Effects of Sodium Chloride on Oviposition Behavior of Aedes albopictus.

This study examined the effectiveness of sodium chloride (NaCl) as an oviposition repellent for Aedes albopictus females. Oviposition responses to 0.5%, 0.75%, 1.00%, 1.25%, and 1.5% solutions of pure NaCl were evaluated over 8 days using ovitraps. Gravid Ae. albopictus females showed a reduction in oviposition at all NaCl concentrations. Compared with controls, the inhibition of oviposition ranged from 84.4% to 97.0% at concentrations above 0.5% NaCl. We also show that NaCl is effective for oviposition control of gravid females when laying their overwintering eggs. Our results showed that a 0.5% NaCl solution is effective for use as an oviposition repellent against Ae. albopictus females.

Effects of short-term, sublethal fipronil and its metabolite on dragonfly feeding activity.

Dragonflies, Sympetrum spp., are indispensable to agriculture and are a central element of culture in Japan. However, S. frequens populations in rice paddy fields have declined in recent decades. Dragonfly larvae are predatory aquatic insects that feed on other organisms found in habitats with slow-moving or standing water. The increasing use of fipronil and neonicotinoid insecticides in agriculture is also increasing exposure to Sympetrum spp. in larval stages through paddy soil and water. The role of fipronil insecticides in the decline of dragonflies is of concern, and we here examine the sublethal effects of this insecticide on the feeding behaviors of two Sympetrum spp. Based on the quantity of prey items consumed and the time to capture prey items, feeding inhibition was determined to be a potential mechanism of the decline of Sympetrum spp. following 48-h exposure to fipronil and fipronil sulfone. Prey consumption by S. infuscatum was significantly reduced for fipronil sulfone at all concentrations (0.01-1000 µg/L). S. frequens exposed to 1, 10, 100 and 1000 µg/L fipronil sulfone had significantly longer prey capture times. Fipronil sulfone was 2.8, 9.7 and 10.5 times more toxic to S. infuscatum than fipronil in terms of acute toxicity, feeding inhibition and delayed toxicity, respectively. In addition, fipronil sulfone was 6.6, 2.9 and 9.1 times more toxic, respectively, to S. frequens than fipronil. Our findings suggest that sublethal effects on feeding inhibition lead to severe mortality at realistic paddy soil and water concentrations. Our results provide the first demonstration that short-term exposure to fipronil and fipronil sulfone can consequently cause significant harm to dragonfly larvae survival due to feeding inhibition. These findings have implications for current pesticide risk assessment and dragonfly protection.