Islands constitute natural laboratories for the study of evolutionary and ecological processes
due to their discrete and isolated nature. Island biotas tend to be species–poor and
disharmonic compared to the mainland; typically, interspecific competition is low, and entire
groups of predators, parasitoids or pathogens are absent from their biotas, so the ecological
space is often not fully saturated. Consequently, species from island assemblages often use a
wider range of resources than their counterparts from the source mainland. Here, I investigate
whether island parasitoid communities have proportionally more generalist species than their
source mainland, and which factors determine island community structure. These questions
were approached using data on the distribution of Ichneumonoidea (Hymenoptera) species
worldwide and with data from a survey conducted in the Macaronesian region. Prior to the
global analyses, I assessed whether islands and archipelagos follow the same species–area
relationship, and identified which islands have comparable inventories. Globally, islands
have proportionally more idiobionts (i.e. generalists) than continental areas. However, there
is a latitudinal gradient in the level of generalism of island parasitoid faunas that correlates
with some environmental factors and island characteristics; the species pool is the most
important determinant of island community structure, together with temperature (for
braconids) or biogeographical region (for ichneumonids). Host and parasitoid larvae
collected in different islands of the Macaronesian region and adjacent mainland were
assigned to Molecular Operational Taxonomic Units using a protocol based on host
dissection and DNA barcoding. At this scale, mainland faunas have proportionally more
koinobiont species and island communities have a greater proportion of idiobionts. Although
overall parasitism rates were similar between islands and mainland, islands had higher
idiobiont parasitism rates than expected by chance. In summary, results from this thesis
indicate that indeed island parasitoid faunas are biased towards generalist species
