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Spatial Analysis of Entomopathogenic Nematodes and Insect Hosts in a Citrus Grove in a Semi-Arid Region in Israel

David Efron, David Nestel, Itamar Glazer
DOI: http://dx.doi.org/10.1603/0046-225X-30.2.254 254-261 First published online: 1 April 2001

Abstract

We investigated the spatial and temporal dispersion patterns of entomopathogenic nematodes (Steinernematidae and Heterorhabditidae) and their host insects in a citrus orchard located in the semiarid region of Israel (the Negev). Spatial patterns of entomopathogenic nematodes were studied in plots differing on their shade level, and at two geographic scales: a macro-scale, which included the entire orchard, and a micro-scale, which investigated the spatial patterns around individual trees. Spatial patterns of insect hosts were only studied at the macro-scale. At the macro-scale, soil samples were obtained from a symmetrical grid in which samples were separated by a distance of ≈20 m; and in the micro-grid, soil samples were separated by a distance of 50 cm. Population levels of entomopathogenic nematodes were spatially autocorrelated using Moran’s I statistics. Population loads of entomopathogenic nematodes, and their spatial and temporal patterns, were not affected by the orchard’s shade level. Entomopathogenic nematode loads were higher during the fall, which coincides with the reported abundance of their main hosts in this region, grubs of Maladera matrida (Argaman). At the investigated scales and distances, we were unable to detect any spatial dependence of entomopathogenic nematode populations or of insect hosts. However, clusters of entomopathogenic nematodes were found to be highly localized in small volumes of soil. At the level of the entire plot area we found a very strong correlation between the number of host insects at a particular time and the level of entomopathogenic nematodes (as indicated by a laboratory bioassay) 1 mo after (shifted-back correlation). We conclude that entomopathogenic nematodes in the Negev orchards have a very low probability of encountering insect hosts, and that under the environmental conditions of the Negev, effective biological control with entomopathogenic nematodes can only be achieved by inundative releases.

  • population dynamics
  • entomopathogenic nematode
  • spatial pattern
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