| Rice planthoppers are the most notorious pests of rice in Asia.The planthopper problem may be effectively managed through enhancement of natural biological control. There are numerous natural enemies, especially predators and parasitoids, in paddy ecosystem, which have great potential in controling rice planthoppers. Therefore, it is crucial to understand the relationships between biodiversity and ecological function in rice ecosystem as well as interactions among planthoppers and predators.The predators usually are generalists that prey on other natural enemies as well. A preliminary result to undersand intraguild predation (IGP) among natural enemies was carried out using functional response experiment and multiplex real time quantitative PCR (MQ-PCR) to explore the IGP in rice ecosystem and the main results were listed as follows:Various ITS&5.8S sequences belonged to main predators and parasitoids from rice field were cloned and aligned. Then species/group-special primers and probes were designed and synthesized. The specificity and sensitivity of these species/group-special primers and probes for the MQ-PCR systems were tested and the results showed that the specialism was perfectly hight and no cross-amplification occurred with unrelated arthropod species. The degrees of sensitivity linked to species/group-special primers and probes were128copy/μl for linyphiidae spiders, theridiidae spider, black miridbug (BMB, Tytthus chinensis Stal), green miridbug (GMB, Cyrtorhinus lividipennis Reuter), Anagrus nilaparvatae and A. flaveolus.640copy/μl for Atypena formosana and Dyschiriognatha dentate and about25copy/μl for A.optabilis, Oligosita sp and O. aesopi.Comparative functional responses of2mirids (GMB and BMB) at different development stages, as well as the direction, symmetry and intensity of intraguild predation between the two species were studied in the laboratory. In the meantime, prey preferences of the two mirid species and the influence of alternative preys on functional responses were also evaluated. The mirids exhibited reciprocal intraguild predation (RIGP). All predator-prey combinations showed type Ⅱ functional responses. Adult female and4th instar nymphs of GMB exhibited higher attack rate to eggs of BPH than those of BMB; both the mirids were more voracious when feeding on intraguild preys than extraguild preys. Alterative preys could release the functional response of GMB to both intra-and extra-guild preys. In contrast, alterative preys had no effect on the functional response of BMB. Though IGPs were symmetrical in the absence of extraguild prey, the presence of extraguild prey could affect responses of the mirids and disrupt the symmetry of RIGP.Five prey species, including white-back planthopper (WBPH), BPH, A. nilaparvatae, Oligosita. sp and the mirid, were tested in guts of2mirids by MQ-PCR throughout the paddy season in subtropical area. The results showed that mirids preyed primarily on WBPH and egg parasitoids in early season, but preyed principally upon BPH and heterospecific mirid in late season, which were consisten with their population development patterns. Predatory capacities of two mirids on2rice planthoppers and Oligosita. sp were similar statistically, but the nymph of GMB preyed more frequently on A, nilaparvatae than the nymph of BMB. The potentials for nymph and adult of the same mirid species to prey upon heterospecific mirid and Oligosita. sp were similar. Moreover, the nymphs of mirid preyed on more rice planthoppers and A. nilaparvatae compared with the adults of counterpart mirid species. The predatory capacities of female and male mirids were similar, but the males of BMB consumed more Oligosita. sp compared with the females.The intraguild predation of main predators, including Pardosa pseudoannulata, Tetragnatha maxillosa, Ummeliata insecticeps, Coleosoma octomaculatum, on two mirid species, Ummeliata insecticeps and Coleosoma octomaculatum were investigated in subtropical paddy fields. The results showed that the predation rates of Pardosa pseudoannulata. Tetragnatha maxillosa on Ummeliata insecticeps and Coleosoma octomaculatum were much higher than those on two mirids. In the meantime, the intraguild predations of main predators on Atypena formosana, Dyschiriognatha dentata and GMB were also imnvestigated in tropical paddy fields and the rersults showed that the predation rates of all the main predators tested on GMB were the highestAll the results mentioned above demonstrated that intraguild predation is common and the effects of extraguild and intraguild predations on preys and predators is related to body size and behavior of the relevant species, as well as community structure. More researche is needed to further understand the mechanism and impacts on natural regulation. |
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