Lecture notes Biodiversity: Exploiters and Exploited Silkworms and Sericulture (BI2EEE4)

8.10.19


L2 – Sericulture: silkworms and mulberries
Keywords:

Univoltine (produce one clutch per year – 1 gen), Bivoltine (2 gens per year - ), multivoltine (tropical
multiple gens per year), horizontal transmission (between individuals), vertical transmission
(between generations)

Lecture:

 Moths: Lepidoptera (complete metamorphosis)
 Cocoons made of silk and used for larvae ballooning (harvested from wild)
o Pus moth – regurgitative wood to make cocoons (camo/protective)
o Silkworm – fiberglass style protective cocoon
o 1 silk thread holds pupae to twig
 Body plan
o True legs hold food while
feeding
o Protuberance – produces silk
o 3 segmented antenna True legs Prolegs (on Anal clasper
o Spinneret = modified salivary gland to spin silk abdomen)
 Silkworm – Bombyx mori
o Order: Lepidopteta
o Domesticated (bred to not fly – improper wing muscles)
 Bred for 5.5k years
 Commercially docile
 Farm 90% of commercially used silk
o Wild relative Bombyx mandarina from China (1 unique domestication event)
 First dyed silK found at 3600BC
 Forbidden expressing of information to other counties or penalty
 Boiled pupa in alkaline solution and removing = single silk string
 Sericulture
o 3 things to happen (women’s job)
 Produce silk cocoons for reeling
 Industry one: Produce eggs
 When pupa weight = 75% and cocoon = 25%
 Don’t let moth emerge as then cocoon broken to break singular silk
strand (unused silk)
 High density growth (have to be social)
 Larger silkworm = more silk produced
 Univoltine – eggs hibernate all winter (in wild), bivoltine (temp and
light dependent) or multivoltine – ↓ quality w/↑# clutches per year
 Montages – where 5th instar larva are placed to pupate
 Hibernation produces better quality silks
 How to break hibernation?
o Friction, warm water, electricity, high temp tested
o 15% HCl, 46֯C, 5 mins = break hibernation
o Bivoltine - ↑temp/light = come out of hibernation

, 8.10.19


 Attempted adaptations: ↑ silk yield, ↓ mortality, ↑ disease
resistance, temp, humidity, ∆ diet (artificial – mulberry = seasonal)
 Industry two: Pupae killed – buy in new eggs
 Newly hatched larva = ants
 Pupae not killed in A. assamensis as have built in-exit hole
 Instar larvae (kept at 27C in first stage)
o Also keep moist (stops caterpillars drying up)
 Drop a degree per stage (↑ body heat produced)
 4th instar = grown worms
 5th instar = gain 80% body mass (at 3/4 weeks)
 How to rear silkworms
o Brushing – slowly giving new mulberry leaves
o Keep warm when small
o Keep alone when ill looking = about to molt
o Don’t touch larvae – put new food on top and then remove
old food
o Remove sick larvae
o ?Don’t keep too many in one container
 Industry three: mulberry production
o Pupation site
 If pupate on food = contamination of food
 Boxes/framework used
 Day 1 – loose framework made from inside out
 Day 2 – framework done
 Day 3 – scaffolding complete
o Making silk
 Dry cocoon 7-8h (100C) – make sure kill and not rotted pupae inside
 Sorted into good shape and awkward
 Remove fiber (dissolved connection in water bath) – bundled and sold
 Remainder used as fertilizer of mulberry trees/animal feed (3/4 of weight)
 Silkworm domestication
o Lost 33-50% nucleotide diversity compared to wild silkworm = domesticated
 Silk gland
o 50% body weight = silk
o Fiber = fibroin (short side chain AAs used = interlock closely = β-pleated sheet w/H
bonds) and sericin (sticks fibroin together)
 Posterior gland = fibroin produced (liquid)
 Anterior gland = gum produced (liquid)
 Spinneret (somehow becomes solid?)
 Pressure and tension applied creates silk orientation and structure
to polymerize
 Silk properties
o ↑ tensile strength, elastic, warm, ↑ dye affinity, does not rot
o Inner = fibroin and outer three layers = sericin
 Fibrin = insoluble but sericin = soluble
 Temp too ↑ = w/sticky sericin protein =hard reel
 Sericin removed by cooking at 100֯C for 1-5min then rapid cooling