D3146: Effects of insect growth regulators on ambrosia beetles (Coleoptera: Curculionidae)

Ambrosia beetles (Xylosandrus spp.) are pests of woody ornamental nurseries. In spring, beetles emerge from the trees in the woods and attack young trees in the nurseries. The female beetles bore through the softwood of the tree, settling in the heartwood where they begin carving galleries. The beetles do not consume the wood, which further minimizes their insecticide exposure. Pyrethroid insecticides are currently used as preventative sprays to repel invading females. Insect growth regulators (IGRs) are known to affect the egg hatch once the adults are exposed (referred to as transovarial activity), which has been reported in several insects, including beetles. Little is known if IGRs can affect the egg hatch if the ambrosia beetle adults were exposed. In 2019, and 2021, studies were conducted to determine the effects of IGRs compared with the efficacy of permethrin against ambrosia beetles. Results showed that novaluron and azadirachtin as stand-alone treatments did not reduce the numbers of ambrosia beetle attacks and emerging ambrosia beetles from the bolts compared with permethrin treatment. Pearson’s correlation analysis showed that the numbers of attack holes and emerging ambrosia beetles from the bolts were significantly correlated. Still, the numbers of attack holes and the ambrosia beetles per attack hole were not significantly associated.