Sensitivity of aquatic life stages of Xanthocnemis zealandica (Odonata : Zygoptera) to azinphos-methyl and carbaryl

The susceptibility (48-h LC50 values) of aquatic life stages of Xanthocnemi s zealandica McLachlan to azinphos-methyl and carbaryl was investigated. Th e LC50 values of azinphos-methyl did not correlate with instar. The most su sceptible stage was instar 7 (LC50 value: 26.6 ppb), and the least suscepti ble were instars 2 (LC50 value: 50.2 ppb) and 13 (LC50 value: 45.1 ppb). In contrast, LC50 values for carbaryl were positively related to larval insta r (instar 2. LC50 value: 156.6 ppb; instar 13: LC50 value: 760 ppb). Damsel fly eggs were exposed to insecticide solutions (azinphos-methyl: control, 0 .04, 0.4, 4, and 40 ppb; carbaryl: 0.6 b and 6, 60, and 600 ppb) and hatchi ng success evaluated. Only carbaryl at 600 ppb reduced hatching success sig nificantly. Although the investigation on eggs was carried out at a higher temperature than the LC50 experiments it can be concluded that the egg stag e is more resilient to both insecticides than the larval stages.