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KEY TO 3rd STAGE LARVAE

 

Of Flies Causing Myiasis

(Contact)

 

 

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[Also See:  Myiasis-causing Arthropods]

       Myiasis caused by the larvae of flies can result in serious health problems even though there have been times when larvae were deliberately introduced to open wounds, which induces rapid healing.  The Posterior Spiracular Plates and Cephalopharyngeal Skeletons of some Diptera larvae are used for identification.   Five important families are Calliphoridae, Gasterophilidae,  Hypodermatidae, Muscidae and Sarcophagidae.

 

The following key separates the five families and important species:    [For links to adults not given herealso see <Muscidae Key>]  Also: Some adults are displayed.

 

 

 

1.  The larva like that of the housefly (Fig. 1); body slender, cylindrical &  tapers anteriorly & more truncate posteriorly  _ _   2

 

     Larva is large, stout and resembles that of a warble, Hypoderma sp.; larva cylindrical or flattened, depressed or pear-shaped

                (Fig. 6)_ _ _ _ _ _ _ _ _ _ _  _ _ _ _ _ _ _ _ _ _ _  _ _ _ _ _ _ _ _ _ _ _  _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 9

 

     Larva has spiny or fleshy lateral, dorsal or terminal processes (Fig. 2)  _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 16

 

2.  The last obvious segment (anal) has a deep concavity holding the spiracles (Fig. 3); each dorsal cornua of the pharyngeal

        sclerite has a   deep posterior incision (Fig. 3)  _ _ _ _ _ _ _ _ _ _ _ Sarcophagidae (Wohlfahrtia spp., Sarcophaga spp.)

 

     The last segment does not have a deep concavity; spiracles are almost flush with the posterior face of anal segment; dorsal

         cornua of the pharyngeal sclerite does not have an incision  _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _  3

 

3.   Openings of posterior spiracles sinuous, short or a bit long; button area  usually deep in the peritreme (Fig. 4 -#8 & #9)_

             _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _Muscidae (part) _ _ _ _ _ _ _ 6

 

         Openings of posterior spiracles long, slender, quite parallel & directed downward (Fig. 4 #5) _ Calliphoridae (part)   6

 

4.   Posterior spiracles are D-shaped; there are 3 sinuous slits in each spiracle's plate (Fig. 4 #8)  _ _ _ _ _  Musca domestica

 

      Posterior spiracles are not D-dhaped; they are rounded or a bit irregular _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _  5

 

5.   Spiracle openings slightly curved & surrounded by large, dense peritreme (Fig. 4 #4)  Muscina stabulans; Muscina spp.

 

     Spiracle openings are S-shaped with a dense peritrreme; a button is located in the center (Fig. 4 #9)  _ Stomoxys calcitrans

 

6.  The peritreme of posterior spiracles is complete and with a distinct button (Fig. 4 #5 & #7)_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

       _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _   Calliphora spp., Lucilia spp., Cynomopsis spp.

 

     The peritreme is not complete and the button not pronounced and barely visible or in a thinner area of the peritreme _ _ _ 7

 

7.  Posterior spiracles with button located in a thinner area of the peritreme (Fig. 195 #6)  _ _ _ _ _ _ _ _ _  Phormia regina

 

     Posterior spiracles without a button are not indicated _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 8

 

8.  The trunks of the trachea that extend from the posterior spiracles are not pigmented (Fig. 4 #2) _  Callitroga macellaria

          ( Also in genera Chrysomya or Cochliomyia)

 

     The trunks intensely pigmented for most of their length (Fig. 187) (The true American screwworm) _ Callitroga americana

         ( Also in genera Chrysomya or Cochliomyia)

 

9.  Each posterior spiracle has 3 distinct slits (Fig. 4 #1, #2, #3)      _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _  10

 

     Each posterior spiracle has many small openings that are without pronounced slits (Fig. 5)  _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 13

 

10.  The larvae are pear-shaped (Fig. 6) and greatly spined;  spiracular openings are straight and located in a deep crater _ _ _ _ _

             _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _  Dermatobia hominis

 

      Larvae are egg-shaped; spiracular openings are bent at the middle and located in a shallow crater  _ _ _ _ Gasterophilidae 

 

11.  Spines located on segments' anterior margins stout & arranged in single row (Fig. 7)  _ _ _ Gasterophilus nasalis  11

 

      The spines are arranged in a double row _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 12

 

12.   Spines on the anterior margins are small, tapering to a fine point; there are no spines on the dorsum of segment #11 and the

              middle of segment #10 (Fig. 7) _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Gasterophilus haemorrhoidalis

 

      The anterior row of spines are thick, more blunt and larger; spines exist on the dorsum of segment #1 and sevral on each side

           of the  dorsum of segment 11 (Fig. 7) _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _  Gasterophilus intestinalis

 

13.   Mouth hooks are not well developed  _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _   Hypodermatidae  14

 

        Mouth hooks are well developed    _ _ _ _ _ _ _ _ _ _ _ _ _  _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _   15

 

14.   The posterior spiracles have their stigmatal plate profoundly cracked and pointing like a funnel toward the button (Fig. 8)_

              _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Hypoderma bovis

 

     The posterior spiracle has a stigmatal plate that is less cracked pointing toward the button (Fig. 8)    Hypoderma lineatum

 

15.   Mouth hooks shaped like a horn; the body has poorly developed spines; the posterior spiracles are heavily sclerotized with

             a button in the center and forming part of the plate (Fig. 8)   _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _  Oestrus ovis

 

     Mouth hooks are not so hard; the body is thickly set with spines or hard scales (Fig. 9); posterior spiracles are divided into

            plates _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _Cynomopsis spp.

 

16.  Larvae are cylindrical, stout and with a long posterior tubular extendable process (Fig. 10) _ _ _ _ _ _ _ _ _ Tubifera spp.

 

      Larvae are not cylindrical and a posterior extended process is absent; lateral and dorsal fleshy processes or spines are

       present   _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _  17

 

17.  The fleshy posterior processes are somewhat feathery (Fig. 11)  _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Fannia scalaris

 

      The fleshy posterior processes are simple and shaped more likes spines (Fig. 11)   _ _ _ _ _ _ _ _ _ _ Fannia canicularis

 

 

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  Key References:     <medvet.ref.htm>    <Hexapoda>

 

Aldrich, J. M.  1916.  Sarcophaga and allies in North America.  Thomas Say Found. Ent. Soc. Amer.

Andre, Emile.  1925.  Sur un cas de myiase cutanee chez l'homme.  Parasitology 17:  173-75.     

Austen, E. E.  1912.  British flies which cause myiasis in man.  Rept. Local Govt. Bd. Pub. Hlth & Med. 66:  5-15

Matheson, R. 1950.  Medical Entomology.  Comstock Publ. Co, Inc.  610 p.

Service, M.  2008.  Medical Entomology For Students.  Cambridge Univ. Press.  289 p

Legner, E. F.  1995.  Biological control of Diptera of medical and veterinary importance.  J. Vector Ecology

        20(1): 59-120.

Legner, E. F..  2000.  Biological control of aquatic Diptera.  p. 847-870.  Contributions to a Manual of

       Palaearctic Diptera,  Vol. 1, Science  Herald, Budapest.  978 p.