Study On Inter-specific Interactions Between Rice Planthoppers And Relevant Mechanism

Rice planthoppers, including brown planthopper (BPH, Nilaparvata lugens (Stal)), white-backed planthopper (WBPH, Sogotalla furcifera (Horvath)) and small brown planthopper (SBPH, Laodelphax striatellus (Fallen)), have sequentially become destructive insect pests in rice ecosystems in Asia since the1960’s. Although great efforts have been made to reduce rice planthopper problems, there are still simultaneous and frequent outbreaks in the new century. Because all three rice planthoppers have the similar biological characteristics, the inter-specific interactions might be important factors related to the outbreaks. In order to explore the inter-specific interactions between planthoppers and relevant mechanism, this study compared the effects of the intra-specific and inter-specific density effects between planthopper species on their main biological parameters, host selectivity, vertical distribution and feeding behavior, as well as feeding-induced nutrition change in host plants. In the meantime, the feeding-induced effects on genes involved in the synthesis and metabolism of amino acids in rice plant were also analyzed using microarray to explore the plant-mediated mechanism in inter-specific interaction between planthopper species.1. Intra-and inter-specific effects of planthoppers on population performance. There were significant intra-specific competitions for all the three rice planthopper species. The intra-specific competitions resulted in prolonged nymphal development durations, lower emergence rates, shorter female adult longevity and lower fecundity as population density increased. Moreover, the intra-specific density effects were interacted with planthopper species and rice varieties. However, the direct inter-specific interaction between rice planthopper species could facilitate their development and reproduction, but the inter-specific facilitations were interacted with planthopper species, WBPH and SBPH received more facilitative effects from BPH but BPH received less facilitation from WBPH and SBPH. When WBPH and SBPH stayed on the same plants, there would be no direct inter-specific facilitation. Meanwhile, there were also significant indirect induced inter-specific facilitations. The previously feeding by one planthopper species could result in induced inter-specific interactions to the subsequently planthopper species. WBPH and SBPH could receive more induced inter-specific facilitative effects from BPH. Therefore, the inter-specific facilitations were asymmetrical, WBPH and SBPH received more benefits from BPH directly and indirectly.2. Inter-specific effects of planthoppers on host selectivity. Inter-specific interaction between planthopper species could affect their host selectivity. The inter-specific interactions between any combinations of two rice planthopper species, such as BPH and WBPH, BPH and SBPH or WBPH and SBPH, would facilitate planthopper species to select the host plants fed by hetero-species, for example WBPH and SBPH preferred to select BPH-infested plant. This phenomenon was also interacted with planthopper species and rice varieties.3. Inter-specific effects of planthoppers on vertical distribution. The inter-specific interactions between planthopper species could affect their vertical distributions on host plants, but the inter-specific effects were interacted with planthopper species and host plant variety. As the time for coexistence of two planthopper species goes on, the direct inter-specific interaction between BPH and WBPH or BPH and SBPH enhanced WBPH or SBPH moving to the main distribution part of BPH. In the meantime, the direct inter-specific interaction between WBPH and SBPH enhanced SBPH moving to the main distribution part of WBPH on the two varieties and WBPH moving to the main distribution part of SBPH on Xiushui11only, so did the indirect induced inter-specific interaction. Planthopper usually preferred to move to the main distribution part of plant previously infested by hetero-planthopper species. Therefore, the direct and indirect induced inter-specific interactions could expand the ecological distribution of rice planthoppers in rice ecosystems.4. Inter-specific effects of planthoppers on feeding behavior. The induced inter-specific interaction could facilitate their feeding behavior, but the facilitative effects were interacted with planthopper species and rice variety. The inter-specific interaction between BPH and WBPH could facilitate their feeding behavior and resulted in reduction of the number of salivary flanges, the durations for NP waveform and the pathway, and increase of the duration for phloem ingestion on plants infested by con-and hetero-specific planthopper, and WBPH excreted more honeydew on plants infested by BPH. The induced inter-specific interaction between BPH and SBPH could also facilitate feeding behavior of SBPH and resulted in reduction of the numbers of salivary flanges, the durations for NP waveform and the pathway, and increase of the duration for the phloem ingestion and honeydew excreted on plants infested by BPH, but not for BPH, and SBPH received more facilitative effects from induced inter-specific interaction and excreted more honeydew on plants infested by BPH. The induced inter-specific interaction of WBPH and SBPH had no effect on their feeding behavior. The comparison of feeding behaviors showed the feeding capacity of BPH was the most effective feeder, but SBPH was the least.5. Inter-specific effects of planthoppers on rice physiological metabolism. Feeding by three planthoppers could reduce the contents of the metal elements, including Mn、Cu、 Ca、Fe in rice plant depending on planthopper species and density. Meanwhile, feeding by BPH could increase the total amino acids, as well as some amino acids, such as Thr、Glu、Gly、Lys、Arg、Ser, but feeding by WBPH and SBPH did not significantly affect the contents of total amino acids and any single amino acid. Although the feeding of three planthoppers caused reduction of the soluble sugar contents, especially for the sugar content, the changes were not significantly. In this experiment, no significant changes of amino acids and soluble sugar in honeydew excreted by three planthopper species on plants infested by con-and hetero-specific planthoppers were detected.6. Preliminary study on molecular mechanism of inter-specific facilitation. The effects on regulation of genes directly involved in the synthesis and metabolism of amino acids in Xiushui11were analyzed using Affymetrix rice genome oligonucleotide microarray for BPH and WBPH. The results showed BPH induced7genes up-regulated and2genes down-regulated which promoted the transformation of nitrogen and the synthesis of seven amino acids (Lys、Ser、Gly、Cys、Phe、Tyr、Trp). The feeding of WBPH induced9amino acids up-regulated and down-regulated, but no significant changes of amino acids were resulted from the enhanced synthesis and metabolism.Finally, our study revealed that there were significant inter-specific facilitation between rice palnthopper species, but the facilitative effects were interacted with planthopper species and host plant variety. In general, WBPH and SBPH received more facilitative effects from BPH, and BPH could also receive some facilitative effects from WBPH, but not from SBPH, which indicated that the level of facilitation between planthopper species might be related to the feeding capacity since BPH was a most effective feeder. The preliminary study on physiological and molecular mechanisms implied that the inter-specific facilitation between planthopper species could be resulted from the feeding induced changes of gene regulations related to synthesis and metabolism of amino acids in host plants. These results could provide some information for us to understand population development patterns of the three planthopper species at multi-species level, but more detail study is needed to further understand the physiological and molecular mechanisms and develop better IPM program for managing planthoppers sustainably.