Egg Disease in Spodoptera litura (Fabricius) Caused by Aspergillus ochraceus and Its Metabolic Phenotype

A pathogenic fungus was isolated from unhatched egg masses of Spodoptera litura (S. litura). The pathogen was identified as Aspergillus ochraceus based on morphological characterization and molecular analyses of the internal transcribed spacer (ITS) region and the β-tubulin gene. The isolate exhibited strong pathogenicity toward S. litura eggs, causing 100% mortality. Phenotypic characteristics were further evaluated using the BIOLOG Phenotype MicroArray (PM) system. A total of 950 distinct growth conditions were assessed across PM plates 1-10. The results indicated that A. ochraceus metabolized 80.85% of the tested carbon sources, 97.26% of nitrogen sources, 91.43% of sulfur sources, and 88.14% of phosphorus sources. Among carbon substrates, carbohydrates were the most efficiently utilized, whereas a wide range of amino acids served as preferred nitrogen sources. In total, 92 distinct nitrogen metabolism pathways were identified. The isolate demonstrated broad osmotic adaptability, growing in media containing up to 6% potassium chloride, 20% ethylene glycol, 5% urea, and 12% sodium lactate. It showed active metabolic activity across a wide pH range (3.5-10.0), with optimal growth observed at pH 6.0. The pathogen exhibited strong decarboxylase activity but lacked deaminase activity in response to various amino acid substrates. To our knowledge, this is the report of an egg disease in S. litura caused by A. ochraceus in China. The pathogen displays broad metabolic versatility across diverse carbon, nitrogen, and sulfur sources, as well as strong tolerance to variations in osmotic pressure, ionic strength, and pH. These findings suggest that disease management strategies targeting this pathogen should be considered in Sterile Insect Technique (SIT)-based mass rearing programs of S. litura.