Sensitivity of aquatic life stages of Xanthocnemis zealandica (Odonata: Zygoptera) to azinphos‐methyi and carbaryi

Abstract

The susceptibility (48‐h LC₅₀ values) of aquatic life stages of Xanthocnemis zealandica McLachlan to azinphos‐methyi and carbaryi was investigated. The LC50 values of azinphos‐methyi did not correlate with instar. The most susceptible stage was instar 7 (LC₅₀ value: 26.6 ppb), and the least susceptible were instars 2 (LC50 value: 50.2 ppb) and 13 (LC₅₀ value: 45.1 ppb). In contrast, LC₅₀ values for carbaryi were positively related to larval instar (instar 2: LC₅₀ value: 156.6 ppb; instar 13: LC₅₀ value: 760 ppb). Damselfly eggs were exposed to insecticide solutions (azinphos‐methyi: control, 0.04, 0.4, 4, and 40 ppb; carbaryi: 0.6 b and 6, 60, and 600 ppb) and hatching success evaluated. Only carbaryi at 600 ppb reduced hatching success significantly. Although the investigation on eggs was carried out at a higher temperature than the LC₅₀ experiments it can be concluded that the egg stage is more resilient to both insecticides than the larval stages.

Keywords:

• azinphos‐methyi
• insecticides
• carbaryi
• egg‐hatching
• instar
• LC₅₀ values
• toxicity
• Odonata