Seasonal Abundance of Liriomyza sativae (Diptera: Agromyzidae) and its Parasitoids on Vegetables in Southern Vietnam

Abstract

Native to the North America, Liriomyza sativae (Blanchard) (Diptera: Agromyzidae) is widespread worldwide but mostly occurs in the temperature regions including South East Asian countries (Spencer, 1973; Murphy and LaSalle, 1999). Recently, L. sativae has been also recorded from China (Zhao and Kang, 2000) and Japan (Iwasaki et al., 2000). In Japan, L. sativae was found for the first time in 1999 in Kyoto and Yamaguchi Prefectures (Iwasaki et al., 2000). This species has quickly spread and become a serious pest of vegetable and ornamental crops in the fields and greenhouses. This rapid spread was mainly caused by transportation of plant materials for greenhouses and plastic tunnels. In northern areas beyond latitude 34 N in China, L. sativae can not overwinter in the outdoors (Zhao and Kang, 2000). In Vietnam, L. sativae is an economically important pest of a wide variety of vegetable and ornamental crops in the open fields (Andersen et al., 2002; Tran et al., 2005a, b). Recent outbreaks of the leafminer were treated by a wide range of conventional insecticides, but control was unsatisfactory (Johansen et al., 2003; Tran and Takagi, 2005). Frequent applications of these broad spectrum insecticides can adversely affect parasitoid abundance in the vegetable agro–ecosystems (Saito et al., 1996; Johansen et al., 2003), can promote the development of pesticide resistance within fly populations (Keil et al., 1985, Johansen et al., 2003; Hofsvang et al., 2005) and frequently lead to an increase in leafminer density (Oatman and Kennedy, 1976; Murphy and LaSalle, 1999). Agromyzid leafminers are known to have rich natural enemy communities. Eighteen species of hymenopteran parasitoids have been recovered from Liriomyza leafminers in central and southern Vietnam. Among them, Neochrysocharis beasleyi Fisher & LaSalle, Neochrysocharis okazakii Kamijo, Neochrysocharis formosa (Westwood) and Asecodes delucchii (Boucek) (Hymenoptera: Eulophidae) are numerically dominant species (Tran et al., 2006). They have played a very important role in leafminer suppression in natural ecosystems and cultivated areas with reduced insecticide use (Johnson et al., 1980; Murphy and LaSalle, 1999). The objectives of this study were to survey damage caused by L. sativae in two important vegetable–growing areas of the Ho Chi Minh City, southern Vietnam, and to monitor the seasonal abundance of the leafminer and its parasitoids. In this paper, the seasonal occurrence of L. sativae in Vietnam and Japan was also discussed. Seasonal Abundance of Liriomyza sativae (Diptera: Agromyzidae) and its Parasitoids on Vegetables in Southern Vietnam