Population density of overwintering larvae of Chilo suppressalis (Lepidoptera: Pyralidae) on host weeds in Mazandaran province

Striped rice stem borer, Chilo suppressalis (Lepidoptera: Pyralidae) is one of the major pests in north part of Iran which causes serious damage. The last larval instar overwinters in the stem of weeds around the fields. Regarding the importance of weeds as overwintering habitat, population density of larvae was studied in three areas; low-, mid-, and up-lands of Mazandaran province and also on three host weeds: Xanthium pensylvanicum, Sorghum halopense, and Amaranthus retroflexus. The results imply on the highest density of larvae in the mid- and up-lands areas and its preference to locate in X. pensylvanicum for overwintering. There was no significant difference between the two other hosts. Results of population fluctuation showed that it had a low increasing of population from October to December; therefore the lowest density was observed in early October and the highest in late December. Results of interaction effect of area × hosts on population density indicated that the highest density located on X. pensylvanicum in the mid- and up-lands areas, and the lowest density on A. retroflexus in low-land part. Based on the results, removing the most important weed which are overwintering habitat for larve from around the rice fields will be resulted to increasing the larval mortality through winter, and therefore decreasing pest population density in crop season.