolate has great potential for use in the control of S. litura at the recommended dose of 5.2 x 108 conidia ml − 1 causing mortality around 60-80%.
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Palavras-chave
Controle biológico, Fungos entomopatogênicos, Insetos sociais, Formigas cortadeiras, Lagarta do tabaco, Biological control, Entomopathogenic fungi, Social insects, Leaf-cutting ants, Tobacco caterpillar