JMR-2017v7n17 - page 12

Journal of Mosquito Research 2017, Vol.7, No.17, 134-141
139
The DO recorded in the rice-fields in this study (range = 6.00 – 7.00 mg/l) were higher than those (i.e., 4.42 – 4.70
mg/l) reported in a reservoir elsewhere in the state (Ibrahim et al., 2009). The higher DO in this study may be due
to high density of phytoplankton that characterize rice-field ecosystem generally (Alshami et al., 2014).
Phytoplanktons are the principal producers of Oxygen, as by-product of photosynthesis, in aquatic habitats
(Alshami et al., 2014).
The BOD recorded in this study is lower than reported by Sangpal et al. (2011) from India, who attributed the high
BOD in the aquatic habitat to excessive discharge of sediment and sewage into the water body. This may mean
that the rice-fields in Minna are not organically or chemically polluted.
The concentrations of turbidity, Nitrate and Chloride were significantly higher in rice-fields where there were no
applications of agrochemicals (i.e., Site A). The higher turbidity in this site may be due to higher run-off discharge
from the surrounding land area. The magnitude of run-off into aquatic habitats is often influenced by
anthropogenic activities in the surrounding area (Leroy
et al., 2002), and this may vary considerably in different
rice-field mosquito larval habitats. The higher Nitrate content of site A may also be due to higher deposition of
sewage, the principal source of Nitrate in aquatic ecosystems
(Mateo-Sagasta and Jacob, 2012). High Nitrate
content may result in algal bloom in aquatic habitats (Glendon et al., 1999) and, hence, increased mosquito
productivity, as the larvae will have access to abundant food supply (Alan et al., 2003).
The concentrations of Alkalinity, Hardness, Sodium and Conductivity were significantly higher in rice-fields with
fertilizer application. This may be an indication of physico-chemical parameters singly affected by chemical
fertilizers in aquatic habitats. Alkalinity and Conductivity, for example, are
known to influence the survival and
productivity of aquatic invertebrates (William, 2000). Therefore, this may mean that rice-fields subjected to only
chemical fertilizer application in Minna produce mosquitoes at differential rates from the other counterpart
habitats subjected to other kind of agrochemical practices. The level of Alkalinity, water hardness and Chloride
recorded in the rice-fields in this study fell within ranges optimum for the productivity of aquatic organisms
including mosquitoes (Ramatake and Morghe, 1998; Idowu et al., 2004; Girgin et al., 2010). The concentration of
Potassium was significantly higher in sites B and C, where there were applications of inorganic fertilizer. This
should be expected, as Potassium is one of the three major components of inorganic fertilizers (i.e., NPK used) in
the study area. However, this may mean that rice farmers in Minna wrongly use the NPK fertilizer for their crops
instead of the Urea (Nitrogen-based) fertilizer, recommended for optimum rice productivity. This assertion is
buttressed by the facts that Nitrate concentration was even higher in rice-fields where there was neither fertilizer
nor herbicide application.
4 Conclusions
Agro-chemical input practices in rice farming in Minna though may enhance yield, significantly alter critical
physic-chemical parameters that condition the development and thriving of mosquitoes in the larval habitats. The
little or no significant effects of the agro-chemical on Temperature, Dissolved Oxygen and Biological Oxygen
Demand may not promote mosquito production but this gain is effectively countered by the enhancement of
Alkalinity, Sodium, Potassium and Conductivity which are critical in mosquito immature development. The strong
correlations between vital physico-chemical parameters indicate that such factors act collectively or perhaps,
in-synergy on mosquito development. This probable relationships between mosquito immature development and
collegiate of physico-chemical parameters requires urgent elucidation. The findings of this study should provide
baseline information for cost-effective management of mosquito productivity in rice wetlands in Minna and, by
extension, in Nigeria as a whole.
Author’s contributions
OIK and SIM designed the experiment; SIM and GY analysed the data; SIM, GAY and UMD wrote the draft manuscript; OIK, SIM
and UAC contributed to writing of the main manuscript; All authors agree with manuscript results and conclusion; finally the
articulated manuscript were read and reviewed together.
1...,2,3,4,5,6,7,8,9,10-11 13,14,15,16
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