Diversity , distribution and seasonal variations of grasshopper populations in Sialkot , Punjab , Pakistan

The study was planned to estimate diversity, distribution and seasonal variations of grasshoppers in croplands of Sialkot, Punjab, Pakistan. The seasonal variations were assessed by sampling 16 randomly selected sites fortnightly during 2015-2016. The specimens were collected by hand picking and using sweep net. Adult grasshoppers were sampled from each site between 10:00 and 15:00 PST under sunny conditions. The collected specimens were killed, identified and preserved. Data were subjected to statistical analysis and interpretations which indicate the presence of 18 species representing 14 Genera, 8 subfamilies and 3 families. The collected specimens represented sub-family Acridinae (genus Acrida) which were found to be the most abundant (372) followed by sub-family Oxyinae (genus Oxya) with 330 specimens whereas their population was consistent in all study sites. Data indices calculated showed greater richness and evenness of species in the studied area. The higher value of Shannon Index (2.722) showed that greater richness and the evenness of species in the sampled areas. Simpson Index value (0.927) showed dominance in terms of more species diversity. Oxya hyla, Oxya japonica and Hieroglyphus banian were the most abundant species whereas Mermiria bivittata was the least common species. Maximum populations were recorded during July-November (61.39 %) with an increasing trend in population size during these months indicating seasonal variations in their populations around the year. The study suggested that sampled area has well established grasshopper populations which require well-knitted pest management strategies to avert economic losses and conserve biodiversity.


Introduction
Sialkot is recognized as an industrial as well as an agricultural city of Pakistan containing about 3.5 million populations and ranked as 6 th largest city of Pakistan.The agricultural productivity in this rice dominated farming system has been threatened due to floods, unexpected rains, industrialization, urbanization and pest infestations.The changes in agricultural land usage practices, cropping patterns and expansions are mainly due to urbanization and industrialization which affects the seasonal distribution patterns of grasshoppers [1].Geographical conditions of Pakistan provide ideal breeding places for grasshoppers which, thus, pose serious threats to crops and pastures both in irrigated fields and rain-fed areas [2].Grasshoppers as major pests of many crops and grasslands, occupy almost all terrestrial habitats and climates are best known for their great potential to damage crops [3].Landscape structure, changing environmental conditions, cropping patterns and farming systems greatly influenced the distribution and variety of the grasshopper species in different parts of world [4].Grasshoppers are the most important natural herbivore in the prairies that intermittently leads to widespread destruction of grasslands and croplands [5].As they have the ability to adapt in varying conditions of moisture, flora at different times and locations [6].
In Pakistan various researchers worked on the crop pests and reported grasshoppers as pests of paddy fields

Sampling procedure
The specimens were collected by hand picking [15] and using sweep net [16] from selected sites fortnightly from July 2015-June 2016.Adult grasshoppers were sampled from each site between 10:00 and 15:00 PST under sunny conditions to maximize the probability of detecting different species @ 250 net sweeps each sampling site to give uniformity in sampling [17].The collected specimens were killed, identified and preserved in wooden box [18].

Taxonomic identification
The specimens were examined under Leica MZ6 microscope.Taxonomic literature, internet sources and identification keys were explored to identify the specimens [19-25].The taxonomic terminology was adopted to proceed for morphological identification process and confirmation of species identification [26-28].The identified collection was deposited in the Laboratory of Systematics and Pest Management, Department of Zoology, University of Gujrat.

Data analysis
The data collected from different sites within the study area were subjected to analysis by applying various ecological indices i.e.Shannon-Wiener index and Simpson Index, to find out the diversity, distribution, abundance and richness [29].To describe grasshopper species and give comparative account of species on different sites and indices were calculated by Shannon-Weaver index (H'), Simpson's diversity index (D).Species abundance was determined as the abundance of a given species relative to the total abundance of all species.Species richness was calculated by considering the total number of species found in the study sites [30].

Results and discussion
An assemblage of 1349 specimens belonging to 18 species was collected from 16 different sites sampled during 2015-2016.The data showed that O. hyla (189), Hieroglyphus banian (179), O. japonica (141), A. gigantea (126), A. turrita (125), D. japonica (104) were most abundant species whereas Trilophidia annulata (15), M. bivittata (9) were least abundant (Table 1).The data indicated that the six (06) species were more abundant in almost all sampling sites within study area i.e.O. hyla, H. banian, O. japonica, A. turrrita, A. gigantea, D. japonica whereas nine (09) species were less common and three (03) species were least common and rarely found in selected study sites (Table 1).Different index values depicted that sampled populations of grasshoppers present more diversity, richness and evenness of species in the selected areas of Sialkot (Table 2).This indicated that species are evenly distributed in the selected area with plenty of foraging available for their populations to grow during different seasons.Most abundant species was O. hyla whereas minimum value for diversity was shown by M. bivittata.Acrididae was represented by 14 species, Tettigoniidae by 2 species and Pygromorphoidae by 2 species.Remaining species belonged to 8 subfamiles (Table 3).The data collected from different sites showed variations in the population size of grasshoppers.Among the 1349 collected specimens, the highest number of specimens were recorded from Kot Maharaj (126) followed by Jatheke (115) and Malkhanwala (100) (Figure 2).Maximum specimens were collected during September (235) followed by August (200) and October (185) whereas lowest number of specimens were collected in the month of January (48) followed by February (53).The data showed increasing trend in the abundance of species from May to September (Figure 3).The species collected from croplands showed variations in species diversity and richness with greater values of evenness that may be due to availability of diverse vegetation during different seasons.However variations in the population size of different species during different months of the year may also be attributed to climatic factors that determine population size.Our results correspond with the findings of earlier workers, positive association between plants and grasshoppers in semi-arid lands [31, 32].However, contrary results were also reported in a study showing there is no influence of plants on grasshoppers' population [33].During the rains in moon soon greater population was recorded from the study area showing greater differences in population abundance from other seasons.The rainfall may also be an important factor playing positive role in diversity of grasshoppers during rainy season [34].In recent studies, Oxya genus associated with rice ecosystem was reported maximum and considered as pest of rice [35].In studies conducted in Bhimber, diversity of grasshoppers was studied and O. hyla was found as the most abundant species [36]

MONTHS Conclusion
The

Figure 1 .
Figure 1.Map showing 16 randomly selected sampling sites in Sialkot, Punjab, Pakistan

Table 3 . Species reported from study area during 2015-2016 from Sialkot, Punjab, Pakistan
Orthoptera (Acrididae).Faun a of British India including Ceylon and Burma.Taylor and Francis, London, 276pp.