Field-evolved resistance in Phthorimaea absoluta to abamectin: genetic foundations, female-linked traits, and cross-resistance pattern.

Background: Phthorimaea absoluta (Meyrick) (Lepidoptera: Gelechiidae) poses a significant challenge in tomato cultivation owing to its increasing resistance to various insecticide classes. This study aimed to characterize the resistance of a field-collected P. absoluta population to abamectin, focusing on its genetic aspects and cross-resistance with other chemical groups, and monitoring the frequency of resistance in other populations.

Results: Significant variability in abamectin susceptibility was observed across P. absoluta populations, with resistance ratios ranging from 2.6- (Juazeiro) to 538-fold (Gravatá). Selective pressure with abamectin on the Gravatá population led to a 50-fold resistance increase over 16 generations (h = 0.186). Abamectin resistance in P. absoluta exhibited incomplete recessiveness, female bias and polyfactorial inheritance involving at least seven genes. Field populations showed ≤56% resistance (homozygous) at the diagnostic concentration of 5 mg L, although control failure was not imminent. Cross-resistance ratios to emamectin benzoate and milbemectin were 1 893 000- and 4506-fold, respectively, indicating a shared resistance mechanism.

Conclusion: Phthorimaea absoluta resistance to abamectin in Brazilian populations is notably high, yet few populations are nearing control failure. The resistance pattern, characterized by incomplete recessiveness, polyfactorial inheritance and maternal linkage, underscores the complexity of managing resistance. Additionally, the broad spectrum of cross-resistance with other insecticides suggests diverse mechanisms at play, emphasizing the need for tailored control and resistance management strategies within this insecticide class. © 2025 Society of Chemical Industry.