The role of urea in the oviposition behaviour of Japanese encephalitis vectors in rice fields of South India

Abstract

The effect of urea on the oviposition behaviour of culicine vectors of Japanese encephalitis was studied in rice fields. Gravid Mosquitoes use a complex integrated sensory system for selecting an oviposition site (Vrtiska & Pappas 1984).Long-range cues, probably involving vision, allow mosquitoes to identify different habitats (Bidlingmayer 1975) tritaeniorhynchus was not always adaptive in site selection, as the females were often found ovipositing on water unsuitable for larval development (Mogi 1978).The objective of the present study was to determine the role of urea, a synthetic nitrogenous fertilizer, as an oviposition attractant/stimulant for the mosquito vectors of Japanese encephalitis (JE) virus. During a routine survey of mosquito immatures, clustering of egg rafts was observed in a localized area in a rice field at Soundarasolapuram village, Cuddalore district, Tamil Nadu State. It was later found that the farmer had selectively treated this patch with urea on the previous day, as he felt the plants were stunted. This observation prompted this exploration of the role of urea on the oviposition behaviour of vectors of JE.This study is a part of the PhD Thesis submitted to Madurai Kamaraj University, Madurai, Tamil Nadu, India. A series of three experiments was conducted in rice fields 10 days after transplantation. Metal quadrats of size 0.1 m 2 open at both ends were used for the experiment. One end of the quadrat was pushed into the bottom mud of the rice field, while the other end remained at least 5 cm above the water surface, thus preventing the mixing of water in the quadrat and the main field. The water in the quadrat was filtered to remove insect predators. In the first experiment, three paddy fields were selected and four quadrats were placed equidistant from each other at least 25 m apart in each of the rice fields sampled in each field. Two quadrats (T1) were treated (surface-applied) with a dose of 1 g urea/0.1 m 2 , while the other two were kept as untreated controls (T2). In the second experiment, the dosage of urea was increased to 2 g urea/0.1 m 2 . In the third experiment, five transplanted rice fields were selected and three quadrats were placed in each field. One set of quadrat was treated with a dose of 1 g urea/0.1 m 2 (T1), the second set (T2) had a one l cylindrical plastic container of diameter 10 cm placed in it; which was filled with mud for 2 cm depth, and urea with similar dosage as that of T1 (1 g/0.1 m 2 ) was sprinkled in the mud filled container. The container was covered with mosquito netting, to prevent the gravid females from contacting the treated water surface, but allowed the volatile fractions to escape into the atmosphere. The container was placed in the centre of the quadrat with its mouth well above the water surface, and with enough space around it so that the gravid females had access to the water surface in the quadrat. The third set of quadrats (T3) without urea application was kept as control for comparison.In all the three experiments, the number of e...

Association between fertilizer-mediated changes in microbial communities and Aedes albopictus growth and survival

“…aegypti, attracting large numbers of gravid females whose offspring experienced low survival rates compared to the controls (Darriet et al 2010). These findings contradict those of field studies where synthetic fertilizers have been shown to act as oviposition attractants and are typically associated with large populations of mosquito larvae (Duguma and Walton 2014; Mutero et al 2004;Muturi et al 2007b;Sanford et al 2005;Sunish et al 2003;Victor and Reuben 2000). Under field conditions, fertilizers may break down rapidly and become utilized by plants and microorganisms.…”

“…Unfortunately, the intensive use of fertilizers comes at major environmental costs including loss of soil fertility, degradation of water quality, changes in species composition and loss of biodiversity, eutrophication and loss of habitat quality in aquatic ecosystems, development of photochemical smog, and rising global concentrations of nitrous oxide, a powerful greenhouse gas (Camargo and Alonso 2006;Hamer et al 2004;Richter 2007;Smil 2000;Vitousek et al 1997). Additionally, fertilizer-enriched aquatic habitats have been shown to harbor large populations of mosquito larvae (Mutero et al 2004;Muturi et al 2007b;Sunish et al 2003;Victor and Reuben 2000) raising concerns about the potential for these chemicals to alter the transmission dynamics of mosquito-borne pathogens. However, our understanding of the link between fertilizers and mosquito-borne diseases is still very limited and further studies on this topic can inform the development of holistic approaches to meet the rising demand for agricultural products while protecting the environment and human health.…”

“…There are several potential mechanisms by which fertilizer application may be associated with an increase in mosquito larval populations. These include alteration of the physical and chemical characteristics of the larval habitats making them attractive oviposition sites for mosquitoes (Mutero et al 2004;Muturi et al 2007b;Sunish et al 1998;Sunish et al 2003;Victor and Reuben 2000), stimulation of diverse microbial assemblages that may enhance egg hatch success rates (Ponnusamy et al 2011) and provide a rich food resource for mosquito larvae (Johnson et al 2010;Victor and Reuben 2000), and direct and indirect negative effects of fertilizers on mosquito predators and competitors allowing the mosquitoes to develop in predation-and competition-free environment (Camargo and Alonso 2006;Sanford et al 2005).…”

Água de abastecimento público de consumo humano e oviposição de Aedes aegypti

“…3,5 Geier et al 15 (1999) showed in a laboratory, that ammonium nitrate is a chemical component which attracts the Aedes aegypti mosquito to their host. That females are attracted to nitrogenous compounds, was also verifi ed by Sunish et al 19 (2003) in egg laying by the Japanese encephalitis vector Culex tritaeniorhynchus. The quantity of ammonium nitrate in the water strongly infl uences the egg laying of this mosquito.…”

Field evaluation of the response ofAedes albopictus(Stegomyia albopicta) to three oviposition attractants and different ovitrap placements using black and clear autocidal ovitraps in a rural area of Same,Timor‐Leste

“…For example, a sheep manure solution with concentrations of nitrogen, phosphorus and potassium of approximately 0.15 g/L, 0.10 g/L and 0.20 g/L, respectively, has been found to be attractive to gravid Aedes notoscriptus (Leisnham et al, 2004;Derraik & Slaney, 2005a, 2005b). It has also been observed that rice fields treated with urea are more attractive as oviposition sites for culicine and anopheline mosquitoes than untreated areas (Victor & Reuben, 2000;Sunish et al, 2003). Ikemoto and Sakaki (1979) found that increased ammonia-nitrogen in rice field water resulted in increased oviposition of Anopheles sinensis (Diptera: Culicidae).…”