Successful Methods of trapping Trombicula (Acarina) with Notes on rearing T. deliensis, Walch

Extract

The parasitic larvae of a number of Trombiculid mites are of economic importance as they include the vectors of scrub typhus, and scrub-itch mites of considerable nuisance value. Methods of trapping these mites and various field and laboratory observations on them are described. The methods were evolved and observations made during the course of work, sponsored by the Medical Research Council, in Imphal, Assam and Compton, Berkshire.

Live unfed larvae in the field may be concentrated and trapped by use of a low cover with a central light-admitting aperture and collecting apparatus. This method proved very efficient in trapping harvest mites (Trombicula autumnalis) in England. The rise in temperature within the trap can be made advantageous.

Guineapigs were chosen as bait animals for the collection of T. autumnalis at Compton, most of the larvae attaching near the anus and genitalia. The larvae fed for between 30 and 60 hours.

Engorged larvae may easily be collected as they leave their host (or dead animals and débris) by the funicular laboratory light-trap described.

Observations are made on the collection of adult mites, and to a lesser extent nymphs, from soil flotation in water. The vertical migration of adults in relation to soil moisture and temperature is discussed.

Observations on the appearance of larvae of T. autumnalis on a chalk-down at Compton showed a sharp seasonal peak in September, 1946, and some evidence is adduced that this was related to a peak in oviposition.

Observations are made on attempts to rear T. deliensis, the scrub typhus vector in Assam, and notes are added on the behaviour of larval and nymphal mites.