Effect of Tukra (Mealybug) Infected Mulberry Leaves on the Quantitative Traits of New Polyvoltine Strain of Silkworm, Bombyx mori L.
The influencing effect of tukra infected mulberry leaves on 5th instar polyvoltine silkworm breed of APM1, rearing was studied since, the maximum leaves consuming at this stage of silkworm life cycle and by utilizing non-infected healthy leaves as control. Interestingly in the experimental batch, larval duration was found to be 12 h lesser than the control batch. Mulberry leaves consumption efficiency and economical characters of silkworm like larval weight, pupation rate, cocoon weight, shell weight and reeling parameters were found higher in the experimental batch than the control batch. The result indicated that tukra infected mulberry feed has no adverse effect on silkworm rearing. Moreover, overall improvement was noticed in tukra infected leaves fed batch and sturdily suggest that even mealybug infected mulberry leaves can also be effectively utilized for the silkworm rearing in acute shortage of healthy mulberry leaves.
The silkworm, Bombyx mori L. is an important economic insect and also
a tool to convert leaf protein into silk. The industrial and commercial use
of silk, the historical and economic importance of production and its application
in all over the world finely contributed to the silkworm promotion as a powerful
laboratory model for the basic research in biology (Ramesh-Babu et al.,
2009). The mealybug, Maconellicoccus sp., belongs to the family Pseudococcidae,
has been reported in India, Bangladesh, Indonesia and identified the species
as Maconellicoccus hirsutus (Green) (Baskaran et al., 1992;
Chatarjee and Sarkar, 1993; Bindroo and Dhar, 1996). Its seasonal incidence,
transmission and severity of mealybug incidence in mulberry and this dreadful
diseases prevalent during the pre-monsoon and summer seasons in sericulture
practicing states of India, causing crop loss up to 4500 kg/ha/year (Muralikumaran
and Baskaran, 1992a, b). The morphological and anatomical changes such as curling
of leaves, thickening and flattening of stems at the growing point observed
in tukra infected mulberry (Sriharan et al., 1979). Through recent studies
with the help of electron microscopic investigation reveals that tukra symptoms
are the manifestation of mealybug, Maconellicoccus hirsutus attack but
the exact molecular level interaction is yet to understand and involvement of
virus was ruled out. Recently discussed on early diagnosis method for the tukra
incidences in mulberry (Sugnana-Kumari et al., 2003) and various studies
on bio-control of the mealybug by beetle, Cryptolaemus montrozieri of
an exotic enemy as a part of pest management program (Manjunath et al.,
1992, 2003; Kishore et al., 1995; Chakraborthy et al., 1999; Katiyar
et al., 2000; Masilamani et al., 2003).
The studies related to the effect of feeding tukra-infected mulberry leaves on different silkworm breeds and its nutritional conversion efficiency was reported by Thangamani and Vivekanandan (1983), Kumar et al. (1992) and Ahmed et al. (1999, 2000). The nutritional efficiency during 4th and 5th instars of silkworm is about 80% of the total food consumption compared to the whole larval period (Ueda, 1965; Magadum et al., 1996; Rahmathulla et al., 2005). In the present study, an effort has been made to examine the nutritional impact of feeding tukra infected leaves on popular polyvoltine silkworm breed (APM1) during the 5th instar over the healthy leaves fed batch.
MATERIALS AND METHODS
Tukra Infected Mulberry Leaves
The V1/S13 varieties of mulberry leaves harvested with typical symptoms
of curling of apical leaves, secretion of white powdery substances by mealybug
in the infected mulberry garden maintained at APSSRDI campus was utilized for
the present study. Healthy mulberry leaves are harvested for the control batch
after confirmation of non-infection of tukra (Fig. 1). The
both mealybug infected and healthy mulberry leaves were utilized for the experiment
was brought from well maintained and irrigated mulberry garden.
The popular polyvoltine breed, APM1 was utilized for the present
study. Silkworm layings of APM1 was incubated, brushed on the freshly
chopped mulberry leaves and reared under standard rearing conditions for two
subsequent trials during the season of February-March and April-May- 2008 (Krishnaswami,
1975). The young larvae (1st-3rd instars) were reared at 27-28°C with 85-90%
relative humidity and the late age larvae (4th and 5th instars) were reared
at 24-26°C with a relative humidity of 70-80%. From 1st to 4th stages, healthy
V1/S13 mulberry leaves variety was fed under standard silkworm rearing conditions.
After resumption from 4th moult, 300 larvae were counted and kept in a plastic
tray and fed with strictly fresh mealybug infected (tukra) V1/S13 varieties
of mulberry leaves (Fig. 2) harvested separately and fed to
the experimental batch till spinning. Simultaneously, another batch was maintained
as a control by strictly fed with healthy V1/S13 varieties of mulberry leaves
(Fig. 3). These batches were maintained in three replications
and repeated for two subsequent trials. Proper care was taken during feeding,
bed cleaning and spinning under hygienic conditions. Fully ripened worms were
collected manually and mounted on plastic collapsible mountage for spinning.
The experiment was conducted in the Silkworm Breeding and Molecular Genetic
Laboratory (SBMG), Andhra Pradesh State Sericulture and Development Institute
(APSSRDI), Kirikera-515 211, Hindupur, Andhra Pradesh, India.
Data Collection on Parameters
Larvae and cocoons were assessed and the data was collected on required parameters
viz., 5th instar larval duration, larval weight, yield per 10,000 larvae, pupation
rate, cocoon weight, shell weight, shell ratio and single cocoon reeling was
carried out by utilizing fifteen
|| Symptoms of mulberry infection with mealybug (tukra). (A)
Mealy bug infected mulberry garden. (B) Curling
||Feeding of mealybug (tukra) infected mulberry leaves to silkworm
larvae (experimental batch)
||Feeding of healthy mulberry leaves to silkworm larvae (control
good cocoons with the help of epprouvette (Mono cocoon reeling equipment) for reeling parameters viz., average single cocoon filament length, non-breakable filament length and cocoon denier. These parameters were calculated with the assistance of the following formulae.
Silkworm Rearing Performance
Fifth instar larval duration of experimental batch was found to be shorter
by 12:00 h (Table 1). Fully grown silkworm (5th instar of
5th day after 2nd feed) average larval weight was observed to be higher in experimental
batch (33.8 g) than control (31.3 g) larvae. The cocoon yield per 10,000 larvae
was higher by number (9194) as well as by weight (12.54 kg) over control batch
(9188) and (12.18 kg), respectively. Average pupation rate was found to exhibit
slightly more in experimental batch (91.77%) than the control batch (90.81%).
Economical Characteristics of Cocoon
The important economic characteristic of higher average single cocoon weight
was 1.364 g and average single cocoon shell weight of 0.233 g with an 17.09%
of silk ratio in experimental batch recorded. Slightly lower average on single
cocoon weight was recorded 1.326 g and average single cocoon shell weight of
0.214 g with an average of 16.15% silk ratio in control batch was revealed (Table
||Silkworm rearing performances of mealybug infected leaves
fed batch over control batch
||Cocoon reeling parameters of mealybug infected leaves fed
batch over control batch
Mono Cocoon Reeling
In reeling parameters the average single cocoon filament length in experimental
batch (726 m) was higher than that of control batch (601 m). In relation to
the non-breakable filament length was also higher in experimental batch (558
m) and lesser in control batch (530 m). Further, the significant difference
between experimental batch (2.2 d) over that of control batch (1.9 d) was observed
with regard to single cocoon denier i.e., size/thickness of silk filament (Table
The tukra infected mulberry leaves with symptoms shown in the Fig. 1, mealybug infected mulberry garden (Fig. 1A), curling of apical leaves (Fig. 1B), secretion of white powdery substances (Kumar et al., 1997) (Fig. 1C), shortening and flattening of internodes, brittleness of leaves, stunted growth, etc. The productive polyvoltine breed, APM1 developed by Andhra Pradesh State Sericulture Research and Development Institute (APSSRDI), Hindupur, A.P., India, utilized as female component in the preparation of commercial cross breed Swarnandhra (Chandrashekharaiah and Babu, 2003). This was chosen for the study to generate necessary information on impact of tukra infected leaves on new polyvoltine breed commercialized in Southern part of India. As tukra incidence is the common problem found in mulberry gardens of India during pre-monsoon and summer which is very prevalent in the southern regions. Certain studies were carried out on tukra disease, its seasonal incidence and its transmission between mulberry plants (Sriharan et al., 1979; Muralikumaran and Baskaran, 1992a, b; Baskaran et al., 1992). The studies revealed that the mealybug infection causes decline in the quantity of mulberry leaves and leads to the serious concern to the sericulture industry particularly to Southern states of India (Baskaran et al., 1992; Manjunath et al., 1993). Very scanty information is available on the effect of feeding mealybug infected mulberry leaves to the silkworm and its nutritional efficiency (Kumar et al., 1992; Ahmed et al., 1999, 2000). Cellular level understanding through electron microscopic studies revealed that occurrence of tukra disease is not due to viral transfection but due to the attack of insect (Babu et al., 2003) and a novel method for early diagnosis of tukra infection in mulberry has also been discussed (Sugnana-Kumari et al., 2003). Changes of nutritional components viz., proteins, sugar, phenols and total chlorophyll etc., in mealybug infected mulberry leaves has also been reported by Umesh Kumar et al. (1990) and Chatterjee and Sarkar (1993). Some researchers objected the need of effective utilization of mealybug infected mulberry leaves for commercial silkworm rearing (Thangamani and Vivekanandan, 1983). As the control of mealybug, application of chemical pesticides are not advised since they harm the silkworms and the biological control agents like Coccinellid, Anagyrus kamali (Moursi) (Hymenoptera: Encyritidae), Cryptomonotrouzieri muls, Dechlovos etc. (Chakraborthy et al., 1999; Katiyar et al., 2000; Manjunath et al., 1992, 1993, 2003; Masilamani et al., 2003; Kishore et al., 1995) are recommended but yet to be practiced commercially.
The present study was undertaken to study the impact of tukra (mealybug) infected mulberry leaves on 5th instar silkworm larvae and its economically important characters with cocoon reeling parameters. Since, the maximum leaves consumption and conversion efficiency was more in the silkworm during the 5th instar (Rahmathulla et al., 2005). February-March and April-May seasons were chosen for the study since this particular dreadful disease incidence on mulberry is prevalent during these months causing severe crop loss (Muralikumaran and Baskaran, 1992b; Baskaran et al., 1992). The 5th stage larval duration found to be less by 12 h. in the experimental batch may be due to rich nutrition aspects in tukra infected mulberry leaves led to the early maturation of eating silkworm larvae than that of control batch. Reduction in larval duration is an advantage to sericulture farmer since it reduces the labour cost of the farmer and without reduction of economically important quantitative traits of silkworm in experimental batch. This may be due to high moisture content found in the mealybug infected mulberry leaves than that of normal mulberry leaves (Ahamed et al., 2000; Umesh-Kumar et al., 1990; Thangamani and Vivekanandan, 1983). Fully grown larval body weight was also found higher in experimental batch suggesting that the nutrient values are not affected in tukra infected mulberry leaves and in conformation with the observations of Ahamed et al. (2000). It is also evident that of tukra infected mulberry leaves has a positive influence on the food and water utilization pattern with respect of most industrial important economical characters such as cocoon and shell weight in the silkworm (Ahamed et al., 1999, 2000; Kumar et al., 1992). As the silkworm is monophagous in nature and derives all nutrients essential for its biological activities from the mulberry leaves only. It is also observed that feeding of tukra infected mulberry leaves to the silkworm shown positive impact on the important economical characters viz., larval duration, cocoon and shell weight with filament length, non-brekable filament length and cocoon denier over the control batch. The most important traits of silkworm in particular to seed farms/farmers is the pupation rate, observed with an average of 91.77% in experimental batch over that of control batch 90.81%, a slight more positive result was noticed. It also revealed that the longer cocoon filament length (726 m) and thicker cocoon filament denier (2.2 d) in mealybug infected leaves fed batch than that of control bath is clearly indicated the presence of more protein in mealy bug infected leaves and its proper assimilation in silkworm. The exact reasons for unaffected these quantitative traits are yet to be studied.
The important problems which are encountered while effective utilization of mealybug infected mulberry leaves for silkworm rearing is attack of black small ants to the infected and storing infected leaves. Moreover, it was impressively observed that of tukra infected mulberry leaves could be utilized more effectively for any kind of silkworm rearing as suggested by Thangamani and Vivekandan (1983) and even for new popular breed of APM1 in acute shortage of healthy mulberry leaves or by mixing with healthy mulberry leaves as potential utilization of entire mulberry leaves produced from the garden.
If mulberry garden is infected with tukra disease, the sericulture farmer or the rearer need not be discouraged. In the present study revealed that the tukra infected mulberry leaves may be effectively utilized even for newly popularized pure polyvoltine breed (APM1) for silkworm rearing since it is not affecting the quantitative traits of the silkworm and obtained an encouraging results in experimental over the control batch. It may be due to the presence or over expression of more nutrients by the stimulation of the pathogen in tukra infected leaf than that of healthy mulberry leaf and emphasis for further research may be given on actual biochemical/biotechnological process.
The authors wish to thank the former director and colleagues of the Moriculture Division as well as other staff of APSSRDI, Kirikera for their encouraging support in the present investigation and preparation of the manuscript.
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