Identification of Thrips Species on Garlic Fields in Hamedan Province and Determination of Dominant Species

Garlic (Allium sativum) (family Amaryllidaceae) are one of important crops in Hamedan province. There are several insects and mites that by feeding on this plant cause to damage garlic yield. Among the insect pests, the most dangerous pests of garlic are thrips species (Insecta: Thysanoptera). In this group, onion thrips, Thrips tabaci Lindeman is widely distributed and is a dominant species. Its sap sucking causes tiny and silvery spots on the leaves that may spread all over the leaf surface with an unfavorable effect on yield production. In addition, imagoes and larvae living and feeding on this plant cause more serious damages. Due to serious damage of thrips in garlic fields of Hamedan province, it is necessary to identify thripsspecies for pest control programs.
Thrips specimens were collected on leaves of garlic in Hamedan province (Maryanaj and Heydareh) situated in the west of Iran, during 2012–2013. Herein, specimens were collected by shaking plants to white dish and specimens were kept in 70 % ethanol and transferred to the laboratory. All collected material was macerated in 5% KOH and subjected to dehydration in an ethanol series before being mounted onto glass slides. Subsequently, thrips specimens mounted onto slides in Hoyer’s medium form of the protocol given in Mirab-balou and Chen (2010). All descriptions, measurements and photos were made with a Leica DM IRB microscope, with a Leica Image 1000 system. Thrips specimens were identified by author in species level. Specimens are deposited in the collection of Department of Plant Protection, College of Agriculture, Ilam University, Iran (ILAMU). In addition, dominant thrips species were also determined. For this purpose, regular samplings were done in fields of two regions of Hamedan province every two weeks, and totally, 2040 specimens (adult) were collected.
The world fauna of Thysanoptera, are presently known to be consisted of about 6000 species placed in two suborders and nine families. A large number of thrips species are considered pests, because they feed on economical crops. In this study, a total of eight species in seven genera and three families were collected and identified, including Aeolothrips intermedius Bagnall and Rhipidothrips gratiosus Uzel from family Aeolothripidae, Aptinothrips rufus (Haliday), Frankliniella intonsa (Trybom), Scolothrips longicornis Priesner, Thrips alliorum (Priesner) and Thrips tabaci Lindeman from family Thripidae, and Haplothrips reuteri (Karny) from family Phlaeothripidae. All of the species existed in two years in both two regions. Thrips tabaci was the dominant species (64.89%) in garlic fields. Among the predatory thrips, Aeolothrips intermedius and Scolothrips longicornis were present in greater numbers. However, their number was not enough to reduce the number of phytophagous thrips. The predatory species feeds mainly on the larvae and imagoes of onion thrips but they feed on mites as well. An identification key for thrips species associated with garlic is also given.
In this study, eight species of thrips were collected on garlic fields of Hamedan province which Thrips tabaci was dominant species (64.89%); and three of which were identified as predatory species. Up to the present, several thrips were collected and recorded from Hamedan province by the author, but there is no study on thrips associated to garlic; therefore, this study was firstly carried out in Hamedan province. There are several insect pests on garlic, and T. tabaci was also reported as important pest on garlic fileds in this province. Onion thrips, T. tabaci is one of the important pests in the world, and it has more than 300 host plants. At present, it is widely distributed in Iran and is a key insect pest in most onion and cotton cultivation areas as well as ornamental plants. In addition, thrips species in the genera Thrips and Frankliniella spread plant diseases through the transmission of viruses, such as Tospoviruses, Tomato Spotted Wilt Virus, and the Impatiens Necrotic Spot Viruses; So, it is necessary to pay more attention to the management of T. tabaci . In garlic crops of Hamedan province, T. tabaci was established on the plant from earlier time to near harvest; and because of high damaging, the farmers used several insecticides within one year.