Seasonal occurrence and life cycle of lotus root nematode Hirschmanniella diversa (Tylenchida: Pratylenchidae) in lotus roots in paddy fields

The lotus root nematode, Hirschmanniella diversa Sher (Tylenchida: Pratylenchidae), causes damage to lotus tubers, and thus decreases its economic value. Few studies have elucidated the life cycle of H. diversa, which is essential to optimize control methods. Therefore, we collected H. diversa from lotus roots and investigated its seasonal population fluctuations, female mating rates, stylet, and body lengths to understand its seasonal occurrence and possibly predict its life cycle. Hirschmanniella diversa were sampled from two lotus paddy fields between 2010 and 2012 in Ibaraki Prefecture, Japan. The occurrence of H. diversa increased with time peaking around late August and early September, then depreciating thereafter. The seasonal breeding period determined by quantifying the number of H. diversa females with spermatheca filled with sperm peaked from April until mid-May and decreased subsequently. Furthermore, overwintered adult H. diversa females laid eggs around June, hence possibly mating between April and May. Second-stage juveniles emerged at the beginning of August and continued developing thereafter. The fourth-stage juveniles or adults overwintered in the lotus roots, weed roots, or soil. The population dynamics of H. diversa in lotus roots in paddy fields determined in this study will be useful for development of control strategies.