ENTM 340 Insect Pests of Trees Turf and Ornamentals�

C. Sadof� Purdue University

Lecture 3 External Anatomy of the Insect� Thorax and Abdomen�

 

1. Why study the Insect Thorax and Abdomen?

    1. Thoracic structure determines how an insect travels and its ability to spread through a crop.�

                                                               i.      Winged insects fly. Wingless walk.

                                                             ii.      Shape of legs and wings indicate how far they can fly or walk.

    1. Abdominal structure is related to reproduction and its ability to utilize a food resource.

                                                               i.      Ovipositor, determines where eggs can be laid,

1.      On or in leaf, wood, bud,soil or other insect

����� c.� As with the rest of this course I will try to examples that are relevant to plant pests and the insects that feed on those pests.�

  1. Insect Segments- Subunits of thoracic and abdominal body regions. (p 35)
    1. Elements of the segment

                                                               i.      Tergum � sclerotized dorsal plate

                                                             ii.      Sternum � ventral sclerotized plate

                                                            iii.      Pleuron- membranous or sclerotized region between tergum and sternum

                                                           iv.      Spiracle � opening of the respiratory system, located in pleuron.� One spiracle on each side.

  1. Thorax � 3 segments that work together to allow insects to fly and walk
    1. Prothorax � First segment behind head

                                                               i.      Bear first pair of true legs

                                                             ii.      �Similar to primitive generalize arthropod segment

    1. Mesothorax

                                                               i.      Bear forewings

                                                             ii.      Bear 2nd pair of legs .

                                                            iii.      Pleuron modified with internal fold to support wing muscle attachments

    1. Metathorax

                                                               i.      Bear hindwings

                                                             ii.      Bear 3nd pair of legs .

                                                            iii.      Pleuron modified with internal fold to support wing muscle attachments

    1. The True Insect leg and Adaptations

                                                               i.      Basic morphology of a true leg..

1.      Coxa- basal part

2.      Trochanter � second part

3.      Femur- 3rd and often longest part (like a thigh)

4.      Tibia � 4th part ( like a calf)

5.      Tarsus � 5th part (1-5 segments) (like a foot)

6.      Pretarsus - 6th part (often a pair of claws)

                                                             ii.      Adaptations

1.      Walking (cursorial) basic model(cockroach or aphid)

2.      Jumping (saltatorial)� =leg with enlarged femur- (grasshopper, or leaf hopper)

3.      Grasping � Leg armed with opposing spines on femur an tibia (Mantid, or Ambush bug foreleg)

4.      Clasping- leg with tibia and tarsus formed into a pincer like structur (hair and pubic lice)

5.      Swimming � leg with some part of tibia or femur flattened into a paddle like organ (water boatman)

6.      Digging � leg with tibia or tarsus modified into scraper like organ (mole cricket, or Japanese beetle grub)

 

    1. �The insect wing

                                                               i.      Forewing attached to mesothorax, hindwing to metathorax

                                                             ii.      Veins serve as support struts

                                                            iii.      Meso and metathoracic segments are reinforced to help support wing muscles during flight.

                                                           iv.      Wings useful identifying insects

1.      Many order names are based on wing characteristics

a.       Diptera � flies - two wings

b.      Lepidoptera- moths and butterflies� scaled wings.

c.       Thysanaptera (thrips= fringed wings)

 

  1. Insect Abdomen
    1. Each segment has a spiracle
    2. Some segments have appendages

                                                               i.      Non-reproductive

1.      Cerci- tactile organs on 11th segment (earwig)

2.      Proleg-� protrusions of abdominal wall (caterpillars, sawflies) position and shape key in identification

3.      Gills- some aquatic insect larvae

                                                             ii.      Reproductive

1.      �Male appendages

a.       copulatory organ (aedeagus)

                                                                                                                                       i.      Bugs are bizarre, dragonflies have 2 aedigi

b.      clasping organ� (parameres)

2.      Female appendages

a.       Ovipositors

                                                                                                                                       i.      Long tubes with blades to cut or drill tissue into which eggs are laid

1.      Ichneumon wasp lays egg into insect

2.      Pigeon Tremex drills egg into oak

                                                                                                                                     ii.      Telesocoping tubes that deposit eggs (moths)

                                                                                                                                    iii.      Eggs dropped (black vine weevil).

Review Questions/ Exercises

 

 

For each of the following leg adaptations think of one insect in the landscape.�

 

Digging ( eg. White grub, or mole cricket)

Jumping (Grasshopper)

Swimming (Waterboatman or Predaceous diving beetle)

Grasping prey (Praying mantid)

Shaving wood (carpenter ant)

Drilling eggs into a pest (parasitic wasp)

 

What is meant by each of the following descriptions of wing adaptation>

Scaly, fringed, hemelyetra, tegmina, elytra, haltere

 

 

Can a female wasp have both a stinger and an ovipositor?

(no- a stinger is a modified ovipositor, therefore parasitic wasps that lay eggs in or on pests can�t sting humans)