Application pattern and persistence of the entomopathogenic nematode Heterorhabditis bacteriophora

Abstract

Abstract Scarab beetle larvae are widespread insect pests that can be controlled by the entomopathogenic nematode Heterorhabditis bacteriophora. The nematode is applied as an inundative biological control agent, which means that large numbers ( ≈2.5×10 9 ha −1 ) are applied uniformly to crops. Nematode persistence in these systems tends to be poor. Many theoretical mechanisms have been proposed whereby spatial structure can promote population persistence. We hypothesized that nematode persistence could be enhanced by applying nematodes in spatial distributions other than the typical uniform distribution. We applied H. bacteriophora ( 2.5×10 9 ha −1 ) to 3×3 m plots of turf in three spatial patterns: (1) uniform distribution; (2) one central circular patch (diameter 1.12 m); and (3) nine individual patches (diameter 0.38 m). Nematode persistence and spatial distribution were monitored over 1 year. In all treatments, nematode numbers declined to similar levels. Over time, the nematodes applied in patches moved from their initial application sites and became more evenly distributed, whereas the distribution of nematodes in plots with uniform application became patchier as nematodes died. No significant differences were observed in nematode numbers or spatial pattern from week 20 until the end of the experiment. Grub densities were measured at the end of the experiment. Nematodes that had been applied uniformly or in nine patches significantly reduced grub numbers, but the one-patch application did not.