Gasterophilus intestinalis
| Gasterophilus intestinalis | |
|---|---|
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| Adult Gasterophilus intestinalis | |
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| G. intestinalis eggs on the foreleg of a horse | |
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Insecta |
| Order: | Diptera |
| Family: | Oestridae |
| Genus: | Gasterophilus |
| Species: | G. intestinalis
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| Binomial name | |
| Gasterophilus intestinalis de Geer 1776
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| Synonyms[1] | |
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Gasterophilus intestinalis, also known as horse bot fly, is a species of insect of the family Oestridae,[2] and is found worldwide.[3] The adults, which have a bumblebee-like appearance, are prominently active in the summer.[4] G. intestinalis is primarily a parasite of horses, mules and donkeys.[5]
Identification
The eggs of G. intestinalis are pale yellow in color,[6] and 1–2 mm (0.039–0.079 in) long.[4] The larvae are yellow or tan.[3] Adults, which are 10–15 mm (0.39–0.59 in) long,[5] look superficially like hairy bumblebees, with a noticeable ovipositor at the end of the abdomen.[4]
Life cycle
The female fly cements individual eggs onto hairs of the forelimbs and shoulders of horses, mules and donkeys.[6][5] Each female lays up to 1000 eggs.[6] In order the hatch, the eggs must be licked by the host animal.[5] If taken into the host's mouth during grooming, the egg will hatch in the mouth.[5] If not, the first instar larva will migrate to the mouth.[5] The larvae develop in the tissue the tongue,[3] in tunnels within 1.5 mm (0.059 in) of the surface.[7] Second instar larvae are swallowed and pass into the host's stomach,[3] and attach to the lining of the stomach, most usually at the junction between the glandular and non-glandular regions of the stomach.[5] The larvae remain in the stomach for 8–10 months,[5] before maturing into third instar larvae.[3] In the spring, the third stage larvae pass out of the host in the feces.[3] Pupation takes place in the soil for a duration of 3–5 weeks, until the adults emerge.[5] Adults are active for only a few weeks in the summer,[4] and, lacking functional mouthparts, live only for a short time.[5]
Effects on the host
Clinical signs are uncommon in host animals.[3] Large numbers of larvae in the stomach can cause pain in the stomach,[3] and, rarely, extremely large infestations may cause an obstruction at the outflow from the stomach to the duodenum.[7] The larvae are usually found incidentally when the host's stomach is examined by endoscope.[3] Often the only sign of infestation is the finding of larvae in the feces.[4] The main impact on the host is the nuisance of the adults as they repeatedly land on the legs when attempting to lay eggs.[4]
Treatment and control
Parasiticides which are effective against the larvae include macrolytic lactones, such as ivermectin and moxidectin, and organophosphates, such as metrifonate (also known as trichlorphon) and dichlorvos.[6]
References
- ^ Tenquist, J.D.; Charleston, W.A.G. (September 1981). "An annotated checklist of ectoparasites of terrestrial mammals in New Zealand". Journal of the Royal Society of New Zealand. 11 (3): 265.
- ^ "Horse Bot Fly - Gasterophilus intestinalis - Overview". Encyclopedia of Life. Retrieved 2018-08-09.
- ^ a b c d e f g h i Hart, Kelsey A. (2012). "Gasterophilus". In Wilson, David A.; Mair, Tim; Sherlock, Ceri (eds.). Clinical Veterinary Advisor. The Horse. Elsevier Saunders. p. 216. ISBN 9781437714494.
- ^ a b c d e f Knottenbelt, Derek C. (2009). "Gasterophilus spp. ('horse bots')". Pascoe's Principles & Practice of Equine Dermatology (2nd ed.). Elsevier/Saunders. pp. 55–56. ISBN 9780702042515.
- ^ a b c d e f g h i j Gunn, Alan; Pitt, Sarah Jane (2012). "4.4.13 Subfamily Gasterophilinae". Parasitology: An Integrated Approach. John Wiley & Sons. p. 173. ISBN 9780470684245.
- ^ a b c d Sager, Heinz; Elsheikha, Hany M. (2011). "Chapter 8. Dieases caused by insects". In Elsheikha, Hany M.; Khan, Naveed Ahmed (eds.). Essentials of Veterinary Parasitology. Caister Academic Press. pp. 115–116. ISBN 9781904455790.
- ^ a b Colwell, D. D. (2006). "Part C: Gasterophilinae host-parasite interactions". In Colwell, Douglas D.; Hall, Martin J. R.; Scholl, Philip J. (eds.). The Oestrid Flies: Biology, Host-parasite Relationships, Impact and Management. CABI Publishing. p. 190. ISBN 9781845931681.
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