Integument, Development, Reproduction, Digestion, Respiration, and Circulation in Insects

Flashcards covering insect integument layers, molting stages, hormones, reproductive systems, digestive tract anatomy, respiration, and open circulatory systems based on lecture notes.

What are the three layers that make up an insect's exoskeleton (cuticle)?

The epicuticle (waterproof outer layer made of lipids and polyphenols), exocuticle (hardened layer of chitin-protein microfibers), and endocuticle (flexible inner layer of unlinked chitin and proteins).

What two primary layers constitute the insect integument?

The cuticle (exoskeleton) and the underlying cellular epidermis.

What is the function of the epidermis in the insect integument, and to what is chitin compared?

The cellular epidermis secretes the proteins, chitin, and lipids that build the cuticle. Chitin provides structural reinforcement within the cuticle, functioning like rebar in concrete.

How do insect muscle attachments and counts compare to those of humans?

Insect muscles attach directly to the inside of their exoskeleton, whereas human muscles attach to internal bones. Grasshoppers have approximately $900$ muscles, while humans have approximately $800$.

What are the major disadvantages of possessing an exoskeleton?

The exoskeleton stays its original size once formed and cannot grow with the body, forcing the insect to undergo molting, which is a dangerous and time-consuming process.

Based on the cellular process of molting, what occurs during apolysis and ecdysis?

During apolysis, the outer cuticle separates from the epidermal cells, which then secrete digestive enzymes and build a new cuticle beneath. During ecdysis, the insect wriggles out of the old exoskeleton (exuviae).

What is the distinction between an instar and a stadium?

An instar is the developmental stage of the insect between two successive molts, whereas a stadium is the duration of time spent in a specific instar.

How do the terms larva, nymph, and naiad differ when identifying immature insects?

Larva refers to immature stages of holometabolous insects; nymph refers to terrestrial immature stages of non-holometabolous insects; and naiad refers to aquatic immature stages of hemimetabolous insects.

What do the terms pharate, teneral, and imago describe?

Pharate describes a developmental stage fully enclosed within the integument of the preceding instar; teneral describes the soft condition of an insect immediately after molting before sclerotization; and imago is the adult form.

What is sclerotization?

The process of polymerization and cross-bonding of chitin and protein that hardens the new insect exoskeleton.

Where is ecdysone produced, and what is its role in the molting process?

Ecdysone is produced by the prothoracic glands (triggered by prothoracicotropic hormone, or PTTH, from the corpora cardiaca) and travels to epidermal cells to stimulate the secretion of molting fluid and new cuticle formation.

Where is Juvenile Hormone (JH) produced, and how does its titer determine the outcome of a molt?

JH is secreted by the corpora allata. High titers of JH during ecdysone-stimulated molts maintain immature larval/nymphal characteristics, whereas the absence of JH during the final molt results in metamorphosis into an adult or pupa.

What function does Juvenile Hormone (JH) serve in adult female insects?

In adult females, JH stimulates egg production (vitellogenesis).

How do Insect Growth Regulators (IGRs) or JH mimics function as insecticides?

JH mimics prevent immature insects from metamorphosing into reproducing adults. Without developing into adults, the insects cannot mate or lay eggs, eventually causing the population to die off.

What concept is demonstrated when unrelated species evolve similar reproductive structures for similar functions?

Convergent evolution.

What are the primary internal organs of the female and male insect reproductive systems?

The female system includes paired ovaries (made of ovarioles), lateral oviducts, common oviduct, spermatheca, accessory glands, and vulva. The male system includes paired testes, vas efferens, vas deferens, seminal vesicles, accessory glands, ejaculatory duct, and aedeagus.

What is the primary function of the spermatheca in female insects?

The spermatheca receives and stores viable sperm following mating, allowing the female to fertilize eggs over an extended period.

What are the differences between oviparity, viviparity, and paedogenesis?

Oviparity is egg laying (frequently using an ovipositor); viviparity is giving birth to live young hatched inside the female; and paedogenesis is reproduction occurring within immature developmental stages.

How many eggs can a termite queen produce in a single day due to her enlarged ovaries?

As many as $30,000$ eggs in a day.

What are the three main regions of the insect alimentary canal, their embryonic origins, and which ones shed their lining during molting?

The foregut (stomodaeum) and hindgut (proctodaeum) originate from ectoderm and are lined with cuticle that sheds during molting. The midgut (mesenteron) originates from endoderm and does not shed a cuticular lining.

What structures compose the foregut, and what are their functions?

The pharynx (muscular swallowing organ), esophagus (transports food), crop (stores food), proventriculus (grinds food and acts as a valve), and salivary glands (secretes lubricating fluid and digestive enzymes).

What are the key functional components of the insect midgut?

The ventriculus (secretes enzymes and absorbs nutrients), gastric caeca (pouch-like extensions housing symbiotic bacteria), and the peritrophic membrane (protects midgut cells while remaining permeable to enzymes and digested nutrients).

What is the primary role of Malpighian tubules in insect physiology?

Located at the midgut-hindgut junction, Malpighian tubules filter nitrogenous waste and harmful substances out of the hemolymph and deposit them into the digestive tract for excretion.

What structures form the insect hindgut, and what is its primary function?

Composed of the ileum, colon, rectum, and anus. Its main functions are dehydrating waste, compressing it into fecal pellets, and expelling it from the body.

How is the insect tracheal system structured for gas exchange?

Air enters through exterior paired openings called spiracles, travels through main tracheal tubes, and branches into tiny tracheoles that directly deliver oxygen to individual cells and tissues.

What are taenidia, and why are they necessary in the tracheal system?

Taenidia are thickened spiral bands of chitin lining the trachea that maintain structural flexibility while preventing the air tubes from collapsing under pressure.

How do holopneustic, hemipneustic, and apneustic respiratory systems differ?

Holopneustic systems have $10$ pairs of functional spiracles; hemipneustic systems have lost at least one pair of spiracles; and apneustic systems lack functional spiracles entirely, relying on cutaneous diffusion.

What is insect blood called, and what are its cellular components?

Insect blood is called hemolymph, and its cellular components are known as hemocytes.

How is the insect open circulatory system arranged?

It features a dorsal vessel consisting of a posterior heart with segmental valves called ostia (which pump hemolymph forward) and an anterior aorta, supplemented by dorsal and ventral diaphragms that create body cavity sinuses.

How is hemolymph propelled into appendages such as wings, antennae, and legs?

Antennal and wing accessory pulsatile organs pump hemolymph into the antennae and wing veins, while legs contain a membrane called a septum that directs hemolymph flow in through one side and out through the other.

What thermoregulatory strategies and adaptations do poikilothermic insects use in cold environments?

Insects rely on ectothermic or endothermic strategies, exhibiting cold hardiness categorized as freezing-susceptible or freezing-tolerant. Some species synthesize antifreeze compounds directly in their hemolymph.