Biology of cotton thistle leaf miner, Pegomya terebrans (Diptera: An-thomyiidae) in Urmia region, Iran

Field and laboratory surveys were carried out to study the biology of cotton thistle leaf miner, Pegomya terebrans (Rondani) in Urmia region. The results showed that the host plant species of this fly are restricted to three species of plants belonging to tribe Cynareae (Asteraceae), including Italian thistle Carduus pycnocephalus L. and two species of cotton thistle namely Onopordum acanthium L. and O. leptolepis DC.. The species has only one generation per year and hibernates as adults. After overwintering, adults become active and mate in late March. Fertile females begin oviposition in early April. The eggs are laid either singly or in groups of up to five in irregular shape under the leaves of the host plants. Depending on the daily temperature, they hatch within 6-10 days and young larvae immediately bores into the leaf and begins consumption in tissues between the leaf surfaces. The species has three larval instars and larval developmental time is 21 to 27 days in natural conditions. The full grown third instar larvae fall to the ground and pupate in the soil at a depth of 1 to 3 cm which its period lasts 4 to 5 months. The emergence of flies begins in mid-October and continues until late-November. They remain inactive for about five months in autumn and winter and become active in early spring, again. The larvae of P. terebrans were parasitized by Biosteres spinaciae (Thomson) in the studied region. Parasitic association between B. spinaciae and P. terebrans is reported for the first time.