Beauveria spp.: agentes de biocontrole de Anticarsia gemmatalis (HÜBNER, 1818) e Chrysodeixis includens (WALKER, 1858)

Abstract

The caterpillars Anticarsia gemmatalis and Chrysodeixis includens are pests in several crops, including soybeans, causing losses of up to 100%. In this way, integrated management with agrochemicals and fungi can guarantee a better response in the field, in addition to reducing the use of agrochemicals and, consequently, the impacts caused by them. However, there is a lack of studies regarding the compatibility of agrochemicals with entomopathogenic fungi when used together in integrated pest management. Given the above, the present study aims to evaluate the specificity and bioinsecticide capacity of B. bassiana (URM2915) and B. brongniartii (URM6504) under the effect of agrochemicals on A. gemmatalis and C. includens, in vitro. For the analysis of the effect of the three agrochemicals on the vegetative growth and sporulation of Beauveria spp. Sabouraud-dextrose agar medium containing agrochemicals and antibiotics was used. An assay with three replications was performed. A reduction in the vegetative growth of B. brongniartii was observed in the presence of fipronil (1.30%), malathion (1.30%) and diazinon (0.80%), but it did not significantly compromise conidiogenesis and conidial viability. B. bassiana showed growth inhibition in the presence of malathion (0.60%), fipronil (1.20%) and diazinon (0.20%). However, only malathion guaranteed a reduction in conidiogenesis (3.50%) and conidial viability (53.13%), proving the incompatibility of this species with this agrochemical. For testing the specificity and virulence of B. bassiana and B. brongniartii in the presence and absence of agrochemicals with A. gemmatalis and C. includens (stages L2-L3), a concentration of 1.0 x 108 conidia/mL-1 was used. An experiment was carried out with three repetitions, totaling 60 caterpillars for each treatment. In the absence of agrochemicals, B. bassiana and B. brongniartii were pathogenic to the caterpillars A. gemmatalis and C. includens with a total mortality rate of 99.9% for A. gemmatalis and for C. includens of 80.3% and 90 .6%, respectively, with a TL50 between 6 and 7 days, respectively. In the presence of agrochemicals, B. bassiana showed a total lethality rate for A. gemmatalis of 99.9%. Confirmed mortality was only evidenced for the group containing 20.9% fipronil and a TL50 of 12.1 days. For C. includens, the total lethality was 90.3%, 80.6% and 70.0%, confirmed mortality was 75.1%, 70.3% and 30.3% and TL50 was 6.9, 12 and 7.0 days for the groups containing fipronil, malathion and diazinon, respectively. For B. brongniartii, the total lethality rate for A. gemmatalis was 99.9%, confirmed mortality was 95.9%, 85.0% and 97.0% and TL50 of 7.0 days for the fipronil-containing groups , malathion and diazinon, respectively. For C. includens the total lethality was 99.3%, 95.6% and 70.4%, confirmed mortality was 95.1%, 92.3% and 70.3% and TL50 was 6.7, 5, 0 and 7.0 days for groups containing fipronil, malathion and diazinon, respectively. Proteases are part of the virulence of Beauveria spp. Proteolytic activity was tested and B. brongniartii and B. bassiana showed positive proteolytic activity in milk-agar minimal medium containing the three agrochemicals in its composition. The results show the specificity of B. bassiana and B. brongniartii with A. gemmatalis and C. includens and the possibility of using these fungi in integrated pest management in the presence of fipronil, diazinon and malathion.