Types of Insect Larva
The larva is a general term to denote young one or immature stage of insect between egg and pupa having complete and hyper metamorphosis (Holometabolus or Endopterygota insects). The larvae are classified into four groups on the basis of development of appendages.
1. Protopod Larva: In this eggs contain little yolk and larvae hatch out from the eggs, while they are still in early stages of embryonic development. The abdomen is devoid of segmentation and head (cephalic) and thoracic appendages are rudimentary e.g. Larvae of Endoparasitic Hymenoptera.
2. Polypod Larva: This type of larva has well segmented body and possesses three pairs of thoracic legs and 2 to 5 pairs of abdominal prolegs. The reparatory system os peripneustaic type i.e. only prothoracic and abdominal spiracles only are open. These larvae are also termed as “Eruciform” (cylindrical type) e.g. larvae of butterflies and moths. On the basis of number and location of prolegs, these larvae are further classified as:
a) Caterpillar
b) Semilooper and
c) Looper.
a. Caterpillar: It is a type of polypod larva which bears 3 pairs of thoracic legs and 5 pairs of prolegs. The prolegs are present on 3, 4, 5, 6, & 10th abdominal segments e.g. Larva of Lemon butter fly, larva of gram pod borer etc.
b. Semilooper: It is a type of polypod larva which bears 3 pairs of thoracic legs and 3 pairs of prolegs. Prolegs are present on 5, 6, and 10th abdominal segments e.g. Castor Semilooper, cotton Semilooper etc.
c. Looper: It is a type of polypod larva which bears 3 pairs of thoracic legs and two pairs of prolegs on 6th and 10th abdominal segments e.g. Cabbage looper.
3. Oligopod Larva: These larvae have well segmented body and they bear well development cephalic (head) appendages and 3 pairs of thoracic legs. The abdominal appendages (prolegs) are absent. In some larvae a pair of cerci or similar caudal processes may be present. On the basis of structure, the oligopod larvae are further classified into two types viz. a) Campodeiform type b) Scarabaeiform type.
a. Campodeiform Type larva: The larva appear like campodea insect (from order Diplura) and hence the name. These larvae have elongated more or less fusiform (i.e. tapering at both the ends). Some what depressed body which is often well sclerotized bearing long thoracic legs and usually a pair of terminal cerci e.g. Lady Bird beetle, lace wing etc.
b. Scarabaeiform Type Larva: This type of larva is shout, fleshy ‘C’ shaped with shorter thoracic legs and without terminal abdominal processes (cerci). They are less active and sluggish e.g. White grub, rhinoceros beetle etc.
4. Apodous Larva: These larvae do not have either thoracic legs or abdominal prolegs (legless) e.g. House fly, fruit fly, honey bee.
The apodous larvae may be classified into following 3 types on the basis of degree of development of head.
a. Eucephalous Larva: This type of larvae have well sclerotized head capsule with relatively reduced of cephalic appendages e.g. Mosquito, mango stem borer etc.
b. Hemiphaous Larva: This type of larvae appreciably reduced head capsule and its appendages. The head can be withdrawn into the thorax e.g. Honey bees, robber lies, horse flies etc.
c. Acephalous Larva: They have no obvious head capsule and cephalic appendages e.g. Larva of house fly.
Significance of Larva Stage: It helps in increasing size and putting on more weight of insect.