EFFECT OF PRE-EXPOSURE ON THE INSECTICIDAL AND REPELLENCY PROPERTIES OF Citrus paradisi PEEL ESSENTIAL OIL AGAINST Tribolium castaneum

Although the use of essential oils (EOs) for pest control has gained popularity due to their biodegradability and ecological safety, a major concern regarding their use is stability. Therefore, this aspect deserves empirical studies to enable potential end users to adopt research findings on the pesticidal potential of EOs. This research investigated the insecticidal and repellence impacts of Soxhlet-extracted grapefruit peel (Citrus paradisi Macfad. (Rutaceae) Lane) EO pre-exposed to air for 0, 0.5, 1 and 2 h (before introducing insects) on Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae). The ethanol diluents were initially allowed to evaporate for 15 min in all treatments. Contact toxicity was tested on larval and adult stages at 5 and 15% concentrations of the EO, while repellency was tested at a 5% concentration. The impacts of EO on adult behavioural activity were also observed 24 h after exposure. Grapefruit EO was effective in controlling T. castaneum adults and larvae at higher doses. Exposure periods had an immediate significant effect on larvae and adult mortalities 1 and 6 h after the insects were introduced. At a 15% concentration, EO with a 0 h pre-exposure period had significantly higher adult and larva mortalities after 6 h than those of 0.5, 1 and 2 h pre-exposure. Regardless of oil pre-exposure, insects were repelled, especially in test periods between 12 and 30 min. Therefore, grapefruit EO could be formulated for increased stability when an immediate impact is needed.