Selected essential oils as insecticides and behaviour-modifying agents of Queensland fruit fly

Introduction: High residual broad-spectrum synthetic pesticides have been used to control tephritid fruit flies, the most economically damaging pest, for many years. Such pesticides cause detrimental effects on human health, non-target organisms, and the environment. These concerns have led to the development of other options, including essential oils (EOs) as agents. The present study investigated EOs as softer toxicants or behaviour -modifying agents against the Queensland fruit fly (Q-fly), Bactrocera tryoni.

Hypothesis: Essential oils have a toxic effect on and/or can modify behaviour of B. tryoni.

Methods: Toxicity was assessed by contact and fumigation assays; behaviour-modifying ability was assessed by oviposition inhibition and four-arm olfactometer assays. Chemical composition of each EO was analyzed by Gas Chromatography-Mass Spectrometry (GC-MS). Gas chromatography-electroantennogram detection (GC-EAD) was used to identify electrophysiologically active compound(s) that might be responsible for repellent activities.

Results: i) Java citronella, lemon-scented tea tree, chamomile, aniseed, citronella grass, yarrow, pennyroyal, and thyme EOs showed contact toxicities with varying degrees (ED50 0.054–0.087 mg/μL) over 24-hours post-exposure. ii) The tested EOs exhibited fumigation toxicities with varying degrees (ED50 3.293–7.258 μL/L air) over 24-hours post-exposure. iii) Pennyroyal repelled significantly both sexes. iv) Aniseed, basil, citronella grass, cumin, java citronella, lemon-scented tea tree, pennyroyal, peppermint and yarrow EOs exhibited significant oviposition inhibition activities. v) GC-MS analysis showed that monoterpenes, monoterpenoids, and sesquiterpenes are the most common compound classes in EOs. vi) GC-EAD analysis identified several electrophysiologically active compounds of basil, aniseed, pennyroyal, thyme, citronella, garlic, and cumin EOs.

Conclusions: Chamomile and garlic EOs exhibited the potential as contact and fumigation toxicants, respectively. The study found pennyroyal as repellent candidate for both sexes and basil, chamomile, citronella, cumin, lemon-scented tea tree, yarrow, and pennyroyal as oviposition inhibitor candidates.