Nonlethal ectoparasitism of the mycophagous nematode Filenchus discrepans (Nematoda: Tylenchidae)

Abstract

Filenchus discrepans ingested hyphal contents of Botrytis cinerea without killing the hyphal cells that they fed on. Individuals of this nematode penetrated B. cinerea hyphae with their stylets, after which intense pulsation of the median bulb and dorsal gland duct followed (indicating salivation). In addition, light pumping of the median bulb (indicating food ingestion) was also observed. Fungal cells continued to show cytoplasmic streaming while the nematode ingested hyphal contents. Moreover, actively growing tips of the hyphae usually continued their growth during and after cytoplasm ingestion by the nematode. In less active, older hyphae the penetrated tip cells stopped growing during nematode feeding. However, the majority of the tip cells resumed growth after feeding by the nematode. The hyphal tips often exhibited an abnormal shape during nematode feeding and gradually regained normal shape and growth afterwards. The growth rate of hyphal tip cells decreased to less than 10% compared with the growth of intact hyphal tip cells during attack by F. discrepans, which often fed on a hyphal cell for up to 3 h. Filenchus discrepans propagated well in B. cinerea cultures and their population growth rate ranged between six- and 11-fold 1 month after incubation. This is the first report of nonlethal ectoparasitism by a mycophagous nematode, showing that the nematode does not kill fungal cells during and after feeding.