Isocycloseram susceptibility baseline, and control failure likelihood in Leucoptera coffeella (Lepidoptera: Lyonetiidae).

Abstract

The coffee leaf miner is a key pest of coffee in Brazil, controlled mostly by chemical insecticides. The recent introduction of isocycloseram (group 30) requires baseline susceptibility data to support resistance management programs. This study established the baseline susceptibility and monitored the resistance of coffee leaf miner populations to isocycloseram in the main coffee-producing regions of Brazil. Fourteen field populations were collected between June and October 2024 for the baseline assays, while 22 populations were monitored until 2024 and 2025. The bioassays revealed significant geographic variation in susceptibility, with lethal concentration LC50 values ranging 7.5-fold (0.95 to 7.11 mg a.i. L-1). Despite this, all populations remained susceptible, with resistance ratio (RR50) ≤ 1.0, indicating absence of preexisting resistance. The diagnostic concentration bioassays showed consistently high mortality (>90%), confirming continuous susceptibility. Efficacy trials with the label dose (150 mg a.i. L-1) resulted in mortality between 93% and 100%, with negligible probability of control failure. The diagnostic concentrations (LC99 = 39.76 mg a.i. L-1) may be used in future monitoring. The monitoring and the adoption of integrated resistance management strategies are fundamental to preserve the long-term efficacy of this insecticide.