Previous work on the effect of temperature and humidity upon the survival of unfed fleas is criticised in respect of experimental technique. In the present investigation measures have been taken to eliminate as many variables as possible and the methods employed to this end are described.
In the experiments, 2027 Xenopsylla cheopis, 999 X. astia and 646 Ceratophyllus fasciatus were employed, all unfed and less than 24 hours old at the commencement of the different experiments. Records were kept individually so that a statistical measure of consistency could be made.
The following conclusions have been reached:
(1) Duration of life of unfed fleas is not influenced by sex.
(2) High temperatures and low humidities tend to shorten life; conversely, low temperatures and high humidities, with a possible optimum of about 90 per cent., tend to produce longer lives.
(3) Humidity is at its maximum efficiency in this respect at about 18° C.
(4) At 37° C. humidity ceases to have any effect upon the duration of life of unfed fleas, and the evidence suggests that there is also a low temperature at which humidity has no influence upon survival.
(5) There is no direct proportion between survival of unfed fleas and saturation deficiency of the atmosphere at any temperature.
Comparing the species, it was found that:
(1) Ceratophyllus fasciatus was the longest lived, at similar atmospheric conditions.
(2) Xenopsylla astia lived longer than X. cheopis at all humidities at 23° C.