Host species of larvae contribute to intraspecific variation of deutonymphs - a case study of Allothrombium fuliginosum (Trombidiformes: Trombidiidae) parasitizing aphids.

Terrestrial parasitengone mites (Prostigmata: Parasitengona) are known for their complex life cycles, with active forms confined to larvae, deutonymphs, and adults, and quiescent proto- and tritonymphal stages. Knowledge of the host range of parasitic larvae of most species is still limited, but it is likely that host choice and suitability may influence intraspecific variation of subsequent developmental instars. In this study we assessed the variation of morphometric traits in unfed deutonymphs of Allothrombium fuliginosum which developed from larvae that had parasitized four different aphid hosts: Acyrthosiphon pisum, Aphis sambuci, Macrosiphum rosae and Hyadaphis sp. Analysis of 48 morphometric traits in 80 deutonymphs revealed significant differences between host groups in 19 traits, with M. rosae contributing the most to observed variability. Principal component analysis showed some distinct clustering of deutonymphs according to the host species parasitized by larvae. The smaller, with respect to basic body measurements, deutonymphs developed from larvae that parasitized M. rosae, despite the overall larger body size of this host. Thus, factors other than host size influence the morphology of mites. The findings enhance our understanding of host-parasite interactions and highlight the need for further insight into sources of intraspecific variability within terrestrial Parasitengona.