Biology of sweet potato weevil, Cylas formicarius F. on sweet potato

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1 J. ent. Res., 38 (1) : (2014) Biology of sweet potato weevil, Cylas formicarius F. on sweet potato M. Devi *, K. Indira Kumar and R.F. Niranjana Department of Agricultural Entomology, Tamil Nadu Agricultural University, Coimbatore , Tamil Nadu, India ABSTRACT The life stages of Cylas formicarius in sweet potato tubers were assessed during first and second generations. In first generation, the highest egg period was recorded in Co-3 (White) (5.50 days). The lowest larval period was recorded in Kanjangad (24.16 days) while highest pupal period was recorded in Kanaka (Red) (7.56 days) and the total life cycle period in days was highest in Co-3 (White) (42.49 days) whereas the lowest mean life cycle period was recorded in Kanjangad (Red) (33.59 days). In the second generation, the highest egg period was recorded in Co-3 (White) (5.80 days), lowest larval period was recorded in Villupuram local (Red) (25.34 days). The highest pupal period was recorded in Kanaka (Red) (7.89 days). The highest total life cycle period was recorded in Co-3 (White) (43.67 days) and lowest total life cycle period was recorded in Villupuram local (Red) (35.40 days). Key words : Sweet potato weevil, life stages, biology, adult longivity, different cultivars. INTRODUCTION Sweet potato (Ipomoea batatas Lam), is a most versatile tropical tuber crop which used as a major source of staple food. The centre of origin of sweet potato is Central America, but the crop is widely grown in many tropical and subtropical countries. Sweet potato is ranked seventh in world staple food production (expressed on a dry matter basis), after wheat, maize, rice, potato, barley and cassava. The sweet potato weevil is widely distributed, wherever this crop is grown and it causes considerable damage to the tubers and the matured vines. The infested tubers develop faint, black spots on them and hence they become un fit for human consumption. Sweet potato weevil is an universal pest and causing extensive damage. The low yield tonnes ha -1 in India is attributed to damage caused by the sweet potato weevil C. formicarius Fab. In India, an yield loss to the extent of 60 to 100 per cent was often noticed (Pillai and Palaniswami, 1984). Based on the economic importance of this crop and the seriousness of the pest C. formicarius, therefore an investigations was undertaken on the Bio-ecology of sweet potato weevil C. formicarius and results are furnished in this paper. Corresponding authour's deviagri84@gmail.com MATERIALS AND METHODS Culturing of sweet potato weevil C. formicarius : Biological studies were carried out under laboratory conditions using nine cultivars viz., Co-3 (White), BCSP-7 (Red), IGSP-7 (Red), IGSP-14 (Red), Arun (White), Kanaka (Red), Kanjangad (Red), Villupuram local (Red) and Karur local (White). Twenty pairs of field collected C. formicarius adults were released on Villupuram local (Red) tubers cut pieces. The tubers were changed on alternate days. The culture was closely monitored and maintained at room temperature. At 45 th day after release new adults were emerged. Fresh adults and grubs thus obtained were used for the laboratory studies to determine oviposition, fecundity, egg period, grub period, pupal period and sex ratio. Total eggs laid and number of eggs hatched in each cultivar and number of unhatched eggs, pupal period were recorded as per Gupta and Pandey, The experiment was conducted as per procedure adopted by Gupta and Pandey, The newly hatched larvae were transferred in to the freshly sliced tubers kept in the polythene bags. The time taken for every instar was recorded till it attained its pupal stage. The transformation from one instar to another instar was identi fied by the inactive condition of the grub. The experiment was replicated thrice. The transformation into pupal stage

2 Journal of Entomological Research, March 2014 was carried on in an enlarged area in the feeding tunnel. The dead ones were replaced by fresh grubs of respective instar and the mortality was corrected as per Abbott (1925). On emergence, the male and female were separated based on external features, following morphological characters and counted. The female were slightly smaller than male, which later becomes larger than male. The antennal club of female were much smaller than the male. The antennal surface of the female was covered with setae, whereas the antennal segments in male was bare except the last segment. RESULTS AND DISCUSSION Life cycle of first and second generation of C. formicarius on different sweet potato cultivars : Life cycle of first and second generation of C. formicarius on different sweet potato cultivars result were furnished in Table 1. While comparing the life cycle of sweet potato weevil, C. formicarius reared on different cultivars over two successive generations, it was recorded that the minimum mean egg period (3.97 days) was recorded in BCSP-7 (Red), whereas the maximum mean egg period (5.65 days) recorded in Co-3 (White). In respect of larval period, the minimum mean larval period (25.07 days) was recorded in Kanjangad (Red), while the maximum mean period (30.36 days) was observed in Co-3 (White). The minimum pupal period (4.88 days) was recorded in Arun (White) and the maximum pupal period (7.72 days) was registered Kanaka (Red). On consolidating the total life cycle period a minimum of days was observed in respect of BCSP-7 (Red), while (43.08 days) was registered in Co-3 (White). Biology of first and second genration C. formicarius on different cultivars of sweet potato tubers : Biology of first and second generation C. formicarius were studied in different cultivars are furnished in Tables 2 and 3. In both generations, the highest mean egg period was recorded in Co-3 (White) i.e., (5.5 ± 0.60 days) and (5.80 ± 0.73 days) respectively and the lowest mean egg period was recorded in BCSP-7 (Red) i.e., (3.93 ± 0.42) and (4.01 ± 0.44 days) respectively. In the first generation the lowest first instar larval period was recorded in Kanjangad (Red) as (4.10 ± 0.48 days), whereas during second generation Table1. Life cycle of first and second generations of C. formicarius on different sweet potato cultivars. Cultivars Egg period (days)# Larval period (days)# Pupal period (days)# Total life cycle period (days)# I Generation II Generation Mean I Generation II Generation Mean I Generation II Generation Mean I Generation II Generation Mean Villupuram local (Red) Karur local (W) IGSP-7 (Red) BCSP -7 (Red) IGSP -14 (Red) Co -3 (White) Arun (White) Kanaka (Red) Kanjangad (Red)

3 Biology of C. formicarius on sweet potato Table 2. Biology of first generation C. formicarius on different sweet potato cultivars. Cultivars Egg period (days)# Larval period (days)# Pupal period I-instar II-instar III- instar Total larval (days)# period Adult longevity (days)# Male Female Villupuram local (Red) 4.03 ± ± ± ± ± ± ± ± 2.80 Karur local (White) 4.60 ± ± ± ± ± ± ± ± 4.92 IGSP-7 (Red) 5.20 ± ± ± ± ± ± ± ± 2.88 BCSP-7 (Red) 3.93 ± ± ± ± ± ± ± ± 4.06 IGSP-14 (Red) 4.33 ± ± ± ± ± ± ± ± 2.86 Co-3 (White) 5.5 ± ± ± ± ± ± ± ± 2.84 Arun (White) 4.46 ± ± ± ± ± ± ± ± 3.76 Kanaka (Red) 4.30 ± ± ± ± ± ± ± ± 9.59 Kanhangad (Red) 4.03 ± ± ± ± ± ± ± ± 4.10 Table 3. Biology of second generation C. formicarius on different sweet potato cultivars. Cultivars Egg period (days)# Larval period (days)# Pupal period I-instar II-instar III- instar Total larval (days)# period Adult longevity (days)# Male Female Villupuram local (Red) 4.27 ± ± ± ± ± ± ± ± 2.81 Karur local (White) 4.80 ± ± ± ± ± ± ± ± 5.01 IGSP-7 (Red) 5.49 ± ± ± ± ± ± ± ± 2.99 BCSP-7 (Red) 4.01 ± ± ± ± ± ± ± ± 3.19 IGSP-14 (Red) 4.78 ± ± ± ± ± ± ± ± 3.21 Co-3 (White) 5.80 ± ± ± ± ± ± ± ± 3.81 Arun (White) 4.78 ± ± ± ± ± ± ± ± 4.21 Kanaka (Red) 4.72 ± ± ± ± ± ± ± ± 8.41 Kanjangad (Red) 4.80 ± ± ± ± ± ± ± ±

4 Journal of Entomological Research, March 2014 Villupuram local (Red) was recorded with (4.18 ± 0.62 days) and the highest first instar larval period was recorded in Karur local (White) (5.30 ± 0.48 days) during first generation, while in second generation Arun (White) was recorded with (5.98 ± 0.71 days). Highest second instar larval period in both generations IGSP-14 (Red) was recorded with (6.30 ± 0.67 days) and (6.98 ± 0.78 days) of second instar larval period which was the lowest. The lowest third instar larval period (12.96 ± 0.79 days) was recorded both Kanjangad (Red) and BCSP-7 (Red) during first generation, whereas in second generation BCSP-7 (Red) was recorded with lowest third instar larval period ± 1.02 days. The highest third instar larval period was recorded in Co-3 (White) as ± 0.70 days and ± 0.82 days during first and second generation respectively. The lowest total larval period was recorded in Kanjangad (Red) as ± 1.94 days during first generation, whereas in second generation Villupuram local (Red) was recorded with the lowest days ± The highest total larval period was recorded in Co-3 (White) during both first (30.06 ± 1.75 days) and second generation respectively ± 2.14 days. The lowest pupal period was recorded in both generation in the cultivars Arun (White) during first 4.53 ± 0.36 days and second 5.23 ± 0.47 days generations and highest was recorded in both generation in Kanaka (Red) as 7.56 ± 0.82 days and 7.89 ± 0.97 days during first and second generation respectively. Lowest adult male longevity was recorded in IGSP-14 (Red) during first ± 2.68 days and second generation ± 3.49 days and highest was recorded in Co-3 (White) ± 3.57 days and Kanjangad (Red) ± 5.81 days during first and second generations. In both generation, the lowest female adult longevity was recorded in Villupuram local (Red) as ± 2.80 days and ± 2.81 days respectively and highest was recorded in Co-3 (White) as ± 2.84 days and ± 3.81 days respectively. During the first generation the lowest egg period (3.93 days) was recorded in BCSP-7 (Red) whereas the highest (5.50 days) was in Co-3 (White) and during second generation the lowest egg period (4.01 days) was recorded in BCSP-7 (Red), whereas the highest (5.80 days) was in Co-3 (White) which is almost in concurrence with the reports of Murakami (1933b) who recorded that the incubation period varied from 4 to 6 days with an average of 5.22 days. The findings are also in accordance with the results of Cockerham et al., (1954) who recorded the egg period as 4 days in summer and 56 days in winter season. During first generation the lowest number of egg (629 numbers) was recorded in Arun (White), whereas highest (876 numbers) was recorded in Co-3 (White) for five pairs of adults. During the second generation lowest number of egg (5680 numbers) was recorded in IGSP-14 (Red), while highest (9680 numbers) was recorded in IGSP-7 (Red). This finding is almost in consonance with the earlier reports of Murakami (1933b), Fukuda (1933) and subramanian (1959), who have reported that the average fecundity of female weevil, C. formicarius was 80.0, 75.8 and eggs per insect respectively. The present data are also have similarity with those of Jayaramaiah (1975), who have recorded eggs per female. In first generation the lowest larval period (24.16 days) was recorded in Kanjangad (Red) while highest larval period (30.06 days) was observed in Co-3 (White) and during the second generation the lowest larval period (25.34 days) was recorded in Villupuram local (Red) while highest larval period (30.66 days) was observed in Co-3 (White) which is almost in agreement with the findings of Subramanian (1959) who reported a mean larval period of days while Jayaramaiah (1975), recorded the larval development period as days. The lowest pupal period was recorded during both generations in Arun (White) as 4.53 and 5.23 days respectively, whereas highest pupal period for first generation 7.13 days was accounted in IGSP-7 (Red) and during the second generation it was registered in Kanaka (Red) (7.89 days). This finding are in agreement with the reports Trehan and Bagal (1948) who reported that the pupal period of sweet potato weevil as 4-11 days. Trehan and Bagal (1948) who reported that the duration of life-cycle may occupy 23 to 45 days. During first generation the total life cycle period was lowest in Kanjangad (Red) (33.59 days). The highest period (42.49 days) was recorded in Co-3 (White). During the second generation the total life cycle period was lowest in Villupuram local (Red) (33.59 days), whereas highest total life cycle period (43.67 days) was recorded in Co-3 (White). These findings are in agreement with earlier reports of 56

5 Biology of C. formicarius on sweet potato Trehan and Bagal (1948) who reported that the duration of total life-cycle period was between 23 and 45 days. In first generation the lowest male adult longevity (85.16 ± 2.68 days) was recorded in IGSP-14 (Red) whereas the highest (91.93 ± 3.57 days) was in Co-3 (91.93 ± 3.57). The lowest female adult longevity (75.60 ± 2.80 days) was recorded in Villupuram local (Red) while highest (81.96 ± 2.84 days) was observed in Co-3 (White). During the second generation the lowest male adult longevity (86.53 ± 3.49 days) was recorded in IGSP-14 (Red) whereas the highest (93.21 ± 5.81 days) in Kanjangad (Red). The lowest female adult longevity (76.30 ± 2.81 days) was recorded in Villupuram local (Red) while highest (88.31 ± 3.81 days) was observed in Co-3 (White). These findings are almost in agreement with the earlier observation Smee (1965) who reported the adult life span extended for several months. Jayaramaiah (1975) also worked out the life span of female and male as 90.5 and 91.1 days respectively, which is also in agreement with the present findings. REFERENCES Abbott, W.S A method of computing the effectiveness of an insecticide. J. Econ. Entomol., 18: Cockerham, K.L., Deen, D.T., Christain, M.B. and Newsom, L.D The biology of the sweet potato weevil. Tech. Bull. La. Agric. Exp. Sta., No. 383, 30 pp. 6. Fukuda, K. 1933, Insect-pests of sweet potato in Fromosa, part I. The sweet potato weevil (in Japanese), Rep. Govt. Res. Inst., Fromosa, Taihoku, 62 : 1-35 (Short Summary in Rev. App. Ent., 22 : 520). Gupta, R.N. and Pandey, N.D Effect of sweet potato varieties on the growth and development of sweet potato weevil, Cylas formicarius Fabricius under laboratory conditions. Indian J. Ent., 55: Jayaramaiah, M Bionomics of sweet potato weevil Cylas formicarius (Fab) (Coleoptera: Curculionidae). Mysore J. Agric. Sci., 9: Murakami, S. 1933b. Result of studies on Cylas formicarius Fabr. 2 (In Japanese) J. pl. Prot., 20: Pillai, K.S. and Palaniswami, M.S Pests of tuber crops. Indian Farming, 33: Smee, L Insect-pests of sweet potato and taro in the territory of Pupua and New Guinea : their habits and control. Papua New Guin. Agric. J., 17: Subramanian, T.C Observations on the biology of Cylas formicarius (Fabricius) at Coimbatore. Madras Agric. J., 46: Trehan, K.N. and S.R. Bagal Life-history, Bionomics and control of sweet potato weevil Cylas formicarius F. in Bombay province, Curr. Sci., 18: (Accepted : February 10, 2014) 57