Lethal and sublethal effects of novaluron, a novel insect growth regulator, on annual bluegrass weevil, Listronotus maculicollis Kirby, lifestages in turfgrass

The development of pyrethroid resistance within annual bluegrass weevil (ABW), Listronotus maculicollis (Kirby), a severe pest of golf course turfgrass in eastern North America, has created a dire need for alternatives to conventional insecticides. This study assessed the efficacy of novaluron, a recently registered benzoylphenyl urea insect growth regulator which inhibits chitin synthesis in developing larvae, as an alternative to conventional neurotoxic insecticides. Field trial treatments were designed to assess the effect of application timing in relation to population development stages, including peak overwintering adult emergence and early-instar (stem-boring) and late-instar (soil-dwelling) larvae. Novaluron was effective at all timings, even when larvae were not yet present (overwintering adult peak). In laboratory assays, novaluron topically applied to adults reduced the recovery of first-instar larvae by 91%–98% and 0%–43% in 2020 and 2021, respectively. Significant ovicidal activity was also observed with reductions of 67%–85% and 35%–68% in 2020 and 2021 trials, respectively. Females treated with 9.3 L ha⁻¹ novaluron experienced reduced fecundity over 8 weeks (52%), though weekly reductions were only significantly different from controls in the first week after exposure. Novaluron-treated adults resumed oviposition after being transferred to untreated turf, suggesting potential recovery from exposure. These studies demonstrate novaluron's effectiveness against a wide range of larval instars which should facilitate flexible application timing in field settings. However, the transient effects observed on adults in laboratory studies may reduce novaluron's reliability as an adulticide.