Effects of forestry host plants, rearing seasons and their interaction on cocoon productivity of tropical tasar silkworm, Antheraea mylitta in uttarakhand

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  • ABSTRACT

    Antheraea mylitta Drury (Lepidoptera: Saturniidae) is a commercial silk producing forest insect of India, but it has never been experimented in Uttarakhand state in spite of the huge availability of its forestry host plants. This is the first study on A. mylitta in Uttarakhand. The goal of this study is to introduce forest based commercial rearing of A. mylitta, in tropical forest areas of Uttarakhand to reduce poverty among forest dependent people. In current study, we assessed the effect of seven forest tree species, rearing seasons, and their interactions on cocoon productivity of Daba (bivoltine) ecorace of A. mylitta in the New Forest of FRI, Dehra Dun during 2012 and 2013 and collected the data that was analysed by two-way completely randomized block factorial design. Post HOC Tukey's HSD test was carried out to compare the homogeneous pairs of means. We also carried out Evaluation Index analysis to rank the tested forestry host plants for better growth and development of A. mylitta under the climatic condition of Uttarakhand. Analysis of variance indicated that cocoon yield of A. mylitta differed significantly between rearing seasons (DF=1, F=88.24, p<0.05) and host plants (DF 6, F= 368.63, p<0.05); however, their interactions were found insignificant (DF=6, F=0.99, p>0.05). In first rearing season of July-August, there was higher cocoon yield than the second season of September-November. Results indicated that Terminalia alata fed larvae showed significantly higher cocoon yield (164.11 cocoons/300 larvae); followed by, T. tomentosa (148.89 cocoons), T. arjuna (140.00 cocoons) and Lagerstroemia speciosa (129.47 cocoons) fed larvae. Whereas, Lagerstroemia tomentosa fed larvae that was used by the first time in India, showed lowest cocoon yield (48.81 cocoons), followed by T. chebula (72.53 cocoons) fed larvae. Cocoon yield of T. tomentosa and T. arjuna fed larvae of A. mylitta did not differ significantly with each other.


  • KEYWORD

    Tropical forests , forest dependent people , forest based livelihood opportunity , vanya sericulture , poverty alleviation , socioeconomic development of Uttarakhand

  • Introduction

    Antheraea mylitta Drury (Lepidoptera: Saturniidae) is a commercial silk producing polyphagous forest insect of India and many poor people in tropical and subtropical forest areas of Bihar, Jharkhand, Chhattisgarh, Madhya Pradesh, Odisha, Andhra Pradesh, Uttar Pradesh Maharashtra and touching the fringes of West Bengal commercially rear its larvae on different forestry host plants for small household income twice or thrice in a year (CSB, 2012). Literature indicates that in recent years, many actions for sustainable exploitation of forest resources have been undertaken (Muafor et al., 2012), but only few study are concerned with commercialization of forest insects to reduce poverty in forested area (De Foliart, 1992). Because, many people still consider insects mainly as a pest; however, they are less aware of the poverty alleviation potential of commercial forest insect like A. mylitta (Bhatia and Yousuf, 2013 b).

    Historically, foundation for the study of insect-host plant relationships was clearly defined by Charles T. Brues in 1920’s (Brues 1920 and 1924); however, there is no reference on effects of forestry host plants, rearing seasons and their interaction on cocoon productivity of tropical tasar silkworm, A. mylitta in any of the Himalayan states of India, including Uttarakhand. It is known that cocoon crops of forest silkworms are influenced by the season and the host plants (Venugopal and Krishnaswami, 1987). The cocoon of A. mylitta shows considerable variations in their colour, size, shape, pupal weight, shell weight, and the silk output (Jolly et at., 1974, 1979) and such variations mainly occur due to climatic conditions, food plants and altitude (Nayak and Guru, 1998b). Several workers have reported that host plants influence the larval weight gain, survival percentage, relative growth rate, pupal weight, adult emergence, and fecundity of different lepidopterans (Basu, 1944; Srivastava, 1959; Thobbi, 1961; Pandey et al., 1968; Singh and Byas, 1975; Dubey et al., 1981).

    In Uttarakhand, rearing of A. mylitta has never been tried in spite of the huge availability of its forestry host plants in tropical forest areas up to an altitudinal range of 610 meter (Thangavelu, 2004). We are concerned to introduce forest based rearing of A. mylitta, as a new forest insect industry in tropical forest areas of Uttarakhand. We believe that introduction of A. mylitta in tropical and subtropical forest areas of Uttarakhand can help in poverty mitigation. We also hypothesize that introduction of A. mylitta may revitalize the sericulture scenario of Uttarakhand by adding one more variety of natural silk in its export basket. Studies have also indicated that when forest dependent people are associated with forest insect industry like rearing of A. mylitta, such income generating activity links livelihood with forest conservation and improves the conditions of forest (Bhatia and Yousuf, 2013 a). This paper deals with effect of forestry host plants, rearing season and their interaction on cocoon productivity of A. mylitta in Dehradun, Uttarakhand.

    Materials and Methods

      >  Out door rearing of A. mylitta on seven forestry host plants

    We investigated the effect of seven forestry host plants (Lagerstroemia speciosa, Lagerstroemia tomentosa, Terminalia alata, Terminalia arjuna, Terminalia bellirica, Terminalia chebula and Terminalia tomentosa), rearing seasons and their interactions on cocoon productivity of Daba (bivoltine) ecorace of tropical tasar silkworm, A. mylitta at New Forest, FRI, Dehradun Uttarakhand (Fig. 1), which is situated at 30° 19’ 56.21” N to 30° 21’ 5.35” N and 77° 58’ 56.81” E to 78° 0’ 59.73” E at 640.08 AMSL. The climate of New Forest, Dehra Dun is moderate due to its location at foot of the Himalayas (WMD, 2011). After carrying out survey of the New Forest and getting administrative approval from the Director, FRI, Dehra Dun, four outdoor experimental rearings of A. mylitta (Fig. 2 to 4), each in July-August and September-November were conducted during the year 2012 and 2013 as per the improved rearing technology of Mathur et al. (1998) and data were collected as per the experimental protocol of the study.

      >  Statistical methods and analysis of Data

    Tested forest tree species were taken as treatments, so there were 07 treatments, and the number of replications was 06. Normality of data was checked before to the statistical analysis. Descriptive statistics were calculated by using Microsoft Excel. Data of first and second rearing seasons were combined together, then treatment wise descriptive statistics were calculated and mean tables were prepared. A two-way completely randomized block factorial design was used to test the significance of difference in the means of variable. We did Factorial ANOVA by using advance statistical software, STATISTICA 10. Rearing season, host plant and their interactions were treated as the main (fixed) effects and cocoon productivity served as dependent variables for block effect. The level of significance was fixed at p=0.05. Post HOC test was carried out by using Tukey’s HSD test to compare the homogeneous pairs of means.

      >  Evaluation Index (EI)

    Evaluation Index [EI] shows an aggregate unit of cocoon yield of A. mylitta reared on a particular host plant in different rearing seasons, which was ca1cuated as per the procedures outlined by Mano et al. (1993, 1998). For cocoon yield, EI of 50 or more than (>) 50 is considered suitable.

    image

    Where, A = Mean of a variable on a particular treatment; B = Over all mean of that variable on all the treatments; C = Over all standard deviation of that variable on all the treatments; 10 = Standard unit and; 50 = Fixed value

    Results

    Analysis of variance for the effect of rearing seasons, host plants and their interactions on cocoon yield (number)/300 larvae of A. mylitta presented in Table 1 reveals that cocoon yield of A. mylitta differed significantly between rearing seasons (DF=1, F=88.24, p<0.05) and host plants (DF 6, F= 368.63, p<0.05); however effect of interactions between rearing season and host plants on cocoon yield was found insignificant (DF=6, F=0.99, p>0.05).

    Fig. 5 indicates that in first rearing season, cocoon yield was significantly higher on all the forestry host plants as compared to the second rearing season. Effect of rearing seasons and host plants on cocoon yield (number) / 300 larvae of A. mylitta, reared on different host plants showing in Table 2 reveals that in first rearing season, T. alata fed larvae showed highest yield of 171.58 cocoons/300 larvae, followed by T. tomentosa (156.75 cocoons), T. arjuna (148.17 cocoons) and L. speciosa (133.17 cocoons) fed larvae. Whereas, L. tomentosa fed larvae showed the lowest cocoon yield of 57.69 cocoons followed by T. chebula (83.54). The corresponding higher values in second rearing season were 156.64, 141.03, 131.81 and 125.77 cocoons/300 larvae fed on T. alata, T. tomentosa, T. arjuna and L. speciosa, respectively.

    Results of Tukey HSD test presented in Table 3 for the effect of rearing seasons on cocoon yield (number) / 300 larvae of A. mylitta, reared on different host plants show that rearing seasons had significant impact on cocoon yield, as overall mean of cocoon yield differed significantly with each other and demonstrated two homogeneous groups of means. Further, Tukey HSD test for the effect of host plants on cocoon yield of A. mylitta presented in Table 4 indicated six homogeneous groups of means that differed significantly from one another. Table indicates that cocoon yield of T. tomentosa (148.89) and T. arjuna (139.99) fed larvae did not differ significantly with each other and formed one homogeneous group. Table 5 showing the results of the Tukey HSD test for the effect of interactions between rearing seasons & host plants on cocoon yield of A. mylitta indicated nine homogeneous groups of means that differed significantly from one another.

    Higher cocoon yield is a desirable character; therefore, a higher value of EI is preferable for better economic returns. Table 6 indicates that four forestry host plants viz., T. alata (61.75), T. tomentosa (58.06), T. arjuna (55.90) and L. speciosa (53.36) scored higher indices (EI >50) and therefore, were found superior to T. bellirica (47.55), L. tomentosa (33.82) and T. chebula (39.57). Our results show that for the best cocoon yield of A. mylitta in Uttarakhand, T. alata is the best-suited food plant followed by T. tomentosa, T. arjuna, and L. speciosa.

    Discussion

    Cocoon yield in A. mylitta is a complex character that depends on interaction of various contributing traits (Sinha et al., 1995). Cocoon crops of A. mylitta depend on developmental vigour of silkworm and rearing season and quality of the host plants (Venugopal and Krishnaswami, 1987). Results of the present study also indicated that cocoon yield of A. mylitta differs significantly between rearing seasons and host plants (p<0.05).

    In present study, higher cocoon yield was found in first rearing season than the second one, which confirms that seasonal variations play a major role in the growth and development of A. mylitta larvae and weight of silk gland that contribute to cocoon yield (Ueda et al., 1969; Takeshita et al., 1975; Mathur and Mathur, 1996). Further, in second rearing season, prolonged larval period due to low temperature (Tamiru et al., 2012) increases caterpillar’s exposure to natural enemies (Isenhour et al., 1987), because larval period is inversely related to temperature and relative humidity (Tamiru et al., 2012).

    We found that forestry host plants showed significant influence on cocoon yield of A. mylitta. It is found that T. alata fed larvae showed highest cocoon yield, followed by T. tomentosa, T. arjuna and L. speciosa fed larvae. Whereas, L. tomentosa fed larvae showed the lowest cocoon yield, followed by T. chebula. It was also found that cocoon yield of T. tomentosa and T. arjuna fed larvae did not differ significantly with each other. Our results are showing the conformity with the findings of Deka and Kumari (2013), who had assessed the effect of T. tomentosa, T. arjuna, T. bellirica, T. chebula, L. speciosa and L. parviflora on rearing performance and cocoon characteristics of A. mylitta in the agro-climatic conditions of Ranchi, Jharkhand and reported comparable performance of T. tomentosa and T. arjuna in cocoon productivity.

    Success of any insect depends mainly upon an optimal diet in both quantity and quality (Hassell and Southwood, 1978), which provides energy, nutrients, and water to carry out life’s activities (Slansky, 1993). Carbohydrates, proteins, and lipids are the main sources of energy at the time of larval-larval, larval-pupal, pupaladult transformation (Krishnaswami, 1978; Thangamani and Vivekanandan, 1984). Higher availability of these nutritional components has been reported in T. alata, T. tomentosa, T arjuna and L. speciosa than T. bellirica, T. chebula and L. tomentosa (Agrawal et al., 1980; Sinha and Jolly, 1971; NISCAIR, 1976).

    Reports are available on moisture contents of the host plant leaves, which have a positive correlation with cocoon productivity of A. mylitta (Krishnaswami, 1978; Thangamani and Vivekanandan, 1984). High moisture content in host plant’s leaves has favourable effects on the palatability and assimilability of nutrients (Parpiev, 1968). Deka and Kumari (2013) found higher leaf moisture content of 72.07% in T. tomentosa, followed by L. speciosa (71.21%) and T. arjuna (70.36%) and recorded cocoon productivity of 86, 80 and 82 cocoons/DFL, respectively. These results support the present findings. Further, some workers (Stride and Stratman, 1962; David and Gardiner, 1966; Jermy et al., 1968; Fraenkel, 1969) have produced experimental evidences in support of the contention that insect becomes “conditioned” to a particular host plant, because food first eaten by a phytophagous insect becomes its subsequent feeding behaviour. In our experimental rearing also, this fact stands true for the larvae of A. mylitta, which adopted L. tomentosa host plants by the first time in Uttarakhand and completed its life cycle.

    Conclusion

    Our results confirmed that for achieving best cocoons productivity of A. mylitta in tropical forest areas of Uttarakhand, T. alata is the best-suited food plant, followed by T. arjuna, T. tomentosa, and L. speciosa. Accordingly, State Forest Department may initiate systematic plantation of T. alata, T. tomentosa, L. speciosa and T. arjuna through their various afforestation, reforestation and plantation programme to create a new forest insect industry of A. mylitta in Uttarakhand to promote its adoption by tribals and rural communities inhabiting in forest fringe areas to improve their livelihood.

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  • [Fig. 1] Map of the study site
    Map of the study site
  • [Fig. 2.] (a). Hatching of A. mylitta, (b). Just hatched larva, (c). Brushed larvae, (d). First instar larvae after 24 h, (e & g). Eaten leaves of L. speciosa and (f & h). First instar larvae before moult.
    (a). Hatching of A. mylitta, (b). Just hatched larva, (c). Brushed larvae, (d). First instar larvae after 24 h, (e & g). Eaten leaves of L. speciosa and (f & h). First instar larvae before moult.
  • [Fig. 3.] (a & b). Moult out 5th instar larva, (c, f, g, h). Grown up fifth instar larva, (d). 5th instar larvae feeding on Terminalia tomentosa and (e). 5th instar larvae feeding on T. bellirica.
    (a & b). Moult out 5th instar larva, (c, f, g, h). Grown up fifth instar larva, (d). 5th instar larvae feeding on Terminalia tomentosa and (e). 5th instar larvae feeding on T. bellirica.
  • [Fig. 4.] (a). Beginning of cocoon spinning by grown up 5th instar larva, (b). Formation of hammock, (c). Spinning inside the cocoon, (d). Fully formed cocoon and (e). Harvested cocoon of A. mylitta from New Forest, FRI, Dehradun.
    (a). Beginning of cocoon spinning by grown up 5th instar larva, (b). Formation of hammock, (c). Spinning inside the cocoon, (d). Fully formed cocoon and (e). Harvested cocoon of A. mylitta from New Forest, FRI, Dehradun.
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  • [Table 1.] Analysis of variance for the effect of rearing seasons, host plants and their interactions on cocoon yield (number)/300 larvae of A. mylitta
    Analysis of variance for the effect of rearing seasons, host plants and their interactions on cocoon yield (number)/300 larvae of A. mylitta
  • [Fig. 5.] Effect of rearing seasons and host plants on cocoon yield of A. mylitta.
    Effect of rearing seasons and host plants on cocoon yield of A. mylitta.
  • [Table 2.] Effect of rearing seasons and host plants on cocoon yield (number) / 300 larvae of A. mylitta, reared on different host plants
    Effect of rearing seasons and host plants on cocoon yield (number) / 300 larvae of A. mylitta, reared on different host plants
  • [Table 3.] Tukey HSD test for the effect of rearing seasons on cocoon yield (number) / 300 larvae of A. mylitta, reared on different host plants
    Tukey HSD test for the effect of rearing seasons on cocoon yield (number) / 300 larvae of A. mylitta, reared on different host plants
  • [Table 4.] Tukey HSD test for the effect of host plants on cocoon yield (number) / 300 larvae of A. mylitta, reared on different host plants
    Tukey HSD test for the effect of host plants on cocoon yield (number) / 300 larvae of A. mylitta, reared on different host plants
  • [Table 5.] Tukey HSD test for the effect of interactions between rearing seasons & host plants on cocoon yield (number) / 300 larvae of A. mylitta
    Tukey HSD test for the effect of interactions between rearing seasons & host plants on cocoon yield (number) / 300 larvae of A. mylitta
  • [Table 6.] Evaluation Index for cocoon yield (number) / 300 larvae of A. mylitta, reared on different host plants
    Evaluation Index for cocoon yield (number) / 300 larvae of A. mylitta, reared on different host plants