0 Mark M Ero Edward L Hamacek Thelma Peek Anthony R Clarke 2010 Australian Journal of Entomology 49 4 324-331 <p><em>Diachasmimorpha kraussii </em>is an endoparasitoid of larval dacine fruit flies. To date, the only host preference study done on <em>D. kraussii </em>has used fruit flies from outside its native range (Australia, Papua New Guinea, Solomon Islands). In contrast, this paper investigates host preference for four fly species (<em>Bactrocera cacuminata</em>, <em>Bactrocera cucumis</em>, <em>Bactrocera jarvisi </em>and <em>Bactrocera tryoni</em>), which occur sympatrically with the wasp in the Australian component of the native range. <em>D. kraussii </em>oviposition preference, host suitability (parasitism rate, number of progeny, sex ratio) and offspring performance measures (body length, hind tibial length, developmental time) were investigated with respect to the four fly species in the laboratory in both no-choice and choice situations. The parasitoid accepted all four fruit fly species for oviposition in both no-choice and choice tests; however, adult wasps only emerged from <em>B. jarvisi </em>and <em>B. tryoni</em>. Through dissection, it was demonstrated that parasitoid eggs were encapsulated in both <em>B. cacuminata </em>and <em>B. cucumis</em>. Between the two suitable hosts, measurements of oviposition preference, host suitability and offspring performance measurements either did not vary significantly or varied in an inconsistent manner. Based on our results, and a related study by other authors, we conclude that <em>D. krausii</em>, at the point of oviposition, cannot discriminate between physiologically suitable and unsuitable hosts.</p>