Survivorship of Caenorhabditis japonica dauer larvae naturally associated with the shield bug, Parastrachia japonensis

Abstract

Caenorhabditis japonica forms an intimate association with the shield bug Parastrachia japonensis. Quiescent dauer larvae (DL) are always found on female shield bugs aggregating on leaves in reproductive diapause throughout the year until the next reproductive period in June, which suggests long-term survival of DL on the shield bugs without propagation. To understand the morphological significance of DL on the shield bug, cryo-scanning electron microscopy (Cryo-SEM) was performed. Cryo-SEM observation revealed that the DL appeared to be partly desiccated, but their lateral alae were not shrunken as seen in the anhydrobiotic nematode Aphelenchoides besseyi. To test DL survivorship on the shield bug, we collected bugs from the field and kept them under several experimental conditions for 3 months. When bugs were kept at 100% relative humidity (RH), very few nematodes were detected. When bugs were exposed to 97% RH using a K2SO4-saturated solution, a small number of nematodes (19 DL/bug) was detected and DL survival was low (33%). At 90% RH in a wooden box, more nematodes (67 DL/bug) were detected and survival was high (54%). These data suggest that DL are able to survive several months on shield bugs by entering a partially desiccated quiescent form.