New Zealand Journal of Marine and Freshwater Research abstracts

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

SÖNKE HARDERSEN^*
STEVE D. WRATTEN

Soil, Plant and Ecological Sciences Division
Ecology and Entomology Group
P. O. Box 84
Lincoln University
Canterbury, New Zealand
email: sonke7hard@aol.com

^*Present address: Tiergartenstrasse 111, 47533  Kleve, Germany.

Abstract  The susceptibility (48-h LC50 values) of aquatic life stages of Xanthocnemis zealandica McLachlan to azinphos-methyl and carbaryl was investigated. The LC50 values of azinphos-methyl 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 carbaryl 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-methyl: control, 0.04, 0.4, 4, and 40 ppb; carbaryl: 0.6 b and 6 , 60, and 600 ppb) and hatching success evaluated. Only carbaryl 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-methyl; insecticides; carbaryl; egg-hatching; instar; LC50 values; toxicity; Odonata

M98054
Received 5 August 1998; accepted 12 August 1999

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