 
  
 ICS 65.020.30  
 
Reference number
DRS 357-2: 2020
© RSB2020
  
 RWANDA 
STANDARD  DRS
357-2
First edition
2020 -mm-dd
Silk cocoon production — Code of practice 
— Part 2: Mulberry silkworm rearing for 
cocoon production  
   
 DRS 357 -2: 2020  
©RSB 2020 - All rights reserved                  ii 
 In order to match with technological development and to keep continuous progress in industries, 
standards are subject to periodic review. Users shall ascertain that they are in possession of the latest 
edition  
 
 
 
 
 
 
 
 
© RSB2020  
All rights reserved. Unless  otherwise specified, no part of this publication may be reproduced or utilized 
in any form or by any means, electronic or mechanical, including photocopying and microfilm, without  
prior written permission from R SB. 
Requests for permission to reproduce thi s document should be addressed to : 
Rwanda Standards  Board  
P.O Box 7099 Kigali -Rwanda  
KK 15 Rd, 49  
Tel. +250 788303492  
Toll Free: 3250  
E-mail: info@rsb.gov.rw  
Website: www.rsb.gov.rw  
ePortal: www.portal.rsb.gov.rw  DRS 357 -2: 2020  
iii                ©RSB2020 - All rights reserved  
 Contents  Page 
Foreword  ................................ ................................ ................................ ................................ ...................... iv 
1 Scope  ................................ ................................ ................................ ................................ ................ 1 
2 Normative references  ................................ ................................ ................................ ....................... 1 
3 Terms and definitions  ................................ ................................ ................................ ...................... 1 
4 Silkworm rearing for cocoon production  ................................ ................................ ........................ 3 
4.1 Life cycle of the Silkworm  ................................ ................................ ................................ ................ 3 
4.2 Incubation of silkworm eggs  ................................ ................................ ................................ ............ 4 
4.2.1  Materials required for incubation  ................................ ................................ ................................ ....4 
4.2.2  Procedures  ................................ ................................ ................................ ................................ .......5 
4.3 Silkworm rearing  ................................ ................................ ................................ .............................. 5 
4.3.1  Facilities f or silkworm rearing  ................................ ................................ ................................ ......... 5 
4.3.2  Rearing spacing  ................................ ................................ ................................ ............................... 8 
4.3.3  Environmental factors affecting silkworm rearing  ................................ ................................ .......... 9 
4.3.4  Feeding  ................................ ................................ ................................ ................................ ...........  10 
4.3.5  Control of pathoge ns ................................ ................................ ................................ .....................  12 
4.3.6  Management of moulting larvae  ................................ ................................ ................................ .... 15 
4.3.7  Mounting of mature silkworms  ................................ ................................ ................................ ...... 16 
4.3.8 Management of silkworms during mounting ................................ ................................ .................  18 
4.3.9  Silk cocoon harvesting  ................................ ................................ ................................ ..................  20 
Annex  A (normative)  Estimation of the quantity of disinfectant  ................................ ..............................  21 
A.1 Calculation of total area of rearing room  ................................ ................................ ......................  21 
A.2 Estimation of formalin solution to be used for rearing house and equipment  ............................  21 
  DRS 357 -2: 2020  
©RSB 2020 - All rights reserved                  iv 
 Foreword  
Rwanda Standard sareprepared by Technical Committees and approved by R wanda Standards Board (RSB) 
Board  of Directors in  accordance with the procedures of RSB, in compliance with Annex 3 of the WTO/TBT 
agreement on the preparation, adoption and application of standards.  
The main task of technical committees is to prepare national standards.  Final Draft Rwanda S tandards 
adop ted by Technical committ ees are ratified  by me mbers of RSB Board of Director s for publication and 
gazettment as Rwanda Standards.  
DRS 357 -2 was prepared by Technical Committee RSB/TC 029, Textile and Leather Technology . 
In the preparation of this standard,  reference was made to the following standard  (s): 
1) Title TAS 8201 -2012 Good practices for silk cocoon production  
2) Sericulture training manual for farmers in Rwanda  
The assistance de rived from the above source is hereby acknowledged with thanks.  
DRS 357 consists of the following parts, under the general title Introdu ctory element — Main element : 
 Part 1: Mulberry leaves production  
 Part 2: Mulberry silkworm rearing  
Part 3: Silk cocoons handling  
Committee membership  
The following organizations were represented on the Technical Committee on Title of TC (RSB/TC nnn) in the 
preparation of this standard.  
Ministry of Trade and Industry (MINICOM)  
University of Rwanda -College of Science and Technology (UR -CST)  
National Agric ultural Export Development Board (NAEB)  
 Rwanda Inspectorate, Competition and Consumer Protection Authority (RICA)  
HeWorks Silk Rwanda Ltd  
Rene Pharmacy  DRS 357 -2: 2020  
v                ©RSB2020 - All rights reserved  
 UTEXRWA Ltd  
OXALIS Ltd  
LIXIL/SATO  
Rwanda Standards Board (RSB) – Secretariat  
  DRS 357 -2: 2020  
©RSB 2020 - All rights reserved                  vi 
 Introduction  
Sericultu re is an agro -based sector, involving rearing silkworms to produce silkworm cocoons and raw silk by 
reeling cocoons. The major sericulture activities comprise of mulberry cultivation to feed the silkw orm larvae, 
silkworm rearing to produce cocoons, reeling  of cocoons to unwind the silk filament and silk processing and 
weaving to gain value added silk products.  
The growth and development of silkworm is greatly influenced by environmental conditions. The biolog ical as 
well as cocoon -related characters are inf luenced by ambient temperature, rearing seasons, quality mulberry 
leaf, and genetic constitution of silkworm strains. Different seasons affect the performance of Bomb yx mori L.  
Silkworm rearing depends on the availability of mulberry leaves. It is occasion ally limited by the dry season, 
which is the time to avoid silkworm rearing because mulberry growing isretarded due to drought and 
exceeding high temperature gives rise to the retardation of silkworm growing.  DRS 357 -2: 2020  
1                ©RSB2020 - All rights reserved  
 Silk cocoon production — Code of practice — Part 2: Mulberry silkworm 
rearing for cocoon production  
1 Scope  
This Draft Rwanda Standard provides guidance on good practices during mulberry silkworms ( Bombyx mori ) 
rearing for cocoon production.  
2 Normative references  
There are no normative references in this document  
3 Terms and definitions  
For the purposes of this standard, the following terms and definitions a pply  
3.1 
Silkworm  
the larva or caterpillar of the Bombyx mori  moth  
3.2 
young silkworm  
silkworm larva from hatched egg to the full grown third instar larva  
3.2.1 
 first instar larva  
larva from hatched egg to before the first moulting  
3.2.2 
second instar larva  
larva after the first moulting to before the second moulting  
3.2.3 
third instar larva  
 larva after the second moulting to before the third moulting   
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 3.3 
moulting  
 moulting is the shedding of skin as worms enter into the next instar  
3.4 
grown  silkworm  
larva from the fourth to the fifth instar  
3.4.1  
fourth instar larva  
larva after the third moulting to before the fourth moulting  
3.4.2 
fifth instar larva  
 larva after the fourth moulting to pupa stage  
3.5 
mature silkworm  
fully grown silkworm at the fifth instar larva that is ready to form its cocoon  
3.6 
mounting frame or cocooning frame  
material on which cocoon is formed  
3.7 
cocoon  
the outer protective shell spun by silkworm larva covering itself before transforming into  pupa stage  
3.8 
fresh cocoon  
cocoon that consists of a live pupa and shell with or without de -flossing  
dried cocoon  DRS 357 -2: 2020  
3                ©RSB2020 - All rights reserved  
 3.9 
defect cocoon or poor cocoon  
cocoon whose shape is with abnormal characteristics i.e. double cocoon, pierced cocoon, inside soile d 
coco on, outside soiled, thin -shelled cocoon, loose -shelled cocoon, thin -ended cocoon, malformed cocoon, 
printed cocoon, crushed cocoon, and mouldy cocoon  
3.10 
pebrine  disease  
protozoan disease of the silkworm, Bombyx mori L . caused mainly by Nosema bombycis Na egeli  and can be 
transmitted via silkworm eggs  
NOTE  This is a devastating disease which causes disastrous losses and is under quarantine control by all sericulture 
countries disease is prohibited  
4 Silkworm rearing for cocoon production  
4.1 Life cycle of the Sil kworm  
The   silkworm passes through 4 distinct stages i.e. egg, larva, pupa and adult during its life cycl e as per 
Figure 1 . The duration may last for 50 -55 days depending on the prevailing climatic conditions.  
  
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Figure 1: Life cycle of the silkworm, Bombyx mori  
 
4.2 Incubation of silkworm eggs  
4.2.1  Materials required  for incubation  
The following are  materials used during incubation  ofBombyx mori   eggs :  
a) Incubator  
b) Incubation trays  
c)  Egg incubation paper boxes  
d)   Khaki Papers rolls  
e)  Polyethylene sheets  
f)  Foam pads  
DRS 357 -2: 2020  
5                ©RSB2020 - All rights reserved  
 g)  room heating facility (e.g. charcoal  and charcoal stoves)  
h)  Hygro-thermometer to monitor t emperature and relative humidity  
i) Tables  
j)  Ant wells / barriers  
4.2.2  Procedure s 
During the incubation of silkworm eggs t he following procedure s are considered :  
a) Put polyet hylene sheet underneath  khaki paper , as bottom cover  in incubation tray  
b) Spread eggs (single layer)  at the bottom of  'incubation paper boxes' in  incubation trays  
c)  Cover arena with translucent plastic sheet  
d) Ensure 24 -250C and 70 – 85% RH  are monitored using  h ygrothermometer  
e) Gently mix eggs once a day using bird feather until pinhead stage (allows average conditions)  
f) Monitor colour changes daily from grey stage to pinhead  
g) At pinhead stage on 8 -9 or  9 -10th day of incubation cover the incubation tray with a black polyethylene 
sheet (black boxing)  
h) After 2 days of black boxing remove black polyethylene sheet preferably at 06:00 hours to expose egg s to 
light 
i) Silkworm larvae will have finished hatching usually b y 10:00 hours and the unhatched ones can be re -
black -boxed  
4.3 Silkworm  rearing  
4.3.1  Facilities for silkworm rearing  
The facilities for silkworm rearing including the rearing house and tools  
4.3.1.1   Silkworm rearing house  
4.3.1.1.1   The longitudinal structure of silkworm rearing house should be located in the direction of East -
West; doors and windows should be in the North -South direction to prevent the direct sunlight into the rearing 
room as per figure 2. The trees planted around th e silkworm house will help to reduce the radiation heat from 
outside.   
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Figure 2: Orientation of the silkworm rearing house  
4.3.1.1.2  The site of silkworm house should be 10 -20 meters away from the living house for better 
sanitation and easier disinfecti on and distance should be kept from the area prone to risk causing adverse 
health effect on silkworms such as area of pesticide application and air -polluted source. In case of risk, there 
shall be preventive measures from rain, direct sunlight onto silkwor ms, silkworm pests e.g. Uzi fly, spider, ant, 
lizard, gecko, and rat.  
4.3.1.1.3  There shall be effective cleaning agents and disinfectants for eliminating mould, bacteria, virus, 
and protozoa on equipment and rearing house and available treatment plan when  the pests attacks the 
silkworms.  
4.3.1.1.4   All the floor of the silkworm house and about one meter wide surroundings may bepaved for 
easy cleaning and better sanitation. At a corner or next to the door a space for mulberry storage is  prepared, 
which is e nough at least for two feedings.  
4.3.1.1.5   The house may be built with concrete frame or wood truss with iron sheet roofing with ceiling to 
reduce heat radiation, a brick or concrete floor, and brick -layered side walls with windows covered by 
mosquito net s.  
4.3.1.1.6   The minimum size of the house is 5 meter wide and 6 meter long (total floor space: 30 m2) to 
rear  2 boxes per rearing.  
4.3.1.1.7   The rearing beds are 1.5 meter wide, 1.5 m height  and 5.0 meter long. Three rows of double 
rearing beds arepla ced on the floor with one meter wide on both sides. And the lower shelf is placed 20 cm 
high from the floor and the upper shelf is set with 90 cm interval vertically between two shelves.  
4.3.1.1.8  The rearing house shall be well ventilated,   and with adeq uate size   
4.3.1.1.9   The rearing house should be near the mulberry field in order to minimize the transportation 
distance thus cutting down on wilting of leaf.  
4.3.1.2  Rearing materials and tools  
The following are materials and tools required for silkworm rearing:  
4.3.1.2.1  Non-recurring materials:  
a) Rearing beds  DRS 357 -2: 2020  
7                ©RSB2020 - All rights reserved  
 b) bed cleaning net  
c) cocooning/mounting frame  
d) leaf harvesting baskets or gunny bags  
e) feeding basket  
f) mulberry storing box  
g) hygro -thermometer  
h) chopping knife for mulberry leaves  
i) chopping board  
j) chopping table  
k) sterile sprayer  
l) masks  
m) pruning saw  
n) disinfection tanks  
o) feathers  
p) foam rubber strips  
q) ant wells  
r) knapsack sprayer  
s) secateur  
t) clean material lining for rearing containers  
u) foot cleaning tray  
v)  wash basin/stand  
w) rearing nets   
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 x) plastic shoes  
y) overcoat  
4.3.1.2.2  Recurring materials:  
a) paraffin paper / plastic sheeting  
b) formalin  
c) bleaching powder  
d) lime 
e) charcoal  
f) charcoal stoves  
g) gloves  
4.3.2  Rearing spacing  
4.3.2.1  Enlarged area of silkworm bed shall be provided in correspondence with each  stage of the silkworm 
development and the density of silkworms should be managed to prevent heat accumulation, increase in  
humidity, litter fermentation, accumulation of metabolic gases and insufficient feeding in case of s ilkworm 
overcrowding.  
4.3.2.2  Different stages of silkworms require different bed space. Spread worms evenly ensuring that they do 
not overlap each other. The rearing space at different stages of silkworms should be as per Table -3 
Table 3 Rearing spacing at different stages of silkworms (20,000 eggs)  
Stage  Bed spacing , m2 
Early period  Later period  
1st instar  0.4 1.6 
2nd instar  1.6 3.2 
3rd instar  3.2 5 
4th instar  5.0 7.5 
5th instar  10 15 DRS 357 -2: 2020  
9                ©RSB2020 - All rights reserved  
  
4.3.3  Environmental factors affecting silkworm rearing  
4.3.3.1  Temperature and relative humidity  
Maintenance of recommended temperature, relative humidity (RH), light and ventilation conditions for every 
stage of rearing are of utmost importance for successful silkworm rearing.The optimum temperature re quired 
for rearing silkworms of different early in stars are as described in Table 1.  
Table1 —Optimum temperature and humidity requirements of silkworm during various stages  
Environmental 
factor  Incubation  1st instar  2nd 
instar  3rd 
instar  4th 
instar  5th instar  Spinning  Cocoon 
storage   
Optimum 
temperature,0C 24-25 26-28 25- 27 24-26 23-25 22- 24 22-23 25 
Relative 
humidity, %  75-80 85-90 80-85 75-80 70-75 65-70 60-70 55 
4.3.3.2  Ventilation  
Injurious gases such as carbon dioxide produced during silkworms breathing and litter fermentation, carbon 
monoxide when farmers burn charcoal to raise temperature, ammonia, sulphur dioxide, and so forth are  
released in the rearing room. Young silkworms are weak against carbon dioxide and ammonia. If the 
concentration of the carbon dioxide gas in a rearing room  exceeds 2%, the growth of silkworm is retarded 
therefore : 
a) Care should be taken to allow fresh air through proper ventilation to keep the toxic gases at a low level.  
Windows of rearing rooms should be kept wide open for better ventilation. Ventilation is more effect ive 
when the humidity of the rearing room is higher than the standard  
b) Incubation room or chamber must be opened/ventilated daily for 10 minutes in the morn ing and evening 
during incubation.  
c) Insecticides and disinfectants are also avoided in the rearing room, during rearing.   
4.3.3.3  Light  
4.3.3.3.1  Silkworms are photosensitive and have a tendency to crawl towards dim light.   Late -age 
Silkworms survive better in 16-hour light and 8 - hour dark periods. However, young -age worm prefers 16 hr 
darkness and 8 hr light period. Rearing under complete lighting or complete darkness is not advisabl e 
4.3.3.3.2   Light should be provided for 12 hours a day, till head pigmentati on stage. At blue egg stage, the 
eggs should be kept in darkness by covering with black paper or cloth to obtain uniform hatching.   
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 4.3.4  Feeding  
4.3.4.1  Frequency of feeding  
The standard frequency of feeding is preferably five times a day morning ( 6-7AM) and (9.00 -10.00  A.M.), 
afternoon (1.00 -2.00P.M.), evening (4.00 -5.00P.M.) and night (9.00 -10.00P.M.). The 1st and 2nd instars may do 
with two feedings a day, 6.00AM and 6.00 PM depending on how fresh the food lasts.  
4.3.4.2  Stages of growth and feeding methods  
4.3.4.2.1  First in star: The young worms should be fed with young tender leaves; 2nd and 3rd leaves from 
the tip of the shoot. These are chopped into small pieces with an optimum size is 0.5 -1.0 cm2 and fed to 
worms for 3 days at least twice a day in the morning and late afternoon. After the 3days the worms go into 
moult which takes 18 - 24 hours (1 day) and the silkworms should not be fed during this period.  
4.3.4.2.2  Second instar : feed 3rd and 4th young glossy leaves. C ontinue feeding chopped leaves with an 
optimum size of 1.5 -2.5 cm2 for3 days. After this period the worms go into moult again.  
4.3.4.2.3  Third instar: continue feeding the silkworms on good leaves harvested from the green part of the 
stem/shoot for three days. After this period silkworms go into moult.  
4.3.4.2.4  Fourth instar: feed worms on whole leaves for 4 Days.  
4.3.4.2.1  Fifth instar:  feed on whole leaves for 7 -8 days. During feeding always maintain a single layer of 
leaves. Avoid over mature, yellow a nd diseased leaves.  
NOTE  The larva duration is variable with the temperature and humidity , in association with the quality 
and the quantity of supplied food  
4.3.4.2.5   Appropriate maturity of mulberry leaves should be considered for each stage of the silk worm 
development in order to provide sufficient nutr ients as per Table 2.  
4.3.4.2.6  Unconsumed leaves should be kept at low level to facilitate airflow, maintain their freshness and 
prevent accumulation of heat and dampness that cause disease to silkworms.  
4.3.4.3  Brushing of silkworms  
When hatched, silkworms get together in a group. The newly hatched silkworms are carefully transferr ed and 
evenly spread over for their healthy growth. The brushing of silkworm is then carried out by evenly spreading 
chopped mulberry  leaf of the appropriate size. Principally young silkworms are reared in a sanitary, balanced 
nutritional condition and environmental conditions of temperature and relative humidity should be co ntrolled as 
per Table -1 
4.3.4.3.1  Brushing time of silkworms  
Silkworms s tart hatching early in the morning and the first feeding will be given at 9:00 a m. Those eggs which 
do not hatch in the morning of the first day are likely to hatch in the morning of the following day . DRS 357 -2: 2020  
11                ©RSB2020 - All rights reserved  
 4.3.4.3.2  Brushing methods  
The following are the methods of bru shing:  
a) Feather method of brushing : This is crude but popular method in the study area. In this method, fresh 
chopped mulberry leaf is sprinkled over the hatched larvae and the larvae crawl to fresh leaves. The n the 
egg card is held vertically over the fresh rearing bed and the larvae are pulled by gentle strokes of the 
feather to fall on the bed.  
b) Husk method : the powder husk is sprinkled over freshly hatched larvae on the egg card. Freshly 
chopped mulberry leaves are sprinkled over the husk. The larvae crawl over the husk to reach the fresh 
leaves. Then the larvae along with the leaves are transferred to the rearing bed by means of feather . 
c) The cloth / paper / net method : thin muslin cloth, or minutely perforated paper or a fine meshed net 
(mosquito net)  is placed along the egg card with fresh chopped leaves. The larvae crawls to the leaves 
are transferred to the bed by taking out the cloth / paper / net and placing on the bed. After brush ing, the 
larvae are spread uniformly with the help of chopsticks.  
4.3.4.4  Recommended quantity of mulberry leaves for silkworms at different stages.  
4.3.4.4.1  The silkworms of the fifth instar ingest 88.6% of the total food consumption, the fourth instar 
ingests 9.4% and the young silkworm from the first instar to the third insta r ingests only 2% of total feeding.  
4.3.4.4.2  The quantity of good quality mulberry leaves shall be sufficient for feeding each lot of silkworms. 
Mulberry leaves should be fresh, clean, without damage from pests and diseases that affect the healt h of 
silkw orms. For the better growth, silkworms should be fed with sufficient quantity o f mulberry leaves as per 
Table 2 . 
Table 2 —Quantity of  mulberry leaves for fearing of 20,000 silkworms  
Stage  Life cycle days  Age/Day  Leaf weight per day  Leaf/shoot remarks per day 
1st 
  
  
  
  1 1st 300 g  Harvest 2nd and 3rd young leaves, chopped  at size of 
0.5 cm× 1.0 cm  
  
  
  2 2nd 350 g  
3 3rd 370 g  
4 4th Molting  
2nd 
  
  
  
  5 1th 750 g  Harvest 3rd and 4th leaves  
  
  
  6 2nd 1250 g  
7 3rd 1800 g  
8 4th Molting  
3rd 
  
  
  9 1st 3 kg 
Harvest leaves that are on the green part of young 
shoot  
  
The 3rd instar larva can feed on entire leaf  10 2nd 4 kg 
11 3rd 5 kg 
12 4th 3 kg 
 13 5th Molting  
4th 14 1st 10 kg     
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  15 2nd 15 kg   Entire leaves  
  16 3rd 20 kg  
17 4th 25kg  
18 5th 10kg  
19 6 Molting   
  
5th 20 1st 30 kg  
 Entire leaves  
  
  
  
  
  
    21 2nd 40 kg  
  22 3rd 50 kg  
  23 4th 60 kg  
  24 5th 70 kg  
  25 6th 80 kg  
  26 7th 90 kg  
  27 8th 50 kg  
  30 9th silkworms start 
cocooning   
 
4.3.5  Control of pathogens  
Silk worms are prone to various pathogens such as bacteria, fungi, viruses and protozoans.  Therefor e, 
maintenance of sanitary conditions through cleaning, disinfection of the rearing house and rearing e quipment 
and isolation of dead silkworms is recommended.  
4.3.5.1  Disinfection of rearing house  
4.3.4.5 .1 The rearing house, its surrounding and rearing equipment should be cleaned thoroughly and 
washed in 5% of bleaching powder solution before receiving silkworm eggs.  
4.3.4.5 .2 Washed materials may be dried in the sun;  
4.3.4.5 .3 Rearing equipment should be arranged inside the rearing house, doors and windows closed 
airtight and 2% formalin is sprayed evenly to drench thoroughly the ceiling, walls, floor, doors, wi ndows as well  
as rearing appliances using a power sprayer.  Personal Protective Equipment (PPE) should be worn whi le 
disinfecting the house as per figure 1  DRS 357 -2: 2020  
13                ©RSB2020 - All rights reserved   
Figure 1 Recommended  personal protective equipment  
4.3.4.5 .4 To allow quick diffusion of formalin molecules th e recommended temperature is 250C and and 
relative humidity of 65% or more;  
4.3.4.5 .5 After spraying, rear ing house should be closed for at least 24 hours and opened only next 
morning before introduction of silkworms;  
4.3.4.5 .6 Display a warning notice in large letters on the door to keep people away. It may read as follows: 
WARNING: “DO NOT ENTER, FORMALDEHYDE GAS DISINFECTION TAKING PLACE”  
4.3.4.5 .7 Before entering the rearing house, hands should be washed with disinfectant, fo ot mat soaked in 
5% bleaching powder and 0.3% slaked lime solution should be placed at the entrance;  
4.3.4.5 .8 Lime dust checks viral infections and keeps the rearing bed less humid. Apply a mixture of lime 
powder (100 grams) and bleaching powder (900 gram s) on the floor, verandas of the rearing houses and 
premises to improve hygiene.  
NOTE  Slaked Lime powder available in local markets is sieved first to get fine powder  
4.3.4.5 .9 Entry of person other than those involved in rearing should be avoided;  
4.3.4.5 .10  Clean the rearing floor with 2% bleaching powder solution before and after bed cleaning;  
4.3.4.5. 11  bed disinfectant should be used when the larvae come out of moult; and  
 
©RSB 2020 - All rights reserved                  14 
 4.3.4.5. 12  Ensure optimal environmental conditions of temperature, humidity, light and aeration.  
4.3.4.5. 13 Estimation of recommended amount of disinfectant is per Annex A.  
4.3.5.2  Disinfection of equipment  
The rearing equipment can be disinfected by dipping as follows:  
a) First wash equipment thoroughly with soap, sun dry and then dip into 5% solution of bleaching powder or 
2% formalin solution for a minimum of 30 minutes in a disinfection tank;  
b) Large equipment such as bed stands, leaf storage chambers, mountages can be disinfected by washing 
and spraying with either 5% bleaching powder solu tion or 2% formalin; and  
c) Disinfection tank may be of the size 200 cm x 150 cm and 60 cm deep and a thickness of 15 cm 
constructed using bricks and cement (water proof).  
4.3.5.3  Bed cleaning  
4.3.5.3.1   Bed cleaning is an important process to ensure the hygiene in t he immediate vicinity of 
silkworms in order to protect them from infection. It should be done in the morning before feeding silkworms, 
once in first instar, twice in second instar after moulting and preferably daily in third, fourth an d fifth instar.  
4.3.5.3.2   It is done after every moult for the young silkworms and every day for the mature worms.  
4.3.5.3.3   During bed cleaning, un -eaten leaves, faeces, abnormal, weak, scrubby, diseased and dead 
silkworm which accumulate on the rearing bed should be colle cted and disposed properly to protect silkworm 
from bad gas and disease -producing germs on the bed.  
4.3.5.3.4   To clean the bed, a net is spread over the silkworms and fresh leaves are evenly distributed on 
top of the net. Silkworms will crawl up to feed o n the fresh leaves on the net which, in turn, are shifted to new 
beds. Any remaining silkworms are transferred using the net to another clean bed/tray, then the wast es are 
discarded.  
4.3.5.3.5   There shall be disposal measures for wastes e.g. silkworm excr ete, mulberry branches and 
leaves after each rearing cycle both inside and surrounding area of the rearing house to prevent the  spread of 
diseases.  
4.3.5.3.6   For the proper disposal, infected larvae should be put in 2% formalin solution before burning or 
burying.  
4.3.5.3 .7  In the preparation of 2 % formalin solution, 1 litre of 40% formalin (commercial) will be mixed 
with 19 litres of water to make 20 litres of spray solution of 2% formalin;  
4.3.4.5.3.8  Hands shall be washed after bed cleaning to prevent disease from spreading  DRS 357 -2: 2020  
15                ©RSB2020 - All rights reserved  4.3.5.3.9   Polyethylene sheets used as bottom cover should be washed with soap and dried in the sun and 
then disinfected in 5% bleaching powder before use. The following is the procedure for bleach solutions 
preparation:  
a)  Dissolve 60 g of slaked lime powder in 20 li tres of water (0.3%);  
b)  Dissolve 1 kg of bleaching powder  in 0.5 litre of slaked lime solution and make a paste;  
c) Pour the above bleaching powder paste to the rest of the slaked lime solution and shake thoroughly.  
d) Cover the container with a lid and keep the  mixture undisturbed for 15 minutes to settle down the un -
dissolved matters.  
NOTE  Use freshly prepared solutions  
4.3.6  Management of moulting larvae  
4.3.6.1  Moulting and post - moulting signs  
4.3.6.1.1  Silkworms undergo 4 moultings in the larval stage and instars are fe d accordingly. The rearer 
must be able to identify when the worms are getting into and out of moult apart from counting days. During 
moulting the bed should be kept dry and uncovered.  
4.3.6.1.2  Moulting Signs: swollen heads, heads raised upwards, reduced m ovements.  
4.3.6.1. 3 Signs of getting out of moult: the worms are active and move around, the mouth part is broader, 
the body is dull with loose skin and shed off skins are easily seen on the bed.  
4.3.6.1. 5 Once the silkworms come out of moult, they should be spread evenly to enhance dryness in the 
bed and to increase the bed space to match with their increasing body size. Silkworms are fed when a ll of 
them have come out of moult.  
4.3.6.2  Precautions for handling the moulting larvae  
4.3.6.2.1   Generally moulting is  uniform when incubation and rearing are done properly while poor 
uniformity of moulting takes place due to diseased larva and handling of moulting larva in a wrong w ay. When 
about 70 -80% of larvae are completely in the moulting stage, feeding should be st opped; unconsumed leaves 
and excreta should be removed and humidity reduced from the rearing house.  
 
 
Figure9:Moultingsilkwormlarva  
4.3.6.2.2   When 90% of silkworms go into the moulting stage, lime powder is dusted or husk is applied to 
reduce the humidity  to 60 -65% RH facilitating the moulting process  and the temperature should be controlled 
as per figure 4.  
 
©RSB 2020 - All rights reserved                  16 The moulting temperature is per figure 4 below:  
 
Figure 10: Optimum temperature for each instar of silkworms  
4.3.6.2.3   The newly moulted silkworms crawl around in search for mulberry. When about 95% of 
silkworms have completed the moulting the first feed of mulberry leaves as given. This first feed is  slightly less 
than the standard dose.  
4.3.6.2.4   After post -moulting of silkworm and before feeding of first meal of each development stage, 
there shall be prevention and disinfection from silkworm diseases by application of lime powder.  
4.3.6.2.5   Slower post -moulting or under grown silkworm than that of the same development stage should 
be collected to  rear separately.  
4.3.6.2.6   Moulting period lasts for about 24 hrs and care should be taken not to disturb silkworms during 
this period.  
4.3.7   Mounting of mature s ilkworms  
4.3.7.1  Mature silk worms signs and handling  
4.3.7.1.1   In about a week of the 5th instar, after  completing the feeding silkworms reaches the maturity 
and are ready to spin silk . Mature silkworms are identified by the following maturity signs:  larvae cease to 
feed, crawling restlessly away from light in search of a corner to attach themselves for spi nning, reduction in 
size by one -third and transparent light yellowish appearance as they are full of silk , release of wet faecal 
matter  
4.3.7.1.2    Ripened silkworms are transferred to the mounting or cocooning frames for spinning cocoons. 
Then the mature silkworm spins thread from its mouth to make the footing for cocooning. This footing is called 
the cocoon floss. Typical examples of mounting frames are shown in figure 17.  
4.3.7.1.3   Silkworms  ripened on different days should be put in separate mountages and unripe silkworms 
should be allowed to continue feeding.  
4.3.7.1. 4  Silkworms should not be disturbed during cocooning for the continuity of the silk thread.  
DRS 357 -2: 2020  
17                ©RSB2020 - All rights reserved  4.3.7.1.5  The mature worms are picked from the rearing beds and trasferred to mountages. Care s hould be 
taken to put the right number of worms on the mountages to avoid overcrowding and formation of doubl e 
cocoons.  
4.3.7.2  Cocooning frames  
In selection the type of cocooning frame, the following factors  should  be considered:  
a) Adequate and equal cocooning spa ce should be  provided.  
b) The frame should be  made of a proper material for the reeling ability of cocoons.  
c) It should be durable.  
d) Mounting can be done easily.  
e) Easy handling and harvesting from the aspect of labour requirement for mounting.  
3) Although few cocooning frames satisfy all these conditions, either rotary cocooning frame or plastic 
cocooning frame is recommended.  
4.3.7.3  Typical  frames  
4) This is made of plastic and each frame is usually made up of about 20 mountains of which height is o f 
which about 6 cm. When mounting, the mountain -shape is straightened out and the frames are spread over 
the tray or rearing bed. Fifty frames are needed per one case of silkworm seeds. The plastic frame s eems to 
be used for a small scale rearing.  
 
5)  
Figure 12: The plastic mounting frames (left) and the bamboo stick frames  
 
©RSB 2020 - All rights reserved                  18 
 4.3.7.4  Methods of mounting  
Method of mounting and control of environmental conditions during mounting affect the quality of coc oons 
considerably. There are several methods of mounting.  
4.3.7.4.1  Picking -up method  
When abou t 10% of silkworms become transparent, they are picked up by hand to place on the cocooning 
frame. By this method, silkworm can be mounted at the right time but it takes a lot of labours. This  method is 
adopted for a small scale rearing of silkworms.  
4.3.7.4.2  Self-mounting / Natural mounting  
In this method, the cocooning frames are placed on the rearing bed and the matured silkworms climb u p to 
search spinning places. This method saves labours required for mounting and the cocoon quality impro ves, as 
only matured s ilkworms mount the frame.  
4.3.8  Management of silkworms during mounting  
4.3.8.1  Protection s during mounting  
The following precautions should be observed:  
a) The temperature shou ld be maintained close to 22 -230C principally and the humidity between 60 -70%. At 
high temperature above 25°C,   the cocoon quality deteriorates.  
b) As high humidity lowers the reeling ability of cocoons, it needs to keep dry condition by using fan or 
ventilator.  
c) The direct sun light should be avoided.  
d) Attention should be also paid o n the damages by rat and ants, because they favour pupa inside a cocoon.  
e) papers should be spread on the floor below the mountages to absorb urine from the worms and changed 
when they become damp.  
f) When about 40% of silkworms have become matured, the cocoon ing frame is placed on the bed.  
g) The frame is placed on the bed for 10 -15 hours. When 80 -85% of spaces are filled with matured 
silkworms, the frame is transferred to the mounting room.  
h) 90 - 100 larvae should be mounted per square foot  DRS 357 -2: 2020  
19                ©RSB2020 - All rights reserved   
Figure 13 Spaced s ilkworms on mounting                              A mature spinning silkworm  
4.3.8.2  Silkworm care during cocoon spinning and pupation  
During cocoon spinning and pupation the following should be taken into account:  
a) The good aeration is required and can be control led by opening all windows but strong winds and strong 
sunlight should be avoided.  
b) Ensure moderate and uniform lighting in mounting room. Silkworms move away from strong light which 
may cause overcrowding on one side, formation of double cocoons or poor q uality cocoons (e.g. uneven 
thickness)  
c) Fallen silkworms on the floor should be mounted on separate mountages. Such worms produce inferior 
cocoons  
d) Keep mountages undisturbed until cocoon harvest to minimize possible injury of delicate  immature pu pae 
4.3.8.3  Manage ment of silkworm ‘urine’ during mounting / spinning  
4.3.8.3.1  Urine must be checked as it raises relative humidity in the rearing room besides staining the 
cocoons  
4.3.8.3.1  Absorbent khaki paper   should be put under the mountages to dry off the urine and  one is using 
plastic sheets change them frequently.  
4.3.8.3.1  When using wooden frames, these should not be stacked on top of each other but rather have the 
frames stand at an oblique angle to give quality cocoons with minimal stain problems  
 
 
©RSB 2020 - All rights reserved                  20 4.3.9  Silk cocoon  harvesting  
4.3.9.1  Pupae maturity  
4.3.9.1.1  Cocoons shall be harvested when pupae become mature enough. Generally the majority of 
silkworms complete cocooning in 2 days after preparing footage and in another 2 days it can become p upa at 
25°C. The pupa, immediate ly after pupation, is very sof t with yellowish body colo ur and may rupture even with 
slight mechanical stress. But after 2 -3 days at 25 ℃, its skin turns to dark brown and hard.  
4.3.9.1.2  Pupal maturity is checked by dissecting randomly selected cocoons and examining condition of 
pupae.  
4.3.9.1.3  Hard and dark brown pupae with dry cocoon shells best time for cocoon harvest (7th or 8th day 
after mounting)  
4.3.9.1.4  Early harvesting injures the delicate pupawhich stains the cocoon with their bleeding. Conve rsely, 
delayed harvesting of cocoons bears a risk of cocoon spoilage by emerging adult moth.  
6)  
Figure 14 - Fully formed pupa  
 
4.3.9.2  Harvesting method  
 Spoiled cocoons are firstly sorted out. This is important because dirty fluid from dead  pupae soils good 
cocoon s and lowers their value. After removing dead  pupae and thin shelled cocoons, the cocoons are 
harvested by hand. Waste cocoons should be put in separate bags not to mix with good cocoons . 
 
DRS 357 -2: 2020  
21                ©RSB2020 - All rights reserved  
 Annex  A 
(normative)  
 
Estimation of the quantity of disinfectant  
A.1 Calculati on of total area of rearing room  
The following is the procedure to calculate the total surface area to be disinfected:  
E.g. Rearing house  size: 20.5m long, 8.5m wide and 2.8 m in height – up to ceiling)  
a)  Area of floor and ceiling:  L  x W x 2  = 20.5 m x 8.5 m x 2 = 348.5 m2 
b)  Area of 2 long side walls:  L  x H x 2  = 20.5 mx 2.8 mx 2 = 114.8 m2 
c) Area of 2 other side walls:  W x H x 2  =   8.5 m x 2.8 mx 2 =   47.6 m2 
d) where L stands for length, W for width and H for height.  
e) Total surface area to be treated = 5 10.9 m2  
A.2 Estimation of formalin solution to be used for rearing house and equipment  
A.2.1  The disinfection of about 17.5 m2 requires 1 litre of 2% formalin solution. Therefore, 510.9 m2 will 
require ହଵ଴ .ଽ
ଵ଻.ହ litres=29.2 litres of 2% formalin  
A.2.2  An equal amount of formalin solution may be required to   spray rearing equipment (following washing 
with bleaching powder).  
A.2.3  A total of 58.4 L of formalin (2%) will therefore be required to disinfect rearing house of 510.9 m2 and 
the rearing equipment ( for specified house above)  
 
 
 
 
  
©RSB 2020 - All rights reserved                  22 
  
  DRS 357 -2: 2020  
 
Price based on nnn pages  
©RSB 2020 - All rights reserved   
  
 