tively autogenous sub-colony (F₉) (94.33±13.69), egg length x width 575.62±18.06 mm x 186.15±9.35 mm of stock colony was significantly larger than selectively autogenous sub-colony (F₉) (560.49±18.96) mm x 177.99±8.40 mm, and mean longevity of adult female of stock colony [41.60(6-61)] was significantly longer than selectively autogenous sub-colony (F₉) [(35.00(5-39)]. The selectively autogenous sub-colony was established and twenty-two successive generations have been colonized.

(Published in Southeast Asian J Trop Med Public Health 2000;31(2):246-251.)

  DEVELOPMENT OF COMPREHENSIVE RAPID TESTS FOR THE SCREENING
  OF CHEMICAL INSECTICIDE RESISTANCE IN MEDICALLY IMPORTANT
  INSECTS (NO. 742)

Raweewan Suwanich¹, Nazni Wasi Ahamad², Lee Han Lim ²

Key words: insecticide resistance, mixed function oxidases, acetylcholinesterases,

                    The kits for detection of resistance mechanism due to mixed function oxidases and acetylcholinesterases were developed. The shelf life of substrates was a major factor for kit development. Therefore the substrates were kept under 2 conditions : at room temperature and 4^oC. The freshly prepared solution was used as the reference standard. The substrates were 3,3’,5,5’ tetramethylbenzidine (TMBZ) for mixed function oxidases test kit (MFO test kit) and acetylthiocholine iodine (ACTH) for acetylcholinesterases test kit (AChE test kit). The substrates from those conditions were used to detect insecticide resistance on Culex quinquefasciatus by enzyme microassay and detected by ELISA reader.

                    As a result, the MFO test kit, which contained either solid or liquid TMBZ was stable for 5 weeks at 4oC but only 3 days at room temperature. For the AChE test kit, the solid ACTH was stable for 4 weeks at 4 ^oC, while the liquid ACTH was stable 3 days either at room temperature or 4 ^oC . The comparision of effectiveness of the test kit and the standard method of enzyme microassay showed no differences.

                    There was direct correlation between intensity of colour due to enzyme and resistance to insecticide. The eye-score method can be adapted for use in the field for the rapid detection of resistance status due to mixed function oxidases and acetylcholinesterases

  STUDY ON DISTRIBUTION OF FLEAS AND FLEA INDEX IN COMMENSAL
  RATS IN BANGKOK METROPOLITAN AREA (NO. 743)

Key words : flea index, commensal rat, vector of plague

                    The occurrence of plague in India in 1994 was a warning sign of the posible reemergence of this disease in Thailand. The surveillance of plague is of interest especially in Bangkok Metropolitan area where commensal rats are abundant. Therefore, the rat and flea surveys were conducted in 47 districts of Bangkok Metropolitan area. The rats were trapped for 3 consecutive nights in a market which was sampling from each district of the Bangkok Metropolis. The trapped rats were identified, then fleas and other ectoparasites were removed by combing. The fleas were mounted on microscopic slides and identified. From the surveys conducted from March to May 2000 in 47 markets a total of 600 rats were trapped and classified into 6 species, namely Rattus norvegicus, R. rattus, R. exulans, Mus musculus and Suncus murinus in which R. norvegicus was the dominant species (91.67%). Only 119 rats (24.05%) were infested with fleas. A total number of flea was 347 and identified as Xenopsylla cheopis (99.71%) and Ctenocephalides felis felis (0.29%).

                    In addition the results showed an update information on specific flea index in Bangkok Metropolitan area. It was 069 which indicated no risk of plague outbreak. However the surveillance of rats and fleas should be done periodically along with the community participation. Since the oriental rat flea (X. cheopis) are of great importance as vector of plague.

  ISOZYMES AND DIFFERENT FORMS OF AEDES AEGYPTI, THE VECTOR OF
  DENGUE VIRUS (NO. 744)

Key words : Aedes aegypti, abdominal tergel scales, isozyme

                    Dengue fever, dengue haemorrhagic fever and dengue shock syndrome were wide distribute in the tropical and subtropical regions. Since 1958 the first serious epidemic of DHF occurred in Bangkok, further outbreaks have occurred annually with peaks every two years, and the outbreaks are more confined to the rainy season. Though the mortality rate is decrease, the dengue cases are increase every year. Aedes aegypti is the main vector of such diseases. Many aspects of research study on these disease agents and vectors have been carried out. In this paper isozyme of the vector were studied in order to see the vairation between the strains and morphology of the mosquito vector.

                    Aedes aegypti larvae were collected from various provinces as the representation provinces of each part of Thailand. The collected larvae were brought to the insectariums of the Department of Medical, Faculty of Tropical Medicine, Mahidol University, to rear until getting the adults, identification and continue rearing the next generation for further studies.

                    For the morphological study, adult mosquitoes 3-5 days old were used to examine the abdominal tergel scale patterns. There