Welcome back to my channel, in today’s video we are going to go over the parts
of the insect mouth and the different kinds of modifications of the mouthparts.
The mouthparts of insect vary greatly but all consist of the same five basic parts;
the labrum, the manidbles, the maxillae, the hypopharynx, and the labium.
As there are different modifications to these mouthparts depending on feeding strategy we will
look at an example of mouthparts used for chewing. The first mouthpart is the labrum.
The labrum is also known as the upper lip of the insect mouthparts.
It is simple and usually biloped in structure. It forms the roof of the mouth and the preoral
cavity, covering the mouth cavity from above. The inner surface, also known as the ventral
surface of the labrum, is called as the epipharynx.
The labrum articulates with the clypeus section of the head.
The function of the labrum is in helping pull food towards the mouth and hold it
in position whilst the insect is feeding. The mandibles are also known as the insect jaws.
They are paired structures, one is found on each side of the head.
They function in grasping, cutting, and crushing food.
They can also function in defence of the insect against predators or competitors.
The mandibles move along the horizontal plane towards each other in the middle.
Each mandible often has a distal cutting edge which has teeth on it,
then further back a molar area that is used for crushing and grinding up food.
The maxillae are also paired structures, with one found on
each side of the head below the mandibles. Each maxillae is made up of several parts.
The basal part of the maxilla is composed of two parts; the cardo, and the stipes.
Attached to the stipes are two lobe structures called the lacinia and the galea.
Another structure known as the maxillary palp comes off laterally from the stipes.
The maxillary palp is segmented. These maxillae function in manipulating
food into the mouth, and in some types of insects are involved in masticating food.
The galea and maxillae palps also function in sensory perception using
mechanoreceptors and chemoreceptors. The next mouthpart is the hypopharynx,
which is a tongue-like structure. In certain insects the hypopharynx
has a pair of lobes, one found on each side, called superlinguae (or superlingua singular).
The hypopharynx divides the oral cavity of the insect into a dorsal and ventral area.
The dorsal area of the oral cavity forms the food pouch, called the cibarium.
The ventral or lower area of the oral cavity forms the salivarium,
which the salivary duct opens up into. The last mouthpart is the labium,
which is also known as the lower lip. The labium forms the base of the
preoral cavity of the insect mouth. It is made up of two larger areas;
the postmentum, and the prementum. The postmentum itself can be divided into
two parts; the submentum, and the mentum. The prementum has a pair of labial palps
that come off each side. At the end of the prementum
there are a pair of glossa then out from these are a pair of paraglossa.
The paraglossa and glossa can be fused which is known as the ligula.
One type of mouthparts that are different , are those specialised for chewing and lapping.
An example of an insect who exhibits this feeding mode is the honey bee.
In mouthparts specialised for chewing and lapping the labrum and mandible remain similar
to those who have just chewing mouthparts. The mandibles function in manipulating wax
and other materials involved in building a nest or hive.
In addition they can be used for a variety of other functions,
such as feeding others and grooming. What has changed is that parts of the maxilla
and labium are modified to form a lapping tongue. The glossae of each labium are elongated and
fused to form a hairy tongue. The end of this modified
tongue is called the flabellum. Out from this tongue on each side
are the labial palps from the labiums. As well as the galea from the maxillae.
Together they form a tubular proboscis surrounding the tongue.
As you can see from this transverse section of the proboscis the two
galea form the top of the proboscis and the two labial palps form the bottom.
Together they form the food canal. How do these mouthparts work when feeding?
In bees this tongue is dipped into the nectar of a flower.
The hairs that cover the tongue cause the nectar to adhere to it.
The tongue then gets retracted moving this nectar back up to the food canal.
Another type of variation in insect mouthparts are those specialised for siphoning.
This is the common mode of feeding used by most moths and butterflies from the order lepidoptera.
In these insects the mandibles are usually greatly reduced or completely absent.
The paired labium are still present on each side of the head, and bear the labial palps.
The hypopharynx is absent, as is the epipharynx.
The galea of the each maxillae are greatly elongated and modified to form the proboscis.
At rest this proboscis is in a coiled position underneath the head.
When in use the proboscis uncoils using an increase in blood pressure of the hemolymph.
The proboscis is used to reach nectar or other liquids.
These liquids are sucked or pumped up through the proboscis by muscular action.
The next variation in mouthparts are those specialised for sponging.
This is a common feeding mode used in many species of flies
from the order diptera, such as the housefly. In these insects the mandibles are absent,
and the maxillae are reduced to a pair of single segmented maxillary palps.
The labium is modified to form a fleshy proboscis with a groove running along the upper surface.
The epipharynx of the labrum and the hypopharynx are present as elongated structures.
These elonagted structures sit in the groove of the proboscis and
form the food and salivary channels. The end of the proboscis is enlarged
and forms the labellum (singular). The labellum is covered in tiny food
channels called pseudotracheae. Saliva gets deposited on to
food though the saliva channel in the hypopharynx, then out the pseudotracheae.
Liquid food get sucked up these tiny food channels then up the proboscis
through the larger food channel. These liquids are brought up the food
channel by capillary action. In blood feeding flies,
the labella bears teeth that are used with muscular action to create a pool of blood
that is brought up through the proboscis. The last variation in insect mouthparts we
are going to go over are those specialised for a piercing and sucking mode of feeding.
There are several different variations of modifications in different
insects other than this one I am describing here to form piercing and sucking mouthparts.
Members of the order hemiptera, also known as the true bugs are the example of insects
we are going to go over that have this type of variation of the mouthparts.
In these insects the labium is elongated and extends downwards.
It also has a groove in it called the labial groove.
The labrum is present but the epipharynx of it is absent as is the hypopharynx.
The paired maxillae and mandibles are modified to form four stylets that sit in the labial groove.
These form a food canal and a salivary canal.
The stylet bundle is used to pierce into a plant and suck up plant sap.
And that concludes this video on the insect mouthparts.