Nervous, Sensory, Endocrine and Exocrine Systems
I.
Nervous System: Structure and Function
II.
Sensory System
A. Mechanoreceptors
B. Chemoreceptors
C. Photoreception
III.
Endocrine System
A. Glands
B. Hormones
C. Molting Revisited
IV. Exocrine System
A. Structure and Function
B. Products of Exocrine system
Neurons
Dendrite – receives stimuli
Axon – transmits information to another neuron or affector
Glial cells – 1 or more cover neuron (insulate, nutrients, conduction)
1mm – 1 m in length
1 – 500 um in diameter
Terminal arborization
perikaryon
Glial Cells
Lighton, J.R.B. and R. Wehner. 1993. Ventilation and
Respiratory metabolism in the thermophilic desert ant,
Cataglyphis bicolor (Hymenoptera, Formicidae). Journal
Of Comparative Physiology B 163:11-17.
Meyer EP, Domanico VJ (1999). Microvillar orientation
in the photoreceptors of the ant Cataglyphis.
Cell and Tissue Res 295/2:355-361
Insect Neurons:
•
•
•
•
Sensory neurons
Interneurons
Motor neurons
Neuroendocrine cells
Ventral nerve cord
1st cluster – subesophageal ganglion (compound fusion of ganglion
of mandibular, maxillary and labial segments. Joined to brain
by cirumesophageal connectives
Typically 3 thoracic ganglia and 1-8 abdominal ganglia (various
degrees of fusion) – often autonomous – ganglion affects that
segment
Zars, T., Fischer, M., Schulz, R. and M. Heisenberg (2000).
Localization of a short-term memory in Drosophila.
Science 288:672-675.
Central Nervous System (CNS)
Brain – most anterior ganglion located in head, dorsal to foregut
Principal association center
1. Protocerebrum: most complex region
Pars intercerebralis (central region on side of midline
Corpora pedunculata (mushroom bodies) related to
complex behavior
Optic lobes lateral
extensions of protocerebrum
leads to compound eyes
2. Deutocerebrum –
Antennae
3. Tritocerebrum – labrum &
Foregut and others
Visceral Nervous System – enervates the viscera. Sometimes
referred to as stomatogastric system
Peripheral Nervous System – comprised of all nerves from the
ganglia of the C&VNS, includes neurons associated w/
sensory structures, muscles, glands, and other effectors
Sensory Systems
A. Mechanoreceptors
B. Chemoreceptors
C. Photoreception
3 ways insects detect sound (airborne, and with a range of ~200 –
3000 Hz):
1 - Johnston’s organ (housed in 2nd antennal segment - Pedical)
2 – Hair sensilla
3 – Tympanum
(Misc Orthoptera, Cicada, Some Leps)
Johnston’s organ (housed in 2nd antennal
segment - Pedicel)
SCAPE -1st ant seg
PEDICEL –
2nd ant seg
Hair sensilla
765X, tip of adult figeater beetle's maxillary galea (Coleoptera – Scarabidae,
Cotinis mutabilis)
Contact sensillum
Chemosensilla
VISION
5653x, ommatidia
Some ants = 1 ommatidia; Dragonflies ~3k
Apposition eye
vs
Superposition eye
Insects detect wavelengths:
2540 – 6000 Å
Humans: 4500 – 7k Å
Some cells can detect near
infrared wavelengths – host
plant location (Weevils)
Hypera postica
ocelli and stematta
Endocrine – Typically ductless and secretions are usually released
into the hemolymph (produce Hormones)
Exocrine – Discharge products via apertures or ducts sometimes
by a particular organ or reservoir (produce Pheromones)
Kopec, S. 1922. Studies on the necessity of the brain for the
inception of insect metamorphosis. Biological
Bulletin 42:323-342.
Slama, K. and C.M. Williams. 1966. The juvinile hormone.
The sensitivity of the bug, Pyrrhocoris apterus to a hormonally
active factor in American paper-pulp. Biological Bulletin
130:235-246.
Cymborowski, B. 1992. Insect Endrocrinology. Elsevier
Publishers, New York.
Juvenile Hormone Mimics
~>60 compounds found in plants that mimic JH
The effects of pesticides on nontarget
organisms and successful biological control
in Costa Rican banana plantations.
Environmental contamination and related
human health problems from pesticide
applications in Costa Rica are at epidemic
levels.
The hormonal modulation of parasitoid
emergence behavior is complex and involves a
suite of hormones including JH, ecdysteroid, and
peptide hormones.
The stability of the parasitization state in
parasitoids is based on endocrine mechanisms.
Species Accumulation -- Ants
Species Richness
50
40
30
20
10
0
0
1
2
C1
C2
C3
C4
C5
CT
C6
MD
L1
PA
L2
GM
4
5
3
Sample
6
MANOVA: Species Richness
and Abundance by Farm Type
and Trap Type
df
Wilks' 
F
P
Farm Type
Trap Type
4, 82
6, 82
0.73
0.17
3.49
19.39
0.025
0.0001
Contrasts
Conv. vs. Other Crops
Low-input vs. Other Crops
Low-input vs. Conv.
2, 41
2, 41
2, 41
0.74
0.90
0.98
7.36
2.17
0.48
0.005
>0.05
>0.05
Source of Variation
Hymenoptera Parasitica
C1
C2
Species Richness
200
C3
C4
C5
C6
L1
L2
Gemlina
Macadamia
Palmito
Citrus
160
120
80
40
0
0
1
2
3
4
Sample
5
6
Molting
1.
2.
3.
4.
5.
6.
Apolysis
New outer epicuticle
Endocuticle digested
Molting fluid reabsorbed
Ecdysis
Sclerotization
Endocrine
Tissue
Protocerebrum
Function
Hormone
PTTH
Activate prothoracic
gland
w/o JH
Prothoracic gland
Ecdysone &
ecdysteroids
Molting & metamorphosis
Molting only
Corpora allata
Juvenile (JH)
functioning of
larval genes
Endocrine system Products
Products of endocrine system: Hormones
Ecdysone – Controls epidermal cells expression of new
exoskeleton and molting fluid.
Produced by prothoracic glands.
ecdysteroid – primary molting hormone
Commonly in two forms alpha and beta synthesized from
cholesterol or some related steroid obtained in food
1.
Endocrine system Products
Products of endocrine system: Hormones
2. Juvenile Hormone – produced by corpora allata controls
modification and expression of the molt (and other functions).
Maintains ‘larval genes’
and subsequent diff in adult development
3 types differing in # C
JH I
JH II (restricted to leps)
JH III (ubiquitous)
*6 others discovered
Endocrine system Products
Products of endocrine system: Hormones
Bursicon Initiates process of sclerotization in teneral insects
Appears to be a programmed response of NS after exposure to
eclosion hormone
Produced in neurosecretory cells in ganglia
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•
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Diapause hormone
Diuretic hormone
Wound healing
Exocrine system
Pheromones and allomones
Known from more than 1000 spp – including single compounds and
mixtures
Releaser substances – immediate effect on cns and behavior
(include social pheromones in Isoptera and queen bees)
more discussions later
Primer substances – trigger a chain
of events (sex attraction, trail following
alert and others)
Exocrine system – Products