XenorhabdusandPhotorhabdus,Bacterial Symbionts of the Entomopathogenic NematodesSteinernemaandHeterorhabditisand theirin vitroLiquid Mass Culture: A Review

Abstract

Entomopathogenic nematodes (EPNs) represent an important part of the spectrum of potentially available biological control agents against insect pests. EPNs of the families Steinernematidae and Heterorhabditidae share a mutualistic relationship with bacteria of the genera Xenorhabdus and Photorhabdus, respectively. Current research on the use of EPNs against key pests of fruit crops in South Africa has the ultimate aim of using nematodes on a commercial scale against key insect pests of such fruit crops as deciduous fruit and citrus. For this objective to be realized, nematodes should be mass produced in vitro in liquid culture. A detailed understanding of the biology and behaviour of the nematode species and the associated bacterial symbiont in relation to their mass production is, therefore, required. The long processing time that is required for nematode cultures, combined with the need for an even distribution of fluids and organisms, result in the cultures being extremely vulnerable to contamination. Nematodes experience a very different environment in liquid culture than they do in nature, and a high level of technological knowledge is required for their successful production. Endemic EPNs are not currently commercially produced in South Africa. This review presents an overview of the current knowledge that is available on the bacterial symbionts and on the biology of the two nematode genera. Optimum growth parameters for the bacteria and the nematodes are discussed for endemic nematode isolates that might have the potential to be mass cultured for commercial application.