The Effect of Relative Humidity on the Activity of the Tropical Rat FleaXenopsylla cheopis(Roths.) (Siphonaptera)

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Abstract
1. The reactions ofXenopsylla cheopisRoths, to uniform and alternative relative humidities have been investigated.2.X. cheopisaggregates in the dry side of the alternative chamber. There is an indication that the intensity of aggregation increases with increase in percentage difference between the alternatives and that it is also high when the alternatives are high in the scale.3. Locomotor activity and speed of movement increase with rise in relative humidity.4. Males kept at 90 per cent. relative humidity for five days aggregate intensely in the drier of the alternatives 65 and 85 per cent. R.H. Similar fleas kept five days at 70 per cent. relative humidity react weakly.5. There is greater activity after five days' exposure to 90 per cent. relative humidity than after exposure to 70 per cent. R.H. for fhe same duration.6. One concludes that high activity in wet air contributes towards aggregation in the dry side and that the intensity of aggregation is affected by the difference in activity which occurs in the fleas at different relative humidities.7. The intensity of aggregation to the alternatives 80 and 90 per cent. relative humidity is unaffected by sex, or by the remains of a blood meal.8. A high klino-kinesis may occur inX. cheopis.9.Nosopsyllus fasciatusreacts in the same way asX. cheopisto uniform and alternative humidities, but there is no evidence of a high klino-kinesis.10. When a roll of lint is dropped into a vessel infested withX. cheopisthe number which jump on to it increases with relative humidity. The number which jumped on to a month-old rat did not show a clear relationship to humidity. Relatively more females than males jumped on to the roll of lint and rat.11. A colony of 25 buck rats was infested withX. cheopis. In relation to size of flea population the flea index increases with rise in relative humidity. The proportion of each sex on a rat, to its respective number in the bedding material, does not appear to bear a simple relationship to humidity.12. Humidity receptors are not confined to the distal three segments of the maxillary palps if indeed there are any there.