Routine insecticide regimes restructure flower-inhabiting thrips on star fruit: suppression of Megalurothrips typicus , resilience of Thrips levatus (Thysanoptera: Thripidae)

Routine agrochemical regimes are pervasive in tropical perennial crops, yet their ecological consequences remain poorly understood. We examined how nonselective insecticide exposure, arising from routine crop protection, shapes species composition, phenology, and population regulation of 2 co-occurring thrips, Megalurothrips typicus Bagnall and Thrips levatus Bhatti (Thysanoptera: Thripidae), in star fruit (Averrhoa carambola L.). We compared a sprayed commercial farm with an unsprayed research farm, combining weekly inflorescence sampling with soil emergence trapping, to track flower-infesting and emerging thrips. Results showed that routine insecticide applications, though targeting other pests, generated chronic nontarget exposure for flower-inhabiting thrips, acting as a strong selective filter. This strongly suppressed M. typicus (>70% to 80% in flowers; >80% in emergence), whereas T. levatus remained demographically stable. Within-species life-stage synchrony persisted, but interspecific synchrony collapsed under spraying; phenology was delayed or destabilized, indicating fragmented timing. The natural male-biased emergence of M. typicus nearly disappeared, consistent with greater male sensitivity in soil-associated stages. Emergence patterns indicated soil pupation in both species, with residues likely elevating M. typicus pupal mortality. Despite shifts in composition and timing, density dependence remained concentrated at the adult-larva transition, with parallel slopes across farms, indicating preserved intrinsic feedbacks, despite chemical pressure. Chronic nontarget insecticide exposure thus restructures flower-inhabiting thrips by suppressing sensitive species, fragmenting phenology, and favoring a tolerant competitor while leaving density-dependent regulation intact. These findings highlight the need for species-specific, phenology-informed management strategies to prevent pesticide-driven species replacement and limit tolerant pest dominance in star fruit and comparable evergreen tropical crops.