Natural occurrence of Metarhizium rileyi on Spodoptera frugiperda larvae in Chihuahua state

The fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith), is the main pest of maize (corn). Its control depends mainly on the use of chemical insecticides, however, these cause adverse effects on the environment and the health of agricultural workers. A viable alternative to these products is the use of biological control agents, such as entomopathogenic microorganisms, highlighting fungi. The fungus Metarhizium rileyi (Farlow) Kepler (Hypocreales: Clavicipitaceae), plays an important role in the population regulation of lepidopteran pests, causing natural epizootics when the conditions for its growth are optimal. The aim of the study was to determine the natural occurrence of M. rileyi fungus on S. frugiperda larvae of in a corn plot. Four hundred fifty-two FAW larvae from all instars were collected from infested maize (corn) plot from Cusihuiriachi, Chihuahua in August and September 2017, where the number of larvae with mycosis was registered. The fungi M. rileyi and Beauveria bassiana (Balsamo) Vuillemin (Hypocreales: Cordycipitaceae) were identified according to their macroscopic and microscopic morphological characters. The temperature, relative humidity (RH) and accumulated precipitation were obtained from the weather stations of Unifrut and INIFAP. The highest percentage (48%) of mycosed larvae by M. rileyi was obtained in the august sampling, where the temperature and RH average was 16.76 degrees C and 80.1%, respectively, and accumulated precipitation of 218 mm. These results suggest that the climatic conditions were optimal for the development of the epizootic in field.