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J. R. AUDY 
months with a peak in October. T. pallida showed one peak in May- June and another in 
September-October (which might suggest that this is a cold-weather species with a 3-4 month 
summer cycle which is extended over some 8 months through the winter). T. palpalis 
resembled T. pallida in having two peaks but it appears to be a true winter species with a peak 
in November followed by a second between January and April, the summer trough being very 
low. A fifth species, T. scutellaris , was not studied by these authors, but it appears to have a 
single peak roughly coinciding with that of T. intermedia. 
The five members of the T. akamushi group thus show different patterns of larval incidence, 
T. akamushi alone dominating the mid-summer. An important point is that though all these 
mites may infest the same hosts, this seasonal behaviour tends to isolate the populations of the 
different species by the phase-dislocation of their various activities. An interesting speculation 
presents itself. The overall climate in a country is broken up by features such as aspect, 
exposure, drainage, and local cloud-formation into a mosaic of local climates — so that for 
example, spring and autumn do not develop exactly in step on the north and south slopes of a 
mountain nor does a prevailing condition produce the same effect in a valley as it does on an 
exposed slope. Such local vagaries of climate, coupled with edaphic factors and perhaps 
phases of behaviour of the hosts, may therefore conceivably tend to set several populations of 
the same species out of step with each other in their life-cycle rhythms, in which case a degree of 
isolation of the populations should tend to develop. The original “ seasonal ” species may 
thus in effect be broken up into a number of isolated populations exposed to different selective 
influences. The writer is not in a position to suggest that something of this sort may explain 
the presence of some of the forms of Leptotrombidium in Japan or of Neotrombicula in America 
and Britain, but such a possibility should be borne in mind when considering the peculiarities 
of speciation in closely similar forms with seasonal individuality. 
Provisional Definition of Taxonomic Units of Old-world Chiggers 
The following list shows the families, subfamilies, genera, and subgenera as accepted by 
Womersley (1952), and Wharton and Fuller (1952), and as tentatively accepted in the present 
paper : 
Abbreviations : 
SUBFAMILIES, GENERA, AND SUBGENERA 
n, a . : nymphs, adults known 
N,A.: known only from nymphs, adults (larvae unknown) 
OIF.: genus /subgenus known only from Old World 
NW . : genus/subgenus known only from New World 
* genus/subgenus described since the publication concerned 
Present paper. 
TROMBICULIDAE ?s. s. 
TROMBICULINAE 
Group A: 
Trombicula 
{ Trombicula s.s .) ?OlF. n.a. . 
(. Eutrombicula s.s.) n.a. 
{. Leptotrombidium s.l.) n.a. 
{ Trombiculindus s.l.) OIF. n. . 
0 Crotiscella ) NW 
{Neotrombicula s.s.) n.a. 
{Blankaartia s.s.) n.a. 
Fonsecia ... 
Tecomatlana 
{ Tecomatlana ) NW. ... 
{ Sauriscus ) OIF. 
( Trisetica ) OIF. 
Wharton and Fuller, 1952. 
TROMBICULIDAE s.l. 
TROMBICULINAE 
Trombicula 
( Trombicula 5./. + ) 
(. Eutrombicula ) 
(. Leptotrombidium 5.5.) 
( Trombiculindus s.s.) ... 
0 Crotiscella ) 
(. Neotrombicula s.s.) ... 
{ Blankaartia s.s.) 
{Fonsecia) 
Tecomatlana 
= Sauriscus — Trisetica 
Womersley, 1952. 
TROMBICULIDAE s.s. 
TROMBICULINAE 
Trombicula 
{Trombicula s.s., partim) 
( Trombicula , partim ) 
{Leptotrombidium s.l.) 
{Trombiculindus s.s.) 
(Crotiscus) 
{Neotrombicula $./. + ) 
Tragardhula ( Blankaartia s.l.) 
Trombicula {Fonsecia) 
Tecomatlana 
— Sauriscus = Trisetica 
STUD. INST. MED. RES. 
