Lecture 8: Regulation of Food Intake Flashcards
How is feeding stimulated?
Feeding is governed by the excitatory state which is affected by the sensory input
Regulation of food intake (3)
External Stimuli
Internal Stimuli
Other factors
External Stimuli
(3) + Description
Olfaction: used to smell the food, consisting of olfactory receptor on the antenna
Gustation: used to taste the food, there are gustatory receptor on the mouthpart
Vision: consisting of the compound eye, used to detect the shape of the food
Internal Stimuli (2)
a. Crop volume
b. Nutrient concentration in the hemolymph
Crop volume
This is apart of the foregut where the food is stored, some digestion occurs through salivary enzymes in the crop
Nutrient concentration in the hemolymph
(3)
Right after the meal, the crop is extended and the insect will not eat until the food that is stored in the crop has passed to the midgut
The midgut is where there is complete digestion and absorption
Insect will not eat when there is high levels of amino acids and sugar in the hemolymph
Other factors associated with regulating food intake
(4)
State of hunger
Nutritional State
Neurohormone levels
Nonassociative learning
Nonassociative Learning
Eg + Description
Habituation: a response as a result of a continuous response of stimuli (Eg. Food)
Stages of Feeding (3)
Biting (Initiation)
Continuation
Termination
Biting Stage (Initiation)
This occurs when there is a direct stimulus of the food where the sensilla (does not only have to be on the mouthpart) is activated
Example of Biting: Blowfly
(2)
The mouth part is present on the tarsi of the blowfly and in this experiment it can be stimulated by sugar
The reason why they were able to find that the mouthpart is located on the tarsi is by presenting sugar to the tarsi leading to the proboscis to extend
Example of Continuation: Blowfly
There are sensilla on the labellum that allows for feeding to proceed
Example of Biting: Locust
(2)
Biting involves the stimulation of the tarsal, maxillary and labial palp sensilla
Ultimately this stimulation leads to the activation of 2000 receptors on the roof of the mouth
Example of Continuation: Locust
After the first bite, the quality of food is then monitor by the cibarial receptor (pouch space in the mouth used to store or chew the food)
Termination of Feeding
(3)
The termination of feeding is due to a decay in the excitatory state
This means that the habituation has decreased leading to the foregut volume to expand as the stretch receptor is activated
When there is high levels of sugar or amino acid in the hemolymph, this would result in a negative feedback to the brain
What can change the Stages of Feeding?
(2)
Temperature and Environmental Factor
Suboesophageal Ganglion
(2)
All the information about the food is going to the suboesophageal ganglion which is apart of the brain located in the head below the esophagus
It controls the insect mouth part, salivary glands and the muscle of the neck
How do insects differ in their feeding behavior?
(2)
Different mouthparts
Various Ingestion mechanism
Phagostimulants
(2) + Eg
Chemical in the food that stimulate the feeding of the insect
In order for the insect to continue feeding, stimulants»_space;» Deterrents
eg: Sugar
Phagodeterrents
Chemical in the food that inhibits the feeding even in the presence of a stimulants
Feeding Ratio
(2)
This is defined as the ratio or balance of stimulants and deterrents
Sensory input from deterrents “outweighs” input from the stimulant by ratio of 8:1 found in caterpillars
Types of Feeding Behaviour (2)
Monophagous
Oligophagous
Polyphagous
Monophagous
These individuals tend to feed on a single plant family
Due to this, they only need few receptors for feeding decisions and few sensory inputs
Oligophagous
These individuals tend to feed a few plant families
Polyphagous (Generalist)
These individuals tend to feed on a number of plant families
Number of Mouthparts in insects
(2) + Description
Caterpillars consisting of 24 mouthpart sensilla
- This indicates that caterpillars are evolutionary evolved compared to grasshopper because they consists of less mouthparts
Grasshoppers consists of 2000 mouthpart sensilla
What happens if you surgically remove the maxillae of the caterpillar?
(2) + Description
This would lead to hyperphagia
- Therefore causing the maxillae to become more sensitive and leading the insect to eat more
Due to the insect eating more, this would lead to acceptance of normally receptor hostplants
Sugar concentration in different insects
BlowFly:
When there is an increase in sugar concentration in the hemolymph, this would result in a decrease in the emptying of the crop into the midgut and increase in meal interval
Sugar concentration in different insects: Locust
(4)
When trehalose is injected into the hemolymph, this would result in a decrease in the emptying of the crop into the midgut
When there is an injection of water into the hemolymph, this would result in crop emptying
There are amino acid receptors in the maxillary palp of the locust. When there is an increase of amino acid in the hemolymph, this would make the sensilla less responsive to amino acid
This is because the receptor of the maxillary palp will become less sensitive
Feeding and Digestion: Salivary glands
(1) + Eg
Are present in piercing / sucking insects
(Diptera/Hemitera)
Saliva of the mosquito
(3)
(Local anesthetic, vasodilator, anticoagulant)
Saliva of the Hemiptera (2)
These digestive enzymes are injected into the food, which breaks down the food to become liquified and sucked up again
These include amylase used to convert starch into sugar or invertase used to convert sucrose into glucose
Aphid Saliva
Consists of pectinases used to drill into the plant tissue and suck up its vascular tissues (phloem) and used in cell wall degradation
Midgut Digestion Enzymes
(3)
Digestion in the form of enzyme secretion occurs in the midgut secreting enzymes known as (3)
Secretagogue
Neural Stimulation
Hormonal Stimulation
Secretagogue
Enzyme stimulating the substance in the food
Neural Stimulation
Stretch receptor on the midgut becomes activated based on the presence of food
Hormonal Stimulation
As the nutritional state of the insect increases, the hormonal stimulation is secreted
Rate of Digestion in the Midgut
Determine by the rate of degradation of polysaccharides to monosaccharides
There are insects that lack an enzyme or nutrient therefore would need to harbor other microorganisms inside their gut to help digest food
This is known as symbiotic relationship
Examples of Symbiotic Relationship
(3) + Description
Transferred on eggshells (eaten by neonates)
Wood wasps need fungus to digest cellulose in the wood
Wood termites obtain cellulase on enteric protozoa and bacteria
- These enteric protozoa and bacteria thrive in an anaerobic region of the hindgut known as the paunch
In the 1760’s an attempt to establish silkworm industry in Georgia (USA) failed
(3)
This is due to the silkworm larvae grew but did not pupate
The method of this experiment is housing the silkworm in a rear cage made out of bald cypress wood
This wood releases a volatile 2 furaldehyde, a natural antiseptic that inhibits 7 bacterial and 2 fungal endosymbionts of silkworm
Essential Nutrition needed in Insect’s diet: Phenylalanine
(2)
Is one of the most important amino acid for larval growth
It is also used for sclerotization
Essential Nutrition needed in Insect’s diet: CHO (2)
Some Diptera can live just on protein without CHO
Some larval stage requires just protein and lipids whereas some adult would just require sucrose
Essential Nutrition needed in Insect’s diet: Cyclitols
This is a nutrition that is important for membrane synthesis (Eg. Plant feeders)
Essential nutiriton needed for the insect diet:
Fat Soluble Vitamin
Vitamin A complex used for vision
Essential Nutrition needed in Insect’s diet: Water Soluble Vitamin
Eg. Ascorbic Acid (B complex)
Essential Nutrition needed in Insect’s diet: Free Fatty Acids (C18)
(2)
Some insects do not require fatty acids
However lepidoptera would need fatty acids in order to pupate and adult form would require free fatty as without it there will exist wing deformities (Slight deficiency)
Essential Nutrition needed in Insect’s diet: Sterols
(2)
Insect cannot synthesize sterols therefore would need to feed on plants to modify phytosterols into cholesterol
Sterol is essential as it allows for the synthesis of ecdysteroids (molting hormone)
Other function of sterol include
(2)
Exerting surface waxes on the epicuticle
Making membrane production
