Comparison of virulence, reproductive potential, and persistence among local Heterorhabditis indica populations for the control of Temnorhynchus baal (Reiche & Saulcy) (Coleoptera: Scarabaeidae) in Egypt

Abstract

The scarab beetle, Temnorhynchus baal (Reiche & Saulcy) (Coleoptera: Scarabaeidae), becomes a key pest of strawberry, especially after increasing its cultivated area and economic importance in Egypt. Few entomopathogenic nematode (EPN) species/strains were tested against this pest, where only a foreign species had good effect comparable to the native populations tested previously. Thirty-eight indigenous Heterorhabditis indica populations were tested against the most damaging, third instar larvae of H. baal in two soil types, where strawberry cultivation prevails. The corrected mortality induced by indigenous H. indica population in T. baal larvae was (99.52 and 98.57%) for 15 populations in the sandy soil and 23 in loamy sand soil, respectively. Overall average of infective juveniles (IJs) per T. baal larva was about (41,000). The average of emerged nematode-IJs from the infected grubs for the 15 EPN populations in sandy soil, (46,960 IJs/grub), was significantly (P < 0.001) higher than that (36,502 IJs/grub) of 23 EPN populations in loamy sand soil. The insignificant difference was detected in the reproductive capacity among nematode populations in T. baal larvae in sandy or loamy sand soil. A highly significant difference was found among total IJ numbers collected 10, 18, 26, and 30 days post-inoculation in sandy or loamy sand soil. The persistence of the H. indica populations in the soil varied greatly. Obtained results suggest further use of at least ten populations of such indigenous nematodes under field conditions.