Polygamy: the possibly significant behavior of Aedes aegypti and Aedes albopictus in relation to the efficient transmission of dengue virus.

The polygamous behavior of male Aedes aegypti (L.) and Ae. albopictus (Skuse) was investigated by co-habiting a newly-emerged male and females in a 30 cm3 cage (1 male: 20 females) for up to 5 consecutive days. As determined by insemination rates, the results indicated that one Ae. aegypti and Ae. albopictus male could successfully mate with 1.10 (0-4), 4.10 (1-8), 5.40 (4-8), 5.10 (2-8), 5.15 (3-9) and 0.20 (0-3), 1.70 (0-3), 2.35 (1-4), 2.30 (0-4), 2.35 (1-4) Ae. aegypti and Ae. albopictus females, respectively on day 1,2,3,4 and 5 consecutively. The possibly significant role of their polygamy in relation to dengue virus transmission is discussed.

The application of ethanol-extracted Gloriosa superba for metaphase chromosome preparation in mosquitos.

The application of ethanol-extracted Gloriosa superba for metaphase chromosome preparation in adult and 4th larva Aedes aegypti revealed that 0.5-8% ethanol-extracted Gl. superba solution could be used instead of 1% colchicine in Hanks' balanced salt solution. For adult mosquitos, the metaphase rates and average number of metaphase chromosomes per positive mosquito after intrathoracic inoculation with 1-2% ethanol-extracted Gl. superba solution were 100% and 11.8 (2-16) -12.6 (3-28) in females, and 80-90% and 16.5 (1-52) - 29.89 (1-72) in males, whereas the inoculation with 1% colchicine solution yielded 80% and 50% metaphase rates, and 18.25 (1-40) and 16.5 (2-53) average number of metaphase chromosomes per positive mosquito in females and males, respectively. For 4th stage larvae, the metaphase rates and average number of metaphase chromosomes per positive mosquito after incubation with 0.5-8% ethanol-extracted Gl. superba solution were 90-100% and 14.42 (1-65) - 64 (19-137), while incubation with 1% colchicine solution yield 100% metaphase rate and 10.9 (7-15) average number of metaphase chromosomes per positive mosquito.

Larvicidal, adulticidal and repellent effects of Kaempferia galanga.

Four fractions of Kaempferia galanga (hexane fraction, dichloromethane fraction 1, dichloromethane fraction 2 and methanolic fraction) were tested for larvicidal activity toward fourth instar Culex quinquefasciatus. The hexane fraction was found to exhibit the highest larvicidal effect with the LC50 of 42.33 ppm. Testing for adulticidal activity, the hexane fraction did not show any promising adulticidal effect. However, it caused a knockdown effect which might be useful as a repellent. It was then tested for repellent activity in human volunteers both in laboratory and field studies. In a laboratory study, the hexane fraction possessed repellency against Aedes aegypti (ED50 value of 30.73 microg/cm2), and provided biting protection for 3 hours. In a field study, it could protect against certain mosquitos, ie, Armigeres subalbatus, Anopheles barbirostris, An. aconitus, Mansonia uniformis, Cx. quinquefasciatus, Cx. gelidus, Cx. tritaeniorhynchus and Ae. aegypti. The hexane fraction did not cause dermal irritation when applied on human skin.

Isoenzyme study and hybridization of two forms of Anopheles sinensis (Diptera: Culicidae) in northern Thailand.

The screening of ten isoenzymes of two forms of Anopheles sinensis, Form A and B, using electrophoretic gels revealed that Est-5(96) allele was the marker in both 4th larva and adult female of An. sinensis Form B, whereas it was lacking in Form A. Hybridization tests of the two sinensis forms were done by induced copulation. The results of crosses indicated that they were genetically compatible, providing viable progeny and completely synaptic polytene chromosomes.

Screening for larvicidal activity of ten carminative plants.

Ten species of plants, reported to possess carminative property, were screened for larvicidal potential against Culex quinquefasciatus by exposing early 4th instar larvae to a series of concentrations of the ethanolic extracts of the plants. Mortality counts were made after 24 hours exposure. Probit analysis using computerized Harvard Programming (Hg1, 2) was employed to determine the LC50, LC95 and LC99 values in order to compare the larvicidal potency of the ten plants. Marked larvicidal effects were seen with Kaempferia galanga, Illicium vernum and Spilanthes acmella having LC50 values of 50.54, 54.11 and 61.43 ppm, respectively.