Applicability of presence-absence and sequential sampling for ovitrap surveillance of Aedes (Diptera: Culicidae) in Chiang Mai, northern Thailand.

Applicability of presence or absence sampling for ovitrap surveillance of Aedes aegypti (L.) and Aedes albopictus (Skuse) was examined for data collected in Chiang Mai, northern Thailand. Distribution of eggs per trap was contagious but did not fit the negative binomial distribution with a common k. The relationship between the mean number of eggs per trap and the proportion of positive traps was described using Gerrard & Chiang's model, which does not assume particular distribution patterns. Using this relation, the mean number of eggs per trap with confidence limits can be estimated without egg counts. Potential usefulness of presence or absence sequential sampling for decision making (when to initiate vector control for prevention of dengue hemorrhagic fever) was shown.

Scale pattern variations of Aedes aegypti in Chiang Mai, northern Thailand.

Abdominal tergal scale pattern variations of Aedes aegypti were studied in Chiang Mai, northern Thailand for specimens reared from eggs laid in ovitraps set monthly both indoors and outdoors in urban and rural areas. The populations predominantly consisted of the dark type form, regardless of macrohabitats (urban vs. rural), microhabitats (indoor vs. outdoor) or seasons (dry vs. rainy). Among 6,003 specimens, no individuals had pale-scales continuing from the tergal base to its apex on the third tergum and posteriorly.

Ovitrap surveys of dengue vector mosquitoes in Chiang Mai, northern Thailand: seasonal shifts in relative abundance of Aedes albopictus and Ae. aegypti.

Aedes aegypti (L.) and Aedes albopictus (Skuse) were surveyed using ovitraps in residential areas in Chiang Mai, northern Thailand. Egg populations (both species inclusive) remained low in the dry season, but increased/decreased exponentially during the first/latter half of the rainy season, respectively. This seasonal pattern was similar to the seasonal distribution of dengue haemorrhagic fever cases in the area. During the dry season (November-March) Ae.aegypti was dominant in urban and indoor ovitraps. With onset of the rainy season in April, relative abundance of Ae.albopictus increased in rural and outdoor ovitraps. Ae.albopictus displaced Ae.aegypti in the latter half of the rainy season in the rural area. Possible mechanisms to account for this seasonal decline of Ae.aegypti and reciprocal fluctuations in relative abundance of Ae.albopictus are discussed in relation to food availability for larvae in container habitats.