Parahost behavior of adult Gasterophilus intestinalis (Diptera: Gasterophilidae) in Delaware.

The research is about the behavioral patterns of the adult ‘Gasterophilus intestinalis’ flies, commonly known as horse bot flies, observed over the summers of 1978 and 1979 near horse pasture on two farms in Newark, Delaware. The study shows the flies’ lifecycle from mating to oviposition, their defense mechanisms, their flight patterns, and their oviposition rates, taking note of their short lifespan.

Observations of the Adult Gasterophilus intestinalis Flies

• The researchers noted a gradual increase in adult fly occurrence over the early summer, with three distinct surges. This observation may suggest predictable behavior that could be used in later pest control efforts.
• In a laboratory setting, the lifespan of the flies was observed to be very short, with males living for 1-3 days, and females for 1-2 days. This quick turnover highlights the urgency these insects display in mating and oviposition (the laying of eggs).

Behaviors and Lifecycles

• The flies exhibited specific flight patterns primarily committed to seeking mates and warding off intraspecific competition. These patterns appear to be heavily dependent on the density of the fly population in a given area.
• Males were observed to assertively defend horses, whether alone or in groups, by hovering around them. Mating predominantly took place near the horses following mid-air coupling.

Oviposition and Life Span

• Female horse bot flies were seen laying eggs in a range of environmental and parahost conditions, suggesting a high degree of adaptability.
• Despite varying oviposition rates, a single female could lay her full stock of 900 eggs in under an hour. This high fertility rate underscores the reproductive potential and capacities of these insects.
• The horses were found to ingest more than 90% of the infective stage larvae through self and mutual grooming. This highlights the efficiency of the flies’ reproductive strategy in ensuring the continuation of the fly’s lifecycle.
• After oviposition, an ovipositor profile identified a female that had spent her eggs. The effective life span of an ovipositing female was observed to be a mere day.

The research gives crucial insights into the behavior and lifecycle of ‘Gasterophilus intestinalis’ flies, which can be significant in future studies and strategies aiming to regulate or control these pests around horses.