Mermithid parasitism, protein turnover and vitellogenesis in the desert locust, Schistocerca gregaria forskål

Abstract

1. 1. Using polyacrylamide disc electrophoresis, eight soluble protein fractions were demonstrable in measurable amounts within the yolk of Schistocerca gregaria. 2. 2. Female locusts were infected 3 days after their imaginal moult with equal doses of Mermis nigrescens ova and electropherograms of their haemolymph and fat body proteins were compared with a group of uninfected (control) females. Effects of the parasite upon host protein turnover were appraised in relation to the host's gonotropic cycle. 3. 3. The nematode caused only a sporadic depletion of vitellogenic and non-vitellogenic protein fractions before and during the vitellogenesis period of controls (initial 2 weeks' infection). The ability of the terminal oocytes to sequester vitellogenic proteins from the host haemolymph was impaired by the parasite, so vitellogenesis commenced but was not completed in infected hosts. 4. 4. At 3 weeks' infection, haemolymph protein fractions were significantly diminished (cf. controls) by parassitism but were not so depleted 3 days later. Concurrently, terminal and penultimate oocytes of infected locusts were resorbed. 5. 5. Effects of the nematode on the insect's fat body soluble proteins preceded analogous changes in haemolymph protein fractions. Two weeks after infection, ten of seventeen soluble protein fractions were significantly depleted in the fat bodies of infected locusts (cf. controls). Three weeks after infection, only six fat body protein bands were significantly depleted in infected insects (cf. controls) whilst four such protein fractions were present at significantly higher levels than in the controls. 6. 6. The nematode stimulates catabolism and/or suppresses anabolism of proteins by the host fat body, to provide a dietary source of amino acids within the haemolymph. This effect of M. nigrescens parasitism upon protein turnover in the locust is discussed in relation to host vitellogenesis, growth requirements of the developing parasite and possible involvement of the host endocrine system.