The golden apple snail Pomacea canaliculata is an invasive pest that causes extensive damage to agricultural production. P. canaliculata is also an intermediate host of Angiostrongylus cantonensis, which causes human eosinophilic meningitis. In this study, the molluscicidal activity and safety profile of a novel molluscicide PBQ [1-(4-chlorophenyl)-3-(pyridin-3-yl)urea] were evaluated. PBQ exhibited strong molluscicidal potency against adult and juvenile snails (LC 50 values of 0.39 and 0.07 mg/L, respectively). In field trials, PBQ killed 99.42% of the snails at 0.25 g a.i./m 2 . An acute toxicity test in rats demonstrated that PBQ is a generally nonhazardous chemical. PBQ is also generally safe for nontarget organisms including Brachydanio rerio, Daphnia magna, and Apis mellifera L. Transcriptomics analysis revealed that PBQ had a significant impact on the carbohydrate and lipid metabolism pathways, which provided insights into its molluscicidal mechanism. These results suggest that PBQ could be developed as an effective and safe molluscicide for P. canaliculata control.

Salinity is one of the most important factors for tidal-affected water bodies including estuaries and tidal river reaches. However, due to the limitations of simultaneous manual monitoring in long-distance areas, studies of estuaries are preferred to tidal reaches. Hence, in this study, we investigated the tidal reach of the Minjiang River and five sets of field observations were used to determine the influence of saltwater intrusion in different seasons. During the dry and wet season with low discharge, the longitudinal salinity profiles showed that a station located about 45 km from the river mouth still suffered from saltwater intrusion especially when the upstream discharge was under 754 m s, where the periodical fluctuation in the salinity remained the same with the water level, but there was a time lag of approximately 4 h compared with the discharge process. However, during the wet season in April and May 2016, the monitored salinity was approximately at the detectable limit of 0.02-0.04 ppt at the station close to the river mouth, which indicated that there was no saltwater exchange into the river, although dual flow directions were observed in the survey periods. The major differences among five survey periods were mainly related to upstream discharge rather than the seasons, the tidal range, and tidal excursion. The conclusions of this study have strategic importance for protecting water sources by guiding the government to assess the optimal freshwater release time and discharge rate to prevent saltwater entering the important tidal-affected river reaches.