Generalist entomopathogens as biological indicators of deforestation and agricultural land use impacts on Waikato soils

The relative abundance of entomopathogenic nematodes and fungi was estimated for 10 sites in each of indigenous forest, pasture, and cropland habitats by baiting soil samples with Galleria larvae. The steinernematid Steinernema feltiae (Filip) was the dominant nematode, occurring in soils from all three habitat types. The heterorhabditid Heterorhabditis zelandica Poinar was recovered only from soils of podocarp (Dacrycarpus dacrydioides (A. Rich.)) forests. Galleria infection by nematodes was higher in soils from forest habitat than in soils from pasture and cropland. Among the sampled forests, nematode infection was higher in soils from podocarp stands than those from broadleaf stands. The deuteromycete fungi Beauveria bassiana (Balsamo) Vuillemin, Metarhizium anisopliae (Metschnikoff) Sorokin, and Paecilomyces cf. cicadae (Miquel) Samson, and a Entomophthorales zygomycete, tentatively identified as a Tarchium species, were recovered from the Galleria baits. Infection of Galleria by B. bassiana and M. anisopliae occurred in soils from all habitat types, while that by P. cicadae occurred only in soils from forest habitats. Tarchium was recovered from a single pasture site. The frequency of Galleria infection by these entomopathogenic fungi collectively, and by B. bassiana alone, was higher in pasture soils than in soils from either forest or cropland. These results are discussed in relation to disturbance effects of land use changes and the potential role of generalist entomopathogens as biological indicators of soil health.