STUDIES ON SPIDER FAUNA OF COASTAL REGION OF INDIA : OBSERVATIONS ON POPULATION FLUCTUATION OF SPIDERS AND THEIR ROLE IN BIOLOGICAL CONTROL OF INSECT PESTS ON PADDY FIELDS OF SUNDARBAN COASTAL REGION , WEST BENGAL ( PART-2 )

Reports on population fluctuation of spiders in Indian coastal regions are very scanty. In Indian sub-continent, various workers viz., Chatterjee & Dutta (1979), Alam et ale (1981), Choudhury & Pal (1984), Biswas (1990), Kamal et al. 1990, Majumder & Tikader (1991), Kamal et ale (1992), Biswas et ale (1993) and Biswas et ale (1995) worked on the population density of spiders only in the paddy fields.

With a view to enhancing our existing knowledge this field study was undertaken in Sundarban coastal eco-system during 1998 to 1999.Collection and observation of insect pests and spider popUlation were carried out in different eco-systems of Sundarban coastal region.
The present paper deals with the population fluctuation of 30 species of spiders in Sundarban coastal eco-system viz., T. Aman-paddy fields, wild bushes, mangrove vegetation and river beds in !elation to their predation on the insect pests in the surrounding areas.Probable impact of the present observations towards biological control of insect pests in T. Aman-paddyfields has been discussed.

MATERIAL AND METHODS
The spider population and their abundance were studied in the paddy fields (T.Aman) associated with wild bushes, mangrove vegetation and river beds of Canning, Gosaba, Basanti and Sagar Island (The study area includes a total of four areas having different host plants and adjacent river beds).
*Zoological Survey of India, M-Block, New Alipore, Kolkata-700 053 Spiders were collected from the selected four areas from different host plants simultaneously by hand picking and by standard hand sweeping net (129 cm in diameter).The random sampling was done by making 100 sweeps in each sampling site at bimonthly intervals from 6 A.M. to 9 A.M. during June 1998 to May 1999.
The collected spider specimens were anaesthetised, killed in a killing jar and finally were preserved in Dudman' s preservative (90 parts 70% ethyl alcohol, 5 parts glycerine and 5 parts glacial acetic acid) in glass vials.The specimens were identified placing them in a petri dish containing ethyl alcohol under a binocular microscope.Each specimen was preserved in a single vial.The preserved specimens of spiders were identified upto species level.

OBSERVATIONS, RESULTS AND DISCUSSION
The present study includes a total of 30 species available in different hostslhabitats viz., paddy fields, adjacent wild bushes, mangrove vegetation and river beds of Sundarban coastal region.1).
In the further study during January 1999 to May 1999, the collection represented 300 examples of 17 species in paddy fields (ratoon) , 438 examples of 19 species in adjacent wild bushes, 189 examples of 18 species in mangrove vegetation and 20 examples of 3 species in river beds (Table 2).
The species viz., Leucauge decorata (Blackwall), Pardosa sumatrana Thorell, Neoscona mukerjei Tikadar, Marpissa mondali Tikader, Cheiracanthium himalayensis Gravely were higher in number in the paddy fields from June 1998 to December 1998 than in the other habitats like adjacent wild bushes, mangrove vegetation and river beds (Table 1).Thereafter, the population gradually decreased in the paddy fields from January 1999 to May 1999 but again increased in the wild bushes and mangrove vegetation (Table 2).The species viz., Lycosa cOOperi Simon, Lycosa choudhuryi Tikader Pardosa annandelei Gravely, Pardosa sumatrana Thorell and P. birmanica Simon were found in the river beds but their occurrence was never found in the mangrove vegetation from June 1998 to December 1998 (Table 1).
The spider popUlation belonging to the genera viz., Argiope, Neoscona, Leu cauge, Larinia, Cyrtophora, Tetragnatha, Oxyopes, Marpissa, Zygoballus, Phidippus and Cheiracanthium were never found in the river beds from June 1998 to May 1999 (Figure 1 and Table 2).The species Pardosa sumatrana Thorell was found in good number in paddy fields (rice plants and ratoon) from June 1998 to May 1999 (Table 1 and Table 2).Marpissa bengalensis Tikader and Neoscona elliptica Tikader and Ball were abundant in wild bushes from June 1998 to December 1998, but scarce in the wild bushes during January 1999 to May 1999 (Table 1 and Table 2)  45 ---------------------------------------------------------- During the present investigation a number of insect pests were recorded from the fields.Of those Scirpophaga insertulus, Nilaparvata lug ens, Nephottetix virescens, Leptocorisa acuta and Orseolia oryzae were found in the paddy fields during August to October 1998.From this study it was found that the Lycosa chaperi Simon fed upon on immature larvae of Nilaparvata lugens at the rate of 5 to 15 pest specimens per day.The species Cheiracanthium himalayensis Gravely could built nest by rolling up paddy leaves within which they retreated (Majumder & Tikader, 1991).These spiders were nocturnal in habit and after coming out from the nests they devoured lepidopteran pests at the rate of 5 to 12 prey per day.Observations made in the present study confirmed with those made by Biswas et ale (1995).The jumping spiders played an important role in controlling the insect pests in the fields.They consumed 6 to 12 dipteran pests per day and captured the prey by jumping upon them.Leucauge decorata Blackwall captured lepidopteran, hemipteran, dipteran and orthopteran pests by trapping them in their beautifully built webs (Biswas et ale 1995).
Table 3 indicates that the occurrence of insect pests viz., Nilaparvata lugens, Scirpophaga incertulus and Leptocorisa acuta were found during August to October 1998.The species viz., Nephottetix virescens and Orseolia oryzae were found maximum from the month of November to December 1998.No insect pest was found from January 1999 to May 1999.

SUMMARY
In the present study, a total of 30 spider species in 17 genera under 6 families were observed in different hosts/habitats in coastal eco-system of Sundarban viz., paddy fields-plants and ratoon, wild bushes, mongrove vegetation and river beds.Among these species, 587 examples of 30 species were observed in the paddy fields from June 1998 to May 1999; The spider population was rich in wild bushes as evident from the fact that 766 examples of 30 species could be recorded there.The population was lesser in mangrove vegetation and river beds than in the paddy field and wild bushes.A total of 322 examples in 15 species was found in mangrove vegetation and 46 examples in 10 species in river beds.This study also recorded a total of 5 insect pests belonging to Diptera (Cecidomyiidae) Hemiptera (Delphacidae, Cicadellidae) and Lepidoptera (Pyralidae) which were captured and devoured by the spider species indicating that the spiders have a good potentiality as biocontrolling agent in paddy fields of the Sundarban coastal ecosystem.

Table 1 .
. List of the Spiders and their abundance in different hostlhabitats in Sundarban coastal eco-system during the month ofJune, 1998 to December, 1998.

Table 2 .
List of the spiders and their abundance in different hostlhabitats in Sundarban coastal eco-system during the month of January 1999 to May 1999.

Table - 1
.List of the spiders and their abundance in different host/habitats in Sunderban coastal eco-system during the month of June ,1998to Dec,199B.

Table 3 .
List of the Insect pests available in the paddy fields in the Sundarban coastal region during the year June 1998 to May 1999.