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Questions and Answers

What is the primary function of simple eyes (ocelli) in insects?

To create a 3D representation of the environment

To produce a high-resolution image

To perceive movement and light orientation (correct)

To analyze color in detail

All insects have complex eyes that provide a complete mosaic vision.

False

What are the two classes of simple eyes in insects?

Dorsal ocelli and lateral ocelli

Insects with only simple eyes are known to scan their environment by moving their _____ back and forth.

head Signup and view all the answers

Match the following features with their descriptions regarding simple eyes (ocelli):

Dorsal ocelli = Arranged in a triangle on the head Lateral ocelli = May occur singly or in groups Structure uniformity = May vary among insect species Vision quality = Less complete than compound eyes Signup and view all the answers

Which sense organ is responsible for detecting light in insects?

Photoreceptors Signup and view all the answers

Compound eyes are found in primitively wingless insects.

False Signup and view all the answers

What are the five basic senses of insects?

Sight, Smell, Taste, Touch, Hearing Signup and view all the answers

The light-receptor apparatus (LRA) comprises _ to _ retinula cells.

6, 8 Signup and view all the answers

Match the following insect senses with their respective receptors:

Sight = Photoreceptors Smell = Chemoreceptors Touch = Mechanoreceptors Hearing = Auditory organs Signup and view all the answers

What is the principal visual organ found in most insects with compound eyes?

Ommatidium Signup and view all the answers

The number of facets in compound eyes is the same across all insect species.

False Signup and view all the answers

What role do pigment cells play in the structure of the compound eye?

They isolate individual ommatidia from one another. Signup and view all the answers

What is the primary function of chemoreceptors in insects?

Detect chemical substances Signup and view all the answers

Taste receptors in insects are only found on their tarsi.

False Signup and view all the answers

What substance do smell receptors in insects detect?

Pheromones Signup and view all the answers

Insects have chemoreceptors that detect _____ through the sense of taste.

molecules Signup and view all the answers

Which of the following insects has a higher number of olfactory sensilla in males compared to workers?

Apis Signup and view all the answers

Match the following types of receptors with their primary function:

Taste Receptors = Sense chemicals in liquids Smell Receptors = Detect airborne pheromones Contact Chemoreceptors = Detect molecules on surfaces Olfactory Sensilla = Sense odor in the environment Signup and view all the answers

Chemoreceptors can only sense chemical substances that are dissolved in liquids.

False Signup and view all the answers

What do olfactory sensilla help insects perceive?

Odors Signup and view all the answers

Study Notes

Insect Senses

Insects have a variety of senses that help them interact with their environment.
These senses allow insects to find food, mates, avoid predators, build nests, and perform crucial internal functions.

Sight (Photoreceptors)

Photoreceptors detect light and are responsible for vision.
Insects have two main types of photoreceptors: Compound Eyes (CE) and Simple Eyes (Ocelli).

Compound Eyes (CE)

CE are the most complex photoreceptors and are involved in forming images.
They are found in most insects, particularly those that fly, and are usually more complex than Simple Eyes.
CE are characterized by a cornea divided into hexagonal facets.
Each facet is part of a sensory unit called an ommatidium.
CE allow insects to perceive images, colors, and movement.
- Dragonflies have up to 20,000 facets.
- Butterflies and Moths have 12,000 or more facets.
- House flies have around 4,000 facets.
- Ants have fewer than 12 facets.

How CE Work

Light is gathered by the lens (cornea).
The lens focuses light through a crystalline cone (CC) onto a light-receptor apparatus (LRA).
The LRA contains 6 - 8 retinula cells (RC) that combine to form a central light sensor (rhabdom).
The CC and LRA are surrounded by pigment cells that isolate each ommatidium from another.
RCs convert light into electrical energy which is transmitted to the brain via nerve fibers.
The individual images from each ommatidium are combined to create a mosaic of the object being viewed.

Simple Eyes (Ocelli)

Ocelli are found in many immature Endopterygota (insects that undergo complete metamorphosis).
They are believed to perceive images, but they likely produce a less complete mosaic and are primarily used for light orientation.
Some insects with only Simple Eyes use head movement to scan their environment.
Ocelli can be similar in structure to individual ommatidia (like those found in caterpillars).
They can also have a single cornea overlying a single receptor unit (like some larvae).
Ocelli are often arranged in a triangle on the head, either dorsally or laterally.

Smell and Taste (Chemoreceptors)

Chemoreceptors detect chemical substances in the environment.
These receptors are responsible for the senses of smell (olfaction) and taste (gustation).

Taste Receptors (Gustation)

Taste receptors are called contact chemoreceptors because they detect chemicals by direct contact.
They are usually found on the mouthparts, antennae (some Hymenoptera), and tarsi (Lepidoptera, Diptera, honeybees).
These receptors are typically hairs or cones with 4 neurons.
They sense molecules from liquids and have fine nerve endings exposed to the environment at the hair tips.
Insects have different taste thresholds for different substances.
- Sugar solutions are usually preferred to distilled water.
- Dilute acids and salt solutions are generally rejected.
Individual taste cells respond to specific molecules.

Smell Receptors (Olfaction)

Smell receptors are found in olfactory sensilla, which are characterized by numerous pores.
They are typically peg-like and have more nerve endings at the surface than taste receptors.
Smell receptors are most numerous on the antennae but can also be found on the palpi of mouthparts.
Males often have more smell receptors than females:
- Male honeybees have about 30,000 olfactory sensilla on the last 8 antennal segments.
- Worker bees have about 6,000 and queens have 2,000.
Smell receptors play a crucial role in insect behavior and development.
- Pheromones are highly specific, volatile substances produced by insects that trigger behavioral and developmental changes in others of the same species.
- These pheromones are perceived through the olfactory sensilla.