Warble stage development of third instars of Hypoderma lineatum (Diptera: Oestridae)

Area of Science:

• Veterinary Entomology
• Parasitology
• Insect Morphology

Background:

• Hypoderma lineatum (common cattle grub) is an insect parasite causing warbles in cattle.
• Larvae undergo molting within subcutaneous warbles, developing through several instars.

Purpose of the Study:

• To observe the in situ development of posterior spiracular plates in third-instar Hypoderma lineatum larvae.
• To determine the developmental timeline and survival rates of H. lineatum larvae within the host.

Main Methods:

• Larvae were monitored in situ after creating breathing holes in uninfested calves.
• Developmental stages of posterior spiracular plates were observed.
• Time to reach specific instars and exit from the host was recorded.

Main Results:

• Larvae reached the 3rd-instar phase 1 stage approximately 28.6 days post-infestation.
• Development through subsequent spiracular plate stages occurred at 5-6 day intervals.
• Larvae reached the pre-exit phase 3 stage in 54.2 days, with an average of 5.5 days to exit the host.
• Overall development to pupariation averaged 59.4 days.
• High survival rates were observed for 3rd instar larvae (86.7% exit), with 93.3% exiting from later stages.

Conclusions:

• The study details the in situ development of Hypoderma lineatum larvae, focusing on posterior spiracular plates.
• Most larval mortality occurs in early instars, with significant survival to host exit for later instars.
• Understanding these developmental timings and survival rates is crucial for cattle grub management.