Modeling Nematodes Regulation By Bacterial Endoparasites

Abstract

Abstract. Some aspects of nematodes regulation by Pasteuria penetrans and other endoparasitic Gramnegative bacteria are revised, together with application modeling tools, in reference to their biocontrol potentials. A review is given about general and more detailed epidemiological models and their applications. The models constants accounting for basic biological factors of the parasites and hosts biology and interactions, are also discussed. Some properties of applied models, including the phase plane representation, the identification of equilibrium points and their cyclic relationships are revised, in reference to the study of field and time series data. A modeling scheme for Pasteuria and nematode dynamics, accounting for the host life cycle and including its developmental stages, is also proposed. Finally, experimental and practical issues concerning nematodes biological control are also discussed. 1. INTRODUCTION The attention of producers and consumers for organic productions increased in recent years. Organic productions are characterized by the exclusive use of natural resources or of compounds already present in nature. In Italy, the surfaces cultivated with these technologies progressively increased in the last decade, reaching in the year 2000 almost one million ha, with further increments expected in the subsequent Plant parasitic nematodes are naturally controlled by several biological antagonists. Among them several fungi are known since the end of the XIX century, thanks to the pioneering observations carried out in agricultural or uncultivated soils (Woronin, 1870; Drechsler, 1934; Duddington, 1957). These studies were subsequently and progressively integrated by observations focusing on the parasitic and predatory activities displayed by nematophagous species commonly isolated from soil (Gray, 1988; Stirling, 1991). Fungi were the first group of antagonists studied, probably because they can easily be cultured in vitro and because of the simple microscopy procedures required for recognition of the hyphal structures involved in parasitism or predation (see Chapters 2 and 3 in this volume for revision of nematophagous fungi). A second group of nematode antagonists is represented by soil bacteria, which are the focus of this chapter