A new insecticide bioassay for assessing the effects of acute insecticide toxicity on lotic insects was developed. It uses first-instar larvae of a net-spinning caddisfly, Cheumatopsyche brevilineata. The test method was suitable for 30 insecticides with a range of action mechanisms. Caddisfly larvae were much more sensitive than daphnids to neonicotinoids. The new bioassay is thus a useful and reliable method for assessing the impact of chemicals such as neonicotinoids, whose risks for lotic insects might be underestimated by the daphnid bioassay.

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.

This paper introduces a new method for the mass-rearing of a typical riverine insect, Cheumatopsyche brevilineata. This caddisfly could be easily reared continuously under laboratory conditions in rotary-flowing water. The rearing system supported the full life cycle year-round, and the culture scale supplied sufficient larvae for bioassays every week. The hatchability of egg masses dipped at F 3 and F 9 but was otherwise stable at Ն70%. The sensitivity of firstinstar larvae to fenitrothion was stable throughout successive generations of a fenitrothion-sensitive strain, and increased gradually in a resistant strain.

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.

The insecticide susceptibility of the brown planthopper, Nilaparvata lugens, and white-backed planthopper, Sogatella furcifera, collected from China and Japan.

e increase in the number of imported cases of dengue fever in Japan is of particular concern as Aedes albopictus is a vector of dengue fever. Due to the potential for insecticide resistance and the impact of insecticides on non-target species, increased attention is being paid to alternative methods of pest control. Placing salt in used tires has been recommended by the Ministry of Health, Labor and Welfare in Japan as a means of controlling mosquitoes. However, the e ectiveness of salt as a larvicide against Ae. albopictus are currently unclear. is study examined the acute toxicity of sodium chloride against rst and fourth larval instars of Ae. albopictus. Acute toxicity tests were conducted according to World Health Organization guidelines. e susceptibility of Ae. albopictus larvae was tested against 0.25%, 0.5%, 0.75%, 1.00%, 1.25% and 1.5% NaCl solutions. Larval mortality was correlated with an increase in NaCl concentration and exposure duration. First instar Ae. albopictus larvae were more sensitive to NaCl than fourth instar, and 72-h LC 90 values for rst and fourth larval instars were 0.49% and 1.01% NaCl, respectively. Our results suggest that the application of 0.5% NaCl to a habitat for 3 days is e ective for Ae. albopictus control.

To determine sensitivity to fenitrothion (MEP), fenobucarb (BPMC) and imidacloprid (IMI) in each larval instar of Cheumatopsyche brevilineata, we carried out 48-hr acute toxicity tests using strains M and K originating from an urban river and an irrigation canal, respectively. First instar was the most sensitive stage to all three insecticides whereas fifth instar was the most insensitive in both strains. Larvae of strain K were significantly more insensitive to MEP through larval growth and to BPMC in second or later instars than larvae of strain M; however, sensitivity to IMI did not differ significantly between strains.

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