Survival and Reproduction of a Laboratory Strain of Body Lice (Phthiraptera: Pediculidae) at Different Ambient Temperatures

Abstract:
In order to elucidate the role of temperature as a crucial survival factor for human body lice (Pediculus humanus humanus), we investigated the influence of different temperature regimes on survival of adult lice after their last blood meal as well as on oviposition and egg hatch rates. The Federal Environment Agency (FEA) maintains a laboratory colony of the human body louse Pediculus humanus humanus for efficacy testing of pediculicides, since the human body louse has proved to be an appropriate test organism for testing products for the control of its subspecies relative, the head louse Pediculus humanus capitis. The lice are reared on rabbits as substitute hosts. The laboratory lice are fed on Chinchilla bastard rabbits 4 to 5 times per week for ca. 15 minutes. Between daily feeding the lice are stored for routine cultivation at 32°C and 45-55% relative humidity and on non-feeding days at 25°C and 45-55% relative humidity. For investigation of survival and reproduction of lice, male and female adults were fed and then subsequently stored at ambient temperatures (TA) between 16°C and 32°C at 45-55% relative humidity. The survival of unfed adults is negatively correlated with increasing temperature, with the longest survival (15 days) at an ambient temperature (TA) of 16°C and the shortest survival at TA 32°C (4-5 days). In contrast to this, oviposition rates as well as egg hatch rates were positively correlated with increase of temperature (1.15 eggs/d/female at TA 22°C and 3.52 eggs/d/female at TA 32 °C). The ambient temperature (TA 25°C or 32°C) female lice experienced before and during oviposition had only a weak influence on egg hatch rates and oviposition rates. Experiments on influence of different temperature regimes revealed that eggs must at least be incubated for 5 days after oviposition at TA > 25°C. Egg which were first incubated at TA 25°C and then transferred to TA 32°C had high hatch rates, indicating that the early development of eggs after oviposition is less temperature sensitive than later development.