Formulação de Metarhizium humberi à base de cera de carnaúba e terra diatomácea para controle focal de Aedes aegypti

Abstract

Introduction: Metarhizium humberi is an entomopathogenic fungus that shows promising activity in the biological control of Aedes aegypti, a vector of arboviruses. Stressful environmental conditions, such as low relative humidity (RH), hinder the insecticidal action of M. humberi. Additives in conidial formulations (C) aim to improve the insecticidal activity of this fungus. Carnauba wax powder (CC) as an additive aims to increase the contact of C on the cuticle, and diatomaceous earth (DE) causes abrasion damage to the vector's epicuticle. Objectives: The aim of this study was to develop a dry formulation for controlling A. aegypti. Materials and Methods: To this end, the in vitro germination of C with CC and/or ED was evaluated, as well as the potential of CC and DE as additives in laboratory, semi-field and field conditions. For in vitro germination tests, C was mixed with CC and/or TD and exposed to 25°C, 43%, 75%, >98% RH and 12 h photophase for 14 days. In in vivo tests: in the greenhouse, adults were exposed to CC and/or ED mixed or not with C for 60 minutes. They were then incubated at 25ºC, 75% RH or >98% RH and 12-hour photophase. For tests in screened cages, adults were exposed to spreading devices with CC and/or ED mixed or not with C. In semifield tests, adults exposed to spreading devices with C, C+CC+DE and control in rainy or dry seasons. For all in vivo tests, mortality was quantified over 15 days. In field tests, dissemination devices with CC+ED and control were placed in four peridomiciliary sites in Goiânia, GO, Brazil, and at the end of each repetition the devices were reviewed and the number of eggs quantified. Results: In the in vitro tests C with CC and/or DE exposed to 43, 75 and >98% RH, had a significant difference in the mean germination in relation to the relative humidities (number of germinated conidia 43% < 75% > 98% RH). Exposure time (14 days) did not affect germination. In laboratory tests at 75% RH, on the 10th day mortality in C (58%) was lower than in C+CC+DE (73%). In the semi-field, mortality in the rainy season for C+CC+DE was 73%, and in the control 17%. In the dry season, C+CC+DE mortality was 92%, C 81% and control 45%. In the field, the number of eggs varied between 84 and 2221 eggs. Conclusions: The additives CC and DE can be used in a formulation with C of M. humberi. CC was not toxic to adults and the C+CC+DE formulation was promising in the dry season. Relevance and impact: The knowledge resulting from this study represents an important advance in the development of an effective and sustainable dry formulation for biological control, contributing to the emergence of new approaches to controlling A. aegypti, a vector with a major impact on tropical medicine and public health.