Effect of different cultivars of sugar beet on population density of the sugar beet weevil Lixus incanescens (Col.: Curculionidae), and its natural enemies under field condition in Razavi Khorasan province

The sugar beet weevil, Lixus incanescens Boh., is an important pest of sugar beet in Razavi Khorasan province. In this research, population density of sugar beet weevil, diversity of its natural enemies, and percentage of larval parasitism were studied on six sugar beet cultivars including Ardabili, Aras, Persia, Flores, Laetitia and Rosirewere studied in an experimental field during 2012 and 2013. In two years, the lowest densities of sugar beet weevil eggs and larvae were observed on Persia. In this study, one larval parasitoid species Bracon intercessor Nees, and three egg predator species: Nabis punctatus A. Costa, Orius niger Wolf. and Chrysoperla carnea Steph. were collected and identified. Amongst the natural enemies of this weevil, B. intercessor had the highest relative abundance. The Shannon diversity index for the complex of natural enemies was greatest on Persia. The value of Morisita–Horn index for the complex of natural enemies between the six sugar beet cultivars were calculated 0.973 to 1. In two years, the highest percentage of larval parasitism was observed on Persia (62.2 and 73.5%, respectively). Furthermore, the percentage of parasitoid females emerged on the weevil-infested plants in Persia and Laetitia was significantly higher than on Ardabili, Aras and Flores. Therefore, it can be concluded that the cultivation of Persia cultivar integrated with using of larval parasitoid B. intercessorcould be useful in the integrated management programs of L. incanescens in sugar beet fields.