Effects of constant temperature and humidity on the development of the larvae and the pupae of the three Indian species of Xenopsylla (Insecta: Siphonaptera)
Our present knowledge of the bionomics of the Indian rat-fleas, Xenopsylla cheopis (Rothschild), X.astia Rothschild and X. brasiliensis (Baker), which are experimentally proved vectors of plague (Webster & Chitre 1930 p. 422), though not equally effective, is incomplete (Hirst 1926, p. 201; Buxton 1938, p. 505); in view of this fact it was deemed necessary to ascertain the effects of different ecological factors on their development. The primary object of this study is to elucidate the causes governing the fluctuations in the flea numbers. The correlation between outbreaks of plague and the abundance and geographical distribution of these species of rat-fleas has been emphasized by many workers (see, for instance, Advisory Committee 1910, p. 568; Cragg 1921, p. 395; 1923, p. 961). In order to assess the wild populations of the fleas, several workers have made use of ‘flea counts’ of domestic rats; this method, as pointed out by Hirst (1926, p. 248) and Buxton (1938, pp. 505, 528), is hardly adequate for the purpose. Fleas do not always live on rats; a vast majority of them remain in the debris or litter of rat burrows, and a very small proportion of them visit their hosts in order to feed. There is not likely to be a fixed ratio between the number of fleas found on rats and those present in burrows (see Leeson i 936, p. 404; Buxton 1938, p. 528). In consequence, it is doubtful whether the flea counts have any significance. An accurate knowledge of the ecological factors that govern the fluctuations of flea populations is essential.