Distribution of unengorged larvae of Leptotrombidium pallidum and other species in and around the rodent nest holes.

The distribution of unengorged larvae of Leptotrombidium pallidum, L. fuji and L. kitasatoi in and around 12 rodent-nest holes in Oita Prefecture, Japan was studied using the Tullgren funnel apparatus. Soil was taken from each nest hole, and the ground-surface soil and litter from the surrounding area A (an inner quadrate of 20 cm x 20 cm except the nest hole), and also from the outer area B (an outer quadrate of 40 cm x 40 cm excluding A and the nest hole) were sampled, separately. The numbers (% of the total) of L. pallidum collected from soil samples of the nest holes and areas A and B were 38 (19.0), 111 (55.5) and 30 (15.0); those of L. fuji were 171 (58.8), 104 (35.7) and 14 (4.8); those of L. kitasatoi were 35 (77.9), 7 (15.6) and 3 (6.7), and those of G. saduski were 20 (50.0), 17 (42.5) and 3 (7.5). The larvae recovered from litter samples were few, representing 0-8.5% of the total. It is shown that unengorged larvae of these species are distributed not only in the nest holes but also in the nearby areas, and exist mainly on (or in) the soil.

The life history of a colony of Leptotrombidium (Leptotrombidium) fletcheri (Womersley & Heaslip) infected with Rickettsia tsutsugamushi.

The life cycle of 5 generations of Leptotrombidium (L.) fletcheri infected with Rickettsia tsutsugamushi and reared under ambient temperatures in Malaysia was presented and compared with a colony reared at a constant 27 degrees C (Neal and Barnett, 1961). In general our colony had a longer generation time (average of 54 days from engorged larvae to adult compared with 37 days) and produced fewer eggs (average of 127.9 compared with 900.0) than the comparison colony. Possible factors causing these differences are discussed.