Entomopathogenic nematodes control Anthonomus testaceosquamosus (Coleoptera: Curculionidae) at the canopy and soil surface levels

The weevil Anthonomus testaceosquamosus is a pest of tropical hibiscus, whose management currently relies on chemical control. More environmentally friendly alternatives are needed, such as the use of entomopathogenic nematodes (EPNs). Initially, five commercially available species of EPNs were used under laboratory exposing individual flower infested buds to a uniform rate of EPNs (Heterorhabditis bacteriophora, Steinernema carpocapsae, S. kraussei, S. feltiae, and S. riobrave) and including the three larval instars as an additional factor. Two species were selected due to a higher larval mortality across different larval instars (S. carpocapsae and S. feltiae) and were used in a greenhouse trial where applications of EPNs were done on individual plants, also testing the benefits of using Barricade® as a protectant. The effects of the foliage-directed applications were also studied in relation to fallen infested buds. There were not significant effects of Barricade®, but S. carpocapsae showed greater larval mortality in both foliage and fallen buds. An additional greenhouse experiment was done using four different rates of S. carpocapsae, a high rate, three quarters, half and a quarter of that high rate, also checking for the effects of foliar applications on fallen infested buds. Effects on larval mortality were rate dependent with not significant differences between the full rate and three quarters of this rate. EPNs can infect the developing larvae of the A. testaceosquamosus inside flower buds at the plant foliage level, but also at the surface level, where fallen infested buds are usually found.