JMR-2017v7n17 - page 7

Journal of Mosquito Research 2017, Vol.7, No.17, 134-141
135
reported loss of diversity resulting from the de-structuring of physico-chemical conditions and alteration of natural
dynamics of biological communities in aquatic ecosystems. Rice agro-ecosystems provide ideal breeding habitats
for mosquito species. For example, rice irrigation farming is associated with the production of vectors that
transmit pathogens to humans, including those responsible for malaria (Muturi et al
.
, 2006).
Large scale environmental modification concomitant with processes such as forest clearing, irrigation
development, human settlement and rice cultivation, inevitably result in changes in surface water quality and
affect the survival of mosquito species breeding in surface water habitats (Yusuf and Olayemi, 2015). The
physicochemical factors in Minna that influence oviposition, survival and spatio-temporal distribution of
mosquito species in rice fields, include salts, dissolve organic and inorganic matter, degree of eutrophication,
turbidity, presence of suspended mud, vegetation, temperature, light or shade and hydrogen ion concentration,
which also may be affected by agrochemical inputs used in rice farming (Yusuf and Olayemi, 2015).
According to Lacey and Lacey (1990), Rice cultivation has traditionally been associated with vector-borne
diseases, especially malaria and Japanese encephalitis. The mosquito vectors of these diseases lay eggs in standing
water and the larvae need about 7-10 days in an aquatic environment to complete development to adults. The
intermittent drying of rice fields was, therefore, tested for its mosquito control potential as far back as the early
twentieth century (Takken et al., 1990). With the introduction of DDT after World War II, water management and
other environmental measures to control mosquitoes were neglected. It is only since the 1980s, after the failure of
the DDT-based eradication campaigns of malaria that environmental control measures are receiving renewed
attention (Van der et al., 2001).
Olayemi et al. (2014) have documented the presence of high densities and diversity of vector mosquito species in
Minna, the capital city of Niger state, and reported that drainages and rice fields were the most productive
mosquito larval habitats in the city. Rice is widely grown in Minna, and is one of the most suitable habitats for
mosquito larva productivity (Olayemi et al., 2014). The impacts of agrochemical inputs on the productivity of rice
field mosquito larval habitats in Nigeria, generally, and Niger state, in particular, have not been well investigated,
thus making sustainable cost effective rice production a problem in the country.
1 Materials and Methods
1.1 Study area
The study was carried out in Minna, the capital of Niger State, Nigeria, located within longitude 6
0
33’E and
latitude 9
0
37’N, on a land area of 88 km
2
and having a population of about 1.2 million inhabitants. Minna has a
typical tropical climate with mean annual temperature of 30.2
o
C, relative humidity of 61% and rainfall of 1334
mm. The climate in the area has two distinct seasons: rainy season (April-October) and a dry season
(November-March), completely devoid of rains. Its vegetation is typically grass-dominated savannah with
scattered short trees (Olayemi et al., 2009). Basically, four types of wetland rice ecosystems are present in Minna,
which include irrigated, rain-fed low upland and wetland rice ecosystems, with the irrigated rice environment
been the dominant (Akintayo, 2011). Farming is a major pre-occupation of the inhabitants of Minna and environs,
with the area particularly famous for rice production; being a staple food in the area.
1.2 Selection of rice field mosquito larval habitats
Questionnaire were administered to farmers to determine the types and combinations of agricultural chemical
inputs, i.e., chemical fertilizer, herbicides or both, commonly used in rice farming in Minna. Thereafter, guided by
the results of the questionnaire test, three types of rice farming chemical inputs sites in two rice field categories,
rain-fed lowland and irrigated ecosystems were selected each with three replicates. The three types of sites were
named: type A (rice fields with no chemical input; serving as Control), type B (rice fields with only fertilizer
application), type C (rice fields with both fertilizer and herbicide application). The sites were widely located at
Fadukpe, Tunga and Chanchaga area of the metropolis (Figure 1).
1,2,3,4,5,6 8,9,10-11,12,13,14,15,16
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