Effects of Sugar Beet Field Margin Vegetation on Population Density of the Sugar Beet Weevil, Lixus incanescens Boheman and the Percentage of its Larval Parasitism

The sugar beet weevil, Lixus incanescens Boheman, is one of the important insect pests of sugar beet, Beta vulgaris L., in Khorasan Razavi province. In this research, the effect of three types of vegetation in the sugar beet field margin on the population density of L. incanescens and its larval parasitism by parasitoid wasps were studied in the experimental fields of Juvein, Khorasan Razavi province from year 2013 to 2014. In this study a sugar beet plant was selected as sampling unit. In two years, the lowest density of eggs (6 and 6.3 eggs per plant, respectively) and larvae (3.1 and 3.3 larvae per plant, respectively) was recorded in the sugar beet field located nearby forage with trees. Also, four larval parasitoid species of L. incanescens including Bracon intercessor Nees, B. kozak Telenga, Eurytoma aciculata Ratzeburg and E. ghilarovi Zerova were collected and identified from the experimental fields. Among identified four parasitoid species, B. intercessor had the highest percentage of larval parasitism in two years (69 and 76%), respectively. In addition, the highest percentage of larval parasitism by each of four parasitoid species and the highest percentage of females of each of them were observed in the sugar beet field located nearby forage with trees. Therefore, it can be concluded that the presence of forage with trees on the margin of the sugar beet fields can increase larval parasitism and reduce population density of L. incanescens. These results could be useful in integrated management of L. incanescens in the sugar beet fields.