Lecture 10: Excretion and Water Balance in Insects

Question 1

Homeostasis (2)

Answer 1

Homeostasis is defined as the constant internal state that maintains the function of the cells

Its main function is to eliminate toxic waste

Question 2

Osmoregulation

Answer 2

Osmoregulation is defined as proper concentration of salt and water

Question 3

The concentration of salt will vary in different insects

(3)

Answer 3

Salinity of freshwater is 0.5 ppt where insects living in freshwater will excrete dilute urine

Salinity of seawater is greater than 35 ppt where insects living in seawater will excrete concentration urine (rich in salts)

Brackish water is a mixture of fresh water and salt water that has a salinity of 17 ppt

Question 4

How much salinity can an insect tolerate

(2)

Answer 4

a. Euryhaline

b. Stenohaline

Question 5

Euryhaline

Eg (2)

Answer 5

Can tolerate a wide variation in salt concentration

Eg: Brine fly and Mosquito Larvae

Question 6

Euryhaline Mosquito Larvae

(3)

Answer 6

These insects live in freshwater to 300% sea water that consists of alkaline salt lakes at pH > 10

Since mosquito larvae are filter feeders they can harvest diluted food from the pond sediments

Their hemolymph osmotic concentration vary less than 2 fold over which is greater than 100 fold change in external salinity

Question 7

Stenohaline

Answer 7

These insects can exist in narrow range of salt concentration and found in low salt environment

Question 8

Feeding mechanisms of Mealworms

(2)

Answer 8

These insects live in very dry environment and eat very dry food to conserve water

They capture less than 15% of their moisture and produce dry feces

Question 9

Feeding Mechanism: Desert Locust

(2)

Answer 9

Can feed on succulent plants therefore leaving moist feces

Can feed on succulent plants therefore leaving moist feces
However if they are starved (w/o water or food) they will excrete dry feces

Question 10

Feeding Mechanism: Rhodnius / Mosquitoes

(2)

Answer 10

These insects consume meals that are 10-20 times their body weight w/in 30 mins

Therefore they will excrete up to 50% of ingested fluids w/in hours and increase their excretion rate by 100-1000 times in a few minute

Question 11

Some insects feed on plants resulting in

(3)

Answer 11

Feeding on high level of toxic compounds found in plants

Feeding on Tobacco (nicotine) Eg: Manduca in Caterpillars

Feeding on Milkweeds is a cardiac glycosides

Question 12

General excretory process

(3) + Description

Answer 12

a. Eliminate most blood solutes which takes place in the Malpighian tubules

b. Selectively reabsorbed useful solutes which takes place in the hindgut

c. Can actively excrete certain toxins which takes place in the Malpighian tubules
- This is b/c insects eat a lot of toxic plants and therefore would need to detoxify them

Question 13

However some toxics are recommended for insects because they can act as

(4)

Answer 13

A. Sequestering (Storage)

B. Nutrition

C. Defense

D. Synthesis (Photosynthesis)

Question 14

Why do some insects have low blood pressure?

Answer 14

This is because there is a dramatic drop in the blood volume that is greater than 50% resulting in dehydration

Question 15

Composition of the Malpighian Tubules

(4)

Answer 15

The Malpighian tubules is present in the midgut and the hindgut and exists as the main excretory organ

It has blinded ended tubules that are 100 micro in diameter and composed of a single layer of epithelial cells

There are 3 cells (Cross section) that consists of multiple tubules making up 4 distinct section

It is a low operating system using minimal energy and makes primary urine (KCI) while also removing nitrogenous waste (> 80%)

Question 16

Nitrogenous waste VS Ammonia

(2)

Answer 16

Nitrogenous waste is NOT toxic therefore does NOT require a lot of H20 to remove it

Some insects can remove ammonium which is very toxic and therefore requires a lot of water to remove it

Question 17

of Malpighian Tubules in Insects

(3)

Answer 17

Hemiptera (4)

Locust (200)

Absent in Aphids and collembola

Question 18

Primary Urine in Malpighian Tubules

(2)

Answer 18

Insects will actively secrete K+ and CI- and other anions resulting in a primary urine

After KCI (primary urine) is formed, it will establish a large concentration gradient b/t the hemolymph and the malpighian tubules

Question 19

How long does it take to filter fluid from waste in insects?

Answer 19

It requires more time for insects to filter blood (hemolymph) by malpighian tubules than vertebrate kidney (Glomeruli)

Question 20

Two important component for excretion

Answer 20

Malpighian Tubules (Secretion)

Hindguts (Ileum, colon, rectum) for reabsorption

Question 21

Secretion of Malpighian Tubules

(2)

Answer 21

The Malpighian tubules can secrete sugar, amino acids (proline), water, KCI, toxins and nitrogenous waste which forms the primary urine

The primary urine will then be push from the Malpighian tubules into the hindgut (ileum, colon, rectum) for reabsorption

Question 22

Cross Section of the Malpighian Tubules

(2)

Answer 22

CL / K- / H20 / SUGAR / AMINO ACIDS enter the malpighian tubules through passive transport

Organic waste & toxics, proline will enter the malpighian tubules through active transport

Question 23

Water reabsorption in the rectum

(2) + Eg

Answer 23

In the hindgut, it is divided into the ileum, colon and rectum

There will be reabsorption of sugar, amino acids and ions

Eg: 95% of the Malpighian fluid is going to be reabsorbed the rectum

Question 24

Stages of Reabsorption (3)

Answer 24

A. H20 from the rectal lumen will enter the rectum pads

B. This will create a concentration gradient to allow for more movement of water into the rectum pad

C. Then H20 will leave the rectum pad and enter the haemocoel

Question 25

Exception of Reabsorption in Locust

(3)

Answer 25

In Locust, the reabsorption occurs in the ileum and is controlled by:

CL pump

In this pump, it consists of a hormone known as: CTSH (Chloride Transport stimulating hormones) and ITP (Ileal Transport peptide)

Question 26

Exception of Malpighian tubules

Crypto nephridium (Mealworms)

(2)

Answer 26

Mealworm consists of crypto nephridium that are distal end of malpighian tubules fused to the rectal wall

The purpose of this is to recycle urine to leave behind dry feces

Question 27

Exception of Malpighian tubules

Desert Beetles

Answer 27

Some desert beetles are absorbing atmosphere moisture from their rectal walls

Question 28

Since insects do not have a filtration system, excretion and water balance is controlled by endocrine (hormones)

(2)

Answer 28

Diuretic Hormones
Antidiuretic Hormones

Question 29

Diuretic Hormones

(3)

Answer 29

These hormones are a group of neuropeptides that range in size from 1000 -2000 daltons

The function is to promote water loss through triggering gut extension and is involved in maintaining water balance

The potent form of diuretic hormone is found in the Corpora Cardiaca (Brain)

Question 30

Antidiuretic Hormones

(2)

Answer 30

Antidiuretic hormone is responsible for preventing H20 loss, and is triggered by dehydration

Its function is to allow for rectal reabsorption of water

Question 30

Antidiuretic Hormones

(2)

Answer 30

Antidiuretic hormone is responsible for preventing H20 loss, and is triggered by dehydration

Its function is to allow for rectal reabsorption of water

Question 31

Example of Diuretic Hormones

Answer 31

Rhodnius

Question 32

Rhodnius (2)

Answer 32

This type of hormone is released when there is an infrequent, large meal that is consumed

This will lead to increase in excretion rate thus excreting 50% of the ingested food w/in hours

Question 33

What happens if you place Rhodnius from the hemolymph of blood fed bug into unfed bug?

Answer 33

This will stimulate diuresis (increase stimulation of urine)

Question 34

What happens if you damage the M-NSC (median neurosecretory cells) responsible for making Rhodnius?

Answer 34

This will cause the insect to swell and there will be no diuresis

Question 35

What happens if you inject M-NSC (median neurosecretory cells) or Cardiacum (CC - stores Diuretic)?

Answer 35

This will stimulate diuresis

Question 36

Role of Proline

(2)

Answer 36

Malpighian tubules will secrete proline and the hindgut has a specific proline carrier

Proline provides energy for reabsorption by the rectum and promote active transport by the CI- pump