WARBLE STAGE DEVELOPMENT OF 3RD INSTARS OF HYPODERMA-LINEATUM (DIPTERA, OESTRIDAE)

Hypoderma lineatum (Villers), the common cattle grub, is an insect par asite that resides in a warble in the subcutaneous tissues of the back s of cattle during a portion of their life cycle. Inside the warble, t he larva undergoes 2 molts to the 3rd instar. In this study, the devel opment of the posterior spiracular plates of the 3rd instar of H. line atum was observed in situ. Larvae were observed to molt to the 3rd-ins tar phase 1 stage of development 28.6 +/- 3.9 d (+/- SD) after digesti ng a breathing hole in the backs of previously uninfested calves. Deve lopment of the spiracular plates through each of the various recogniza ble stages occurred on a 5-6-d interval. It took 54.2 +/- 5.1 d in the back for larvae to develop to the phase 3 stage, the stage reached be fore larvae exit the host. The average elapsed time from the 3rd-insta r phase 3 stage to exit from the host was 5.5 +/- 2.9 d. Of 22 larvae that were followed from arrival in the back to pupariation, the elapse d time was 59.4 +/- 6.1 d. Most larval mortality occurred in the back during the Ist and 2nd instar. Of larvae surviving to the 3rd instar, 86.7% successfully exited from the host. Of 3rd instars surviving to t he phase 2 goldplate or phase 3 stage, 93.3% exited successfully from the host.