Assessing Insect Growth Regulator Resistance Using Bioassays: A Systematic Review and Meta-Analysis of Methoprene and...

This systematic review and meta-analysis aims to: (1) characterize the distribution of published inhibition of emergence (IE₅₀, IE₉₀, and IE₉₅) reference values for pyriproxyfen and methoprene in Culex pipiens [L.], Aedes aegypti [L.], and Aedes albopictus [Skuse]; (2) generate combined-effect IE values using a DerSimonian and Laird (DL) random-effects model to establish benchmarks for future resistance assessments; and (3) compare these combined-effect IE values with previously published literature. A systematic search was conducted in PubMed, SciELO, J-STAGE, and Google Scholar up to 10 February 2025, following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Eligible studies were primary, peer-reviewed literature that aligned with World Health Organization (WHO) protocols for insect growth regulator (IGR) resistance testing, specifically those reporting susceptible reference IE values from continuous immersion dose-response bioassays analyzed using probit regression. A total of 72 unique studies that aligned with WHO protocols were assessed for publication bias using a funnel plot and Egger's regression. Sensitivity and subgroup analyses were conducted to evaluate individual study contributions to the overall combined effect. Heterogeneity (I²) and combined effect values were estimated for 18 different species/active ingredient/IE concentration subgroup pairings. Heterogeneity (I²) ranged from 29.32 to 99.78% between the 18 subgroups, indicating inconsistency within the literature. The DL combined effect IE₅₀ varied from 0.048 ppb for Cx. pipiens exposed to pyriproxyfen to 1.818 ppb for Ae. albopictus exposed to methoprene. A certainty analysis indicated that 1 combined effect value exhibited high certainty, 8 out of 18 pairings were moderately certain, 6 exhibited low certainty and 3 exhibited very low certainty. The main causes of uncertainty (ranked) were inconsistency between studies, imprecision of the combined effect size, and possible publication bias. Our findings indicate that (1) robust DL combined effect IE₅₀ values could be established for all species/IGR pairings, providing essential benchmarks for future resistance assessments; (2) substantial heterogeneity among susceptible laboratory colonies complicates resistance detection in field-collected mosquitoes; and (3) a significant portion of the literature relies on reference mosquito strains that are likely not fully susceptible, further complicating resistance detection. This study was not registered and was supported by the North Shore Mosquito Abatement District.