Lethal and Sublethal Effects of Contact Insecticides and Horticultural Oils on the Hibiscus Bud Weevil, Anthonomus testaceosquamosus Linell (Coleoptera: Curculionidae)

Simple Summary The invasive hibiscus bud weevil (HBW), Anthonomus testaceosquamosus Linell (Coleoptera: Curculionidae), has presented a challenge to ornamental nurseries in Florida since its arrival in 2017. Hibiscus flowers drop from plants because of HBW feeding and oviposition, which results in plants that are unattractive and subsequently not purchased by consumers. To help growers manage the HBW, we measured the lethal and sublethal effects on HBW adults caused by 21 different insecticide and horticultural oil products. Laboratory Experiments: Horticultural oil products only caused mortality when they were directly sprayed on HBW adults. Diflubenzuron, pyrethrins, spinetoram plus sulfoxaflor, and spirotetramat were selected for further analysis in Contact Toxicity Experiments and Greenhouse Experiments because these products caused either significant mortality and/or a reduction in feeding and oviposition in HBW adults. Contact Toxicity Experiments: Pyrethrins, spinetoram plus sulfoxaflor, and spirotetramat were highly toxic to HBW adults. Greenhouse Experiments: Pyrethrins application significantly reduced HBW adult feeding/oviposition on, and the number of larvae within, hibiscus buds. We recommend that HBW infestations be managed with rotations of diflubenzuron, pyrethrins, spinetoram plus sulfoxaflor, spirotetramat, and horticultural oils, as the rotation of products belonging to different insecticide groups can reduce the risk of resistance development while still providing control. In 2017, the hibiscus bud weevil (HBW), Anthonomus testaceosquamosus Linell (Coleoptera: Curculionidae), was found outside of its native range of Mexico and Texas, infesting hibiscus plants in Florida. Therefore, we selected 21 different insecticide and horticultural oil products to evaluate their effects on the reproductive rate, feeding, and oviposition behavior of the HBW. In laboratory experiments, significant mortality was observed in adult weevils exposed to diflubenzuron-treated hibiscus leaves and buds, and hibiscus buds treated with diflubenzuron contained the fewest number of eggs and feeding/oviposition holes. Among horticultural oil products, significant mortality was only observed in experiments in which adult weevils were directly sprayed (direct experiments). Pyrethrins and spinetoram plus sulfoxaflor reduced the oviposition rate and caused significant mortality in direct experiments. Diflubenzuron, pyrethrins, spinetoram plus sulfoxaflor, and spirotetramat were further tested via contact toxicity experiments and greenhouse experiments. Contact toxicity experiments demonstrated that the tested insecticides (except diflubenzuron) were highly toxic to HBW adults. In greenhouse experiments, only those hibiscus plants treated with pyrethrins had significantly fewer feeding/oviposition holes and larvae within their flower buds when compared to control (water-treated) plants. These results constitute an important first step in the identification of effective chemical control options for the HBW.

Automated summary

The invasive hibiscus bud weevil has posed a challenge to ornamental nurseries in Florida since 2017. Feeding and oviposition by the weevil results in dropped flowers, making the plants unattractive for consumers. In order to help growers manage the weevil, 21 different insecticide and horticultural oil products were tested for their effects on the weevil adults. Some of the tested products showed significant reduction in feeding and oviposition behavior, providing effective control options.