Preliminary Study on Survey and Population Dynamic of the Terrestrial Snail (Pfeiffer) (Hygromiidae, Mollusca) at Crop Fields in Fayoum Governorate, Egypt.

<b>Background and Objective:</b> <i>Monacha obstructa</i> has a serious harmful impact as agricultural pest infested field crops, fruits, vegetables and ornamental plants nurseries in multiple Egyptian governorates. The objective of this research was estimating the population dynamic of the terrestrial gastropod species <i>Monacha obstructa</i> (Pfeiffer) (Hygromiidae) on two economic crop fields and its correlation with temperature degree and relative humidity, the level of infestation on other economic crops had been estimated as well. <b>Materials and Methods:</b> This study was conducted in three sites in Fayoum governorate, 1) Forkous village at Tamiya District, 2) Dar Ramadsite including the Experimental farm and research station of the Faculty of Agriculture, Fayoum University, Fayoum District and 3) Feedimeen village at Sannoris District. The distribution and population dynamics of <i>Monacha obstructa</i> were assessed as one of dominant species on two field crops Egyptian clover <i>Trifolium alexandrinum </i>L. and wheat <i>Triticum aestivum</i> L. at Forkous village, Tamiya District and Dar Ramad site, Fayoum District, during two successive seasons 2016/2017 and 2017/2018. <b>Results:</b> Majority of the examined crops in the sites were found with heavy infestation of this species, while the two species <i>Cochlicella acuta</i> (Müller) (Geomitridae) and <i>Massylaea vermiculata </i>(Müller) (Helicidae) recorded in December, 2017 and in January, 2018, respectively, on mango trees in Feedimeen at Sannoris district for only one time. High density of <i>M. obstructa</i> recorded on Egyptian clover more than wheat at Forkous village and Dar Ramad site for the both seasons in this study. <b>Conclusion:</b> Results concluded that <i>Monacha obstructa</i> has a serious harmful impact as agricultural pest infested field crops, fruits, vegetables and ornamental plants nurseries in Forkous village and Dar Ramad site, respectively.