The Local Dispersal Of The Rice Water Weevil And Its Relationships With Habitat Quality

The rice water weevil (Lissorhoptrus oryzophilus Kuschel) (Coleoptera: Curculionidae) is an alien insect pest which invaded China in the 1980s. In many newly introduced regions, its geographical distribution has been expanding. But the detailed process and ecological mechanism were not well understood.The field survey carried out in 4 sampling regions in 2 watersheds in the subtropical rice ecosystem in Yueqing, Zhejiang, showed that the distribution of the density of the overwintered rice water weevils (represented by the number of plant leaves with feeding scars, Ns) was negatively and significantly correlated with the distance from the overwintering site (D) (e.g. grass habitat in hilly ramp), which could be described by a linear regression function as: NsO = -0.0346D+4.8975 (R~2=0.9063, P=0.0001). The maximum distance with RWW existence in 142m from overwintering site. Ns was negatively correlated with existence of barnyardgrass Echinochloa crusgalli L, but positively with Leersia herxandra. A good stepwise regression equation was established to describe the distribution of Ns with multiple parameters of habitat quality, and D.In the 2-year field experiments, host plant preference and dispersal of the rice water weevil adults of the 1st generation emerged from the 1st cropping season rice were measured on newly transplanted plants of different species and/or growth stage. The weevil preferred significantly to barnyardgrass over Leersia herxandr and Cyperus difformis L with rice at the least, while the age of the plant did not affect such preference. But mean size of feeding scar in on younger plants were larger than in older plants.The total length of feeding scars on a plant hill was linear correlated with thenumber of feeding scars for all four plant species and all transplanting dates, but the regression coefficient in rice was lower than in bamyardgrass.The dispersal pattern of the rice water weevil of the 1st generation shaped as the closer the more, the far the fewer. The horizontal mean velocity of the weevil of the 1st generation on younger bamyardgrass plants was estimated as 7.2 cm/day, larger than in rice of same age (6.1 cm/day), while no significant difference among the plant species of earlier transplanting (>14 days after transplanting).