Evol Ecol Res 5: 397-409 (2003)     Full PDF if your library subscribes.

Effects of a parasite mite on life-history variation in two grasshopper species

David H. Branson*

Ecology Center, Utah State University, Logan, UT 84322, USA

Address all correspondence to David Branson, USDA-ARS, 1500 N. Central Avenue, Sidney, MT 59270, USA.
e-mail: dbranson@ars.usda.gov


Parasites often have large effects on the life-history patterns of their hosts. There is a need to examine how observed life-history patterns of parasitized organisms under field conditions fit theoretical predictions. I conducted a field experiment to examine the effects of an ectoparasitic grasshopper mite on survival and reproductive allocation in two grasshoppers with different life-history characteristics, Melanoplus sanguinipes and Ageneotettix deorum. Proportional survival was lower in mite-parasitized A. deorum during the period of mite parasitism, but not in M. sanguinipes. As predicted in response to a short-lived parasite, females in both species had reduced initial and total reproduction. Egg production declined by 39–44% with mite parasitism in the two species of grasshoppers studied. Parasitized females of both species completed development of a lower percentage of ovarioles initiating development. Future reproduction of A. deorum females was unaffected by parasitism. However, future reproduction of parasitized M. sanguinipes remained lower at the end of the experiment, indicating parasitism had an effect on reproduction up to 40 days after mite parasites left M. sanguinipes females. There were no interactions between population density and mite parasitism on reproductive allocation or survival in M. sanguinipes. Parasitized females of both species appeared to differentially allocate resources in response to parasitism. The reduced reproduction in parasitized individuals probably resulted from the inability of grasshoppers to increase resource intake to compensate for the direct or indirect costs of parasitism.

Keywords: Eutrombidium locustorum, Melanoplus sanguinipes, parasitism, reproductive allocation.

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