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AUDY & HARRISON 
dispersed hosts. Secondly, the vector species T. akamushi and T. deliensis at least have a 
particularly short feeding-time, many other common species taking several times longer to 
complete their feed on the host. The number of vector mites occurring on various populations 
of hosts must therefore be multiplied accordingly before populations which they represent can 
be compared with the populations represented by the infestation data for most of the other 
important species. 
A third adjustment must be made to allow for the short feeding-time of the vector species 
and the particular conditions of collecting. Many of the forest animals collected by the 
aborigines spend a day or even two days in the trap before they reach the laboratory. The 
exact time spent in the traps is often difficult to discover, but sampling surveys suggest that 
about one-third of the animals have been trapped during the night before delivery, one-third 
during the previous night, and the remaining third during the night before that. Applying 
the known feeding-times of the mites (Harrison 1953, this Study p. 171) to these estimates we 
conclude that the observed infestation rates by T. deliensis should be multiplied by one and a 
half, whereas most of the other mites, being of longer feeding-time, will be very little affected. 
Interpreted in the light of these three adjustments, it is clear that the vector mites asso- 
ciated with the commensal rats occur in enormously greater numbers than do any other 
trombiculid mites in the area investigated. This has also been suggested by investigations 
made elsewhere, as for example in Imphal in 1945, and it would probably be safe to generalise 
this observation over the area of distribution of the vectors, excepting possibly in those places 
where their distribution overlaps with that of various species of trombiculids causing scrub- 
itch. Table 3 is discussed elsewhere in this study in relation to the taxonomic and ecological 
relations of these mites (Audy 1953b). 
Miscellaneous Collections 
The major collections from North Borneo and Sarawak, in collaboration with Traub and 
Tom Harrisson, are not discussed here. A survey has been made outside Selangor each year, 
in several cases in the interests of the armed services. Several more such surveys are planned 
for the time when certain areas will be free from bandits. The following four surveys were 
particularly intensive; a number of lesser ones have also been carried out. 
Abandoned Pineapple Estate, Kota Tinggi, Johore 
(10 days — January, 1948) 
Description — Approximately 5,000 acres of overgrown pineapple estate surrounded by 
forest at mile 17, Johore Bahru to Kota Tinggi road, in the extreme south of the peninsula. 
This was to be an important military training centre, and a combined malaria and scrub-typhus 
survey was carried out. All three officers of this unit, supported by three assistants, and by 
Captain Hooper, R.A.M.C., and two R.A.M.C. other ranks from the School of Hygiene at 
Singapore, were occupied on the typhus survey between January 12 and 21, 1948. 
The area had been cleared of forest and planted with pineapples between 1932 and 1934. 
This usually leads to a good deal of soil erosion. In 1940-41, roughly the eastern half of the 
plantation was allowed to revert to scrub under “regeneration control”: lalang grass was 
weeded out at 6-monthly intervals. Pineapple growing continued during the Japanese 
occupation in a desultory fashion at the extreme west section. A small village grew up round 
a sawmill in the centre of the estate, 3 miles from the main road; from it a road goes 
deeply into the forest. 
At the time of our visit, the estate, comprising low hills rising 100-200 feet (to 2-300 ft. 
altitude), was mostly covered with 4-6 foot high “bracken' ’ ( Gleichenia ) undergrowth, with 
young trees along the watercourses, especially Adinandra dumosa which is characteristic of 
STUD. INST. MED. RES. 
