The parasitoid wasp Protaphidius nawaii parasitizes the aphid Stomaphis japonica, which is obligatorily attended by several species of ants of genus Lasius. Subgenus Lasius or Dendrolasius ants use different defense strategies to protect the aphids that they attend (Lasius, shelter building; Dendrolasius, aggressive attack). We performed molecular phylogenetic analysis based on partial mitochondrial DNA sequences of P. nawaii and found that the parasitoid wasp consists of two highly differentiated genetic lineages. Although these two lineages distributed sympatrically, one tends to parasitize aphids attended by ants of subgenus Lasius, and the other parasitizes aphids attended by ants of subgenus Dendrolasius. The two lineages of P. nawaii appear to exhibit different oviposition behaviors adapted to the different aphid-protection strategies of the two ant subgenera.
Keywords: Aphidiinae; ant–aphid mutualism; ant–parasitoid interaction; earthen shelters; host specificity; oviposition behavior; parasitism.