Graduate Thesis Or Dissertation
 

Studies on Heterostylum robustum (Osten Sacken) (Diptera : Bombyliidae), a parasite of Nomia melanderi

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  • Heterostylum robustum (Osten Sacken) is the principal parasite of the alkali bee, Nomia melanderi Ckll., one of the most efficient pollinators of alfalfa in the western United States. The purpose of the study was to determine the incidence of parasitism and to investigate the biology of H. robustum. The fly overwinters as a mature larva, pupating in the spring in a cell just beneath the soil surface. The mature pupa moves to the surface, the adult emerges, and the fly leaves to mate and forage. Mating takes place at or near the host nesting site. The adult feeds almost exclusively on alfalfa nectar. Eggs are deposited near or into bee nests by the hovering female. Larval development proceeds through three instars including an active first instar or planidium, which must implant upon the host. Egg laying potential is estimated to be an average of 300 eggs per female per day. The incubation period averaged 9.5 days under simulated nest conditions in the laboratory. Percentages of parasitism by the fly in Oregon varied from less than one percent to nearly 70 percent, averaging eight to ten percent. Factors adversely affecting the survival potential of the parasite are inability of the planidium to contact a host; dessication of and external damage to the ova; predation by native birds; heavy host-flight activity; effect of freezing temperatures on overwintered larvae; and inaccessability of bee holes to ovipositing females. Other factors in favor of . the host include extensive area of the nesting site and recently established bee beds. A literature search and correspondence with specialists were conducted to establish the taxonomic position and distribution of H. robustum. Sections on "description" and "methods and apparatus" are included. Comparisons and contrasts to related taxa and observations by other workers are mentioned where pertinent. An addendum, which covers work done since the study was completed to date, follows the main text.
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file details EppleyRichardK1964.pdf 2017-08-16 Pubblico Scaricare