Chigger mites (Acariformes: Trombiculidae) of Southeast Asia, including Myanmar, Malaysia, Brunei, Singapore, Indonesia, Thailand, Cambodia, Vietnam, and the Philippines have been revised based on reference data and examination of type materials in European collections of chiggers. For 450 species of 49 genera synonymy, collection data on types, lists of known host species and lists of countries are given. The lists of hosts include in total 649 valid species and subspecies of mammals, birds, reptiles, amphibians, and arthropods. Two new synonyms were established: Doloisia (Doloisia) Oudemans, 1910 (= Doloisia (Trisetoisia) Vercammen-Grandjean, 1968, syn. nov.) and Gahrliepia lui Chen and Hsu, 1955 (= Gahrliepia (Gateria) octosetosa Chen, Hsu and Wang, 1956, syn. nov.). Twenty-seven new combinations were proposed: Walchia (Ripiaspichia) biliranensis (Brown, 1997), comb. nov., Walchia (Ripiaspichia) huberti (Upham and Nadchatram, 1968), comb. nov., Walchia (Ripiaspichia) parmulaseta (Brown, 1997), comb. nov., and Walchia (Ripiaspichia) serrata (Brown and Goff, 1988), comb. nov., transferred from Gahrliepia Oudemans, 1912; Farrellioides consuetum (Womersley, 1952), comb. nov. (originally in Trombicula Berlese, 1905), Farrellioides nakatae (Nadchatram and Traub, 1964), comb. nov. (originally in Leptotrombidium Nagayo, Miyagawa, Mitamura and Imamura, 1916), and Farrellioides striatum (Nadchatram and Traub, 1964), comb. nov. (originally in Leptotrombidium), transferred from Euschoengastia Ewing, 1938; Guntheria (Phyllacarus) bushlandi (Philip, 1947), comb. nov. (originally in Ascoschoengastia Ewing, 1946), transferred from Guntherana Womersley and Heaslip, 1943 (syn. of Guntheria Womersley, 1939); Kayella masta (Traub and Sundermeyer, 1950), comb. nov. (originally in Ascoschoengastia), transferred from Cordiseta Hoffmann, 1954; Neoschoengastia stekolnikovi (Kalúz, 2016), comb. nov., transferred from Hypogastia Vercammen-Grandjean, 1967; Susa chiropteraphilus (Brown, 1997), comb. nov., Susa masawanensis (Brown, 1998), comb. nov., and Susa palawanensis (Brown and Goff, 1988), comb. nov., transferred from Cheladonta Lipovsky, Crossley and Loomis, 1955; Ericotrombidium cosmetopode (Vercammen-Grandjean and Langston, 1971), comb. nov., transferred from Leptotrombidium; Eutrombicula gigarara (Brown, 1997), comb. nov., transferred from Siseca Audy, 1956; Microtrombicula eltoni (Audy, 1956), comb. nov., transferred from Eltonella Audy, 1956; Trombiculindus alethrix (Traub and Nadchatram, 1967), comb. nov., Trombiculindus cuteanum (Vercammen-Grandjean and Langston, 1976), comb. nov., Trombiculindus frondosum (Traub and Nadchatram, 1967), comb. nov., Trombiculindus hastatum (Gater, 1932), comb. nov., Trombiculindus lepismatum (Traub and Nadchatram, 1967), comb. nov., Trombiculindus limi (Traub and Nadchatram, 1967), comb. nov., Trombiculindus maxwelli (Traub and Nadchatram, 1967), comb. nov., Trombiculindus roseannleilaniae (Brown, 1992), comb. nov., Trombiculindus sarisatum (Traub and Nadchatram, 1967), comb. nov., Trombiculindus vanpeeneni (Hadi and Carney, 1977), comb. nov., and Trombiculindus yooni (Traub and Nadchatram, 1967), comb. nov., transferred from Leptotrombidium.
Mite foci were fenced above and below ground to prevent the entry of host animals and to prevent the migration of mites within the soil. Weekly counts were made over a period of thirty weeks with larvae being collected at the beginning and end of the study, but not during the intervening period of hot, dry weather. Post-larval forms can survive for long periods and mite foci can remain productive without being visited by the host animals. Mite foci may be missed by normal survey methods during hot, dry weather.
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.
Leptotrombidium (Leptotrombidium) umbricola, described here as a new species, is a member of the L. (L.) deliense group and most closely resembles L. (L.) vivericola. L. (L.) umbricola was collected from the ground surface and from animal hosts, in similar habitats to the scrub typhus vector, L. (L.) deliense. The host and habitat distribution records and the Rickettsia tsutsugamushi infection rates within unengorged specimens suggest that L. (L.) umbricola may be an important vector of scrub typhus in Peninsular Malaysia.
Orientia tsutsugamushi is the causative agent of scrub typhus vectored by larval stages of trombiculid mites (chiggers) that occur in most tropical regions of Southeast Asia. A total of 242 chiggers extracted from eight small mammals captured from a positive scrub typhus locality in Kelantan, Malaysia, were screened for the presence of O. tsutsugamushi. The chiggers were grouped in 16 pools for extraction of DNA prior to screening of O. tsutsugamushi based on the nucleotide sequence of 56-kDa type specific antigen (TSA) gene using nested polymerase chain reaction. Two species of on-host chiggers were identified, the one, Leptotrombidium deliense, much more dominant (94.8%) than the other, Ascoshoengastia sp. (5.2%). The pathogen was detected in two pools (12.5%) of L. deliense recovered from Rattus rattus and Tupaia sp. The 56-kDa TSA gene sequence analysis revealed the O. tsutsugamushi harboured in those chiggers were Karp prototype strain with high similarity (99.3%). Findings of this study strongly supported the existence of scrub typhus infections in certain parts of Malaysia which agrees with previous local reports. Moreover, this study highlighted the pressing need of a large-scale close observation of O. tsutsugamushi DNA sequences from chiggers that can probably be collected from other positive scrub typhus localities to precisely provide the distribution and prevalence of this zoonotic pathogen.
Four commercial repellents were evaluated in the laboratory against Leptotrombidium deliense chiggers. Both in vitro and in vivo methods were used to determine repellency of the compounds. The repellents were Kellis (containing citronella oil, jojoba oil and tea tree oil), Kaps (containing citronella oil), BioZ (containing citronella oil, geranium oil and lemon grass oil) and Off (containing DEET). The combination of three active ingredients: citronella oil, geranium oil, lemon grass oil gave the highest repellency (87%) followed by DEET (84%). In vitro repellencies ranged from 73% to 87%. There was no significant difference between the four products. All the repellents had 100% in vivo repellency compared to 41-57% for the controls.
Two commercial repellants were evaluated in the laboratory against Leptotrombidium fletcheri chiggers. The active ingredient in one was DEET and in the other was citrus oil. Excito-toxicity effect was studied and it was determined by the time ("escape time") chiggers took to move off filter papers treated with the repellants. All chiggers exposed on filter papers treated with DEET died and did not move off the treated papers. None of the chiggers that were placed on papers treated with citrus oil were killed. Escape times on papers treated with a 2-sec spray of citrus oil were longer than those for the 4- and 8-sec sprays. The weights of citrus oil deposited increased with increasing spray times. Electron microscopy showed that the repellants had no effect on the texture of the filter papers. It was concluded that the spray containing DEET was more effective; however, both repellants should be further evaluated under field conditions for protection against chigger bites.
Studies of larval mite populations along transects, as measured with black plates, were conducted in forest and grassland habitats for a period of 67 weeks. Larvae of both Leptotrombidium (Leptotrombidium) deliense and L. (L.) fletcheri were influenced greatly by rainfall, with the larvae being abundant and easily collected during periods of heavy rainfall and difficult or impossible to collect during dry periods. Simulated rainfall maintained larval populations for longer periods during dry weather.
The populations of scrub typhus vector chiggers were compared in two developing oil palm areas, one 5 years old and the other 7 years old at the inception of the study. Both areas were located within the same oil palm scheme in central Peninsular Malaysia. Leptotrombidium (L.) deliense, a principal vector of scrub typhus in Malaysia, was found in reduced numbers in the older oil palm habitat. This reduction is attributed to changes in the microhabitat, specifically the elimination of grasses between the oil palm trees due to canopy shading and to cultural practices.
Leptotrombidium (Leptotrombidium) arenicola Traub, a vector of scrub typhus, had previously been found to occur in the coastal vegetation behind the edge of open sand along the beaches of Peninsular Malaysia. Surveys of the west coast beaches of Sabah and Sarawak were conducted to determine if this species occurs in similar habitat in East Malaysia on the island of Borneo. Leptotrombidium (L.) arenicola was not collected from the eighteen sites studied. Of the 11,982 mite larvae collected, 55 per cent were L.(L.) deliense (Walch), a well-known, widespread vector of scrub typhus.
A dot-immunobinding assay (DIBA) was compared with a direct fluorescent antibody technique (DFAT) for the detection of Rickettsia tsutsugamushi infection in Leptotrombidium fletcheri (Womersley & Heaslip). Laboratory colonies of infected and noninfected chiggers were examined. The relative proportions of positive, negative, and indeterminate results were significantly different between DIBA and DFAT for infected but not for noninfected chiggers. DIBA was more sensitive and had a better negative predictive value and a lower false negative percentage than DFAT. It was concluded that DIBA is a suitable alternative to DFAT for detecting scrub typhus infection in chiggers.
Five pesticides were evaluated against laboratory colonies of Leptotrombidium fletcheri (Womersly and Heaslip) by the Pasteur pipet technique. The pesticides were dieldrin (LC50 = 3.6 ppm, LC99 = 18.2 ppm), bromopropylate (LC50 = 9.2 ppm, LC99 = 239.6 ppm), dicofol (LC50 = 27.8 ppm, LC99 = 118.1 ppm), fenthion (LC50 = 15.4 ppm, LC99 = 29.7 ppm), and malathion (LC50 = 84.7 ppm, LC99 = 313.9 ppm). Dieldrin was the most toxic. Dicofol was recommended for further evaluation in field trials.