Influence of soil moisture on survival and oviposition of Romanomermis iyengari a mermithid nematode parasite of mosquitoes.

The oviposition pattern of Romanomermis iyengari (Nematoda: Mermithidae) in relation to the moisture level in the soil was studied by seeding postparasites into two sets of 12 cm soil columns. While one set of the soil column was allowed to dry over a period of 60 days, the other set was maintained at a constant level of 15-20% moisture throughout the soil column. In the soil column maintained at constant moisture level, the postparasites oviposited primarily in the upper 3 cm layer (80-97%). In the soil column which was allowed to dry the percentages of eggs laid in the upper 3 cm layer were 96, 24 and 6 respectively on D20, D30 and D40 after seeding and the moisture levels on respective days were 12, 5 and 3%. On corresponding days the postparasites laid 1, 56 and 42% of the eggs in the lower most layer (9-12 cm) and the moisture levels were respectively 15, 10 and 9%. The results indicate that the adult nematodes migrated towards the bottom layer of the soil and laid eggs as the moisture of the upper layers decreased.