Survival and efficacy of entomopathogenic nematodes on exposed surfaces

Abstract

Entomopathogenic nematodes (EPN) species differ in their capability to withstand rapid desiccation (RD). Infective juveniles of Steinernema carpocapsae are a better adaptable and tolerant than Steinernema feltiae or Heterorhabditis bacteriophora as, an optimal RH of > 90% is required by S. feltiae and H. bacteriophora while maintaining RH equivalent to 74% could sustain survival of S. carpocapsae under RD. Our findings from infectivity suggest that following application, shrunk IJs are acquired passively by the larvae, probably rehydrate and resume infection within the insect gut. Water loss rate is a key factor affecting survival of S. carpocapsae on exposed surfaces. The present study provides the foundation for characterizing mechanism of rapid rate of water loss in EPN. ATR-FTIR is a rapid and reliable method for analysis of water loss. Changes in peak intensity was observed at 3100-3600 cm^-1 (OH bonds of water), 2854 cm^-1 (CH stretching of symmetric CH₂, acyl chains), 2924 cm^-1 (CH stretching of anti-symmetric CH₂, lipid packing heterogeneity), 1634 cm^-1 (amide I bonds) indicate major regions for hydration dependent changes in all EPN species. FTIR data also indicates that, S. carpocapsae contains strong water interacting regions in their biochemical profile, which could be an influencing factor in their water holding capacity under RD. ATR-FTIR were correlated to water content determined gravimetrically by using Partial Least square -Regression and FTIR multivariate method, which could be used to screen a formulation's potential to maintain or delay the rate of water loss in a rapid and efficient manner.