Insect leg

This is for education purpose only by Dr.J.Roopavathy

1. Dr.J.Rooapvathy Assistant Professor Department of Zoology INSECT LEGS

2. TYPICAL INSECT LEG Insect leg consists of six segments They are: 1. basal coxa ( coxae ) which articulates with the thorax at the pleuron region 2. Small trochanter 3. Femur (Femora) 4. Tibia (Tibiae) 5. Segmented tarsus (tarsi) 6. Pretarsus

3. The coxa has smaller anterior region and a larger posterior region called the meron The articulation is brought about by ball and socket joint It may be monocondylic that allows rotatory movement or dicondylic that permits only back and forth movement The trochanter articulates with the coxa but usually forms an immovable attachment with the femur The next two segments called the femur and tibia are typically the longest

4. The tarsus which is derived from a single segment is usually divided into individual tarsomeres The number of tarsomeres varies from three to five and it is often used as a taxonomic tool The basal segment is often larger than others and called the basitarsus The structures distal to the tarsus are collectively called the pretarsus The pretarsus consist of a single claws or a pair of claws and one or more pads called the pulvillus ( Pulvilli ), bulbous lobe like arolium or empodium or bristles

5. Locomotory Modifications of the Insect leg Although an insects legs are locomotory in function, they are extensively modified to perform varied functions Both the immature and the adults have thoracic legs However, there are apodous (lacking legs) larvae (fly maggots) and adults (female scale insects, Homoptera ) There are different kinds of legs they are 1. Ambulatorial (Walking leg) 2. Cursorial (Walking and Running leg) 3. Fossorial (Digging or Burrowing leg) 4. Raptorial (Predatory or Grasping leg) 5. Saltatorial (Leaping and Jumping leg) 6. Natatorial (Swimming leg) 7. Scansorial (Climbing or Clinging leg)

6. AMBULATORIAL (Walking leg) Forelegs and midlegs are well adapted for walking eg : Grasshoppers CURSORIAL (Walking and Running) Typically developed inset legs with long femur and tibia that are well adapted for walking and running eg : Cockroach

7. FOSSORIAL ( Digging or Burrowing leg) The forelegs are highly modified with short, broad and large toothed fore -femora, the principal digging organ; strong and stout tibiae with distal tines to loosen the soil and heavily sclerotized claws adapted for digging eg : Mole Cricket

8. Raptorial (Predatory or grasping leg) The forelegs are modified for grabbing and holding the prey It is common in predatory insects eg : Praying Mantids Their forelegs are prehensile and suited for prey capturing and are of little use in locomotion The long and mobile coxa facilitates an extended reach to capture the prey Raptorial legs are also used to hold the female during mating eg : Dytiscus , Coleoptera .

9. SATATORIAL (Leaping, Jumping leg) The trochanter is fused with femur. The femora of the hind legs are enlarged to accommodate the muscles used in jumping eg : Grasshoppers NATATORIAL (Swimming leg) The legs of several aquatic insects are modified to facilitate swimming eg : aquatic bugs( Hemiptera ) and adult predaceous diving beetles. Their femur, tibia and first four tarsomeres are broad and flat with marginal setae and together function as oars

10. SCANSORIAL (Climbing or Clinging leg) The legs are adapted for climbing on or clinging the host in ecto -parasitic insets eg : Mallophaga . Their tibiae are stout and having thumb like processes at one side. The large claw presses against the thumb like process and form an efficient clinging or climbing mechanism as the forefinger works against the thumb of human beings while grasping an object

11. OTHER MODIFICATIONS Apart from the modifications associated with the locomotory functions, in Protura the legs are articulated in an elevated position, anterior to the body and the legs are probably Sensory in function Many insects also use their legs to groom parts of the body to remove detritus particles for instance, the assassin bugs , the neuropterans and the dipterans in the act of grooming hold the antennae between their forelegs The mosquitoes have a comb consisting of several rows of setae at the distal end of the foretibia

12. The combs in the act of scrapping run along the proboscis or antennae in rapid stroke Schistocerca has cleaning groove between the first and second pads of the tarsomeres The legs of many insect bears various structure eg : The hind tibiae the honey bees bear pollen basket or Corbiculum which is engaged in the gathering of pollen from the flowers they visit. Rows of stiff spines on the inner side of hind basitarsus serve as a pollen comb that collects pollen from the midlegs and abdomen . A row stout bristles at the distal end of tibia and a small plate fringed with hairs at the basal end of basitarsus collectively called the pollen packer that stores the pollen the corbiculum

13. The pollen in the corbiculum is transported to the hive Exactly same quantity pollen by weight are arranged between the combs to maintain balance in flight The foreleg of males of some species of diving beetles bear large suction discs on the tarsi which are used for grasping the female during copulation The spiny ad closely placed legs of dragonflies and damsleflies are held together as a basket to scoop the prey during flight Their legs are not useful in locomotion

14. The tarsal and pretarsal segments are also distinctly modified For example, the pad – like pulvillus is found on the lower surface of each tarsal segment Some insect have a bulbous, lobe like structure, the empodium , which arise from the end part of the unguitractor plate and also is located between the claws eg . Robber fly Varied degree of reduction of legs occurs in some insects For instance, in some butterflies the anterior tarsi are reduced or the forelegs are nonfunctional The hind femora of certain species of short – horned grasshoppers have short, peg – like structures with which they rub the forewings and produce a sound The long – horned grasshoppers and crickets possess oval auditory organs or tympana at the base of each foretibia

15. Reduction in the legs is often associated with the sedentary or some other specialized habits such as burrowing Some species like the bagworms are totally spodous and they live in bags constructed by the larvae Parasitic female strpsipterans do not have legs

16. Thank you REFERENCE THE INSECT: STRUCTURE , FUNCTION AND BIODIVERSIY BY DUNSTON P. AMBROSE