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Chapter

ENVS 2210 Chapter Notes -Ecdysone, Ontogeny, Moulting


Department
Environmental Sciences
Course Code
ENVS 2210
Professor
Ernesto Guzman

Page:
of 4
UNIT 04: Growing Up to Be a Bee
Holometabolous insects go through 4 main life stages:
1) Egg embryo develops and hatches into nondescript larva that is a feeding machine
2) Larva white, maggot-like larvae put on weight at stupendous rate then stop eating and
major changes start to unfold larva pupates
3) Pupa larva metamorphoses into adult bee metamorphosis is quicker for queen, slower for
worker and slowest for drone
4) Adult
Hormones control transformations in life of insects
o Hormones keep larvae young
o Hormones signal exoskeleton to dissolve itself and regrow so insects can get bigger and
change shape in metamorphosis
CHAPTER 12 From Egg to Adult
Queen is only individual who normally lays eggs in a colony of honeybees
o Queen inserts abdomen into cells of comb and deposits one egg on bottom of cell
o To fertilize egg, queen liberates few sperm from her spermatheca (sperm are minute)
o On egg, sperm finds a way to micropyle, minute hole tough and protective of chorion
o One sperm navigates micropyle, penetrates thin vitelline membrane and reach egg
nucleus, floating in yolk to bring fertilization
o Nuclei move to the periphery of egg, under vitelline membrane, whether they become
arranged in layer of cells, blastoderm
o Cells on convex side (underbelly) of egg become larger and layer starts to fold inwards
as embryo starts to become recognizable
After 3 days as egg, embryo shows head, buds for mouthparts and antennae (and spiracles)
o Over next 6 days, larva grows 1500 times in weight (14 segments)
o During next period, it goes through 5 larval stages
o Interior is full of ventriculus intestine exists through anus body cavity contains
haemolymph and fat body
o only purpose of larva is eating and growing fed and tended by workers
after 6 days, larva occupies entire cell and stops feeding
o spins cocoon of silk secreted by the silk glands
o larva starts to metamorphose within old larval cuticle, within silken cocoon
o start of pupal stage
after 12 days as pupa, worker bee is ready to emerge (eclose)
o adult bee breaks out of larval cuticle and chews its way out of its cocoon and through
capping to emerge as callow
o must wait few days for new cuticle to tan and harden before she can fly or sting
FIGURE 12.4
holometbolism: form of insect development from egg to larva to pupa to adult
Queen
Workers
Drone
Egg stage
3 days
3 days
3 days
Larval stage
5.5 days
6 days
6.5 days
Pupal stage
7.5 days
12 days
14.5 days
Total dvpmt time
16 days
21 days
24 days
TABLE 12-1
CHAPTER 13 Nutrition
heterotrophic: rely largely on organic sources for the minerals they need depend on organic
carbon sources for energy, and organic nitrogen and sulphur sources for proteins and body
building
honeybees are herbivorous heterotrophs attain nutrition from plants, mostly flowers, as
nectar and pollen
o pollen contains:
25% protein
10% free amino acids
25% carbohydrates
Remaining % is made up of lipids, enzymes, co-enzymes, pigments, vitamins,
sterols and minerals
o Each pollen grain is multicellular microgametophyte and mobile component of sexual
reproduction in plants
Nectar- mostly sugary liquid or syrup transformed into honey which is mostly sugar fuel for
activity
10 amino acids essential for honeybee growth:
1) Arginine
2) Histidine
3) Lysine
4) Tryptophan
5) Phenyalanine
6) Methionine
7) Threonine
8) Leucine
9) Isoleucine
10) Valine
Honeybees require vitamins many coenzymes important in metabolism and interaction with
enzymes, contain vitamins as part of their molecular structure pollen is crucial as it is rich in
vitamins
Brood food/royal jelly produced by hypopharyngeal and mandibular glands of young nurse
bees
All larval bees fed royal jelly, but duration of feeding with rich food is important in determining
caste of adult bee
Rate of food intake probably regulates activity of the corpora allata
High levels of juvenile hormone in body of developing larva induces differentiation into queen
Progressive provisioners: continually provide their brood with food (ex. honeybees and
bumblebees)
Mass provisioners: provide their larval with all food that is needed for growth from egg to
adulthood at time egg is laid (ex. stingless bees only)
CHAPTER 14 Raging Hormones
Hormones: chemicals in animals and plants that regulate bodily processes such as growth,
metabolism, reproduction, functioning of various organs
o Hormones are secreted into endocrine glands ductless glands
When secreted into body, hormones bond with specific plasma or carrier
proteins that prevent them from degenerating prematurely
Carriers keep hormones from becoming immediately absorbed by tissues they
affect (target tissues)
Hormone’s presence initiates biochemical cascade of reactions that influence
activity of cells making up tissues and organs
2 most important hormones in honeybees:
1) Moulting hormone (Ecdysone) - secreted by prothoracic glands
2) Juvenile hormone (Neotinin) - secreted by the corpora allata
o both involved in regulating and coordinating growth and development of bees
o Growth requires moulting because exoskeleton does not provide space necessary for
growth insects shed exoskeleton
o In bee larvae larval growth takes place in spurts but without shedding of entire larval
skin each time
only when metamorphosis takes place is larval skin entirely shed
remains as shell around pupa
Metamorphosis: involves all structural changes in organism from egg to adult form during
development
o in bees process by which egg becomes larva pupa adult or imago
Hormonal Regulation in insects
important chemical messengers are secreted by neurons and known as neurosecretions
neurohaemal organs provide interface with the haemolymph by which neurosecretions
become circulated throughout insect’s body (ex. Corpora Cardiaca & Corpora Allata)
*REFER TO PAGE 88 FOR FULL PROCESS OF HORMONE SECRETION*
prothoracicotropic hormone is protein and released from corpora cardiac in most insects
becomes stimulated to produce and liberate ecdysone or moulting hormone
Juvenile hormone is a terpene characteristically composed of short hydrocarbon chains, to
which other simple chemical components are attached
Moulting hormone (ecdysone) is similar in structure to steroids and with almost the same
structure as cholesterol
Bursicon comes from the neurosecretory cells in the thoracic and abdominal ganglia
involved in hardening of insect cuticle (without it, the cuticle remains soft and wings would have
no strength to work)
*REFER TO PAGE 90 FOR DIAGRAM OF PROCESS OF SHEDDING EXOSKELETON*
When enough juvenile hormone is present, it dominates metamorphosis, permitting larval
growth, but inhibiting pupal formation
But when J.H. concentration is low and ecdysone dominates, a pupa forms