Pathogenicity and virulence of eight Brazilian entomopathogenic nematodes against two stored product pests under laboratory conditions
The maize weevil (Sitophilus zeamais Motschulsky, 1885) and the red flour beetle (Tribolium castaneum Herbst, 1797) are among the most economically significant coleopteran pests affecting stored products worldwide. Their infestations result in substantial quantitative and qualitative losses due to grain damage by both larvae and adults. Conventional control strategies rely heavily on chemical insecticides, which pose risks of environmental contamination and contribute to the development of resistant pest populations. As a sustainable alternative, entomopathogenic nematodes (EPN) offer potential for the biological control of insects in cryptic habitats. This study aimed to evaluate the pathogenicity and virulence of eight Brazilian EPN isolates, six from the genus Heterorhabditis and two from Steinernema, against adults of S. zeamais and T. castaneum under laboratory conditions. In addition, S. carpocapsae and H. bacteriophora were included as positive controls. All EPN demonstrated pathogenicity against both pest species, with Steinernema carpocapsae, Steinernema sp. CER21, S. brazilense, and Heterorhabditis amazonensis MC01 showing mortality rates above 25% at a concentration of 1,000 infective juveniles (IJ)mL−1. Subsequent virulence assays revealed that S. carpocapsae and S. brazilense caused the highest mortality in S. zeamais, reaching 86.7% and 76.4%, respectively, at 5,000 IJ.mL−1. For T. castaneum, S. brazilense, and S. carpocapsae caused mortality rates of 69.1% and 56.7%, respectively, at the same concentration. Lethal concentration estimates indicated that S. carpocapsae exhibited slightly higher efficiency against S. zeamais (LC90 = 4,699 IJ.mL−1) compared to S. brazilense (LC90 = 5,497 IJ.mL−1), with values in proximity. Similarly, for T. castaneum, both nematodes showed comparable virulence, with LC90 values of 7,482 IJ.mL−1 for S. carpocapsae and 6,480 IJ.mL−1 for S. brazilense. These findings demonstrate the high potential of S. brazilense as biological control agent against key pests of stored grains.