BIOECOLOGY ON Lepidiota sp. Indet. (COLEOPTERA: SCARABAEIDAE)

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dc.contributor.advisorBaruah, A.A.L.H.
dc.contributor.authorGogoi, Dhanalakhi
dc.date.accessioned2019-05-30T11:16:40Z
dc.date.available2019-05-30T11:16:40Z
dc.date.issued2017-07
dc.description.abstractField and laboratory experiments were carried out at Ramie Research Station, Sorbhog and nearby areas and at Soil Arthropod Laboratory of the Department of Entomology, Assam Agricultural University, Jorhat during 2013 - 2017 to engender comprehensive information on the bioecology of Lepidiota albistigma Burmeister, (Coleoptera: Scarabaeidae), a major white grub species endemic to Lower Brahmaputra Valley of Assam. Experimental results confirmed the annual life cycle of L. albistigma with a mean duration of 336.30 ± 14.25 days. The pre-ovippositional, ovipositional and post-ovipositional period were 8.83 ± 0.75, 3.03 ± 0.76 and 9.13 ± 0.73 days, respectively. The mean fecundity was 22.20 ± 1.1 numbers. Eggs were creamywhite, opaque and elongated in shape with mean length and breadth of 5.61 ± 0.40 mm and 4.32 ± 0.36 mm, respectively. Mean incubation period was found to be10.73 ± 2.02 days. There were three larval instars with the duration of third instar (237.11 ±4.86 days) being significantly longer than the first (22.29 ± 1.10 days) and second (39.65 ± 2.90 days) instar. Mean pupal duration was recorded to be 23.36 ± 1.18 days. The mean length and width of first (16.12 ± 0.77 and 4.37 ± 0.54 mm), second (37.60 ± 1.30 and 9.16 ± 0.46) and third (80.28 ± 2.61 and 13.68 ± 0.63 mm) instar grubs were significantly different from each other.The mean length and width of pupae were recorded to be 43.76 ± 1.32 and 16.53 ± 0.60 mm, respectively. Sexual dimorphism based on adult morphometrics revealed that females (61.58 ± 1.64 mm) were significantly longer than males (57.34 ± 0.85 mm). The length of head plus thorax and abdomen were significantly longer in females (27.23 ± 0.55 mm and 24.36 ± 1.30 mm) than in males (23.88 ± 0.41 mm and 23.80 ± 1.30 mm). The mean length of forelegs (31.20 ± 0.79 mm), mid legs (32.77 ± 0.30 mm) and hind legs (42.42 ± 0.97 mm) were significantly longer in females than the males (Foreleg: 28.244 ± 0.61, Mid legs: 30.42 ± 0.18 mm; Hind leg: 41.32 ± 1.41 mm) but the claws in males were strongly bifid. The female alimentary canal (324.94 ± 7.05 mm) was significantly longer than males (315.80 ± 8.74 mm). Both male and female reproductive system exhibited synchronous attainment of sexual maturity. Distinct sexual dimorphism was also observed in the antennal segments and in antenna sensilla types. Scanning electron microscopic studies revealed 14 different types of sensilla in male and 9 types in female. Lamellae were significantly longer in males. Field surveys revealed that mango, guava, mussaenda, ixora, Assam lemon, arecanut, periwinkle, pomelo, betelvine, thuja, croton and black pepper were the primary hosts for adults. Feeding status of adults was further confirmed by presence of food materials in their dissected alimentary canals. Further, sterozoom microscopic images of mandibles and maxillae of both sexes exhibit dentations which indicated that mandibles and maxillae were fitted for phytophagy with probable application in digging of soil for burrowing. Host specificity test revealed that potato, colocassia, green gram and sugarcane to be the most preferred hosts of grubs. Studies on habitat selection by grubs of L. albistigma at five different ecosystems revealed thatgrubs were significantly more abundantat grasslands which were located near water sources. Grubs of L. albistigma were more abundant at soil depths of 0 - 10 cm and 11 - 20 cm in grassland and cultivated lands. In grasslands, grubs showed significant preference for soil depths of 0 - 10 cm (3.79 ± 3.34) and 11 -20 cm (2.31 ± 2.09). In cultivated fields, the highest population was recorded at the depth of 11 - 20 cm (2.78 ± 1.54) which significantly differed with other depths. There is no significant difference in abundance of grubs at 0 - 10 cm (1.40 ± 1.22), 21- 30 cm (1.40 ± 1.22) and 31- 40 cm (0.57 ± 1.22). The mechanism of survival of grubs were examined by means of a simulation model which displayed that the grubs were atleast able to survive upto 3 days under water whereas, under simulated conditions they survived upto 15 days. SEM results indicated presence of one pair of thoracic and eight pair of abdominal fictional spiracles which denoted that the respiratory system of the grub is peripneustic. The spiracles are characterized by external structures consisting of a central bulla which is surrounded by a smooth cresent shaped sieve/spiracular plate with numerous aeropyles. Absence of a conventional spiraclular opening, presence of a convex projecting central bulla in place of the opening, sclerotized and smooth sieve plate with ultramicroscopic (< 3 micron wide) aeropyles might have provided protection against entry of water into the tracheoles, allowing only gaseous exchange Observations on relative abundance of L. albistigma indicated that the highest population of grubs were recorded during the month of August whereas lowest was recorded during December, 2014 - 15. Correlation studies between L. albistigma grubs and soil physico-chemical parameters revealed that among all physical parameters, sand (r = -0.693) and silt content (r = -0.845) had significant negative correlations whereas, clay (r = 0.839) recorded a significant positive correlation. Among the chemical parameters, soil organic matter content (r = 0.901) and available nitrogen (r = 0.963) had significant positive correlation with grub population. Microbial investigation on the gut content of third instar grubs of L. albistigma revealed 20 different bacterial cultures of which 5 bacterial cultures designated as B2, B5, B11, B14 and B17 had the highest colony forming unit/ml. Bacterial flora considerably varied in size, colour, pigmentation, margins and elevation and as well as in utilization of carbohydrates and their response to various enzymes.en_US
dc.identifier.urihttp://krishikosh.egranth.ac.in/handle/1/5810105902
dc.keywordsBIOECOLOGY, Lepidiotaen_US
dc.language.isoenen_US
dc.publisherAAU, Jorhaten_US
dc.subEntomologyen_US
dc.subjectnullen_US
dc.themeBIOECOLOGY ON Lepidiota sp. Indet. (COLEOPTERA: SCARABAEIDAE)en_US
dc.these.typePh.Den_US
dc.titleBIOECOLOGY ON Lepidiota sp. Indet. (COLEOPTERA: SCARABAEIDAE)en_US
dc.typeThesisen_US
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