Survival of entomopathogenic nematodes within host cadavers in dry soil

Abstract

Our objectives were to determine whether entomopathogenic nematode emergence from host cadavers is influenced by soil moisture, whether the nematodes can survive adverse desiccating conditions in the soil by remaining within the host cadaver, and whether differences in such an adaptation occur among species. In the first experiment, wax moth larvae killed by Steinernema glaseri, Steinernema carpocapsae, Steinernema riobravis, or Heterorhabditis bacteriophora were placed in soil water potentials ranging from −500 MPa (very dry) to −0.006 MPa (moist). No infective juveniles (Us) emerged from cadavers at −500 MPa, and only few S. glaseri and S. carpocapsae emerged at −40 MPa. Large numbers of IJs emerged at ≥ −5 MPa from cadavers containing S. carpocapsae, S. glaseri, or H. bacteriophora. S. riobrauis emerged only at ≥ −0.3 MPa. In the second experiment, cadavers were left in dry soil (−40 MPa) for various periods of time before being rehydrated. The number of Us emerging per cadaver and the infectivity of the emerged IJs were determined. IJ emergence declined with the time that the cadavers were left in dry soil. Regression analysis predicted that IJ emergence from cadavers with S. glaseri, S. carpocapsae, H. bacteriophora, or S. riobravis would stop after 27, 62, 80, and 111 days, respectively, in dry soil. We hypothesize that S. carpocapsae, a sit-and-wait forager, survives longer than S. glaseri because it is adapted to infect insects near the soil surface, whereas S. glaseri, an actively searching forager, is adapted to infect insects deeper in the soil profile. Cadavers colonized by S. carpocapsae, therefore, are more likely to be exposed to dehydrating conditions. H. bacteriophora, an actively searching forager, may survive longer within cadavers because the gummous consistency of its host cadavers retains moisture very efficiently. S. riobrauis may survive for considerable lengths of time within cadavers in adaptation to the subtropical, semiarid climate of its geographic area of origin.