Prospection and fungal virulence associated with Mahanarva spectabilis (Distant) (Hemiptera: Cercopidae) in an Amazon silvopastoral system
Keywords:
entomopathogenic fungus, pasture spittlebug, mortality, biological control.Abstract
Brachiaria spp. are susceptible to attacks by the spittlebug Mahanarva spectabilis (Distant) (Hemiptera: Cercopidae). Biological control of this pest insect is rarely used, in part because of a lack of diversity in commercialized pathogens effective against such pests. However, fungal infection of M. spectabilis has been noted in some tropical silvopastoral systems, which rarely have problems with pest insects. This study surveyed the fungi found in association with M. spectabilis in a silvopastoral system in Brazil and made a preliminary assessment of their virulence. Infected spittlebugs were collected in a silvopastoral system in Brazil, from which 5 types of fungi were isolated and identified by morphological analysis. Conidia of each wild fungus and a commercial strain of Metarhizum anisopliae (Metschn.) Sorokin (Clavicipitaceae) were diluted in a 1% NaCl solution at a concentration of 1×104 conidia per mL. In the laboratory, eggs and nymphs of M. spectabilis were placed in acrylic boxes within a climate-controlled chamber at 25 °C. In a non-acclimatized greenhouse, eggs and nymphs were placed on potted Brachiaria decumbens Stapf (Poaceae). Solutions of the 6 fungi and a control (pure saline) were applied to M. spectabilis in both conditions (acrylic box in laboratory and potted Brachiaria in a greenhouse). The most virulent fungi (UFMG 11443 and 11444) caused more than 90% of unviable eggs and mortality of nymphs. Other fungi tested (UFMG 11440, 11441, and 11442) were equally or more effective than the commercial M. anisopliae, causing over 50% unviable eggs or nymph mortality. All isolated fungi showed potential for use as biological control agents against M. spectabilis.
Key Words: entomopathogenic fungus; pasture spittlebug; mortality; biological control
Resumo
Pastagens com Brachiaria spp. geralmente sofrem ataques severos pela cigarrinha Mahanarva spectabilis (Distant) (Hemiptera: Cercopidae). O controle
biológico desse inseto tem sido pouco utilizado, principalmente porque há poucos entomopatógenos comercialmente disponíveis. Entretanto, M. spectabilis infectada por fungos tem sido encontrada em alguns sistemas silvipastoris (SSP) tropicais, os quais raramente apresentam problemas com insetos-praga. Este estudo é uma prospecção de fungos encontrados em associação com M. spectabilis e uma análise preliminar de sua virulência. Cigarrinhas infectadas foram coletadas em um SSP no Brasil, das quais cinco tipos de fungos foram isolados e identificados por análises morfológica e molecular. Conídios de cada um dos fungos selvagens e de uma linhagem comercial de Metarhizum anisopliae (Metschn.) Sorokin (Clavicipitaceae) foram diluídos em solução de NaCl 1% a uma concentração de 104 conídios/mL. No laboratório, ovos e ninfas de M. spectabilis foram colocados em caixas de acrílico, no interior de uma câmara climática a 25ºC. Em uma casa-de-vegetação não-climatizada, ovos e ninfas foram depositados na base de plantas de Brachiaria decumbens Stapf (Poaceae) cultivadas em vasos. As seis soluções com fungos e um controle com solução salina pura foram aplicados sobre M. spectabilis em ambas condições. Os fungos mais virulentos foram codificados como UFMG 11443 e 11444, ambos causando
mais de 90% de inviabilidade dos ovos e mortalidade de ovos edas ninfas. Os demais fungos UFMG 11440, 11441 e 11442 foram igualmente ou mais
eficientes que a cepa comercial de M. anisopliae, com mais de 50% de ovos inviáveis ou mortalidade das ninfas. Todos os fungos selvagens isolados
mostraram potencial como agentes de controle biológico para uso contra M. spectabilis.
Palavras Chave: fungos entomopatogênicos; cigarrinha-das-pastagens; mortalidade; controle biológico
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