Effect of temperature on survival of Australian entomopathogenic nematodes and their virulence against the Queensland fruit fly, Bactrocera tryoni

Abstract

Entomopathogenic nematodes (EPNs) are commonly used biocontrol agents of insect pests, with a wide range of commercially available isolates targeting specific pests. New isolates are, however, required to improve pest control across a wider range of environmental conditions for target pests, including emerging threats. We assessed the effect of temperature on survival and virulence of 17 Australian isolates of five EPN species (Heterorhabditis bacteriophora, Heterorhabditis indica, Heterorhabditis marelatus, Heterorhabditis zealandica and Steinernema feltiae) against larvae and pupae of the Queensland fruit fly, Bactrocera tryoni. All isolates still infected and killed larvae after infective juveniles (IJ) had been kept without insect hosts at 15 °C, 25 °C or 30 °C for two weeks, indicating their potential to remain viable under field conditions. However, the mean LD50 value ranged from 35 to 150 and was generally lower at 15 °C than at 25 °C and 30 °C. Similarly, after IJs had been kept at 25 °C for 1–3 weeks without insect hosts, all isolates infected B. tryoni larvae, with mean LD50 values ranging from 25 to 144. Interestingly, 15 isolates infected and killed B. tryoni pupae after one week, with a mean LD50 value between 130 and 209, but only two isolates after two weeks, with a mean LD50 value between 229 to 209. No pupal mortality was seen after three weeks. In absence of hosts, EPNs survived longer at 15 °C and 25 °C than at 30 °C. Complete EPN mortality occurred after nine weeks at 30 °C, and after 18 weeks at 15 °C and 25 °C, except for some survival in one S. feltiae isolate (Sf.ECCS). Overall, six isolates of H. indica (Hi.HRN2, Hi.LMI2, Hi.QF6), H. bacteriophora (Hb.HIE), H. zealandica (Hz.NAR1) and S. feltiae (Sf.ECCS) performed best and need further testing as potential biocontrol agents against B. tryoni under semi-field and field conditions.

Effects of storage temperature on viability and virulence of entomopathogenic nematodes Heterorhabditis bacteriophora Poinar, 1976 (Rhabditida: Heterorhabditidae), Steinernema carpocapsae Weiser, 1955 and Steinernema feltiae Filipjev, 1934 (Rhabditida: Steinernematidae)

“…However, studies investigating the differences in the efficacy of EPN after storage at different temperatures for certain periods, as done in this study, are very few (Aryal et al, 2022). Similar to the present study is the study by Aryal et al 2022, who reported using the EPN species isolated from Australia; H. bacteriophora, H. zealandica, H. indica and S. felitae. According to their results, H. zealandica had the highest virulence at 25 and 30°C.…”

“…These studies mostly focused on the virulence effects of EPN on different hosts at different temperatures (Nimkingrat et al, 2013;Ulu & Susurluk, 2014;Baimey et al, 2015;Yan et al, 2020). However, studies investigating the differences in the efficacy of EPN after storage at different temperatures for certain periods, as done in this study, are very few (Aryal et al, 2022). Similar to the present study is the study by Aryal et al 2022, who reported using the EPN species isolated from Australia; H. bacteriophora, H. zealandica, H. indica and S. felitae.…”

Impact of Abiotic and Biotic Environmental Conditions on the Development and Infectivity of Entomopathogenic Nematodes in Agricultural Soils

“…Nematodes that are in anabiosis are more tolerant of extreme temperatures than nematodes that are active under these unfavorable conditions [124]. Nematode strains that are used in the biocontrol of pests of living plants are active at temperatures between 10 • C and 30 • C [146][147][148].…”