Entomopathogenic nematodes to control the hibiscus bud weevil Anthonomus testaceosquamosus (Coleoptera: Curculionidae), above ground and on soil surface

The hibiscus bud weevil (HBW), Anthonomus testaceosquamosus, is a pest of tropical hibiscus (Hibiscus rosa-sinensis). Chemical insecticides are currently used for its management, but environmentally friendly alternatives are needed. In laboratory evaluations, five commercially available entomopathogenic nematodes (EPNs) (Heterorhabditis bacteriophora, Steinernema carpocapsae, S. kraussei, S. feltiae, and S. riobrave) were evaluated. Infested flower buds with either first, second, or third instar larvae were treated with a rate of approximately 500 infective juveniles (IJs) per bud. Two EPN species were selected for further evaluation in greenhouse experiments due to a high larval mortality (S. carpocapsae and S. feltiae). EPNs, alone or with a fire gel that served as a protectant, were applied to HBW-infested plants using a rate of approximately 500,000 IJ m⁻². The effects of foliage-directed applications were also studied in relation to infested fallen buds. There were no effects of the fire gel, but S. carpocapsae showed high HBW larval mortality in both foliage and fallen buds. In a subsequent greenhouse experiment, different rates of S. carpocapsae were tested, including a rate of approximately 428,525 IJ m⁻² and 75%, 50%, and 25% of that initial rate. Effects on larval mortality were rate-dependent with no difference observed between the full rate and 75% of this rate, making the latter rate a cost-effective alternative. This study demonstrates that S. carpocapsae can infect developing HBW larvae inside hibiscus flower buds at the canopy and soil surface levels, where fallen infested buds are usually free of control.