Isolation, identification and virulence of the local entomopathogenic nematode Heterorhabditis indica in the southern Philippines against the sugarcane white grub, Leucopholis irrorata (Chevrolat) (Coleoptera: Scarabaeidae)

Abstract

Entomopathogenic nematodes (EPNs) are used as biocontrol agents of diverse insect pests. EPN diversity study was conducted in the southern Philippines (Cotabato province), encompassing a total of 5 municipalities with 25 Barangays (villages) for the potential biocontrol of the sugarcane white grub, Leucopholis irrorata. Of the 25 soil samples collected, only 5 harbored nematodes by using the Galleria-baiting technique. Through preliminary assessment of morphological data and confirmation analysis of D2-D3 segments of the 28S rDNA, locally-isolated nematodes were identified as Heterorhabditis indica (1 isolate), Metarhabditis rainai (3 isolates) and Oscheius rugaonensis (1 isolate). Moreover, the virulence of the H. indica (KRR4) infective juveniles (IJs) isolated from sugarcane soils was assessed against the target local insect pests, L. irrorata grubs under laboratory conditions. The mean mortality (%) caused by H. indica isolate KRR4 on L. irrorata at different dosages (10, 50, 100, 150, 200 and 300 IJs/grub) ranged from 37.5–100% after 24 h of exposure. The LD50 required to kill 50% of the L. irrorata grub population was 5.5 ± 2 IJs/grub. The virulence indicated that local H. indica