The stem weevil complex is among the most important groups of insect pests affecting oilseed rape crops, with Ceutorhynchus napi and Ceutorhynchus pallidactylus frequently occurring under field conditions. Since both species are generally monitored using the same trapping tools and are considered together in crop protection practice, their coexistence may influence infestation assessment at both crop and plant level. The aim of this study was to evaluate the coexistence of C. napi and C. pallidactylus in oilseed rape and to assess its implications for infestation assessment and protection measures. The research was conducted in 2025 and 2026, during the period from 27 February to 3 April, in two locations from western Romania, using a semi-early hybrid. The methodology included adult monitoring with yellow traps, manual plant assessments using a metric frame, and species identification with portable and digital microscopy. One experimental place was assessed under untreated conditions, while the second was monitored under phytosanitary protection. The originality of the study lies in documenting the frequent coexistence of the two species under practical crop conditions and in relating this coexistence to the localization of plant damage. The results showed a slight dominance of C. pallidactylus in yellow-trap captures in both years, while co-infested plants represented 64.8% of the total assessed material. The most frequent symptom recorded at plant level was splitting towards the stem base, whereas galleries in petioles and damage in secondary branches were less frequent. Mean larval presence associated with C. napi was consistently higher than that recorded for C. pallidactylus, indicating a more persistent internal stem attack. Although adult captures declined strongly in the treated place after insecticide application, coexistence remained evident in both places and in both years. The results highlight the need to combine trap monitoring with direct plant assessment for a more accurate interpretation of stem weevil infestation in oilseed rape.

oilseed rape, stem weevils, Ceutorhynchus napi, Ceutorhynchus pallidactylus, coexistence, co-infestation, yellow traps, plant damage

agronomy

Presentation: poster