• Anaesthesia;
  • behaviour;
  • consumption;
  • German cockroach;
  • movement;
  • toxic bait

Abstract.  Carbon dioxide anaesthesia differentially affects the knockdown and recovery of cockroaches, depending on the strain and the length of time that the colony has been subjected to a CO2 regime. Adult males from two laboratory and two field-collected strains of German cockroaches, Blattella germanica, are knocked down within 7–45 s after exposure to CO2. After 5 min of CO2 exposure, presumptive recovery (i.e. the time for the cockroach to right itself after knockdown) for laboratory strains occurs significantly sooner than for field-collected strains. Control cockroaches, exposed to compressed air rather than CO2, exit harbourage cups rapidly (≤3.20 min). However, although allowed a recovery period of 5 min, significant movement impairment occurs for all cockroach strains anaesthetized with CO2. Carbon dioxide exposure significantly reduces consumption of 2.15% hydramethylnon bait and delays mortality even when 24 h is allowed for recovery before bait placement. Cockroaches allowed to recover for 48 h after 5 min of CO2 exposure consume significantly more bait and die significantly faster than CO2 exposed groups allowed 24 h of recovery, and mortality is not significantly different from nonanaesthetized bait-fed controls.