Evaluation of two wheat cropping systems for enhancing biological control of the wheat thrips, Haplothrips tritici (Thys.: Phlaeothripidae)

The wheat thrips, Haplothrips tritici Kurd., is an important pest of wheat crop, Triticum aestivum L., in Ardabil region, northwestern Iran. Strip cropping of wheat and alfalfa, Medicago sativa L., is a suitable strategy for improving the effectiveness of biocontrol agents of the wheat thrips. In this research, population density of the wheat thrips, and species richness and abundance of its predators were studied in the strip cropping of wheat and alfalfa (three-year old) and the monoculture of wheat during field surveys from 2010 to 2011. Sampling from each of two wheat cropping systems was conducted from the stem elongation until ripening stages. Number of the wheat thrips and predators per plant were recorded in each sample date. The population density of the wheat thrips in the strip cropping of wheat-alfalfa was significantly lower than that of monoculture of wheat. Five species of predators were recorded in the monoculture of wheat and 15 species of predators were recorded in the strip cropping of wheat-alfalfa. The Shannon diversity index for predators in the strip cropping of wheat-alfalfa was significantly higher than that for monoculture of wheat. The Morisita-Horn index between two wheat cropping systems was calculated 0.842. The species richness and abundance of predators in the strip cropping of wheat-alfalfa were greater than the monoculture of wheat. Therefore, it can be concluded that the strip cropping of wheat-alfalfa increases the species diversity of the predators and reduces the population density of H. tritici. Quantifying the species richness and abundance of predators in the wheat fields is an important step in the management of the wheat thrips.