| Rice accounts for more than65%of caloric intake in the low-income countries in tropical Asia and is the most important staple food worldwide. Rice planthoppers, included the brown planthopper Nilaparvata lugens, the white-backed planthopper Sogatella furcifera and the small planthopper Laodelphax striatellus, with an annual average occurrence area of26.7million hectares during2005-2007in China, outbreak frequently in recent years, have been the most destructive insect pests of rice in China and other rice growing Asia countries. It has become the substantial threats to the world food security. Enhancement of biological control and increase of ecosystem service functions by ecological engineering measures have become a staple strategy to maximize efficiency of insect pest management and to realize the agro-ecosystem sustainability. The primary target of ecological engineering is to conserve and utilize the natural enemy agents effectively by providing them with non-host foods such as nectar and pollen when hosts are not available, for foods have a deep influence on the longevity, searching efficiency and parasitism(predation) capacity of the female enemies.In this paper, the effect of flowering plants on the main natural enemies of rice planthoppers, Anagrus sp and Cyrtorhinus lividipennis, have been studied. The major findings are as follows:1. The "Y"-tube olfactometer was used to evaluate the preference of the main natural enemies of egg-stage planthoppers to various plant flowers. Results showed that Anagrus wasps and C. lividipennis had different responses to various plant flowers, Anagrus wasps (A. nilaparvatae and A. optabilis) preferted to the flowers of Impatiens balsamena, Emilia sonchifolia and Sesamum indicum, while C. lividipennis adult showed a significant preference to the flowers of Tagetes erecta and Emilia sonchifolia.2. The longevities of Anagrus spp. fed with sesame flowers were significantly longer than that without flowers., meanwhile four kind of flowers, T. erecta, S. indicum, E. sonchifolia and Trida procumbens could markedly prolong female longevity of C. lividipennis, especially fed on T. erecta flower, the female longevity reached at the longest with60.48h. However, flowers of S. indicum and T. erecta were ineffective for C. lividipennis males. Additionally, the longevity of C. lividipennis fed with sesame flowers plus brown planthopper eggs for three days was strongly prolonged compared to that without flowers. The predation on brown planthopper eggs and fecundity of C. lividipennis within three days were significantly improved by feding on sesame plants both with flowers and without flowers, while sesame flower have the most strongly impact. It was implied that the other organs or honey-like nutrional components in sesame plant also had a positive role on C. lividipennis.3. The amount of BPH eggs parasitized by A. nilaparvatae and A. optabilis with sesame flowers were significantly higher than that without flowers, and the effects of various flowers on the predation of C. lividipennis differed, in which sesame flower was the most effective. The predation of C. lividipennis fed with sesame with flowers and BPH eggs was significantly enhanced, while no influence was recorded in the predation of C. lividipennis by feeding with flowering T. procumbens plant. The predation of C. lividipennis male adult on BPH nymphs could be obviously incresed by the flowering plants of T. procumbens, E. sonchifolia, T. erecta and S. indicum, with the most optimum of E. sonchifolia.The handling time (Th) of A. nilaparvataes on BPH eggs with sesame flowers was shorter than that without flowers. The theoretical maximum of BPH eggs parasized by A. nilapai-vataes with sesame flowers reached at78.74eggs/day, which was much higher than that without flowers at44.05eggs/day. The search efficiency of C. lividipennis female adult was significantly improved by T. erecta and sesame plants both with flowers and without flowers, however, its handling time (Th) was significantly reduced as fed with seame plants compared to that without flowers, while no difference was found in handling time between plants of T. erecta with flowers and without flowers. The theoretical maximum of attacked BPH eggs by the C. lividipennis male adult was significantly increased as fed on sesame plants with and without flowers, and on the plants with flowers of T. erecta, E. sonchifolia and T. procumbens. The searching efficiency(a) of C. lividipennis male adult was not improved by E. sonchifolia without flowers. The handling time (Th) can be significantly reduced while the theoretical maximum of its predation was35.71eggs/day higher than the control at24.39eggs/day. Those results were implied that all tested flowering plants could improve the searching efficiency(a) of C. lividipennis except E. sonchifolia with flowers, however, only the flowering sesame could significantly reduce the handling time (Th).4. Nymphal duration of the next generation of female mirid bug (C. lividipennis) was significantly shortened when fed with all the tested flowering plants. However, the duration of male nymphs was shortened only fed with sesame and E. sonchifolia plants. Still, the next generation of male and female ratio of C. lividipennis was not affected by the treatment of flowering plants. In addition, the predation number of the fourth instar nymphs and the next generation of C. lividipennis female adult were significantly enhanced by T. procumbens, E. sonchifolia, T. erecta and sesame, in which sesame is the most effective to the fourth instar nymphs and T. erecta is the most effective to female adult. The handling time (Th) of fourth instar nymphs to BPH eggs was distinctly reduced when fed with sesame (with flowers), T. erecta (with flowers) and E. sonchifolia (with flowers). The theoretical maximum of its predation was the highest at26.32eggs/day in feeding sesame with flowers, followed by T. erecta (with flowers) at20.00eggs/day and E. sonchifolia (with flowers) at18.52eggs/day. The handling time (Th) of the next generation C. lividipennis female adult and male adult can be obviously reduced by sesame and T. erecta plants, but sesame with flowers produced the optimum results. The theoretical maximum number of its predation by male and female could reach to as high as37.04eggs/day and29.41eggs/day, respectively.5. Egg parasitoids of rice planthoppers overwintered in Gramineous host weeds in the ecological engineering areas where sesame planted on bund during the rice season, and in the farmers’field where rice pests were managed by traditional chemical control, have been sampled and identified in Jinhua. Digitaria spp was found as the perfect host for Oligosita (Trichogramma) and Alopecurus and Leersia were the suitable hosts for Anagrus spp and contributed a key role in conserving the population of Anagrus spp. before rice growing season. During rice season, much more parasitic natural enemies were collected by sweep net, yellow sticky boards, yellow pan, BPH egg bait traps and blower-vac machine in the rice ecosystem when planted sesames. |
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