Selection of entomogenous nematodes from the families Steinernematidae and Heterorhabditidae (Nematoda) to control grass grub (Costelytra zealandica (White)) and porina (Wiseana cervinata Walker) larvae in pasture

Abstract

Eight strains of nematode from the families Steinernematidae and Heterorhabditidae and their associated bacteria, Xenorhabdus spp. (Enterobacteriaceae), were taxonomically characterized and evaluated for their ability to control larvae of the pasture pests Costelytra zealandica (White) (Coleoptera: Scarabaeidae) and Wiseana cervinata Walker (Lepidoptera: Hepialidae) at winter soil temperatures in Canterbury, New Zealand.

Using morphological/morphometric measurements of infective, male, and female nematodes reared in Galleria mellonella L. larvae at 20ºC, it was not possible to distinguish between two strains of Steinernema bibiollis (Bovien) or between three strains of Heterorhabditis spp. S. bibionis strain CA reared at 10ºC and Heterorhabditis bacteriophora Poinar strain V16 reared on X. luminescens cultured on nurient agar, had different measurements from the same strains reared at 20ºC in G. mellonella larvae.

Although biochemical and physiological tests were inadequate for distinguishing between strains of Xenorhabdus spp., DNA restriction endonuclease electrophoresis gave results that allowed differentiation between strains of X. luminescens Thomas and Poinar.

Pathogenicity tests were carried out using 25 ml vials filled with soil, each containing a single c. zealandica or w. cervinata larva. H. bacteriophora strain Vl6 was the most pathogenic to c. zealandica larvae at 20°e. S. bibionis strain CA was the most pathogenic nematode studied for w. cervinata larvae at 10ºC. Migration across 1% water agar was used to assess the activity of each nematode strain at 7.5ºC and 10ºC. S. bibionis strain CA was the most active at both temperatures. Two strains of S. bibionis reproduced in G. mellonella at 10ºC after 60 days, strain CA produced the highest number of infectives. Growth of Xenorhabdus spp. at 10ºC was assessed using samples of cultures grown in nutrient broth. The strain that multiplied the most rapidly at 10ºC, had been isolated from s. bibionis strain CA.

In 1.8 1 pots kept at 2-12ºC, S. bibiollis strain CA was the most pathogenic to porina larvae. During a field experiment conducted in winter (2-11ºC) on Canterbury pasture, S. bibionis strain CA applied at the rate of 400,000 infectives /m², achieved 60% control of porina larvae.