9.1 Introduction

Malaria is one of the major public health problems in the world. More than one hundred countries in the world are reported to be indigenous for malaria ⁽¹⁾. The annual occurrence of malaria is estimated at 250 million. The number of deaths attributed to malaria is enormous estimated at 2.5 million ⁽²⁾. In tropical Africa it is estimated that about 150 million people are chronically infected. It is also estimated that one million infants and young children the annually from Plasmodium Falciparum malaria ^(3,4).

In Tanzania malaria is a leading public health problem. Malaria and perinatal mortality are the two largest causes of life years lost. Malaria alone accounts for 16.67 percent of all reported deaths in Tanzania, while perinatal mortality accounts for 13.34 percent of all deaths ⁽⁵⁾. Malaria is also one of the leading causes of morbidity in all regions of Tanzania, ranging from 24.4 percent in Rukwa region, to 42.2 percent in Kigoma ⁽⁶⁾. The prevalence of malaria in Dar es Salaam is high and it has been found to be 48.9 percent ⁽⁷⁾.

The problem of malaria in this country is getting worse for several reasons. These include resistance to first line antimalarial drugs i.e chloroquine, and amodiaquine ⁽⁸⁾. The problem is made worse by mosquitoes developing resistance to some insecticides such as organochlorides, eg DDT ⁽⁹⁾. Even without the resistance efforts to institute control measures have become less due to lack of resources. Of recent malaria has been observed to occur even in high altitude areas like of Kilimanjaro, Iringa, and Arusha ⁽¹⁰⁾ This is attributed to climate becoming warmer thus providing suitable habitats for breeding malaria vector (mosquito). Increased human developmental activities such as construction and soil excavation, improper disposal of containers, and poor sanitation especially in squatters in urban areas all contribute to increased breeding sites for the mosquito vector. Malaria transmission occurs throughout the year, greatly influenced by high temperatures, and humidity, with the highest transmission following the rainy seasons. Low coastal belts and shores of Lake Victoria have the highest transmission.

As malaria vector, Mosquitoes is one of the most important single group of insects with regard to public health. It is a remarkably adaptable and fully cosmopolitan group with over 3,000 species distributed throughout the world ⁽²¹⁾. Few, if any, areas where water is available for their larvae development are free from these insects. Throughout human history, mosquitoes have been a constant impediment to progress, causing great suffering on account of their blood-sucking habits and their ability to support and transmit disease-causing organisms.

Despite natural forces and the extension of environmental changes produced by man, mosquitoes continue to thrive wherever there are human populations. Climatological factors have a considerable influence on mosquitoes and thus on their control. In order to survive mosquitoes must adapt to a given range of climatic conditions. The success of a species or population depends on a complex of environmental conditions any one of which alone, or in combination, may act as a limiting factor; the optimum combination will support the largest population.

All stages in the life cycle of a mosquito are dependent upon a number of environmental factors for their survival and development. Some common and measurable environmental factors, such as wind, light, temperature, rainfall, and humidity, have a known relationship to the survival of mosquitoes that can be used as me basis of an index for use in surveillance and control.