Lecture 9: Dietary Utilization by Insect (Quantitative Nutrition) Flashcards
Identify two ways in which insect nutrition is studied
Insect nutrition can be studied in two ways
Determine the essential nutrient that is needed for growth and development
Determine the efficiency of converting ingested food into their own biomass
Determine the essential nutrient that is needed for growth and development
This includes feeding an insect a nutrient at a time and monitoring the growth and development for a period of time
Determine the efficiency of converting ingested food into their own biomass
For this, we would need to determine the ecological constraints (Eg. sometimes insects can find food whereas sometimes they cannot, specialists would have to find the same food every single time)
Methodology of Studying Insect’s Nutrition
(3)
Weight the insect BEFORE and AFTER feeding
Weight the diet BEFORE and AFTER feeding
Weight the frass (poop) of the insect
What information does the methology of studying insect nutrition provide us with?
(5)
a. RGR (relative growth rate)
b. RCR (Relative consumption rate)
c. ECD (efficiency of conversion of digested food)
d. ECI (efficiency of conversion of ingested food)
e. AD (approximate digestibility)
RGR
Definition + Equation
Relative growth Rate
Weight (mg) gained per day / average larval weight (mg)
RCR
Definition + Equation
Relative Consumption Rate
Mg ingested per day / Average larval weight (mg)
ECI
Definition + Equation
Efficiency of conversion of ingested food
[ weight (mg) gained / mg food ingested ] x 100
ECD
Definition + Equation
Efficiency of conversion of digested food
[ weight (mg) gained / (mg ingested - mg frass) ] x 100
Why is it that ECD can never be 100%
ECD can never be 100% because energy is loss throughout
AD
Definition + Equation
Approximate digestibility (amount of food that is absorbed)
[ mg ingested - mg frass ] / [mg ingested ] x 100
Shortcut Nutritional Parameters (3)
RGR = ECI x RCR
ECI = AD x ECD
1 - ECD = Metabolic Cost
Highest RGR
Eg (2)
Forb feeding (leaves / herbs feeders) Hemiptera and Lepidoptera
Lowest RGR
Eg (2)
Eg. Aquatic Detritivores (eg. Stonefly, mayfly naiads)
HIghest RCR
Eg (2)
And how come these insects are the highest RCR?
Tree feeding Hymenoptera
Forb feeding Lepidoptera
This is because these insect eat twice their body weight
Lowest RCR
2 Eg + Explanation
Predatory insects (these insect would not be able to get food all the time, limited prey)
Wood feeding insect (may not contain the enzyme cellulose)
Highest ECI (%)
Eg (2)
Eg. Seed- feeding Hemiptera (these insects feed on protein rich seeds)
Eg. Blood feeders (Diptera)
Lowest ECI (%)
Eg (2)
Eg: Aquatic Detritivores (Mayflies naiads, Stoneflies naiads, Dragonflies naiads)
Eg. True feeding Hymenoptera
Highest ECD (%)
Eg (2)
Eg. Seed-feeding Hemiptera
Eg. Blood feeders (Diptera)
Lowest ECD (%)
Eg (2)
Eg. Ants - perform a number of activities, are very active and always moving
Eg. Stored grain feeders
Highest AD (%)
Eg (2)
Eg. Forb feeding Coleoptera
Eg. Predatory Insects
Lowest AD (%)
Eg. Dung feeding insects (do not obtain much nutrient because there are low nutrient in feces)
Major Requirements for Optimal Growth
(3)
All insects need nitrogen in the forms of amino acid and protein as nitrogen is important for the exoskeleton of an insect
Plants can provide 0.03% - 7.0% of nitrogen for plant eating insects
Whereas insect that prey on other insects will provide about 7-14% nitrogen
Relationship b/t Nitrogen and RGR + ECI
(2)
There is a positive correlation b/t RGR and ECI with Nitrogen
This indicate that as nitrogen increases so does RGR and ECI
Other Major Nutrient Requirements for Insects
(1) + 2 Description
Water
- Is a major factor for larval growth
- There is a strong positive relationship between water and ECI and RGR particularly in the Lepidoptera
Physiological efficiency model
As nitrogen and water increases, this leads to the increase in growth rate (RGR) and AD (absorption of food)
Bernays Studies based on the amino acid of Locust
(2)
Found that ONLY phenylalanine had a significant effect on the diet of Locust
Concluded that phenylalanine increase 30% of its weight and 25% increase in ECI
Conclusion of Bernays Studies on Locust
(2)
Found that phenylalanine is very important for forming the integument of an insect
As locust have large integument therefore would require more phenylalanine whereas smaller insect do not require as much
Determine the effect of water on ECI
(2)
Found that there is a higher water content in forbes rather than tree therefore the ECI value is higher in forbes
This indicate that high water content yields high ECI
What happens when nutrients are lacking in the diet?
(2)
- When there is an increase in consumption rate (RCR) this means insect would want to get more in order to obtain the right nutrient
- When there is a decrease in consumption rate (RCR), this means the growth rate would decrease.
Are holometabolous insects more efficient than hemimetabolous ones?
Conclusion found that since hemimetabolous develop external wings therefore their cuticles % is larger than holometabolous
Nutrient Self- Selection: Can insects select a nutritionally optimal diet if given a choice?
Found that “Self-selectors” had lower RGR, ECI and RCR than control larvae
Why do “Self-selectors” grow slower?
This is because these self-selectors waste time and energy switching foods
