Eco-taxonomic studies on the surface grasshopper, Chrotogonus trachypterus (Blanchard) in south western Rajasthan
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Date
2008
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Publisher
MPUAT, Udaipur
Abstract
Studies on the pyrgomorphid fauna and the eco-taxonomy of the surface grasshopper [Chrotogonus trachypterus (Blanchard)]
in south western Rajasthan were undertaken. The survey conducted in the five districts of Rajasthan viz., Banswara, Dungarpur,
Rajsamand, Sirohi and Udaipur during 2005-06 and 2006-07 resulted in five species of short horned grasshoppers belonging to the
family Pyrgomorphidae; i.e., Chrotogonus trachypterus (Blanchard), Chrotogonus oxypterus (Blanchard), Atractomorpha crenulata
Fabricius Pyrgomorpha bispinosa Walker and Poekilocerus pictus Fabricius. Of these, C. trachypterus and C. oxypterus were
relatively more abundant in Udaipur district than in the other four districts surveyed. The species A. crenulata and P. bispinosa had a
relatively equal representation in all the districts, but their numerical abundance was a little more in the district Banswara as compared
to the other four districts surveyed. The species P. pictus was relatively more in district Rajsamand and was not recorded from the
district Banswara. During both years, the two species of Chrotogonus (C. trachypterus and C. oxypterus) had the highest mean density
in the month of February and maximum relative density in the month of May in all the districts. The mean density for A. crenulata
was the maximum during the month of August and the relative density in August and September in all the districts. The grasshopper,
Pyrgomorpha bispinosa had the maximum mean density and relative density as well, during the month of August in all the districts
surveyed. The monsoon season (August-September) happened to comprise greater diversity of the Pyrgomorphids than the spring
season (February-March) based on the Simpson and Shannon Weiner Diversity Index values.
* Ph. D. Scholar, Department of Agricultural Zoology & Entomology, RCA, Udaipur
** Associate Professor, Department of Agricultural Zoology & Entomology, RCA, Udaipur
The species of Chrotogonus are closely similar and no satisfactory field characters exist by which they may be distinguished.
A comprehensive systematic account of the Pyrgomorphid genera of the Indian sub-continent from available literature and databases
has been presented.
The females laid eggs in moist soil at a depth of 2 to 4 cm. The egg pods measured 32.845 ± 0.519 mm long and 2.485 ± 0.029
mm broad, respectively; with an average number of 7.500 ± 0.249 egg pods per female. The average length and width of the egg was
3.483 ± 0.064 mm and 0.955 ± 0.010 mm, respectively, with an average of 9.050 ± 0.560 eggs per pod. The mean number of eggs laid
per female was 65.500 ± 4.365. The incubation period was 22.975 ± 1.015 days under laboratory conditions. The total nymphal period
(six instars) took from 43.50 to 53.50 days with an average of 48.513 ± 0.496 days. The length of adult male body was 14.983 ± 0.077
mm, while that of the female was 20.436 ± 0.506 mm. The female was distinctly bigger than the male. The pre-oviposition,
oviposition and post-oviposition periods were 18.000 ± 0.793, 36.150 ± 2.075 and 12.250 ± 1.039 days, respectively. Adult longevity
of males and females was observed to be 54.350 ± 3.005 and 66.400 ± 3.210 days, respectively under laboratory conditions.
The coefficient of variation worked out for the different linear morphometric variations was the maximum for the numbers of
spines on the outer fore legs in males (19.33 %) and outer middle legs in females (16.15 %). In both males and females the lower
sternum width showed the lowest coefficient of variation (3.47 and 4.87% respectively). The lengths of antennae, tegmina, hind wing,
body up to genitalia/ wing tip, pronotum, and the sternal region were relatively more for the females than the males; similarly the
width of tegmina, body, pronotum, and the sternal region were also relatively more for the females. A comparison of the compounded
ratios for some of the morphological traits showed that the ratio between length of hind femur and width of vertex (F/v) was the
maximum (7.335 + 0.132 and 7.151 + 0.124) for the males and females, respectively. The lowest ratio happened to be for the ratio
between the length and width of the pronotum (P/p) for both the males as well as the females (0.686 + 0.014 and 0.624 + 0.009).
The effect of food plants as indicated by the growth index for hoppers showed the following descending order of preference
lucerne > wheat > barley > mixed food > oats > gram > Bermuda grass > spinach > nutgrass > pigweed. The hopper duration was
shortest when they were fed lucerne. Hopper survival on lucerne, wheat and barley was 100 percent, whereas hopper survival was
lowest when reared on pigweed; however, irrespective of the host plant, the sixth instar hoppers developed into fledglings, showing a
cent per cent survival. The effect of different host plants on food utilization indices evinced that efficiency of conversion of ingested
food (ECI) was high, when the hoppers were reared either on wheat or mixed food, but pigweed followed by nutgrass had
significantly the lowest ECI. The AD was high when the hoppers were reared on lucerne and significantly low in gram. The efficacy
of conversion of digested food (ECD) into body substances was significantly the maximum for hoppers raised on wheat and was
significantly the lowest for hoppers on pigweed.
Description
Eco-taxonomic studies on the surface grasshopper,
Chrotogonus trachypterus (Blanchard) in south western
Rajasthan
Keywords
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Citation
Jat and Swaminathanm, 2008