Lee, Richard E., Jr.

Timm, Robert M.

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416 NOTES AND COMMENTS cytological evolution. If inversions have a role in spe- group of the genus Drosophila IV. The hydei ciation in Drosophila, this role remains obscure and subgroup. Texas Univ. Publ. 6205:73-83. most likely is a minor one. -. 1962~.  Cytological studies of the repleta group of the genus Drosophila V. The mulleri subgroup. Texas Univ. Publ. 6205:85-117. , 1962d. Cytological studies of the repleta Financial support for the work cited in this note was provided by the Natural Science and Engineer- group of the genus Drosophila VI. The fasciola ing Research Council of Canada. subgroup. Texas Univ. Publ. 6205:119-134. -. 1963. Cytology and phylogeny in Drosoph- ila. Amer. Natur. 97:333-352. CARSON,H .  L. 1975. Genetics of speciation. Amer. Natur. 109:83-92 -. 1978. Speciation and sexual selection in Hawaiian Drosophila, p. 93-107. I n  P.  F .  Brus- sard (ed.), Ecological Genetics: The Interface. Springer-Verlag, N.Y.  JOHNSON,W. R., AND W. B. HEED. Chromosomal polymorphism in the desert-adapted species Dro- sophila mojavensis. Evolution. I n  press. METTLER,L. E .  1963. Drosophila mojavensis baja, a new form in the mulleri complex. Dros. Inf. Serv. 38:57. WASSERMAN, 1962a. Cytological studies of the M.  repleta group of the genus Drosophila 111. The mercatorum subgroup.  Texas Univ.  Publ .  6205:63-71. -. . 19626. Cytological studies of the repleta Evolutton, 36(2), 1982, pp. 4 1 6 4 1 i  WHARTON,L. T .  1942. Analysis of the repleta group of Drosophila. Texas Univ. Publ. 9228:23-53. WHITE, M. J. D. 1978. Modes of Speciation. W. H .  Freeman and Company, San Francisco. Z o u ~ o s ,  E.  1981a. The chromosomal basis of via- bility in interspecific hybrids between Drosophila arizonensis and Drosophila mojavensis. Can. J. Genet. Cytol. 23:65-72. , 19816. An autosome - k' chromosome com- bination that causes sterility in Drosophila mo- javensis - Drosophila arizonensis hybrids. Dros. Inf. Serv. 97:703-718. . 1981c. The chromosomal basis of sexual iso- lation in two sibling species of Drosophila: D .  arizonensis and D. mojavensis. Genetics. I n  press. Corresponding Editor: J.  Patton IS HOST CASTRATION AN EVOLUTIONARY STRATEGY O F  BOT FLIES? ROBERTM. TIMIVIAND RICHARD E.  LEE, JR. Division of Mammals, Field Museum of Satural  History, Chicago, Illinois 60605 and Department of Biology, University of Houston, Houston, Texas 77004 Received April 14. 1981. In  a review of host castration, Baudoin (1975) de- veloped several hypotheses on why parasites, and bot flies (Diptera: Cuterebridae) in particular, should castrate their hosts. Many of his ideas on the strategy of host castration by parasites are appealing from an evolutionary point of view in that they incorporate increased fitness of the parasites. For example, cas- trated male hosts would provide the parasite with "a) increased energy availability, b) increased host viability and c) increased host growth" (Baudoin, 1975, p. 344). However, Baudoin's basic assumption, that bot flies castrate their hosts, is erroneous. Fitch (1857) was the first to suggest that bot flies castrated their hosts. He proposed the name "emas- culator" for the chipmunk bot. In recent years, sev- eral papers have been cited repeatedly as providing evidence that castration does occur (i.e., Dalmat, Revised July 5, 1981 1942, 1943; Wecker, 1962; Dunaway et al.,  1967; Getz, 1970; Hensley, 1976). None provide clear-cut evidence for host castration. A number of current parasitology, medical entomology, and veterinary texts contain blanket statements that bot flies emas- culate their hosts (i.e., Chandler and Read, 1961; Krull, 1969; Cheng, 1973; Noble and Noble, 1976). Seton (1920) did question whether host castration actually occurs, but unfortunately his paper has been largely ignored. Thus, the concept of host castration has been thoroughly entrenched in the literature in spite of the fact there is no supporting evidence. Our work on Cuterebra emasculator parasitizing the eastern chipmunk, Tamias striatus, and C. fon- tinella parasitizing the white-footed mouse, Pero-myscus leucopus, demonstrated that bot flies are found exclusively in the subcutaneous region be-tween the skin and underlying muscle (Timm and 417 NOTES AND COMMENTS Cook, 1979; Timm and Lee, 1981). They do not con- sume muscle or reproductive tissue, but rather feed on "tissue debris and exudate produced" (Payne and Cosgrove, 1966, p. 212). Generally, but not always, the site of larval development is in the posterior third of the host's body. I t  is usually found ventrally and the specific site is unrelated to the gonads. Bot flies are found on both male and female hosts in approx- imately equal numbers. Upon emergence of the ma- ture larvae, the wound heals rapidly, with few ap- parent aftereffects. These observations on the life cycle of Cuterebra have been borne out by other in- vestigators (Bennett, 1955; Payne et al.,  1965; Dun- away et al.,  1967). Why is it that numerous workers have reported host castration by bot flies? First, a capsule that su- perficially resembles the testis is formed around a developing bot; this capsule may have been mistaken for a "consumed testis." On occasion, bot flies locat- ed in the scrotum may displace a testis anteriorly andlor dorsally; the larval bot then occupies the scro- tal sac where the casual observer expects to find a testis (see photographs in Timm and Lee, 1981). And finally, bots located in the inguinal region of the fe- male rodent create a pocket of swollen skin that su- perficially resembles a scrotum. Again, the casual observer removing the skin of the host would find bots where testicles were expected, although a more thorough examination within the body cavity would have revealed female reproductive organs. Recent reviews by Kuris (19i4) and Baudoin (1975) provide comprehensive treatment of host castration put into modern evolutionary context. Numerous cases of host castration by parasites have been doc- umented; however, to date there are relatively few cases of vertebrate hosts being castrated and none as a result of parasitism by an arthropod (see Kuris, 1974; Moser and Taylor, 1978). Our work and a sur- vey of the literature provides no evidence to sub- stantiate host castration by bot flies. Bot fly parasit- ism may cause a temporary cessation of reproductive function, particularly in male hosts if the bot dis- places the testis into the abdomen or if larvae me- chanically prevent copulation. We must conclude, however, that parasitic castration is not an "evolved strategy" of bot flies. BAUDOIN,M. 1975. Host castration as a parasitic strategy. Evolution 29:335-352. BENNETT, G. F.  1955. Studies on Cuterebra emas- culator Fitch 1856 (Diptera: Cuterebridae) and a discussion of the status of the genus Cephenemyia Ltr. 1818. Can. J. Zool. 33:75-98. CHANDLER,A. C. ,  AND C. P. READ. 1961. Intro- duction to Parasitology. John Wiley & Sons, N.Y. 822 p. CHENG, T .  C. 1973. General Parasitology. Academ- ic Press, N.Y. 965 p. DALMAT,H .  T .  1942. A new parasitic fly (Cutereb- ridae) from the northern white-footed mouse. J. N.Y. Entomol. Soc. 50:45-59. . 1943. A contribution to the knowledge of the rodent warble flies (Cuterebridae). J. Para- sitol. 29:311-318. DUNAWAY,P. B. ,  J. A. PAYNE, L .  L. LEW'IS, AND J. D.  STORY. 196i. Incidence and effects of Cu-terebra in Peromyscus. J. Mamm. 48:38-5 1. FITCH, A. 	 1857. Third report on the noxious and other insects of the state of New York. Trans. N.Y. State Agr. Soc. 16:315490. GETZ, L. L. 1970. Botfly infestations in Microtus pennsylvanicus in southern Wisconsin. Amer. Midl. Nat. 84:187-197. HENSLEY,M.  S. 1976. Prevalence of cuterebrid par- asitism among woodmice in Virginia. J. Wildl. Dis. 12:172-179. KRULL, W. H. 1969. Veterinary Parasitology. Univ. Kansas Press, Lawrence. 599 p. KURIS, A. M. 1974. Trophic interactions: similarity of parasitic castrators to parasitoids. Quart. Rev. Biol. 49: 129-148. MOSER, M . ,  AND S. TAYLOR. 1978. Effects of the copepod Cardiodectes medusaeus on the latern- fish Stenobrachius leucopsams with notes on hy- percastration by the hydroid Hydrichthys sp. Can. J. Zool. 56:2372-2376. NOBLE, E .  R. ,  AND G. A. NOBLE. 1976. Parasitol- ogy: the Biology of Animal Parasites. Lea & Fe-biger, Philadelphia. 566 p. PAYNE, J. A., AND G. E. COSGROVE.1966. Tissue changes following Cuterebra infestation in ro-dents. Amer. Midl. Nat. 75:205-2 13. PAYNE,J. A, ,  P. B. DUNAWAY, G. D. MARTIN, AND J. D.  STORY. 1965. Effects of Cuterebra angus- tifrons on plasma proteins of Peromyscus leuco- pus. J. Parasitol. 5 1: 1004-1008. SETON, E. T.  1920. Does the Cuterebra ever emas- culate its host? J. Mamm. 1:94-95. TIMM, R. M.,  AND E.  F .  COOK. 1979. The effect of bot fly larvae on reproduction in white-footed mice, Peromyscus leucopus. Amer. Midl. Nat. 101:211-217. TIMM, R. M . ,  AND R. E .  LEE, JR. 1981. Do hot flies, Cuterebra (Diptera: Cuterebridae), emas-culate their hosts? J. Med. Entomol. 18:333-336. WECKER, S. C. 1962. The effects of bot fly parasit- ism on a local population of the white-footed mouse. Ecology 43:561-565. Corresponding Editor: D. J. Futuyma 

Is host castration an evolutionary strategy of bot flies?

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Is host castration an evolutionary strategy of bot flies?

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