-The fungus Metarhizium anisopliae var. acridum, strain CG 423, was tested under field conditions against the gregarious grasshopper Rhammatocerus schistocercoides (Rehn) (Orthoptera: Acrididae). Conidia formulated in a racemic mixture of soybean oil and kerosene were sprayed under field conditions using an ultralow-volume hand-held atomizer Ulva Plus adjusted to deliver 2.9 L/ha. Bands composed of 2 nd instar nymphs were treated with either 5.0x10 12 or 1.0x10 13 viable conidia/ha. The number of insects in each band was estimated at day one following spraying and by the end of the field trial (15 to 16 days posttreatment). Reductions in population size reached, in average, 65.8% and 80.4% for bands treated with the higher and lower dosage, respectively. For both dosages, total mortality rates of insects collected at two days post-application, and kept in cages for 14 days under lab conditions, showed no significant differences as compared to that obtained with insects collected immediately after spraying. Healthy insects were fed to native grasses sprayed on the field with 1.0x10 13 viable conidia/ha. Mortality levels of the nymphs fed on grasses collected two and four days post-application were not affected when compared to nymphs fed on grasses collected immediately following application.Index terms: biological control, microbial pesticide, entomogenous fungus, grasshopper, oil formulation. Efeito de duas dosagens de Metarhizium anisopliae var. acridum contra Rhammatocerus schistocercoides RehnResumo -O fungo Metarhizium anisopliae var. acridum, isolado CG 423, foi avaliado em condições de campo como agente de controle biológico do gafanhoto gregário Rhammatocerus schistocercoides (Rehn) (Orthoptera: Acrididae). Conídios formulados em uma mistura racêmica de óleo de soja e querosene foram pulverizados no campo com a utilização de um atomizador rotativo manual Ulva Plus, calibrado para aplicação de 2,9 L/ha. Bandos com ninfas de 2 o estádio foram tratados com o equivalente a 5,0x10 12 ou 1,0x10 13 conídios viáveis/ha. O número de insetos em cada bando foi estimado no 1 o dia após a aplicação e ao final do experimento (15 a 16 dias após tratamento). Reduções populacionais médias de 65,8% e 80,4% foram observadas nos bandos tratados com a maior e menor dosagem, respectivamente. Para as dosagens avaliadas, a mortalidade total de insetos coletados aos dois dias após a aplicação e mantidos em gaiolas durante 14 dias, no laboratório, não apresentou diferença significativa daquela obtida para insetos coletados imediatamente após a pulverização. Insetos sadios foram alimentados com gramíneas nativas pulverizadas no campo com 1,0x10 13 conídios viáveis/ha. As taxas de mortalidade observadas nas ninfas alimentadas com capim coletado aos dois e quatro dias após a pulverização não foram afetadas quando comparadas com ninfas alimentadas com capim coletado imediatamente após a pulverização.Termos para indexação: controle biológico, pesticida microbiano, fungo entomopatogênico, gafanhoto, formulação oleosa.
Rhammatocerus schistocercoides is a serious pest of several crops and native pastures in Mato Grosso State, Brazil (8). The reduction or replacement of chemical insecticides by mycoinsecticides to control this insect is under investigation (5,6). Metarhizium anisopliae var. acridum (= M. flavoviride; 1) is very infective to R. schistocercoides (6, 10), and Beauveria bassiana to Melanoplus sanguinipes (3). During previous research at Embrapa Genetic Resources and Biotechnology it was noted that M. anisopliae var. acridum sporulated profusely within dried cadavers of R. schistocercoides (10). We report here on a laboratory experiment devised to compare internal and external sporulation of M. anisopliae var. acridum and B. bassiana on R. schistocercoides cadavers kept in humid and dry conditions.Insects. Insects used in this study were collected in the field (Silvânia, GO, Brazil) and maintained in 60 cm x 60 cm x 80 cm cages in the laboratory at 25°C and 12h photophase. They were fed sugar cane leaves, oats and wheat germ during 15 days before testing, without regard to gender.Fungal isolates and culture. Isolates CG 423 (M. anisopliae var. acridum) and CG 425 (B. bassiana) were provided by Embrapa Genetic Resources and Biotechnology, Collection of Entomopathogenic Fungi, Brasília, DF. The isolate CG 423 was first found infecting the pallid grasshopper Schistocerca pallens in Rio Grande do Norte State (7), and the isolate CG 425 infecting R. schistocercoides in Mato Grosso (5). The fungi were cultured in SDAY (1% neopeptone, 2% dextrose, 1.5% agar, and 1% yeast extract, completed to 1000 ml distilled water, ph calibrated to 6.2) after retrieval from storage in liquid nitrogen. For the bioassay, the fungi were culture in rice as described by Magalhães and Frazão (4).Bioassay. Groups of 30 R. schistocercoides adults were tested with either M. anisopliae var. acridum (CG 423) or B. bassiana (CG 425). To perform the bioassays, insects were individually inoculated with 3 µl of a conidial suspension (5000 conidia/insect) applied on the right pleural region with a micropipette. Insects were maintained in 17 cm x 21 cm x 25 cm cages (10/cage) at 25°C and 12 photophase and were fed sugar cane leaves, oats and wheat germ. Dead adults were removed daily. One femur was dissected from each insect and a drop of hemolymph was extracted and observed under the microscope for presence of blastospores. SPORULATION OF METARHIZIUM ANISOPLIAE ABSTRACTThe sporulation of the fungi Metarhizium anisopliae var. acridum and Beauveria bassiana in cadavers of the grasshopper Rhammatocerus schistocercoides was studied in dry and humid environments. Both fungi were equally virulent against R. schistocercoides. However, internally, M. anisopliae produced more conidia than B. bassiana at 53% and 75% relative humidity. Externally, there was no sporulation at 53% and 75% RH, and M. anisopliae produced more conidia than B. bassiana at 100% RH.
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