Molecular Identification of Entomopathogenic Nematode Isolates from the Philippines and their Biological Control Potential Against Lepidopteran Pests of Corn

Abstract

In search for local entomopathogenic nematode (EPN) species as a biological control agent of lepidopterous insect pests of corn, a survey for EPN in the major islands in the Philippines was conducted. Seven EPN populations from 279 soil samples were isolated using Ostrinia furnacalis, the key target insect pest of corn in the country, as bait. Analysis of the ITS1-5.8S-ITS2 ribosomal DNA sequence revealed the presence of Steinernema abbasi, Steinernema minutum, Steinernema tami, and Heterorhabditis indica. The pathogenicity of these EPN was tested in Ostrinia furnacalis, Spodoptera litura, and Helicoverpa armigera larvae under laboratory conditions. All the EPN isolates were pathogenic to the lepidopteran species with, H. indica PBCB and S. abbasi MBLB exhibiting the highest virulence (88%-99.33% and 90%-100% mortality, respectively) at 48 hr post infection (HPI) and thus, further studies were done on these two EPN. The highest penetration rate at 48 HPI was observed in H. armigera infected with S. abbasi MBLB (28.15%), while the lowest was in O. furnacalis infected with H. indica PBCB (14.25%). Nonetheless, based on LC 50 at 48 HPI, H. indica PBCB was most virulent to S. litura (8.89 IJ per larva), but not significantly different from O. furnacalis (10.52 IJ per larva). Steinernema abbasi MBLB was most virulent to O. furnacalis (10.98 IJ per larva), but not significantly different to S. litura (17.08 IJ per larva). LT 50 estimates showed that O. furnacalis was significantly the most susceptible to H. indica PBCB (21.90 hr) and S. abbasi (21.18 hr). Our results suggest that H. indica PBCB and S. abbasi MBLB are good candidates as biological control agents against these insect pests of corn. Moreover, O. furnacalis as alternative bait for EPN was discussed. To date, this is the most extensive research on Philippine EPN, comprised of wide sampling coverage, molecular identification and bioefficacy assays.

Survey and identification of entomopathogenic nematodes in the province of Cotabato, Philippines, for biocontrol potential against the tobacco cutworm, Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae)

“…From a total of 50 soil samples collected from peanut and grassland areas, only 5 harbored nematodes indicating a recovery rate of 10%. This low recovery rate is congruent with several previous studies on EPNs recovery in different surveys worldwide (Caoili et al 2018 andKour et al 2020). Several abiotic and biotic factors may likely influence the recovery of nematodes in the soil such as soil texture, moisture, pH, and vegetation (Abate et al 2018 andCampos-Herrera et al 2019).…”

“…Similar result, H. indica, was reported to be very effective against S. litura under laboratory and field conditions (Gokte-Narkhedkar et al 2019). Caoili et al (2018) likewise reported that H. indica (PBCB), an isolate from Luzon island, Philippines, was highly virulent against S. litura, with percentage mean mortality of 88.67%. However, they had a higher LC 50 value (8.89 IJs/larva) at 48 h post inoculation.…”

“…For instance, S. carpocapsae induced a high mortality against S. litura from tobacco and cotton (Abdel-Razek and Abdelgawad 2007). In the case of H. indica, it was reported to be highly virulent and effective for the control of S. litura larvae (Acharya et al 2020) in corn, cotton, and vegetable crops (Caoili et al 2018).…”

A study on Xenorhabdus and Photorhabdus isolates from Northeastern Thailand: Identification, antibacterial activity, and association with entomopathogenic nematode hosts

“…This result was similar to that reported by Brodie [ 31 ] from Fiji Islands (7.3%), Valadas [ 32 ] from Portugal (6.7%), and Hatting [ 33 ] from South Africa (5%). However, this rate was higher than those reported by Caoili [ 34 ] from the Philippines (2.5%), Majić [ 35 ] from Croatia (2.0%), and Noujeim [ 36 ] from Lebanon (1%). Higher prevalence of EPNs in soil from that determined in the present study was observed by Kanga [ 37 ] from Southern Cameroon (10.4%), Khatri-Chhetri [ 38 ] in Nepal (10.5%), and Malan [ 39 ] in South Africa (17%).…”

A survey of entomopathogenic nematodes and their symbiotic bacteria in agricultural areas of northern Thailand

“…were recovered from citrus orchards in South Africa (Malan et al ., 2011). Steinernema abbasi, S. minutum, Steinernema tami and H. indica were found to be present in the agricultural and forested areas in the Philippines (Caoili et al ., 2018). Including in the present study, S. siamkayai was isolated from the field and horticulture crops.…”