Patogenicidade de fungos filamentosos na sobrevivência e desenvolvimento de Spodoptera frugiperda resistentes e suscetíveis a proteínas cry

Abstract

The fall armyworm, Spodoptera frugiperda, is a major agricultural pest with significant economic impact, particularly in crops such as maize (Zea mays L.). Its control is primarily achieved through the use of chemical insecticides and genetically modified plants, such as those containing Bacillus thuringiensis (Bt) Cry proteins, which have insecticidal activity. However, the pest's ability to develop resistance to these methods has hindered its control, necessitating more sustainable and effective alternatives. The use of biological control strategies involving entomopathogenic microorganisms, such as filamentous fungi, has gained attention due to their diverse mechanisms of action and low likelihood of resistance. In addition to conidia, which can be applied directly to pests, fungi also release bioactive compounds that have effects both on direct pest control and on insect physiological processes, such as reducing survival, decreasing development rates, and even interfering with reproduction. As new species of filamentous fungi with entomopathogenic properties are discovered, there is an increasing need for studies on their secondary metabolites to better understand their mechanisms of action, potential applications, and efficacy in pest management. Thus, the aim of this study was to evaluate the virulence of filamentous fungi on 1st and 3rd instar S. frugiperda larvae resistant and susceptible to Cry proteins, as well as to investigate the effects of fungal filtrates on the pest’s development and reproduction. The fungi used in the study were Aspergillus aureolatus E25, A. keveii CF292, A. sydowii GMA3, Epicoccum nigrum [isolates A2C32, A2S61, and 185A], Penicillium chermesinum 102, P. flavigenum 3.1.A, Lecanicillium aphanocladi (ONI5), and Fusarium sp. (FPW). To evaluate virulence, third-instar larvae were exposed to conidia from different fungal isolates, as well as to diets contaminated with conidial suspensions. For the development study, fungal filtrates were applied to diets and offered to neonate S. frugiperda larvae, with mortality being observed. Eggs from surviving adults were collected, and larval development, longevity, and reproductive parameters were monitored. The results showed that none of the fungi were virulent to both Cry-resistant and Cry-susceptible populations, but fungal filtrates were highly efficient, reducing larval survival and development time. The isolates A2S61 and ONI5 showed the highest mortality rates, reaching 64%, while A2C32 and E25 impacted adult longevity, and ONI5 and GMA3 reduced larval development time. These results highlight the importance of ongoing research to enhance the use and formulation of fungi as biological control agents. Therefore, the application of filamentous fungi and their derivatives can be a sustainable and effective strategy for managing S. frugiperda, helping reduce dependence on chemical products, protect the environment, and provide a viable solution for pest control in agricultural systems.