Effect of mini-sprinkler irrigation system on Heterorhabditis baujardi LPP7 (Nematoda: Heterorhabditidae) infective juvenile

Juan Carlos Lara,Rogério Figueiredo Daher,Cláudia Dolinski,Elias Fernandes De Sousa

doi:10.1590/s0103-90162008000400017

Abstract

Entomopathogenic nematodes (EPNs) are currently being used as successful biological control agents of soil-dwelling insect pests. Previous field and greenhouse studies demonstrated that application techniques and non-biotic factors (temperature and pressure) have a significant effect on EPNs efficacy. The objective of this study was to evaluate the influence of an irrigation spray application system on the viability, infectivity and host search capability of Heterorhabditis baujardi LPP7 (Nematoda: Heterorhabditidae) infective juveniles (IJ). Two assays were proposed. Their viability was evaluated under the microscope after the IJ passed through the irrigation system. Infectivity on Galleria mellonella larvae, and host search capability, as evidenced by larval mortality, were evaluated in containers (Experiment 1). In the field (Experiment 2), mortality of G. mellonella larvae was evaluated under different nematode concentrations (0, 100,000, 300,000 and 500,000 IJ per tree). No differences were recorded on the viability, infectivity and host search capability of the IJ in Experiment 1. In Experiment 2, differences were recorded among the different concentrations used (p < 0.05), and a higher mortality was observed at the highest nematode concentration (28.3% and 37% in each one of the two experiment repetitions). This irrigation system did not affected adversely the viability, infectivity and host search capability of H. baujardi LPP7.

Highlights

Heterorhabditis Poinar (Nematoda: Heterorhabditidae) is an obligatory pathogen of insects, known as entomopathogenic nematode (EPN)
(cruiser or ambusher foraging strategy), they can enter through body openings or through the cuticle, reach the hemocoel and release the symbiotic bacteria held in their intestines (Photorhabdus spp.) (Poinar-Jr., 1990)
Infected hosts die within 48-72 h, and the nematodes feed on the symbiotic bacteria and insect tissues (Grewal & Georgis, 1999; Lewis et al, 1992)

Summary

Introduction

Heterorhabditis Poinar (Nematoda: Heterorhabditidae) is an obligatory pathogen of insects, known as entomopathogenic nematode (EPN). The majority of mini-sprinkler equipments do not generate enough pressure to cause physical damage to nematodes, but it is not known if the passage through spray systems would affect their host search capability (Grewal, 1998). This study demonstrates the effects resulting from the passage of a cruiser EPN, H. baujardi LPP7 Phan, Subbotin, Nguyen & Moens, through a surface spray irrigation system that uses mini-sprinklers, evaluated on the basis of its viability, infectivity and host search capability at the infective juvenile stage in soil containers and under field conditions.

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Conclusion