Abstract
In central Japan Ganaspis xanthopoda and Asobara japonica commonly parasitize the larvae of frugivorous drosophilids, mainly in montane forests, and urban environments and small groves, respectively. These two parasitoids start reproduction about one month later than their host drosophilids, probably to avoid searching for hosts when host density is low in early spring. It is likely that the local variation in the abundance of these parasitoids and a temporal refuge for their hosts contribute to the persistence of this parasitoid-host community. The forest species, G. xanthopoda, parasitized at least three Drosophila species that are abundant in forests, supporting the hypothesis that parasitoids are better adapted to attack frequently-encountered host species. This parasitoid did not parasitize drosophilid species that are phylogenetically distantly-related to the three host species or less frequent in forests. Benefits of using such species as host would not exceed the costs of evolving virulence to them. Another parasitoid, A. japonica, parasitized various indigenous and exotic drosophilid species including those that it rarely encountered in the field. It is not clear why this species has such a wide host range.
Highlights
How the abundance of a species is determined is one of central issues in ecology
In a previous paper (Mitsui et al, 2007), the Ganaspis individuals that emerged from D. simulans Sturtevant, D. lutescens Okada, D. auraria Peng, D. rufa Kikkawa & Peng, D. suzukii (Matsumura), Scaptodrosophila coracina (Kikkawa & Peng) and S. subtilis (Kikkawa & Peng) were identified as G
In the urban area (Machida), D. simulans was abundant and D. auraria frequent; the former was almost restricted to urban areas, whereas the latter was common in small groves
Summary
How the abundance of a species is determined is one of central issues in ecology. Theoretical studies on the dynamics of interaction in parasitoid-host systems suggest that these systems are stable if there is spatial heterogeneity in parasitism or there are refuges for hosts The community studied is composed of two major parasitoids, Ganaspis xanthopoda (Ashmead) (Hymenoptera: Figitidae) and Asobara japonica Belokobylskij (Hymenoptera: Braconidae), and several species of drosophilids (Nishiharu, 1980; Mitsui et al, 2007; Ideo et al, 2008) For this area, the distribution, abundance and seasonality of the drosophilid flies are well documented (Nishiharu, 1980; Beppu, 2000, 2006; Mitsui & Kimura, 2000a, b; Mitsui et al, 2010), whereas little is known about the ecology of the parasitoids (Mitsui et al, 2007; Ideo et al, 2008). If the frequency of encounter with antagonists fluctuates between generations, generalist host resistance and partially specialist parasitoid virulence are favoured (Lapchin, 2002) In this paper, it was assessed whether these models explain the association of the present parasitoid and drosophilid species
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