Horse Bot Fly

Life Cycle

Gasterophilis intestinalis, or the horse bot fly, ihas an annual life cycle. Studies have shown egg counts peak in the fall (Piol et al., 2009; Sánchez-Andrade, 2010). This is most likely due to the easier mobility that comes with higher precipitation during the fall season and other limiting resources (Güiris et al., 2010). Most commonly, the eggs are found attached to hairs of the more anterior limbs of their host (Pilo et al., 2009). The eggs are triggered to molt to the first stage larvae through contact with the host’s saliva (Sánchez-Andrade, 2010). Therefore, it is advantageous for them to be in an area that their host can reach with its mouth, which the host ofteThird Instar Larvan uses as a means to relieve the irritation of the eggs’ existence.

After about a month in the host’s mouth, the eggs will molt to the next stage larvae. This second instar larvae then begin to transcend down the digestive tract toward the stomach. In the stomach another molt occurs, producing the third stage larvae. These larvae stick to the mucosa of the walls of the digestive tract for eight to ten months where they can obtain nutrients from their host (Roelfstra, 2010; Sánchez-Andrade, 2010). Third stage larvae then exit, along with all other waste, through the anus of the host. Studies have shown this occurs most commonly in the spring (Sánchez-Andrade, 2010). Some studies figure this out by actually counting the number of larvae in feces (Güiris et al., 2010), while other studies analyze the fluctuations in the host’s immune response to the parasite (Sánchez-Andrade, 2010).                                                                Pest and Diseases Image Library,

Next, the third stage larvae go through a process of pupation over the summer, in which the amount of tiLarva in Pupation Periodme it takes fluctuates along with the temperature. Usually, it takes a little over a month for adult flies to emerge (Sánchez-Andrade, 2010). They must find a male or female counterpart rather quickly because adult flies only live for a little over a week. This typically is not difficult. Once a new setting is introduced to a fly, high egg deposits, successful life cycles and short generation times allow for a boom in numbers. Upon meeting, fertilization only takes a matter of minutes. Then, after a couple hours, the female is ready to deposit her eggs onto a host (Featured Creature, 1996). Optimal conditions include no rainfall and a temperature above 15 °C for flight ability (Sánchez-Andrade, 2010). Also, it is more advantageous for the continuation        Photo Taken by Benoit Martha                        of her heredity to deposit a few eggs on different hosts (Featured Creature, 1996). This starts the cycle over again.

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