Rl. Bossard et al., Effects of circadian rhythms and other bioassay factors on cat flea (Pulicidae : Siphonaptera) susceptibility to insecticides, J KAN ENT S, 73(1), 2000, pp. 21-29
Variability in insecticide susceptibilities during nylon-disk bioassays of
adult cat fleas (Ctenocephalides felis) due to the time of day the bioassay
was conducted, illumination, density of insects, sex ratio, and CO, exposu
re was investigated. Also examined were illumination effects on flea circad
ian rhythms, as recorded by time-lapse video under 4 lighting conditions (1
2:12 L:D, 12:12 L:D with photophase at night, continuous light, or continuo
us red light simulating darkness), and respiration in bioassay tubes.
The time of day when the bioassay was started (00:30, 7:00, 12:30, 18:30),
dark or light exposure, density (5, 10, 30 fleas/bioassay tube), and sex of
the flea had no effect on mortality. After 24 hr, fleas that had been immo
bilized with CO2 during sexing were more susceptible than unsexed fleas not
exposed to CO2. At 4 and 16 hr, there was no difference. Unsexed fleas imm
obilized with CO2 had intermediate susceptibility.
Fleas showed 24-hr circadian rhythms. When under 12:12 L:D and continuous r
ed light, peak activity was at 21:00 while respiration peaked at 18:00. Act
ivity shifted 6 hr earlier under 12:12 L:D reverse photoperiod. Under conti
nuous light or dark, endogenous rhythms occurred. Respiration of fleas in d
arkness was usually lower than in light. Though activity of fleas varied, i
nsecticide susceptibility was not affected by these conditions. Other facto
rs must contribute to high variability in cat flea susceptibility.