Environmental tolerance of infective juveniles differs among nematodes arising from host cadaver versus aqueous suspension

Authors: GULZAR, SEHRISH - University Of Faisalabad; USMAN, MUHAMMAD - University Of Faisalabad; WAKIL, WAQAS - University Of Faisalabad; GULCU, BARIS - Duzce University; HAZIR, CANANA - Adnan Mederes University; KARAGOZ, MEHMET - Adnan Mederes University; HAZIR, SELCUK - Adnan Mederes University; Shapiro Ilan, David

Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/3/2020
Publication Date: 8/12/2020
Citation: Gulzar, S., Usman, M., Wakil, W., Gulcu, B., Hazir, C., Karagoz, M., Hazir, S., Shapiro Ilan, D.I. 2020. Environmental tolerance of infective juveniles differs among nematodes arising from host cadaver versus aqueous suspension. Journal of Invertebrate Pathology. 175: 107452. https://doi.org/10.1016/j.jip.2020.107452.
DOI: https://doi.org/10.1016/j.jip.2020.107452

Interpretive Summary: Entomopathogenic nematodes (also known as beneficial nematodes) are small round worms that are natural bio-insecticides. Unlike some nematodes that are harmful to plants or mammals these beneficial nematodes only kill insect pests in a safe and environmentally-friendly manner. Beneficial nematodes are applied to control insect pests in a variety of cropping systems. The nematodes are usually applied in water (aqueous suspension) using standard agricultural spray equipment. However, the nematodes can also be applied using the “cadaver” approach. In the cadaver approach, the nematodes are applied to the target site in their infected host cadavers (the dead insects with the nematodes growing inside), and pest suppression is achieved by the progeny nematodes that emerge. The cadaver approach has been shown to have various advantages over aqueous application including improved nematode dispersal and infectivity. However, potential differences in environmental stress tolerance among nematodes applied in the cadaver approach vs. aqueous approach have not been explored previously. Our objective was to investigate the impact of environmental stress (extremes in temperature and desiccation) on nematodes applied in aqueous vs. the cadaver method. Our findings indicated that cadaver-applied nematodes were superior in stress tolerance to heat and desiccation compared with nematodes applied in water. Therefore, nematodes applied using the cadaver method could be used in a wider range of environmental conditions, and may persist longer, than those applied in standard aqueous applications. Also, the results in the cadaver approach are more representative of natural entomopathogenic nematode ecology. Our results increase the attraction of using the novel cadaver approach in a broad array of cropping systems.

Technical Abstract: Environmental factors such as temperature and desiccation impact the survival and efficacy of entomopathogenic nematodes (EPNs). Most studies on environmental tolerance have focused on EPNs applied in aqueous suspension. Another approach for EPN application is via infected host cadavers. Emergence in host cadavers is also more representative of nematodes in natural populations. In prior studies, certain advantages in fitness have been observed with the cadaver application approach relative to aqueous application, yet the impact of environmental stress on these approaches requires investigation. In this study, we compared the effects of various temperatures (heat and cold) and desiccation intervals (48 and 72 hr) on the survival, virulence and reproductive capacity of Heterorhabditis bacteriophora and Steinernema glaseri when applied via cadaver versus aqueous. In the heat tolerance bioassays, following exposure to 30 ºC, 35 ºC and 37. 5 ºC, nematodes (from both species) in the cadaver treatments exhibited higher survival, and reproductive capacity compared with aqueous application. No survival was observed above 37.5 ºC regardless of species or application approach. In cold tolerance, no differences were observed between the cadaver and aqueous treatments after a sequence of exposures from 10 ºC to -2 ºC. In desiccation assays, following exposure to 85% relative humidity for 2 or 3 days, nematodes (from both species) exhibited higher survival and reproduction in the cadaver treatment than in the aqueous treatment, whereas no differences were observed in virulence. This is the first study to find differential stress tolerance among nematodes emerged from infected host cadavers versus those applied in aqueous suspension. Our findings indicate additional advantages when using the cadaver approach for biocontrol applications, and suggest EPNs existing in natural populations may have broader environmental tolerance than those applied via aqueous suspension.