Seasonal variation of Hemiptera community of a temple pond of Cachar District, Assam, northeastern India
Kankana Das 1 & Susmita Gupta 2
1,2 Department of Ecology & Environmental Science, Assam University, Silchar, Assam 788011, India
Email: 1 firstname.lastname@example.org, 2 email@example.com (corresponding author)
Aquatic biodiversity is one of the most essential characteristics of an aquatic ecosystem for maintaining stability and a means of coping with any environmental change (Vinson & Hawkins 1998). Aquatic hemipterans stand out as an important group of aquatic insects, which are considered important in environmental reclamation of aquatic habitats and are often used to gauge toxins in an environment (Jansson 1987; Papacek 2001; Wollmann 2001). They are also considered important fish food and many fishing lures are modeled after aquatic hemipterans (McCafferty 1981).
Studies on aquatic hemipterans in the ponds and wetlands of Assam are very few (Chetri et al. 1997; Majumdar & Gupta 2004; Kalita 2008; Das & Gupta 2010) and from southern Assam there are only two published works. This study attempts to understand the temporal variation of the Hemiptera insect community of a temple pond, a 200-year old permanent system situated within a tea estate near Silchar City of Cachar District, Assam along with the physico-chemical properties of the water of the pond (Fig. 1). Further it is essential to know the status of the ecosystem since the temple pond is a sacred one for the people of the locality and is used for religious activities. As pollution status of water bodies are expressed as biological and physico-chemical parameters (Lenat et al. 1980), the results of this study can be of use for successful management of the pond.
Materials and Methods
The Bharambaba Temple pond (24027ÕN & 25008ÕE) is very close to the quarters of Silcoorie Tea Estate near Silchar City of Cachar District, Assam. The pond is adjacent to the temple facing the highway on one side and the back of the temple on the other side. The system is mainly covered by macrophytes like Nelumbo nucifera (Water Lotus), Hygrorhiza aristata (Indian Lotus), Cynodon dactylon (Bermuda Grass), Philotria sp. etc. The insects were collected in the pre-monsoon (March–May), monsoon (June–August), post-monsoon (September–November) and in winter (December–February) by the Kick method (during March 2007 to February 2008), whereby the vegetation was disturbed and a circular net (mesh size 60µm) was dragged around the vegetation for one minute (Brittain 1974; Subramanian & Sivaramakrishnan 2007). Three such drags constituted a sample. Collected insects were immediately sorted and preserved in 70% ethyl alcohol. They were later identified using Dewinter Advance Stereozoom Microscope with the help of standard keys (Bal & Basu 1994a,b; Thirumalai 1994, 2007; ZSI 2004) and with the help of experts from the Zoological Survey of India. Meteorological data were obtained from the Meteorological Department, Silchar. During each sampling water sample was also collected for estimating physico-chemical properties of water such as water temperature (WT), transparency, pH, electrical conductivity (EC), dissolved oxygen (DO), total alkalinity (TA), free CO2, total dissolved solid (TDS), and total suspended solids (TSS). They were estimated by the standard methods (APHA 2005). The diversity indices namely Shannon-Weiner and Berger-Parker index of dominance were worked out by Biodiversity Professional V. 2.0. The statistical analysis was done by SPSS V. 12.0.
Results AND Discussion
The present study recorded seven families, 11 genera and 14 species of the order Hemiptera in the pond. The families were Corixidae, Gerridae, Aphididae, Mesoveliidae, Notonectidae, Nepidae and Belostomatidae. The species were Micronecta haliploides, Micronecta (Basileonecta) scutellaris scutellaris (Stl) (Corixidae); Neogerris parvula (Stl), Limnogonus nitidus (Mayr), Tenagogerris sp., Rhagadotarsus sp. (Gerridae); Enithares ciliata (Fabricius), Anisops lundbladiana Landsbury, (Notonectidae); Diplonychus rusticus (Fabricius), Diplonychus annulatus (Fabricius) (Belostomatidae); Ranatra elongata (Fabricius), Ranatra varipes varipes Stl (Nepidae); Mesovelia vittigera Horvath (Mesoveliidae); Rhopalosiphum nymphaeae (Linnaeus)(Aphididae). The highest population of Hemiptera was recorded in the post-monsoon followed by monsoon and pre-monsoon (Fig. 2). Since in winter, the quantity of water in the system is reduced and the peripheral area of the system dries up, the effluents released from the neighbouring factories may have affected the insect density.
The study revealed the presence of the highest number of families (7) in the post-monsoon and the lowest in winter (4). Among all the hemipteran families in all the seasons, the highest population of Hemiptera belonged to the family Notonectidae in the post monsoon and the same family dominated the community in all other seasons except during the monsoon, when Corixidae was the highest in number followed by Notonectidae. Across the seasons either of the two families dominated. This might be due to their ubiquity and abundance in temporary and permanent pools (Eitam et al. 2002). Further they are tolerant to chemical and biological stress and are typically capable of surviving in any permanent water. According to Wollmann (2001) the family Corixidae has been found to have an amazing ability to survive in polluted waters. Aphididae, although present throughout the year, were recorded in large numbers only in the post-monsoon season on the leaves of Nelumbo nucifera (Water Lotus). The population of Belostomatidae was the lowest in all the seasons except the post monsoon where it was replaced by Nepidae, recorded only in that season in very low numbers (Fig. 3).
Ravera (2001) and Sandin & Johnson (2000) were of the view that diversity and biotic indices may be influenced by any stresses, including pollution. Ludwig & Reynolds (1988) opined that the total number of species and evenness are two distinct components of diversity. In the temple pond the highest number of species were recorded in the post-monsoon (14) followed by monsoon (10), pre-monsoon (9) and winter (7) ( Fig. 4). The study revealed that in all the seasons diversity index values ( H/ ) were always less than one and the highest Shannon Weiner (H/) diversity index was recorded in the post-monsoon. Highest evenness index (J/) and Berger Parker index of dominance was recorded in the pre-monsoon and winter, respectively (Table 1).
According to EngelmannÕs Scale (Engelmann 1978) the dominant species of the pond were Micronecta haliploides, Anisops lundbladiana Landsbury, Rhopalosiphum nymphaeae (Linnaeus) and Mesovelia vittigera Horvath followed by subdominant species Micronecta (Basileonecta) scutellaris scutellaris (Stl ), Neogerris parvula (Stl), and Rhagadotarsus sp. Others were recedent species i.e the value of their relative abundance was within the range 1.1–3.1. The number of dominant species in the pond was four out of 14 species of the same order (Table 2). A similar study made on a pond of Midnapore Town of West Bengal found only one dominant species out of 20 species of different orders (Jana et al. 2009).
This study clearly depicted dominance of different species in different seasons indicating temporal niche separation. In the post-monsoon the density of Rhopalosiphum nymphaeae (Linnaeus) was found to be the highest, closely followed by Enithares ciliata (Fabricius). While in the monsoon the density of Micronecta scutellaris scutellaris (Stal) was the highest, in the pre-monsoon and winter Anisops lundbladiana Landsbury was the highest (Fig. 4). In the post monsoon period simultaneous dominant occurrence of two species Rhopalosiphum nymphaeae (Linnaeus) and Enithares ciliata was possible due to their different food choices. Rhopalosiphum nymphaeae (Linnaeus) is a polyphagus species feeding on a variety of host plants and Enithares ciliata is an aggressive predator. It is known that insects of the family Notonectidae are predators and attack many pelagic and benthic invertebrates including their own larvae (Cooper et al. 1985; Giller 1986). In the present investigation special attention was drawn to Rhopalosiphum nymphaeae (Linnaeus) found on the leaves of Nelumbo nucifera, which is otherwise not very common in this region. It was recorded in all the seasons in the pond and in the post monsoon period it was abundant. In a few studies on the aquatic hemipterans in Brahmaputra Valley, Assam (Chetri et al. 1997; Kalita 2008; Hazarika & Goswami 2010) Rhopalosiphum nymphaeae (Linnaeus) was recorded by Kalita (2008) in Deepor Beel, a Ramsar site in As-sam.
Investigations on the environmental variables, revealed that air temperature and water temperature ranged from 28.10 to 330C and 25.11 to 31.040C, respectively, in different seasons. While pH varied from 4.42 to 7.24, total alkalinity varied from 60.54 to 65.78 mgl-1 and free CO2 varied from 9.58 to 11.79 mgl-1. Highest DO (8.22mgl-1) was recorded in the pre-monsoon and the lowest (6.06mgl-1) in winter. A similar range of DO was recorded in a study made by Narayan et al. (2007) in a temple pond in district Etawah (UP). Lowest DO in winter might be due to decomposition of macrophytes present in the edges of the pond due to lowering of the water level. Rainfall showed significant positive relationship with WT, pH and negative relationship with DO. A similar significant negative relationship was recorded in a previous study in a floodplain lake of the same area (Laskar & Gupta 2009). Inverse relationship of DO with rainfall is because of the entry of surface runoff which is likely to carry fertlizers and organic residues from the agricultural fields in the catchment. According to Singhal et al. (1986) during the monsoon surface runoff carries waste and sewage from the surrounding areas into the low lying beds of the floodplain lakes, thereby increasing the respiratory activity of the heterotrophic organisms and lowering the DO concentration of the water. TSS was highest (21.34mgl-1) in the monsoon and always less than the TDS (23.12–42.12 mgl-1) in all the seasons which conformed to the fact that in most natural waters TSS is always less than TDS ( Moss 1980) (Table 3 & 4).
No significant correlations of insect diversity with any of the environmental variables throughout the study period could be recorded. Insect density also showed a similar pattern except one record of significant negative relationship with free CO2. All these can be explained by the fact that life of hemipterans do not depend entirely on water quality (Mackie 2001). As vegetation richness increases with wetland age (Mulhouse & Galatowitch 2003; Jahr & Crow 2005), the 200 year old pond has nurtured a rich variety of macrophytes. As hemipterans are known to feed on phytoplankton, zooplankton, insects, and small vertebrates (Gilbert & Burns 1999; Hampton et al. 2000), it can be said that these macrophytes with increased habitat structural complexities have provided additional food and living space within the water column for different species.
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