Lecture 9: Dietary Utilization by Insect (Quantitative Nutrition)

Question 1

Identify two ways in which insect nutrition is studied
Insect nutrition can be studied in two ways

Answer 1

Determine the essential nutrient that is needed for growth and development

Determine the efficiency of converting ingested food into their own biomass

Question 2

Determine the essential nutrient that is needed for growth and development

Answer 2

This includes feeding an insect a nutrient at a time and monitoring the growth and development for a period of time

Question 3

Determine the efficiency of converting ingested food into their own biomass

Answer 3

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)

Question 4

Methodology of Studying Insect’s Nutrition

(3)

Answer 4

Weight the insect BEFORE and AFTER feeding

Weight the diet BEFORE and AFTER feeding

Weight the frass (poop) of the insect

Question 5

What information does the methology of studying insect nutrition provide us with?

(5)

Answer 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)

Question 6

RGR

Definition + Equation

Answer 6

Relative growth Rate

Weight (mg) gained per day / average larval weight (mg)

Question 7

RCR
Definition + Equation

Answer 7

Relative Consumption Rate

Mg ingested per day / Average larval weight (mg)

Question 8

ECI

Definition + Equation

Answer 8

Efficiency of conversion of ingested food

[ weight (mg) gained / mg food ingested ] x 100

Question 9

ECD

Definition + Equation

Answer 9

Efficiency of conversion of digested food

[ weight (mg) gained / (mg ingested - mg frass) ] x 100

Question 10

Why is it that ECD can never be 100%

Answer 10

ECD can never be 100% because energy is loss throughout

Question 11

AD

Definition + Equation

Answer 11

Approximate digestibility (amount of food that is absorbed)

[ mg ingested - mg frass ] / [mg ingested ] x 100

Question 12

Shortcut Nutritional Parameters (3)

Answer 12

RGR = ECI x RCR

ECI = AD x ECD

1 - ECD = Metabolic Cost

Question 13

Highest RGR

Eg (2)

Answer 13

Forb feeding (leaves / herbs feeders) Hemiptera and Lepidoptera

Question 14

Lowest RGR

Eg (2)

Answer 14

Eg. Aquatic Detritivores (eg. Stonefly, mayfly naiads)

Question 15

HIghest RCR

Eg (2)

And how come these insects are the highest RCR?

Answer 15

Tree feeding Hymenoptera

Forb feeding Lepidoptera

This is because these insect eat twice their body weight

Question 16

Lowest RCR

2 Eg + Explanation

Answer 16

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)

Question 17

Highest ECI (%)

Eg (2)

Answer 17

Eg. Seed- feeding Hemiptera (these insects feed on protein rich seeds)

Eg. Blood feeders (Diptera)

Question 18

Lowest ECI (%)

Eg (2)

Answer 18

Eg: Aquatic Detritivores (Mayflies naiads, Stoneflies naiads, Dragonflies naiads)

Eg. True feeding Hymenoptera

Question 19

Highest ECD (%)

Eg (2)

Answer 19

Eg. Seed-feeding Hemiptera

Eg. Blood feeders (Diptera)

Question 20

Lowest ECD (%)

Eg (2)

Answer 20

Eg. Ants - perform a number of activities, are very active and always moving

Eg. Stored grain feeders

Question 21

Highest AD (%)

Eg (2)

Answer 21

Eg. Forb feeding Coleoptera

Eg. Predatory Insects

Question 22

Lowest AD (%)

Answer 22

Eg. Dung feeding insects (do not obtain much nutrient because there are low nutrient in feces)

Question 23

Major Requirements for Optimal Growth

(3)

Answer 23

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

Question 24

Relationship b/t Nitrogen and RGR + ECI

(2)

Answer 24

There is a positive correlation b/t RGR and ECI with Nitrogen

This indicate that as nitrogen increases so does RGR and ECI

Question 25

Other Major Nutrient Requirements for Insects (1) + 2 Description

Answer 25

Water - Is a major factor for larval growth - There is a strong positive relationship between water and ECI and RGR particularly in the Lepidoptera

Question 26

Physiological efficiency model

Answer 26

As nitrogen and water increases, this leads to the increase in growth rate (RGR) and AD (absorption of food)

Question 27

Bernays Studies based on the amino acid of Locust (2)

Answer 27

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

Question 28

Conclusion of Bernays Studies on Locust (2)

Answer 28

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

Question 29

Determine the effect of water on ECI (2)

Answer 29

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

Question 30

What happens when nutrients are lacking in the diet? (2)

Answer 30

- 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.

Question 31

Are holometabolous insects more efficient than hemimetabolous ones?

Answer 31

Conclusion found that since hemimetabolous develop external wings therefore their cuticles % is larger than holometabolous

Question 32

Nutrient Self- Selection: Can insects select a nutritionally optimal diet if given a choice?

Answer 32

Found that “Self-selectors” had lower RGR, ECI and RCR than control larvae

Question 33

Why do “Self-selectors” grow slower?

Answer 33

This is because these self-selectors waste time and energy switching foods