Study On The Pest Control By Spiders In The Pasture Of Arid Area In North Hebei, China

The present study is a part of the research program entitled "The spider community in the pasture of arid areas of North Hebei and its effect in the biological control of main pests" supported by Natural Sciences Foundation of Hebei Province. In the paper the current progress in the researches of biological control in agriculture in the world are reviewed and the development strategies of integrated pest management using spider are briefly summarized as well.Spiders are a kind of important natural enemies of agricultural pests. The numbers of species and individuals are more abundant than other kinds of predators in the natural enemies of pests. From 2002 to 2003 qualitative and quantitative investigations of spiders were carried on in different grass-cultivated areas and the grass patches surrounded with fence in Bashang, Hebei Province. From the view of interactions between grasses-pests-spiders as a whole the species compositions and dominant species of spiders and pests were investigated under different environment conditions and grass species. Besides, studies were also made on the on the functional responses and efficiency of searching activities of spiders to the main pests. The results showed as follows:1. In the investigation totally 125 species have been found belonging to 16 families. Among them, five species (namely, Pardosa agrestis, P. astrigera, Neoscona adianta, Xysticus striatipes and Theridion impressum) were selected as representatives for studying the effect as natural enemies on the control of pests. The influence of densities of preys and spiders themselves on the survival of five species of pests has been observed and experienced in the grass-cultivated areas and the grass patches. Studies indicated that the function of control were shown obviously by the spiders to different pests as: Pardosa agrestis to Polymerus vulneratus, Lygus lucorum and Chorihippus hammarstroemi; Neoscona adianta to Adelphowris linealatus and Lygus lucorum; Pardosa astrigera to Lioshyssus hyalinu and Lygus lucorum; Xysticus striatipes to Polymerus vulneratus, Adelphowris linealatus and Lygus lucorum; Theridion impressum to Lioshyssus hyalinus, Adelphowris linealatus and Lygus lucorum.2. Research also showed that the predation effect of spiders used for study to the main pests were increasing with the density of preys and decreasing with the density of the spiders themselves with a certain range. This predatory effect is coincident with Holling- II type-Na=aTNt,/(l+ aThNt) and the equation of Hassell-Varley-A=aP-m. Theexperimental result has been tested by x and the error was not prominent.3. Analysis of searching efficiency showed that it decreased while the density of preys increased, that is to say, the natural enemies searching preys more actively; but in the condition of high density of preys their searching activity reduced.