Susceptibility of white grubs from forestry and sugarcane plantations in South Africa to entomopathogenic nematodes

Abstract

The control of white grub (Coleoptera: Scarabaeidae) pests of sugarcane and forest plantations is difficult due to their cryptic nature and resistance to chemicals. This study evaluated the potential use of entomopathogenic nematodes (EPNs) as an alternative control method. Laboratory bioassays were performed with 12 locally isolated EPN species to determine the susceptibility of third instar larvae of the white grubs Schizonycha affinis Boheman, Pegylis sommeri Burmeister, Monochelus sp. and Maladera sp. 4. Concentration trials to determine lethal dosages for three of the white grub species were performed using Heterorhabditis zealandica Poinar MJ2C. Bioassays were performed to determine whether nematodes could develop inside the cadavers of S. affinis and P. sommeri as these had shown the lowest susceptibility to EPNs. The mortality percentage of the white grubs, although varying significantly, was found to be low for most of the EPN species, except H. zealandica. The highest percentage mortality of white grubs was observed at four weeks post inoculation with the rate of mortality being highest in the first week. Schizonycha affinis had the lowest LD50 of 38 Infective juveniles (IJs) per larva after 28 days, compared to Maladera sp. 4, with 284 IJs per larva, and P. sommeri, with 1035 IJs per larva. The dissection of insect cadavers revealed possible limiting factors for low susceptibility, due to the nematodes and their associated symbiotic bacteria’s inability to infect the insect haemocoel, with no EPNs being found inside some of the cadavers.

Natural infection of white grubs (Coleoptera: Scarabaeidae) with entomopathogenic nematodes in the KwaZulu-Natal province of South Africa

“…In terms of the pathogenicity of the isolated nematodes on third instar larvae of white grubs, Katumanyane et al . (2023) showed that Steinernema fabii provided 63 % mortality of Maladera sp. 4 in soil bioassays.…”

To live free or being a parasite: The optimal foraging behavior may favor the evolution of entomopathogenic nematodes

“…While R. regina is a natural entomopathogen of P. polyphylla, it remains uncertain whether this specificity extends to other white grubs [65]. White grubs exhibit a diverse array of behavioral, morphological, physiological, and immunological defenses, suggesting the possibility of different host preferences [66,67]. Therefore, future research should explore how these attributes influence the foraging behavior of nematodes.…”

Control of the sweet potato weevil (cylas puncticollis) with entomopathogenic nematodes.

“…A lot of work has been done in South Africa, mostly under laboratory environment, Vernon et al (2021), conducted a study in controlling false codling moth (FCM), Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae) using several entomopathogenic nematode (EPNs) and entomopathogenic fungus (EPFs) species, that were identified from soil samples collected from orchards and vineyards throughout the Western Cape province in South Africa. Katumanyane et al (2023), also conducted a study in "Susceptibility of white grubs from forestry and sugarcane plantations in South Africa to entomopathogenic nematodes". He concluded that; the dissection of insect cadavers revealed possible limiting factors for low susceptibility, due to the nematodes and their associated symbiotic bacteria's inability to infect the insect haemocoel, with no EPNs being found inside some of the cadavers.…”