Animalia-Arthropoda-Insecta

Vonai Moyo

external image insect.JPG
http://www.villageofpinehurst.org/Portals/0/Boards%20and%20Commissions/insect.JPG


edited by: Meru Nangia
Yasheka Sharma
Sarah Schwazrschild
Hilary Stepansky
Jesse Carmen
Hanna Zhu
Rachel Kornetsky
Josh Czik
Becca Levenson
Kevin Nayer
Brittany Marcus-Blank
Arielle Reiter
Omer Zaidi
Sarah Vlach
NK
Sam Blatchford
DP
SS
GR
Ethan Richman

Introduction
Insects are part of the clade Ecdysozoa of kingdom Animalia. One of several phyla of Ecdysozoa is Arthropoda, the phylum under which the class Insecta falls. Arthropoda is a very successful phyla of Animalia, represented in nearly all the habitats of the biosphere. Arthropods have been very successful in species diversity, distribution, and population count, coming to represent approximately 2/3 of all organisms.

Diagnostic Characteristics of Arthropods
The arthropod population amounts to an estimated billion billion, nearly 1 million of which have been described as an insect species. The phylum arthropoda is characterized by segmentation, a hard exoskeleton, and joined appendages. The cuticle covering the body of an arthropod provides for the animal’s protection. It also provides for attachment to the animal’s segments, which are specialized for various functions and thus help to create an efficient body plan. Often, arthropods must shed their old exoskeleton and secrete a larger one in order to grow. This is known as molting/ecdysis, and requires a lot of energy, thus leaving the animal temporarily vulnerable to predators and other dangers). The most commonly known characteristic of insects is having a head, thorax, and an abdomen.

Acquiring and digesting food
Insects have a complete digestive tract. Within a complete digestive tract, food processing occurs within the tube-like alimentary canal (6 SES). This canal runs from then insect's mouth to its anus (6 SES). The alimentary canal is composed of three main functional regions: the foregut (known as the stomodeum), midgut (known as the mesenteron), and hindgut (known as the proctodeum) (6 SES). The foregut starts at the mouth of an insect, and its purpose is to mechanically digest the insect's food (6 SES). Some chemical digestion also occurs here in regards to the salivary glands and resevoirs (help chemically break down food via saliva mixing with food) (6 SES). The midgut is where the majority of the chemical digestion occurs as well as absorption of the water and nutrients from the ingested material (6 SES). The hindgut also regulates absorption of water and salts from waste products of ingested food (6 SES). These waste products are then excreted from the hindgut through the insect's anus (6 SES). Their mouthparts differ relating to their feeding habits. Insects ingest food through their mouth which is located on the head. An insect’s mouthpart can be either for biting, chewing, or sucking, or any combination of the three.
external image digestivesystem.jpg
http://insects.about.com/od/morphology/ss/internalanatomy_3.htm
As you can see, in the picture, #30, the saliva glands, travels through the saliva glands and mixes with the food and aid in breaking it down. #27 is the foregut, where mostly large food particles are broken down, still with the help of saliva. #13, the midgut, breaks down foods through enzymes. Microvilli on the walls of the midgut, with increased surface area, help reabsord nutrients. #16 is the hindgut, where undigestive particles join with uric acid (from Malphigian tubulues) to form waste pellets. The rectum absords any remaining water and the pellet is finally released via #17, the anus. (AR, 12).
Sensing the environment

Insects have developed various methods through which they are able to sense their environment. These senses allow them to see, hear, smell and touch in a manner that is comparable to that of human beings.
Insects’ Sense of Smell – Insects use chemical signals, known as pheromones, to ‘smell’ their surroundings. On an insect’s antenna are proteins, called Pheromone-binding proteins (PBP). These proteins change shape when exposed to certain pheromones and this sends a chemical signal to different nerve endings within the insect. Insects also have the ability to release different pheromones. Insects utilize this method to communicate with members of their species, locate food, and participate in mating rituals. [2 Nangia]
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different insect antennae (OZ)

Insects’ Sense of Sight – Insects ability to see varies on the strength of their other senses. Insects that have highly developed chemical receptors have more basic eyes, whereas organisms that are less developed tend to have more complex eyes. Insect larvae and some developed insects are either blind or have very basic eyes that can only differentiate between light and dark. Most adult insect eyes have compound eyes that have the ability to see colors. The majority of insects have eyes that are bichromatic, which means they cannot distinguish between pure colors and a mix of colors. These insects also have a limited color spectrum. There are a few insects that are trichromatic, like humans, which means they have three pigment receptors in their eyes. However, their visible spectrum is very different than ours. They are not able to see the lower frequency light that we are able to, such as red. However, they are able to see higher frequency light than that in our range, such at ultraviolet light. [3 Nangia]
Insects’ Sense of Sound – Many, but not all, insects have the ability to hear sounds, and they utilize one of four methods to do so. This first is tympanum, which uses tympanal organs. Tympanal organs occur in pair and are thin membranes stretched across an air space and connected to the nervous system. This membrane senses that vibrations caused by sounds and sends the signals to the nervous system. This is the method used by insects such as grasshoppers, crickets, and cicadidaes. The second hearing organ is known as the Johnston's Organ, which sense sound through hairs on the antennal scape. The third method is the use of auditory hairs on the insect’s body, and the fourth method involves the use of the Pilifer, a unique organ found only in the head of certain types of Hawk Moths. [4 Nangia]
Insects’ Sense of Touch – Touch is an extremely important sense to insects, and many have developed different methods through which they detect mechanical stimulus. One extremely common method is called Trichoid sensilla. Hairs on the insect’s body are attached to nerves, so when the insect comes in contacts with something, a signal is sent to the nervous system. Other organs that sense touch use changes in air pressure or changes in the stresses being applied to the insect cuticle. [4 Nangia]
The insect nervous system is made of a brain and a pair of ventral nerve cords (bundles of nerves that run on the "belly" side of the insect, instead of the back) that meet at the brain (1). The brain is made up of three pairs of ganglia. The first pair, called the protocerebrum, receive information from the eyes. The second pair, the deutocerebrum, processes information from the antennae. The third pair, the tritocerebrum, combines the information from both the protocerebrum and the deutocerebrum. The three pairs of thoracic ganglia in the thorax control the movement of legs and wings, and the abdominal ganglia control the movement of the abdomen (9). Insects also have segmental ganglia, groups of neurons placed at segments of the insect's body (1) [HZ].


Locomotion
Insects move mainly through flight, having one or two pairs of wings coming out of the thorax. Unlike flying vertebrates such as birds, insects can fly without giving up usage of their walking legs, and are thus much less clumsy. Flight is helpful in escaping predators, finding food, mating, and relocating. Relocation for insects (as for other flying animals) is faster than that of animals that can crawl on the ground.
Certain insect species use patterns of movement as a form of communication. For example, honeybees communicate the location of food to their hive-mates by an elaborate dance. This dance can communicate the direction and distance of food from the hive, showing that a wide spectrum of information can be spread through movement. (8) [KN]
Insects stay balanced because at least three of their legs are kept on the ground in a formation that enhances stability. A common way to maintain balance while walking is to have two legs on the ground on one side and one leg on the ground on the other side so that they form a tripod. In this example three legs are on the ground moving backwards while three legs are in the air moving forwards. When the raised legs have moved forward they make contact with the ground and the back legs lift up, so the whole pattern is repeated. (11) (BMB)


A dragonfly has 6 legs but is unable to walk! The legs are only used for grabbing and holding onto insects, a dragonfly's prey, while flying. How's that for bizarre? (DP) http://www.cssplay.co.uk/menu/slides/dragonfly.jpg
A dragonfly has 6 legs but is unable to walk! The legs are only used for grabbing and holding onto insects, a dragonfly's prey, while flying. How's that for bizarre? (DP) http://www.cssplay.co.uk/menu/slides/dragonfly.jpg


Respiration
Terrestrial arthropods generally have internal surfaces specialized for gas exchange. Insects have specialized organs (for gas exchange), which allow for the diffusion of respiratory gases in spite of the exoskeleton.
Insects exchange carbon dioxide and oxygen between the air and their tissues using the tracheal system, which is a system of air-filled tubes. these are branched air ducts leading into the inside from pores in the cuticle, and carrying oxygen directly to cells. Aquatic forms may exchange gases through the body wall or their gills.(5. Sharma)
Insecta breathe through a tracheal system, similar to the beginning of the human lung system. The trachea have openings to the the extrenal environemnt (known as spiracles) and inside the animal the trachea break down into finner tubes, which carry gases to the organs. (HS 7)
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The tracheal system of an insect. (VM)

Metabolic waste removal
Insects dispose of their waste through the anus at the end of the abdomen. They have specialized glands which serve to regulate the hemolymph’s salt balance, excreting unnecessary/excess materials, or indigestible substances through the process of defecation. Body fluids pass back into the body, nitrogenous wastes empty into the insect's gut. Water is reabsorbed and waste is expelled from the insect. (5. Sharma)


Circulation

Arthropods use an open circulatory system, which involves the movement of the fluid hemolymph through pores, valves, and short arteries. The hemolymph also moves through well-developed sensory organs, such as eyes, olfactory receptors for smell, and antennae for smell and touch. The hemolymph finally goes into sinuses, spaces from which it reenters the heart. Pores that are usually equipped with valves allow for the reentrance of blood into the insect’s heart.
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The circulatory system of a grasshopper. (15)(RJS)
Self protection
Flight plays a major role in an insect’s self-protection, as it allows the animal to remove itself from a dangerous situation faster than walking. Flight provides a major advantage, as many of an insect’s predators live on the ground. The piercing and chewing mouthparts of different insect help with protection as well, as do the pinchers or stinging organs of many insects. The hard exoskeleton of insects also assists with self-protection, providing a partial shield to any danger the insect comes about. Another way insects protect themselves is through the coloring of their body. Predators have learned that bright colors such as red,yellow, and blue mean danger this bug is poisonous or tastes bad, and they tend not to eat those bugs. Besides using colors to stand out againt predators, insects also have the ability to blend in with their surrounds, such a green, leafy shubbery or the wood of trees, which make them hard for predators to find. (GR, 14)
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This is the stinger on the abdomen of a hornet. When the hornet feels threatened by another organism, it stings the creature. The stinger releases toxins inside the creature once stung. (JAC) http://www.muenster.org/hornissenschutz/dr_billig/stachel5.jpg
Osmotic balance
Osmotic water balance is an animal’s regulation of the amount and pressure of the water it holds, in order to maintain a stable internal environment. The relative strength and impermeability to water of the cuticle is responsible for insects’ water regulation. *This impermeability is largely responsible for the transition of many arthropods from water to land. The cuticle of an arthropod is its exoskeleton. This cuticle (or exoskeleton) can vary in texture throughout different parts of the body. At some parts of the body it is hard and thick while at other parts of the body it is soft and flexible. It is the exoskeleton’s thickness and protective characteristics that allow the insect to be impermeable to water. (Jesse Carmen) [8]


Temperature balance
Temperature balance, similarly to water regulation, is very important to an animals’ maintenance of a stable internal environment. Insects are endothermic, meaning they have control over their internal body temperature, with a great ability to raise it. In flying insects, this ability is dependent on muscles which produce great amounts of heat when in action. Shivering is also very useful for flying insects, producing heat before the insects “takes off”. It is very important that high temperatures be maintained in the thorax during flight, as this is where the flight muscles are located.

Insects and Disease (RK)
Because many insects can serve as host sites for micro-organisms such as bacteria, viruses, and protozoans, insects have been known as transmitters of disease to humans throughout history. The micro-organism is known as the pathogen and the insect as the vector in this relationship. Some insects easily spread disease because of their ability to bit. Commonly known insect transmitted diseases by mosquitos are Malaria, West Nile Virus, and Yellow Fever. Tick bites by infected ticks can lead to lyme disease and infected fleas were responsible for the transmission of the Plague (10).mosquito_65147_7.jpgBecause mosquitos are able to get past the outside layer of skin on organisms which organisms like humans use to protect themselves against diseases. Since mosquitos are able to do that, they are able to transmit diseases like the ones listed above (11 BL)


Review Questions:
  • Explain the function of the alimentary canal. (SV)
  • List and explain insects' methods of self protection. (NK)
  • How do insects sense their enviorment?(SB)
  • Pheremones are involved in many processes for insects. Explain the different uses and what pheremones are. (DJ)
  • What makes the respiratory system of insects so different from the respiratory systems of many other organisms? (SS)
  • Why do insects "shiver"? (ER)
Sources: Campbell, Neil A., and Jane B. Reece. Biology. 6th ed. Boston: Benjamin-Cummings Company, 2002.=

[2] "Exposing Insects' Sense of Smell." UC Newsroom. 04 Jan. 2002. University of CalifoRnia. 30 Nov. 2008 <http://www.universityofcalifornia.edu/news/article/3836>.
[3] Ross, Michelle. "Insect Color Vision." A Moment of Science. 13 July 2005. Indiana University. 30 Nov. 2008 <http://amos.indiana.edu/library/scripts/insectvision.html>.
[4] Ramel, Gordon. "Introduction to Insect Anatomy: What Makes an Insect an Insect??" Insects Home Page. 29 Sept. 2008. Earth-Life Web Productions. 30 Nov. 2008 <http://www.earthlife.net/insects/six.html>.
[5] Myers, Phill. "Class Insecta". Animal Diversity Web. University of Michigan Museum of Zoology. 30 Nov. 2008. <http://animaldiversity.ummz.umich.edu/site/accounts/information/Insecta.html>
[6] Meyer, John R. "Digestion and Excretory Systems." Insect Physiology. 17 Feb. 2006. NC State University. 2 Dec. 2008.<http://www.cals.ncsu.edu/course/ent425/tutorial/digest.html#1>
(7) Myers, P. 2001. "Insecta" (On-line), Animal Diversity Web. Accessed December 02, 2008 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Insecta.html.
(8) Campbell, Neil A., and Jane B. Reece. Biology. 6th ed. Boston: Benjamin-Cummings Company, 2002.
[9] Meyer, John R. "Nervous System." General Entomology -- NC State University. 17 Feb. 2006. 6 December 2008 <http://www.cals.ncsu.edu/course/ent425/tutorial/nerves.html>.
(10) "Insect Borne Diseases" The Travel Doctor. 2002. 7 Dec. 2008 http://www.traveldoctor.co.uk/insects.htm.>.
(11) "Mosquito Control Projects". Department of Environmental Quality. 2008.7 Dec. 2008. http://www.michigan.gov/deq/0,1607,7-135-3313_46123_24554---,00.html.
(11)
Cofer, David. "Insect Locomotion." Mindcreators.com. 2002. 7 Dec. 2008 http://www.mindcreators.com/insectlocomotion.htm.
(12) Hadley, Debbie. "The Insect Digestive System." About.com. Dec 7 2008. <http://insects.about.com/od/morphology/ss/internalanatomy_3.htm>.
(13) 15 Dec 2008 <http://www.cartage.org.lb/en/themes/sciences/lifescience/GeneralBiology/Physiology/RespiratorySystem/MethodsRespiration/insectexch.gif>
(14) "Garden Insects." 2008. Buglogical Control Systems INC. 18 Dec. 2008 <http://www.gardeninsects.com/faq.asp>.
(15)Loren, Karl. "The Blood Circulation System." 18 Dec 2008 <http://www.chelationtherapyonline.com/articles/p198.htm>.