Seasonal activity and biology of cotton thistle stem-boring weevil Lixus cardui biocontrol agent of cotton thistles, Onopordum spp. in Urmia region

Cotton thistles, Onopordum spp. (Asteraceae), are native plants belong to Mediterranean basin, southwest and central Asia. Their reproduction is entirely by seed and the plants are biennial. The biology of cotton thistles stem-boring weevil, Lixus cardui Olivier, was studied on Onopordum acanthium and O. leptolepis in fields and rangelands in Urmia. The results of this study showed that, the stem-boring weevil has a single generation per year and overwinters as adult whithin the dried stems of host plants. The adults emerge from the dead stems, in late April. After emerging, they start to feed on the leaf tissues of host plants and mate from time to time. Then females chew holes into the stem, and lay eggs either singly or in batches of up to 5 in a row the each hole. Females cover their eggs with plant fiber that had been chewed away to make the hole for protection. Each female laid a mean of 35±3.63 eggs during her life span. Eggs hatch 6-8 days after oviposition and the young larvae bore into the stem and feed on the tissue. The full grown larvae produce pupal cell in the stem and eventually pupate. After 9-13 days, pupa develops into a new generation of adults within the stems in summer. These adults remain inactive in the dried stems until the following spring. The total life cycle from egg to adult ranges from 37 to 48 days under natural conditions.