Modifications of circulatory system in insects

In insects the circulatory system is of closed type ie, there are no blood vessels as like in animals. The body organs are simply bathed in the body fluid.

                                               Dorsal vessel

Extends from near the caudal end of the body , through the thorax ,and terminates in the head

It is clearly delineated intotwo regions poterior heart and anterior aorta.

•Normally open anteriorly ,ending abruptly  in most insects but in orthopteroids it open as a gutter.

•In adult Lepidoptera and some Hymenoptera it loops down between longitudinal flight muscles.

•  Dorsal vessel has longitudinal muscles strands in Heteroptera.

Posteriorly closed except in larval mayfly, where 3 vessels diverge to the caudal filaments from the heart.

Segmentation   Tettigonidae, 

                            Dictyoptera, ==>12 pairs

                            Grylloblattidae 

                           Lucanus cervus ==> 7 pairs

                            Japygidae(dipluran) ==>10 pairs

                                                                                     

                                                          Heart

•Larvae of dragonfly and the cranefly heart is divided into chambers by valves in front of each pair of incurrent ostia.

•In Ephemeroptera larvae ostia are so long that they meet across lumen.

         •In orthopteroids heart has a chambered appearance .

                                                                           Incurrent ostia

Vertical slit like openings in the lateral wall of heart.Blood enters the heart through this opening. Maximum of 12 pairs are seen, 3 thoraxic and 9 abdominal. But varies in insects

•Blattodea        -   12 pairs

•Lepidoptera    -   7 or 8

•Hymenoptera -  5 pairs

•Housefly          -   4

•Heteroptera    -   2 or 3 pairs

                                                                 Excurrent ostia

Heamolymph leaves heart through this. Restricted to hearts of

•Thysanura

•Orthoptera            paired ventrolateral opening

•plecoptera

•Embioptera                  unpaired ostia

    Blattodea and mantodea  No excurrent ostia. Instead have segmental vessels  that extent laterally through which blood leaves heart.

• orthoptera larval lepidoptera and adult coleoptera branches of segmental nerves combine to form lateral cardiac nerve running along each side of heart

•In locust ,a group of nerves  in each ganglion send axons to heart

                                                          Alary muscles

•Generally stretch from one side of body to the other just below the heart but in Hyalophora they are directly connected to heart with intercalated discs

Orthoptera 12 pairs

Honey bee and larval chironomidae 2 pairs

                                             Ventral muscles

•Horizontal septum laterally attached to sternite

•Ventral diaphragm present in both larvae and adult of almost all insects but

•In Mecoptera lepidoptera and nematocerous diptera only adult has ventral diaphragm

•In thorax of grasshopper it is delicate membrane but solid  muscular sheet in abdomen

Pulsatile organ

•Diptera and coleoptera Pulsatile organ only in mesothorax

•Pulsatile organs in antennae have ampullae from which a fine tube extends to tip of antennae

•Thysanura ,plecoptera ampullae lacks muscles

It only directs flow of heamolymph from aorta to antennae

  Dermapetra –compressor muscles

•Cercal heamolymph vessels

    Ephemeroptera -from heart to cercus

     Plecoptera         - do not connect with heart         open directly to perivisceral cavity

                                                    Circulation

•In hemimetabolous and larval holometabolous insects blood pumped forwad through the heart at systole

•In adult lepidoptera, coleoptera  & diptera blood shunted backwords and forwards between thorax and abdomen because of seperation of heamocoel by

                  movable flap of fatty tissue in lepidoptera

                  large air sac  in diptera

                                                                          Haemolymph

•Exopterygota-   Na and Cl ions more & K ,Mg ,Ca less

•Endopterygota -reduction of Cl ions & increase in organic acids

•In Apis major blood sugar is glucose instead of trehalose.

•Blood plasma of chironomid larva has heamoglobin.

Functions of blood

Ø  Transport food materials and hormones

Ø  Eversion of protrusible structures such as         ptilinum in diptera & penis of certain insects

Ø Waste removal

Ø Thermoregulation

Ø Defence

                                                        Haemocytes

•Female insects have more heamocyte count than males

•Endopterygota larvae have more heamocytes

    Exopterygota  adult have more

•Aphids 1800  heamocytes per microliter

    Bark bug 15000 per microliter

    cockroach 80000 per microliter

•Blood pressure of locust is very low

•Heart beat

        from 14 beats /minutes  in lucanus to 150 in      compodea

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Prepared by
Varsha Vijayan
Dept. Of Entomology
Kerala Agricultural University