Relationship between larval habitat characteristics and malaria vectorial capacity of adult Anopheles dirus in Chanthaburi Province, Thailand

Field studies were conducted in Tha-Mai District, Chanthaburi Province. Larval habitat characteristics of 42 gem pits were examined from November 1986 through June 1988. Larvae were found in pits containing clear water under full or partial shade. Relationships between habitat characteristics and density were tested by stepwise regression analysis. High dissolved oxygen and humidity and low pH were associated with higher densities. Populations fluctuated with rainfall. Stepwise logistic regression analysis was used to predict the occurrence of An. dirus. Populations were positively correlated with humidity and collection water temperature but negatively correlated with pH and minimum water temperature. Variations in occurrence and density also were related to predators (Notonectidae and fish).;High minimum water temperature and rainfall were correlated with decreases in wing length among both emerging males and females. High turbidity was associated with increased size in male but not in female. Seasonal variation in the size of both sexes was related to rainfall. Minimum water temperature, pH, protein and rainfall were correlated with the survivorship of emerging An. dirus. Adult size was positively correlated with survivorship but not as strongly as in lab-reared populations.;Mean wing length of nulliparous females (3.035 mm) was not significantly smaller than parous females (3.039 mm). However, there was a significant difference when seasonal variation was considered. Since size variation was correlated with rainfall and minimum air temperature, females tended to be smaller in the rainy season and larger (with a higher parity rate) in the dry season. On average, ;Four size classes of An. dirus were reared from different larval densities. Higher densities produced smaller adults with lower survivorship. Larger females took larger blood meals and thereby were more susceptible to infection by artificial feeding with cultured P. falciparum gametocytes.