Sarhad J. Agric. Vol.24, No.1, 2008

EFFECT OF LIGHT AND DARK EXPOSURE ON THE DIFFERENT LIFE PARAMETERS OF SILK WORM, BOMBYX MORI L. (BOMBYCIDAE: LEPIDOPTERA)

Toheed Iqbal*, Mian Inayatullah*, Amna Sadozai** and Imtiaz Ali Khan*

ABSTRACT The performance of the Japanese race of silkworm, Bombyx mori L. (Bombycidae: Lepidoptera) was studied at Sericulture Wing, Forest Department Peshawar under laboratory conditions of 25 + 2 ºC temperature and 70 + 10 % relative humidity in complete dark (24 hours) and a complete light (24 hours) condition. The results showed that mean life cycle of B. mori was 62 days in dark and 68 days in light. The diurnal variation in the activity persisted in constant darkness, but was suppressed by constant light. Mean cocoon weight was 1.06 gm in dark and 0.9 gm in light. Mean shell weight in dark and light was 0.2 gm and 0.16 gm, respectively. Shell ratio in dark was 19.40 gm, whereas it was 18.35 gm in light. Percentage of sex ratio (F:M) was 56:44 in dark, whereas it was 42:58 in light. Mortality percent of larvae kept in dark was lower (13.3 %) than in light (24.4 %). Mean fecundity of the adults emerged from larvae kept in dark and light was 112.6 and 46.7 eggs/f, respectively. Generally, that the duration of life cycle, cocoon weight, shell weight, percent shell ratio, percent sex ratio, percent mortality, and fecundity of the larvae reared in dark was significantly better than the larvae kept in light condition.

Keywords: Bombyx mori, Light and Dark Exposure, Life parameters, Biology, Fecundity.

INTRODUCTION Sericulture is the science of rearing silkworm for the industry. If the textile industry is provided with commercial production of raw silk, and includes the adequate raw silk, Pakistan can not only save its operations, which are required for the production of precious foreign exchange (i.e., reduce imports), but silk fiber (Krishnaswami et al., 1973). The larvae of can also improve its economy by exporting the Bombyx mori L. (Bombycidae: Lepidoptera) are surplus commodity. Since the majority of population caterpillars that are about 4 cm long, including their lives in rural areas and villagers including men, horned tail. They are buff-colored with brown women and children can increase their income thoracic markings. The adults are moths with a 4 cm through the rearing of B. mori in their spare time. The wingspan. They are also buff-colored, but have thin process of rearing is completed before wheat harvest. brown lines on their whole bodies (Herbison-Evans, Even they can easily get two generations of B. mori 1997). Another silkworm, Bombyx mandarina one after the other (Ishfaq and Akram, 1999). appears to be a wild race of B. mori (Savela, 1998). Silk worm, Bombyx mori (should be B. mori ) is the Researchers have conducted experiments to find out common species used for the production of silk. high yielding strains of B. mori and mulberry. Silkworm undergoes complete metamorphosis that is Different species of mulberry may have their life cycle passes through four stages, egg compositional differences and might lead to vary (embryo), larva, pupa, and moth (adult) (Anonymous, effects on B. mori growth and silk production 1998). (Mahmood et al. , 1987). The growth rate of B. mori larvae and subsequent silk production depend mainly Silk is mostly used in manufacturing of cloth. It is on the nutrient content of mulberry leaves. Fukuda also used in making of surgical sutures, artificial (1960) reported that about 70% of silk protein blood vessel, tire lining, parachute, electric insulating produced by the B. mori is directly derived from the material, oil protein and artificial vitamins. Waste protein contents of mulberry leaves. The nutritive material (excreta) of B. mori is used as an artificial value of mulberry leaves varies due to species and diet for animals and as green manure for crops leaf maturity of the plant. Hoffman and Subramanian (Ishfaq and Ikram, 1999). In Pakistan, sericulture is (2005) found in their experiment on the role of light practiced in all the four provinces and Azad and exposure on the final stages of development of Jammu Kashmir. The main activity of natural silk Anopheles stephensi that there was a significant production is practiced around the irrigated forest reduction in the development of adult mosquitoes plantation of Changa Manga, Kamalia, Chichawatni when larvae were bred in the absence of light and Multan in Punjab province (Anonymous, 1990). compared with the control group bred in alternating Pakistan’s economy largely depends on agriculture 12h light and 12h dark. It has been observed that and its raw products. The production of raw silk is electric light can affect the behavior of nocturnal inadequate to meet requirements of the textile insects. A high level of illumination causes night

* Department of Entomology, NWFP Agricultural University Peshawar – Pakistan. ** Sericulture Wing, Forest Department, NWFP, Peshawar – Pakistan. Toheed Iqbal, et al. effect of light and dark exposure of the different life …… 76

flying insects to settle as they would normally do at Chopped mulberry leaves were provided as larval daybreak so feeding, breeding and egg laying food 5 times a day, with an interval of 4hours, activities cease. Furthermore, it was found that starting from 6:00 am. Leaves were chopped into artificial light can affect mating of moths e.g., small pieces because the 1st instar larvae are very females do not produce the sex pheromones to attract small to feed on large pieces of leaves. Since leaves males (Anonymous, 1998). Less work has been done are chopped into small pieces, they therefore, become on the impact of artificial lightning on other insects, dry and hard soon and larvae are unable to feed on but Bratton (1990) reported that mayfly life cycle these leaves. The Larvae were, therefore, provided may be disrupted, while Crowson (1981) mentioned with fresh leaves after every 4 hours. that the survival of the glowworm is threatened by outdoor lighting. Life cycle was recorded under both conditions from hatching till spinning. Bed change was done twice a In Pakistan, experiments have been conducted on day in the 2nd and 3 rd instars, and daily in full grown providing nutritious leaves of different mulberry larvae i.e., 4 th and 5 th instars. The emerged larvae species/varieties for high yield of silk. But, no work were recorded. Percentage mortality was recorded by has been done on the effect of light and dark on the counting dead individuals in larval, pupal and adult life cycle of B. mori . Keeping in view the importance stages. of silk worm, an experiment was conducted at the Sericulture Wing, Forest Department Peshawar, Sanata branches were provided to full grown larvae N.W.F.P. to investigate the effect of light and dark on as cocoonages, so that full grown larvae get space for the duration of life span, cocoon weight, shell weight, spinning. After completion of cocoon formation, cocoon shell ratio, % sex ratio, percent mortality and cocoons were harvested and weighed by the fecundity of B. mori under similar conditions of following formula: temperature and humidity. Cocoon weight = Weight of pupa + Weight of shell MATERIALS AND METHODS A study was conducted on the effect of light and dark Afterwards, the cocoons were cut and weight of shell conditions on the life cycle of B. mori at Sericulture was taken by the following formulae: Wing, Forest Department, Shami Road, Peshawar. weight of cocoon shell The aim was to observe the differences in the B. mori Cocoon shell ratio= /weight of cocoon x 100 cycle under complete light and dark condition. Sexing was done at pupal stage by using taxonomic In the experiment, Japanese race of B mori was characters. Males have a spot, whereas females have reared under laboratory conditions of 25+2ºC and 70 a “U” shaped structure at the posterior end of the th + 10 % RH up to 5 larval instar. There were two abdomen. (Ishfaq and Ikram, 1999). Number of eggs experimental units (light and dark) with 3 laid/female was counted for each female. The data replications. Each replication is consisted of 15 was analyzed by using ANOVA. Means were larvae. The experiments were laid out in a separated utilizing the LSD. Completely Randomized Design (CRD). RESULTS AND DISCUSSION Rearing chambers (incubators), rearing trays and all Overall performance of B. mori larvae kept in dark other tools were disinfected with 2% formalin and light for 24 hours provided with same conditions solution. Eggs of B. mori were placed in incubator for of temperature (25 + 5 ºC) and humidity (70 + 10 %) 12 days at 25 – 28ºC (2ºC increase/2days) and 70 – is shown in Table I. The larvae in kept dark 85% RH (2% increase/2days). The temperature and expressed significantly better results than the larvae RH were automatically controlled inside the rearing in light in respect of cocoon weight, shell weight, chamber at the desired levels. B. mori is very shell ratio, percent sex ratio, percent mortality and sensitive to environmental conditions, e.g. humidity fecundity. When B. mori entrained to a 12h light/12h and temperature, therefore, both these changes were dark lighting schedule, the HIOMT like activity maintained at 25 +2ºC and 70+10% RH. showed a significant diurnal variation with high levels during the dark period (Itoh et al., 2004). Larvae of 1 st instar were selected from the bulk, and placed in two incubators, one with light for 24 hours The total life span of B. mori in dark and light (complete light) and the other having no light for 24 conditions, with means of 62 and 68 days, hours (complete dark). respectively, were significantly different (Table II).

Sarhad J. Agric. Vol.24, No.1, 2008 77

CONCLUSIONS AND RECOMMENDATIONS temperature (25+5 ºC). Further more, the life cycle of From the present results, it is concluded that B. mori B. mori was longer in dark than in light conditions. shows shorter life cycle, more cocoon weight, more shell weight, more shell ratio, more female: male Further studies are needed to be done to investigate ratio, less mortality, and maximum fecundity in dark these and other life parameters at other temperature conditions than in light conditions, when kept under and relative humidity conditions with feeding various the same conditions of humidity (70+10%) and natural and artificial diets.

Table 1. Performance of Bombyx mori kept under light and dark conditions at 25+5 ºC and 70+10%RH Cocoon Wt. Shell Wt. Shell Ratio Sex Ratio (% Fecundity Condition (gm) (gm) (%) F) Mortality (%) Dark 1.06 A 0.20 A 19.40 A 55.55 A 13.33 A 112.62 A Light 0.92 B 0.16 B 18.35 B 42.21 B 24.44 B 46.70 B *Means followed by different letters are significantly different at 5% probability level (LSD)

Table 2. Life cycle duration (days) of Bombyx mori kept under light and dark conditions at 25+5ºC and 70+10%RH Condition Egg Larva Pupa Adult Total Lifespan Dark (days) 10-12 31-34 12-14 4-7 57-67 Light (days) 10-12 34-37 14-16 5-8 63-73

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