Bioactivity of five monoterpenoid vapours to Tribolium confusum (du Val) (Coleoptera: Tenebrionidae)

Five monoterpenoids (terpinen-4-ol, 1,8-cineole, linalool, R-(+)-limonene and geraniol) were tested in vapour form against different stages of Tribolium confusum. Terpinen-4-ol (with LC50 values ranging between 1.1 and 109.4 μl/l air), (R)-(+)-limonene (with LC50 values ranging between 4 and 278 μl/l air) and 1,8-cineole (with LC50 values ranging between 3.5 and 466 μl/l air) were the most toxic to all stages tested, followed by linalool (with LC50 values ranging between 8.6 and 183.5 μl/l air) while the least toxic monoterpenoid tested was geraniol with LC50 values ranging between 607 and 1627 μl/l air. In all cases, except for geraniol, third-instar larvae were the most susceptible stage and 3-day-old eggs most tolerant. Apart from the observed direct toxicity, exposure of females to the vapours led in some cases to lower fecundity and egg hatchability. All monoterpenoids tested revealed insect growth regulator (IGR)-like properties when applied to 3-day-old pupae, producing adultoids and deformed adults.