MALAYSIAN PARASITES V 
SPECIES OF EUSCHONGASTIA SENSU LATO (ACARINA TROMBICULIDAE) 
FROM BORNEO 
By 
ROBERT TRAUB and J. R. AUDY 
This paper describes the larvae of six new species of Euschongastia Ewing, 1938. Five of 
these were collected by the joint U.S. Army and Colonial Office research units on Mt. Kinabalu, 
and the sixth was collected both in Sarawak (in collaboration with Mr. Tom Harrisson) and in 
the Kinabalu and Beaufort areas of North Borneo. The circumstances of the collections have 
been described in the previous paper (Traub and Audy, 1953, this Study , p. 45). As in 
other papers of this series, a species is first described in detail and only salient differences are 
described for subsequent closely-related species. 
The genus Euschongastia is here taken in a broad sense to include the oudemansi-group 
placed in the genus Walchiella by Fuller, 1952. Chiggers of this genus are important and very 
abundant parasites of rodents, and it is to be expected that at least some of them are of medical 
significance. This is supported, for example, by the isolation by Traub et al. (1950) of the 
rickettsiae of scrub typhus from a species of Euschongastia subsequently described as E. audyi 
(Womersley, 1952)*. The chiggers had been collected from a squirrel in the primary forest in 
Malaya. Gispen, also in 1950, reported the isolation of the rickettsiae of murine typhus from 
E. indica (Hirst, 1915) in Indonesia. Although no New World species of Euschongastia is 
definitely known to bite man, various species may be responsible for transmission of infections 
among their animal hosts, and thus be of considerable indirect medical importance. 
Euschongastia indicella n. sp. (figs. 1-8). 
Diagtiosis of larva. — In the E. indica group, and close to E. labuanensis Womersley, 1952 
in having a very small scutum, but separable from it in that the posterior margin of the scutum 
in the new species is slightly convex, not concave (PSB 20 or more, not 11), the ALs are 
relatively quite removed from the anterior margin (closer to margin of sensillary bases than to 
anterior margin of scutum) instead of being submarginal; there are only about 30-34 dorsal 
setae, arranged 2.8.6...., instead of 62 arranged 2. 10. 10. 10.... 
Description of Larva. — Body: Subovate, about 250 x 1850. when slightly engorged. Eyes apparently 
1 T ij about 4.5a. in diameter; slightly closer to level of AL than PL. Gnathosome: Chelicerae each about 
three times as long as broad at base; lacking dorsal teeth, with a small subapical medial and also lateral 
tooth forming characteristic tricuspid cap. Palpal coxae and femora punctate. Palpal setal formula 
b(N)/b/bbb+ ; the degree of fraying rather variable but setae usually with 1-3 short barbules. Palpal 
tarsus with a basal striated rod and about 5 bristles, most of these branched. Palpal claw 2-pronged, 
medial prong somewhat longer than lateral. Galeal seta N (i.e. nude). Palpal coxal seta with 3 branches. 
Scutum: very small (PW less than 5010.) ; about three-fourths as long as broad at maximum; somewhat 
trapezoidal, but anterior margin not much shorter than posterior margin, lateral margins slightly concave ; 
anterior margin almost straight; posterior margin slightly convex, almost straight, but laterally mildly 
sinuate. Scutal setae short, none equal to half of PW ; barbs very short so that setae appear tomentose or 
roughly pubescent. With distinct ridges anterior to sensillary bases. Sensillae clavate; clothed with 
long spicules (5a). AL setae displaced caudad, nearer to the sensillary ridge that to anterior margin. 
Body Setae: Dorsal setae similar to scutal setae; about 32-34 in number, usually arranged 2. 8. 6. 6.4. 4(2). 2. 
With about 30-34 ventral setae, of which about 12 are postanals (caudal setae). True ventral setae about 
12-14U, distinctly branched and apically more acuminate than are the caudals and true dorsals. Legs: 
Coxae and legs punctate. All coxae unisetose, the setae slender and with inapparent branches. Seta on 
coxa II nude; others resembling the pair of sternal setae between junction of coxae I and II and the sternal 
pair between coxae III. Seta on coxa III midway between midpoint and anterior margin. Posterior 
* This species was originally cited as E. indica. Since then this chigger, which is a dominant and characteristic parasite 
of tree-living mammals in the Malayan forests, has been identified with E. audyi described by Wcmersley in 1952 frcm material 
from South Burma ( J.R.A . coll., viii.1945). It is also present in North Borneo and Sarawak. 
MALA YA, No. 26 , 1953 
