Water mites as parasites of Hemiptera. What is their role in the interactions between native and alien Corixidae?

Abstract

The invasive species Trichocorixa verticalis verticalis (TVV) is originally from North America and has become the dominant Corixidae species in saline wetlands in the south-western Iberian Peninsula. We report on field studies and laboratory experiments which compare infection levels, prevalence and PO (Phenoloxidasa) activity of parasitic water mites between TVV and native Hemipterans in Doñana, and consider the implications for the success of the invasion by TVV. We conducted a laboratory experiment to infect different hemipteran species including TVV with the mite Eylais infundibulifera at 5 and 10 g/l salinity. We quantified Phenoloxidase (PO) activity, a key immune response in insects. PO and prevalence of mites were also quantified in field samples collected from Doñana. The effects of parasitism on the immune response of species studied (Sigara lateralis; S. scripta; S. stagnalis; Corixa affinis and TVV) as indicated by a decrease of PO activity were significant but varied between species. Field data show corixids were much more affected by water mites than other aquatic insects in Doñana ponds., and that TVV suffers higher infection levels by mites than native corixidae. These data are supported by higher infection rates for TVV in laboratory experiments. In contrast to "enemy release", our results suggest that the invasion success of TVV in natural wetlands of low salinity may be limited owing to a higher susceptibility to parasitic mites compared with native species. TVV is highly dominant in wetlands too saline for mites.