Eficácia de Cordyceps javanica sozinho ou em combinação com inseticidas químicos no controle de Bemisia tabaci MEAM1 e persistência em folhas de soja
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2019-08-30
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Universidade Federal de Goiás
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The whitefly Bemisia tabaci causes direct damage by sap suction and toxin injection, and indirect damage by fumagine and transmission of more than 300 species of viruses to plants. Cordyceps javanica has been found to cause natural epizootic diseases and is an alternative for the management of resistant whitefly populations. The objectives of this study were: (1) to determine the susceptibility of all B. tabaci nymphal stages to three C. javanica isolates by observing the effect of different climatic conditions on screened virulence; (2) evaluate the efficiency and persistence of C. javanica and the association of the fungus with chemical insecticides in the control of whitefly. No differences in susceptibility were observed between C. javanica isolates for 1st, 2nd and 3rd instar nymphs; mortalities ranged from 63.7-87.8% to 5 × 107 conidia mL-1. The 4th instar was less susceptible to isolates (≤15.5% mortality). However, adults who emerged from 4th instar nymphs were highly susceptible (adult mortality and ringworm ranged from 75.6 to 93.2%). In our study, temperature was more detrimental to Cordyceps virulence in Bemisia nymphs than relative humidity. The BRM 27666 isolate was selected for field efficiency tests because of its ability to grow extensively on the leaf surface and produce a high amount of conidia under wet conditions. In all experiments, a pressurized CO2 spray with dropleg bars was used (they spray the leaves upwards). The percentage of sporulated nymphs ranged from 47 - 59.1% to 25.4 - 41.3% for unformulated (3 applications of 1 × 1012 conidia ha-1) and formulated (1 application of 2 × 1011 conidia ha-1), respectively, after 28 days. Nymph mortality increased after joint action with parasitoids (67.9 - 81.6%) in fungal treatments. The persistence of C. javanica conidia was significantly reduced at 48 h. After combining the fungus with the chemical insecticides, the percentage of mycosis ranged from 20.2 to 35% after 26 days, except the fungus + pyriproxyfen (≤9.4%). In general, after the joint action of natural enemies, the mortality of nymphs in fungal treatments ranged from 90.3 to 98.1%. The high potential of C. javanica in whitefly control has been demonstrated in our field and screenhouse experiments. Based on this, C. javanica BRM 27666 was selected as a promising isolate in whitefly control. A C. javanica conidia-based mycoinsecticide has been developed and is under registration in Brazil for the control of whitefly in several crops.
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BOAVENTURA , H. A. Eficácia de Cordyceps javanica sozinho ou em combinação com inseticidas químicos no controle de Bemisia tabaci MEAM1 e persistência em folhas de soja. 2019. 94 f. Dissertação (Mestrado em Agronomia) - Universidade Federal de Goiás, Goiânia, 2019.