نامه انجمن حشرهشناسی ایران (Dec 2014)
Effect of strip cropping of sugar beet-alfalfa on population density of the sugar beet weevil, Lixus incanescens (Col.: Curculionidae) and species diversity of its natural enemies
Abstract
The sugar beet weevil, Lixus incanescens Boheman, is an important insect pest of sugar beet, Beta vulgaris L., in many parts of Iran. Strip cropping of sugar beet and alfalfa, Medicago sativa L., is a suitable strategy for improving the effectiveness of biocontrol agents of the sugar beet weevil. In this research, the population density of the sugar beet weevil and diversity of its natural enemies were studied in the strip cropping of sugar beet-alfalfa in comparison with the monoculture of sugar beet, in Juvein countryside, Khorasan Razavi province, from 2012 to 2013. In each sampling, the abundance of the sugar beet weevil and its natural enemies per plant were recorded. The densities of the sugar beet weevils in the strip cropping were significantly lower comparing to the monoculture. The larva of the hymenopteran parasitoid species Bracon intercessor Nees in both culture systems as well as seven egg predator species in strip cropping system and three egg predator species in the monoculture system were found. The percentage of larval parasitism and the densities of each predator in the strip cropping were significantly higher than the monoculture. The Shannon diversity index for the complexity of natural enemies in the strip cropping was higher comparing to the monoculture. The value of Morisita-Horn index for the complexity of the natural enemies between the experimental sugar beet cropping systems was calculated as 0.923. Based on these results, we have concluded that the strip cropping of sugar beet-alfalfa leads to higher diversity of natural enemies of the sugar beet weevil and lower population density of L. incanescens. In addition, the quantification of the predators’ species richness and abundance in the sugar beet fields remains as an effective method to improve the management of the sugar beet weevil.
