Characterization of entomopathogenic nematodes and symbiotic bacteria active against Spodoptera frugiperda (Lepidoptera: Noctuidae) and contribution of bacterial urease to the insecticidal effect.

摘要

Entomopathogenic nematodes carrying symbiotic bacteria represent one of the best non-chemical strategies for insect control. Infective juveniles of Heterorhabditidae and Steinernematidae nematodes actively seek the host in the soil, penetrating through insect's openings to reach the hemocoel where symbiotic bacteria in the genera Photorhabdus or Xenorhabdus, respectively, are released. The bacteria replicate and produce virulence factors that rapidly kill the insect host, providing nutrients for the nematodes development and reproduction within the insect cadaver. More studies are necessary to better understand the factors implicated in the nematode-bacteria association, particularly focusing the bacterial symbionts, the final effectors of the insect death. Our group has shown that ureases are lethal to some groups of insects and may contribute to the entomopathogenic properties of the symbiotic bacteria. The fall armyworm Spodoptera frugiperda (Lepidoptera: Noctuidae) is one of the major insect pests in corn (Zea mays) crops in Brazil, with infestations resulting in reduction up to 39% yield and losses amounting US$ 500 million annually. Native strains of entomopathogenic nematodes active against S. frugiperda represent a promising alternative to the intensive use of chemical insecticides to control fall armyworm population in corn plantations. In this study we screened soil nematodes collected in the south region of Brazil for pathogenicity against S. frugiperda. Symbiotic bacteria associated with these nematodes were isolated and characterized. We also evaluated urease production by the symbiotic bacteria in vitro and along the course of infection in S. frugiperda and demonstrated that urease production correlated positively to their entomopathogenicity.