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PubMed1993

Dynamics of population densities and vegetation associations of Anopheles albimanus larvae in a coastal area of southern Chiapas, Mexico.

Spatial and seasonal variations on Anopheles albimanus larval densities and their plant associations were investigated in larval habitats in southern Mexico between April 1989 and May 1990. Thirty-four plant groups were dominant in larval habitats. Dense larval populations were associated with 3 genera of plants, Cynodon, Echinocloa and Fimbristylis and no larvae were found in habitats with Salvinia and Rhizophora. Low significant positive or negative associations were documented with the other 12 plant genera. Larval habitats were classified according to the morphology of their dominant plants. Higher larval densities were observed in the groups characterized by relatively short emergent vegetation. The distribution of habitat-types within 5 identified vegetation units showed a significantly dependent relationship. For the entire study period, highest larval densities were detected in flooded pasture/grassland vegetation units. For all vegetation units, higher larval densities were found when the dominant plant type covered between 25-50% of the breeding site. The integration of data from habitat-types into vegetation units did not result in loss of information.

Animals↗
PubMedDate not supplied

[Method of determination of population density of the Aedes (Culicidae)].

For 6 years 16 species of the genus Aedes were recorded from the territory of Leningrad. To judge by the per cent ratio between mosquitoes and their larvae, such species as A. caspius dorsalic and A. flavescens such blood of man unwillingly and A. cantans and A. cinereus attack man in general. The abundance of Aedes population within the territory of Leningrad was estimated on the number of pupae per 1 m2 in various types of water bodies for the whole reproduction season by means of multiplication of the number of papae per 1 m2 by the whole area where aquatic stages of mosquitoes were observed.

Aedes↗
PubMed2000

Impact of climatic change on the northern latitude limit and population density of the disease-transmitting European tick Ixodes ricinus.

We examined whether a reported northward expansion of the geographic distribution limit of the disease-transmitting tick Ixodes ricinus and an increased tick density between the early 1980s and mid-1990s in Sweden was related to climatic changes. The annual number of days with minimum temperatures above vital bioclimatic thresholds for the tick's life-cycle dynamics were related to tick density in both the early 1980s and the mid-1990s in 20 districts in central and northern Sweden. The winters were markedly milder in all of the study areas in the 1990s as compared to the 1980s. Our results indicate that the reported northern shift in the distribution limit of ticks is related to fewer days during the winter seasons with low minimum temperatures, i.e., below -12 degrees C. At high latitudes, low winter temperatures had the clearest impact on tick distribution. Further south, a combination of mild winters (fewer days with minimum temperatures below -7 degrees C) and extended spring and autumn seasons (more days with minimum temperatures from 5 to 8 degrees C) was related to increases in tick density. We conclude that the relatively mild climate of the 1990s in Sweden is probably one of the primary reasons for the observed increase of density and geographic range of I. ricinus ticks.

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