Welcome to JAAN's science class!!

Big hi to all of you! I'm an undergraduate following a Bsc in bioscience. Trust me I know the feeling of surfing around the net for ages and getting nothing in return! Or getting something worthless for the time we spent surfing. So I started this blog adding the science stuff I have noted which I think might help someone in their home work. Ok then enjoy!

05 June 2011

Moulting and cuticle formation of insects

Hormones such as Ecdysone and bursicon play an important role during the events in moulting.

Apolysis
·         Epidermal cells divide and change their shape.
·         These cells separate from the inner surface of the old endocuticle and leave out the sub-cuticular space.
·         This space is consisting of moulting fluid, proteinase and chitinase.
·         These enzymes are inactive in this stage.

Formation of the epicuticle
·         Cuticulin is deposited below the moulting fluid and above the epidermis.
·         This forms the new Cuticulin layer.
·         Inner protein epicuticle is deposited under the Cuticulin layer.

Deposition of new procuticle
·         Deposition of procuticle occurs beneath the Cuticulin layer.
·         After the deposition enzymes in the moulting fluid activate and digest the old endocuticle.
·         Only a thin layer of the old endocuticle is left out.
·         This layer is called as Ecdysial membrane. These lines are located in the median lines of head and thorax.
·         Weak lines appear along this Ecdysial layer.
·         Wax secretion occurs on to the surface of the new cuticle.

Ecdysis
·         Moulting fluid and digested old endocuticle are absorbed.
·         Intake of the air and muscular contractions cause the insect’s body to swell.
·         This leads the old exoskeleton to split open along the weak lines.
·         Insect draws itself out.
·         All parts of the old cuticle are shed.
·         This old cuticle is called as cast skin.

Expansion of the new procuticle
·         New cuticle is soft and pale.
·         At this moment new procuticle expands before it hardens.

Hardening and darkening of cuticle
·         Hardening of the cuticle is known as sclerotization.
·         This forms sclerites which are rigid plates of exoskeleton.
·         It also darkens the cuticle. This is known as tanning.

Deposition of the new endocuticle
·         New endocuticle deposits after the moulting and tanning.

01 June 2011

Orientation of insect head: Prognathous, Hypognathous and Opisthognathous

·         Three types of orientation.
                                i.            Prognathous: orientated horizontally. Mouth parts are pointed forward.
                              ii.            Hypognathous: orientated vertically. Mouth parts are pointed down.
                            iii.            Opisthognathous: orientated obliquely. Mouthparts are pointed backward.

Prognathous
·         Mouthparts are pointing forward.
·         Mouthparts are anterior in position.
·         Long axis is horizontal.
·         Mostly carnivore insects have this type of orientation.
·         Ex: Stick insect

Hypognathous
·         Mouthparts are pointing downward.
·         Mouthparts are ventral.
·         Long axis is vertical.
·         Mostly herbivore insects contain this type.
·         Ex: Grasshopper.

Opisthognathous
·         Mouthparts are pointing backward.
·         Mouthparts are directed down between coxae of legs.
·         This is known as proboscis.
·         Long axis is horizontal.
·         Ex: Plant sucking bugs.