The Asian rice gall midge (RGM), Orseolia oryzae (Wood-Mason) is a serious pest of rice in most of Asia including Laos. Most improved varieties currently being recommended in Laos are susceptible to gall midge damage, and it is a major yield constraint in wet-season lowland rice crops in parts of Central and Southern Laos. This study was undertaken as part of a program for the development of gall midge resistant improved varieties. An evaluation of relative gall midge susceptibility of traditional lowland varieties, improved lowland varieties, and breeding lines was carried out during the 2008 and 2009 wet-seasons, in a gall midge “hot spot” in Nahang-Noi village, Atsaphone district of Savannakhet province. A total of 48 entries (comprising 11 traditional varieties, 24 improved varieties and 13 promising lines) were assessed for gall midge resistance. The entries included a resistant check (the traditional variety Muang Nga), and a known susceptible check (the Lao improved variety, Tha Dok Kham 11 (TDK11). The varieties and breeding lines were sourced from the National Rice and Cash Crops Research Center and the Plant Protection Center near Vientiane Capital, the Thasano Rice Research and Seed Multiplication of Savannakhet Province, and the Phone Ngam Rice Research and Seed Multiplication Center of Champassak Province. The results showed that compared with local varieties, the improved varieties and promising lines were generally more susceptible to gall midge, with a wide range of levels of infestation. In the 2008 and 2009 wet-seasons, only one entry, the local variety, Kai Noi Deng (LG14024), exhibited resistance to gall midge damage, with less than 5% of silver shoots; a 
further two entries (TDK25 and TDK42) were classified as being moderately resistant (with  6-15% silver shoots); the remaining 45 entries were classified as susceptible, with more than  51% of silver shoots. The two improved varieties, TDK25 and TDK42 exhibited a relative lower level of gall midge susceptibility than other improved varieties, with both varieties showing an ability to compensate for gall midge damage. These varieties might therefore be more appropriate than varieties currently being used, in this locality and in other areas reporting high levels of gall midge damage throughout the country, including the districts of Phalanxay, Atsaphangthong  29 and Atsaphone in Savannakhet province. However, the assessment of potential of these varieties needs to be undertaken in different areas with chronic gall midge problems, as well as under the different growing conditions in the lowland environment throughout the country.

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