TAXONOMY OF TROMBICULIDS 
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of branching. It is necessary to show at least all the bases of setae in order to help the worker 
confronted with a specimen in which setae may be missing. 
Certain features are so regularly present that nothing whatever is gained by their 
enumeration in every description. The five special setae on tarsus I are an example. Only 
the rare deviation from this need be noted, as in the case of the multiple spurs in Phrynacarus. 
Regarding the body setae, Audy (1952:153) has appealed for a standardisation in the 
description of the dorsal (DS), caudal or postanal (CS) and ventral (VS) setae. The following 
is an example of a standard description suggested by him: “ Body setae: DS fairly slender, 
similar to PL scutal setae, with short barbs, arranged in rows but with irregular setae medially 
and laterally in the first row and laterally in other rows, e.g., 2.4.10.4.12.6.6.4, totalling 44-60 DS 
(42 to 32M-; humeral setae 45^) -j- caudal setae (CS) in rows on level of and behind anus, 14-16 
CS (total setae of dorsal type 64-74) + 22-26 VS (27^) more slender, with two or three lateral 
barbs and a free pointed tip, arranged roughly in rows and more or less distinct from the caudal 
setae. One pair of sternal setae between coxae I and two pairs of sternal setae between coxae 
III.” Reasons for attention to these differences are given under the genus Fonsecia below 
(p. 148). 
3. Convergence in larval characters. — The very close resemblance between Trombicula 
munda and Euschongastia indica , mentioned on p. 154, is one example of a troublesome problem 
for the taxonomist. The occurrence of T. munda on particular hosts in company with large 
numbers of E. indica and E. audyi , e.g. on Rattus r. diardii in houses, may be interpreted by 
assuming that its life-cycle is passed mostly in or near the nests of its hosts. The resemblance 
between munda and indica would appear to be due to a convergence of characters, and in this 
particular instance this convergence might possibly be associated with the similar habitats which 
the two species appear to share. The present writer is reluctant to assume that there need be 
any particular taxonomic relationship between these two species in spite of the morphological 
evidence. It is obvious that the nymph of munda is of exceptional taxonomic interest, but 
efforts to obtain it have so far failed because this is an uncommon species. 
Another example of convergence is to be found in T. beltrani Hoffman (from a bat in 
Mexico), of which the scutum, the curved claws, and the peculiar small angulated (but not 
toothed) chelicers, give the larva a curiously close resemblance to members of Doloisia sensu 
lato, from ground-mammals in Malaysia and Africa. Both these examples of convergence are 
incidentally between the indica- and Doloisia- groups, which have many features in common 
(p. 154), and what we take to be the subgenus Trombicula. 
When the genus Neoschongastia (see p. 155) is studied intensively it will be necessary to 
consider to what extent the characteristic submergence of the scutum is or is not a polyphyletic 
character, associated perhaps with the avian habitats, possibly resulting in a convergence of 
characters in larvae which should in fact be accommodated in several genera. 
4. Complexes of “ seasonal ” forms. — The presence in the same country of a number of 
closely related species which differ not only morphologically but in having different seasonal 
incidences is extremely interesting. Examples are species of Leptotrombidium in Japan (Nagayo 
et al. 1927), of Neotrombicula in North America (Brennan and Wharton, 1950) and the forms of 
T. (. Neotrombicula ) autumnalis in Britain (Richards, 1949). There is a possibility here of a 
form of ecological subspeciation which is worth investigation. 
For example, the species of Leptotrombidium {akamushi- group) studied by Nagayo et al. in 
north-west Honshu, Japan, showed different seasonal incidences. T. akamushi was the 
dominant species in mid-summer (a single peak of 21 mites per vole was recorded for August, 
1919, dropping to a negligible number in October). T. intermedia appeared for only three 
MALAYA , No. 26, 1953 
