Molluscicidal activity and biochemical impacts of borrelidins against an aquatic invasive snail Pomacea canaliculata for crop protection.

The invasive golden apple snail Pomacea canaliculata is one of the devastating threats to aquatic ecosystems and wetland agriculture worldwide. Macrolides from microbes display various advantages over other compounds in controlling snails. However, emergence of antibiotic-resistant phenotypes against certain macrolides in the field appeals for exploring more effectively molluscicidal macrolides. Here, two borrelidins, borrelidin BN1 and BN2, from the extract of a Streptomyces strain fermentation were evaluated for molluscicidal potential against P. canaliculata using both immersion and contact bioassay methods. Borrelidin BN1 (borrelidin A) presented a significant molluscicidal activity comparable to the chemical pesticide metaldehyde, and had a much lower median lethal concentration value (LC, 522.984 μg·ml) than avermectin B1 at 72 h of contact-killing treatment. Snail growth was inhibited by borrelidin BN1 more than by metaldehyde at sublethal concentrations, consistent with responses of key biochemical parameters. Exposure to borrelidin BN1 decreased the activity of acetylcholinesterase (AChE), glutathione S-transferase (GST), aspartate aminotransferase (AST), alanine aminotransferase (ALT) as well as the levels of energy reserves and sex steroids in snail tissues, while increased the activity of superoxide dismutase (SOD), catalase (CAT), lactate dehydrogenase (LDH) and the level of lipid peroxidation (LPO). Further application assay confirmed that borrelidin BN1 protected crop plant Zizania latifolia from P. canaliculata damage via suppressing snail population density. These findings suggest great potential of borrelidin BN1 as a molluscicide. Additionally, its higher activity than the stereoisomeric borrelidin BN2 (borrelidin F) implied better molluscicidal borrelidins could be acquired through structural optimization.