Abstract:
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 preexposure,
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.
