Salinity and pollution effects on survival and infectivity of Heleidomermis magnapapula (Stichosomida: Mermithidae) for Culicoides variipennis sonorensis (Diptera: Ceratopogonidae)

Abstract

The mermithid nematode parasite Heleidomermis magnapapula Poinar & Mullens was tested for tolerance to MgSO4, NaCl, and dairy waste in water. Significant 24-h adult mortality was observed at 300-400 mM NaCl or MgSO4. Preparasite mortality >24 h was significantly less in 50 mM NaCl (used as control) when compared with plain spring water, NaCl concentrations >100 mM, or MgSO4 concentrations >10 mM. Preparasite infectivity for larvae of Culicoides variipennis sonorensis Wirth & Jones was inhibited at salinities >50 and 150 mM MgSO4 and NaCl, respectively. Adult H. magnapapula survived well at manure concentrations <25%, but preparasite survival and infectivity were poor at manure concentrations >12.5%. In general, tolerance of saline and polluted conditions was in the order adult females > adult males > preparasites. Relative to other aquatic mermithids, H. magnapapula is euryhaline, and its tolerance for salinity and manure pollution matches typical dairy wastewater pond levels where the host larvae are most abundant. Some wastewater pond habitats are too saline or polluted for the nematode to function well, and some relatively pristine C. v. sonorensis habitats, such as desert streams, might be too clean for the parasite. Intolerance of salinity probably explains the lack of the parasite in saline habitats inhabited by C. v. occidentalis.