Excretion and Water Balance Flashcards
Insects, like most animals, must Maintain and eliminate what?
Maintain a reasonably constant blood composition and total water content for cell viability and must eliminate toxic wastes
Where can Euryhaline mosquito larvae survive and how?
In everything from fresh water to 300% sea water and alkaline salt lakes
- Drink their own body weight every few hours to harvest dilute food from pond sediments (Filter feeders)
Where do mealworms live, what do they eat and what kind of excrement do they produce?
- Lives in dry environment, eats dry food and produces dry excrement
Desert locusts, what do they eat and what kind of excrement do they produce?
- consume own weight in succulent plants and produce moist excreta unless they are starved in which case they produce dry excreta
What is the general nature of the excretory process? why do they take place?
- Eliminate most blood solutes non-selectively; takes place in the malpighian tubules
- Selectively reabsorb useful solutes; takes place in the hindgut (mostly)
- Actively secrete certain toxins (malpighian tubules
why would insects feed on toxic plants?
- nutrution
- defense
- synthesis
What happens during dehydration for an insect?
-low blood pressure and a dramatic drop in blood volume during dehydration
Why are the effects not especially detrimental?
Hemolymph is not used for gas exchange
What is a consequence of of dehydration?
Formation of primary urine in insects cannot occur by pressure driven filtration
What do most insects actively secrete?
K+ (with Cl- as anion) forming KCl rich urine
What does an insects KCl rich urine cause?
A large concentration gradient between the hemolymph and malpighian tubule lumen for diffusion of all other blood solutes
What is the main excretory organ in insects?
Malpighian tubules
What is the structure of malpighian tubules?
Blind-ended tubules composed of a single layer of epithelial cells (3 cells when seen in a cross-section.
- can be differentiated histologically along their length with up to 4 distinct sections
Which insects lack malpighian tubules?
Aphids and collembola
What are Malpighian tubules?
A slowly operating system for secretion of primary urine
Why are all the nutrients excreted and then reabsorbed as needed?
It is energetically more favorable cause it is easier to reabsorb needed molecules passively than to actively excrete all unneeded ones
What is the main excretory product?
Uric acid
What is the main function of the excretory system?
Removed nitrogenous (metabolic) wastes
Which takes longer to completely filter their blood, humans or insects?
Insects
What do mapighian tubules secrete?
sugars, amino acids, water, KCl, toxins and nitrogenous wastes
Where is primary urine secreted?
from the Malpighian tubules to the hind gut
Where is a major source of water balance in the insect (where most water is reabsorbed)?
Rectum
What is reabsorbed in the hindgut?
sugars, amino acids and ions (to maintain osmolity of the hemolymph)
What does reabsorption of water in the rectum facilitate?
K+ secretion in the malpighian tubules
Where are the distal ends of the malpighian tubules fused?
the rectal wall
What does diuretic hormone do?
- stimulates diuresis
- Promotes water loss
What does antidiuretic hormone do?
- Prevents water loss by promoting fluid reabsorption in the hindgut
What is diuretic hormone stimulated by?
Distention of the gut
What is anti diuretic hormone stimulated by?
Dehydration
What is Rhodnius?
Hemolymph from bloodfed bug is injected into an unfed bug which stimulates diuresis
What does cauterization of mNSC cells in the brain cause?
Causes insect to swell (no diuresis)
What does an injection of mNSC cause?
Diuresis
What are diurestic hormones?
group of neuropeptides ranging in size
- more potent form found in the corpora cardiaca; form produced in the brain is a precursor
What are some endocrine factors that increase absorption of water?
- antidiuretic hormone
- Homogenates of corpora cardiaca or ventral ganglioa stimulate up to 5-fold increase in reabsorption in the ileum of locusts
What secretes proline and where is it reabsorbed?
secreted in the malpighian tubules and reabsorbed in the rectum
What is proline utilized as?
an energy source to drive active transport in metabolically active rectum tissue
Where is the proline secreted by the malpighian tubules completely utilized?
by the mitochondria of the hindgut which have a specific proline carrier
What is feeding governed by?
a central excitatory state which is affected by sensory input
What are external stimuli?
Olfaction, gustation
What are internal stimuli?
Crop volume, nutrient concentrations in hemolymph
What factors can the responsiveness of sensilla vary with?
- state of hunger ( time since last meal)
- Nutritional state
- Neurohormone levels
- Nonassociative learning
where does control of feeding reside?
the sub-oesophageal ganglion
What is the sub-oesophageal ganglion?
fusion of the mandibular, maxillary and labial ganglia; considered part of the brain
What separate factors are involved in each step of feeding?
- Biting (=initiation)
- Continuation
- Termination
Feeding mechanisms almost always depend on what?
some direct stimulus from the food to the Sensilla
How does feeding work in Blowflies?
Stimulation of the tarsal sensilla by sugars etc. Leads to extension of the proboscis; sensilla on the labellum then determine if feeding proceeds
How does feeding work in Schistocerca?
Tarsal, maxillary, and labial palp sensila all need to be stimulated to initiate biting; after the first bite, quality of the food is monitored by cibarial receptors
Are more or less receptors needed for specialized feeders?
Fewer are needed
What are phagostimulants?
Stimulus necessary for initiation and often continuation of feeding
What are phagodeterrents?
Stimulants that can inhibit feeding even in the presence of stimulants
What does acceptance of food and feeding rate usually result from?
The ratio or balance of stimulants and deterrents in the food
Do stimulants or deterrents change the amount of time it takes for an insect to start eating?
no
What is effected by the presence of stimulants or deterrents in food?
total amount of food eaten
What regulates the termination of feeding?
- Thought based on the decay of the excitatory state through:
- Chemosensory adaptation or habituation
- Increased foregut volume detected through stretch receptors
- Negative feedback from nutrients or hormonal factors in the hemolymph
Which mouthparts are salivary glands especially important for?
piercing/sucking mouthparts
What does the saliva of blood feeders include?
- Local anesthetics
- Vasodialators
- Anticoagulants
What is contained within the saliva of sucking plant feeders?
Digestive enzymes such as amylase or invertase
What does aphid saliva contain? Why?
Pectinases - facilitate penetration of the stylets through plant tissues to the vascular tissues (Phloem)
What can enzyme secretion in the midgut be regulated by?
- Secretagogue
- Neural Stimulation
- Hormonal stimulation
What is Secretagogue?
An enzyme stimulating substance in food
What are the neural Stimulators that signal the presence of food in the midgut?
Stretch receptors
How does hormonal secretion regulate secretion of enzymes?
Hormones respond to nutritional state of the insect
What is the rate of digestion determined by?
the rate of degradation of polysaccharides to monosaccharides
What is the Paunch?
An Anaerobic region of the hindgut
What does an insect need for proper nutrition? (6)
- 10 essential amino acids
- Cyclitols
- Fat-soluble vitamins
- Water-soluble vitamins
- Free fatty acids
- Sterols
Which amino acid is the most important for larval growth?
phenylalanine
What are cyclitols needed for?
Membrane synthesis
What is vitamin A complex used for?
vision
What happens if a lepidoperan has a defficiency in free fatty acids?
Many cannot pupate or have wing deformities as adults
Can insects synthesize sterols?
no
How do plant feeding insects obtain sterols?
Modify phytosterols to cholesterol which is essential for synthesis of ecdysteroids, etc.
What are sterols used for?
molting hormones
What is the relative growth rate of an insect?
= Weight gained per day/ average larval weight
What is the relative consumption rate of an insect?
= Mg ingested per day/ average larval weight
What is the efficiency of conversion of ingested food?
= Weight mg gained/ mg food ingested x 100
What is the Efficiency of Conversion of digested food?
= Weight mg gained/(mg ingested-mg frass(poop)) x 100
What is the Approximate Digestibility of an insect?
= (mg ingested - mg frass(poop))/mg ingested x 100
What is the calculation for metabolic cost of an insect?
1- ECD
Which insects have the highest RGR? Lowest?
Highest = Forb-feeding homoptera Lowest = Aquatic detrivores
Which insects have the highest/lowest RCR?
Highest = Tree feeders Lowest = Predatory insects
Which insects have the highest/lowest ECI %?
Highest = Seed-feeding hemiptera Lowest = Aquatic detrivores
Which insects have the highest/lowest ECD %?
Highest = Seed-feeding hemiptera Lowest = Ants
Which insects have the highest/lowest AD %?
Highest = Forb-feeding coleoptera Lowest = Dung-feeding insects
What is a major requirement for optimal growth?
Nitrogen (Amino acids, proteins)
What are RGR and ECI positively correlated with?
% Dietary N
Why do insects have a specific need for Amino N?
Cause exoskeleton is composed of up to 20% aa derivatives
What is Phenylalanine important for?
Formation of the integument
What is water a major influencer of?
Larval growth
Can insects partially compensate for reduced food quality?
yes
Which is more efficient, Holometobolous insects or hemimetabolous insects? Why?
Holometabolous insects because most of food they eat goes to the integument
Why do self selectors of diet grow slower?
They waste time and energy switching foods
