Effects of mermithid parasitism on the haemolymph of the larval blackflies Prosimulium mixtum/fuscum and Simulium venustum

The haemolymph of larvae of Prosimulium mixtum Syme & Davies/P. fuscum Syme & Davies and Simulium venustum Say parasitised by the mermithid nematode Neomesomermis flumenalis was compared with that of unparasitised hosts with respect to protein, amino acid and carbohydrate composition. The mermithid depleted most protein fractions in a non-selective manner in both hosts. In P. mixtum/P. fuscum, the levels of most amino compounds were reduced by mermithid parasitism, but these metabolites were approximately evenly divided into 3 categories (decreased, increased and unaffected by parasitism) in S. venustum. The mermithid caused a significant decrease of haemolymph glucose levels in both host species but did not affect blood trehalose concentrations. These effects of parasitism are discussed in relation to the nematode's nutritional requirements.ADDITIONAL ABSTRACT:Haemolymph of larval Prosimulium mixtum/fuscum and Simulium venustum naturally infected with Neomesomermis flumenalis was compared with that of non-infected hosts. The mermithid depleted most protein fractions in a non-selective manner in both host species. In P. mixtum/fuscum the levels of 21 of the 32 amino compounds were reduced by infection, 5 were increased and 6 were unaltered. In S. venustum the levels of 14 amino compounds were increased, 10 were decreased and 8 remained unaltered. Levels of trehalose were unaffected by infection in both hosts, but blood glucose levels were severely reduced, particularly in P. mixtum/fuscum..