Studies On The Ecological Basis Of Parasitoids On The Control Of The Natural Population Of The Vegetable Leafminer Liriomyza Sativae (Diptera: Agromyzidae) In Hainan

Common species of leafminers (Agromyzidae) and their parasites on the vegetables of beans, gourds, solanceous fruits and greens in Hainan were investigated and the interspecific association between the vegetable leafminer, Liriomyza sativae Blanchard and its parasites was analyzed by means of the coefficient of interspeicfic association. The tracking-down efficiency was evaluated with the measurements of the niche widths and niche overlaps for the vegetable leafminer and its parasites in terms of time and space dimension. The life table of natural population grouped with the death factors was also constructed to study the parasitoids on the control of the natural population of the vegetable leafminer.Three species of leafminer, L. sativae Blanchard, L. bryoniae (Kaltenbach) and Chromatomyia horticola Goureau were reared from the attacked leaves of the vegetables of beans, gourds, solanceous fruits and greens in Hainan. Among them, L. sativae Blanchard was found the dominant species on the vegetables of beans, gourds and solanceous fruits, and L. bryoniae (Kaltenbach) on gourds and solanceous fruits, Chromatomyia horticola Goureau on greens.Ten parasites which belong to the families of Braconidae, Eulophidae, Mymaridae, Scelionidae, Encyritidae and Elasmidae were reared from the larvaes and pupaes of leafminers on the attacked leaves of the vegetables of beans, gourds, solanceous fruits and greens in Hainan. Six species belonging to two families (Braconidae and Eulophidae) were identified: Opius dimidiatus (Ashmead) (Braconidae), and Chrysocharis pentheus (Walker), Chrysocharis oscinidis Ashmead, Hemiptarsenus varicornis (Girault), Chrysonotomyia punctiventris (Crawford) and Chrysonotomyia Formosa (Westwood) (Eulophidae). Among them, Chrysocharis pentheus (Walker) was the dominant species.The investigations showed that the respective parasitized percentages of the leafminers on the vegetables of beans, gourds, solanceous fruits and greens inHainan were 27.9%, 25.1%, 22.9% and 21.5%, and 26.0% on the average. The respective parasitized percentages of the vegetable leafminer on beans, gourds, solanceous fruits and greens were 29.1%, 33.0% and 18.0%, and 27.1% on the average. Parasitoids played an important role on the population control of the leafminers in Hainan.The coefficient of interspeicfic association between the vegetable leafminer and its parasites was 0.8658, indicating a significant positive interspeicfic association and a distinct dependent relationship between the parasites and their host.The respective niche widths for the vegetable leafminer and its parasites were 0.8759 and 0.8141 on time dimension, 0.7805 and 0.7527 on space dimension, and 0.6836 and 0.6128 on time-space dimension. The niche widths of the parasites were smaller than that of the vegetable leafminer. This suggested that the parasites were more concentrated than the vegetable leafminer in range and homogeneity on time, space and time-space dimension. The respective niche overlaps for the vegetable leafminer and its parasites on time, space, and time-space dimension were 1.1476, 1.2273 and 1.1875. The niche overlaps were obvious, suggesting that the occurrence of the vegetable leaafminer and their parasites was synchronized on time and similarly distributed on space.Analysis of the data from the natural population life table with the exclusion index of population control (EIPC) showed that the death of larvaes caused by parasitoids was the important factor which indicated effectiveness of control of the vegetable leafminer. The EIPC value of the parasitoids was 3.1817, suggesting the population of the next generation would increase by 3.1817 times if the parasitoids were excluded.