Survey of Relative Frequency and Biodiversity Indicators Changes of Thrips Species (Insecta: Thysanoptera) in Different Alfalfa Cuttings in Eyvan City (Ilam Province)

Alfalfa (Medicago sativa L.), also called lucerne, is the most important forage which cultivated in the most parts of the world. The main source of alfalfa is Southwest Asia, especially Iran. Alfalfa is a perennial forage legume which normally lives four to eight years, but can live more than 20 years, depending on type of its variety and climate. In the most regions, alfalfa is generally harvested three to four times and can be done up to 12 times per year. Many types of insects are found in alfalfa fields including beneficial, and harmful insects, which feed on the leaves, flowers, root and seeds. Amongst them, thrips are a group of insects belonging to the order Thysanoptera. Thrips have been considered in most areas. Different species of thrips have been recorded on alfalfa fields in western Iran i.e. Odontothrips confosus Priesner, Odontothrips iranensis Mirab-balou et Chen, Thrips tabaci, Frankliniella intonsa (Trybom), F. pallida (Uzel), Haplothrips reuteri (Karny) and Neohydatothrips gracilicornis (Williams).Therefore, it is critical to determine the biodiversity status of the thrips in order to manage its population.

To study the biodiversity of thrips species in different alfalfa cuttings, the sampling was weekly carried out during April to the middle of September 2016 in alfalfa fields (1-year-old, 3-years-old and 4-year-old) of Eyvan city (Ilam province), the west of Iran. The specimens were collected using shaking alfalfa plants in a white tray and transferred them to vials containing 75% ethanol. After transferring to the laboratory, all thrips specimens were mounted onto slides, and identified at the species level. The dominant thrips species were determined and biodiversity of thrips species in different alfalfa cuttings was calculated by biodiversity indices i.e. Shannon-Wiener, Simpson, Margalef and Evenness Shannon.

In the present study, 10 thrips species belonging to six genera and four different families were collected and identified from alfalfa fields. Among the collected species, the highest and the lowest frequency was obtained for Thrips tabaci (59.12%) and Tenothrips frici (0.24%), respectively. According to the calculations, the Shannon-Wiener, Simpson, Margalef and Evenness Shannon indices in 1-year-old alfalfa field were 2.71 ± 0.04, 0.92 ± 0.04, 3.49 ± 0.02 and 0.89 ± 0.01, in 3-year-old alfalfa field were 2.26 ± 0.09, 0.88 ± 0.009, 2.58 ± 0.18 and 0.91 ± 0.006, and in 4-year-old alfalfa field were 2.09 ± 0.14, 0.85 ± 0.01, 2.31 ± 0.29 and 0.92 ± 0.01, respectively. The results showed that the Shannon-Weiner, Simpson and Margalef indices of thrips species in 1-year-old alfalfa field were significantly higher than the 3 and 4-year-old alfalfa, however, the Evenness Shannon in 4-years-old alfalfa field was more than 1-year-old and 3-years-old alfalfa fields, this difference was not significant.

In this study, Shannon-Wiener index values varied between at least 2.09 in a 4-year-old alfalfa and a maximum of 2.71 in a 1-year-old alfalfa fields. The range of Shannon-Weiner index variables from 0 –5 and typically from 1.5 - 3.5. Lower values of this range indicates the presence of tension in the environment and instability, and more than it showed an increasing the biodiversity of the area. These values are good in comparison to the range of Shannon-Weiner index variables, which are generally between 1.5 and 3 in their sources. As the age of the plant raises, the amount of food decreases, so, insects less likely tend to establish on the host plants, and their variety will be reduced. Thrips tabaci is one of the most important pests with more than 300 host plants in the world. Considering that in the present study T. tabaci is a dominant species in the alfalfa fields, its infestation level should be managed correctly with respect to control method.