The volatile organic compounds (VOCs) released from herbivore-infested plants can be used as chemical signals by parasitoids during host location. In this research, we investigated the VOC chemical signals for the parasitoid Aphytis melinus to discriminate between Aonidiella aurantii (California red scale)-infested fruit and non-infested fruit on three different citrus species. First, we identified the chemical stimuli emanating from non-infested and A. aurantii-infested citrus fruits via solid phase microextraction (SPME) and gas chromatography-mass spectrometry (GC-MS) analyses and identified 34 volatile organic compounds (VOCs). The GC-MS analysis showed qualitative and quantitative differences between VOCs emitted from non-infested and infested citrus fruit. Two VOCs, d-limonene and β-ocimene, were significantly increased in all infested fruit, regardless of the fruit species. The response of the female adult A. melinus to olfactory cues associated with A. aurantii infested fruit was evaluated using a Y-tube olfactometer. In two-choice behavioural assays, A. melinus females preferred infested citrus cues over non-infested fruit. Females showed positive chemotaxis toward these VOCs in all tested combinations involving two dosages of synthetic compounds, d-limonene and β-ocimene, except for d-limonene at a dosage of 10 μL/mL. The application of these VOCs may help to enhance the effectiveness of bio-control programs and parasitoid mass-rearing techniques.

Export of Pink Lady apples from Australia has been significantly affected by infestations of adult eucalyptus weevils (Gonipterus platensis Marelli). These weevils cling tenaciously to the pedicel of apple fruit when selecting overwintering sites. As a result, apples infested with live G. platensis adults lead to rejection for export. Since the Montreal Protocol restricted use of methyl bromide as postharvest treatment, it was necessary to consider alternative safer fumigants for disinfestation of eucalyptus weevil. Laboratory experiments were conducted using concentrations of 5, 10, 15, 20, 25, 30, 40, and 80 mg/liter of ethyl formate. Complete control (100% mortality) was achieved at 25-30 mg/liter of ethyl formate at 22-24 C for 24-h exposure without apples. However, with 90-95% of the volume full of apples, complete control was achieved at 40 mg/liter of ethyl formate at 22-24 C for 24-h exposure. No phytotoxicity was observed and after one day aeration, residue of ethyl formate declined to natural levels (0.05-0.2 mg/kg). Five ethyl formate field trials were conducted in cool storages (capacity from 250-900 tons) and 100% kill of eucalyptus weevils were achieved at 50-55 mg/liter at 7-10 C for 24 h. Ethyl formate has great potential for preshipment treatment of apples. Its use is considerably cheaper and safer than already existing fumigants like methyl bromide and phosphine.

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Export celery (Apium graveolens var. dulce) from Australia has been affected by a natural infestation of purple scum springtails (Hypogastrura vernalis). These insects live inside the celery head, contaminating fresh celery, but do not cause any visible damage. As a result, purple scum springtail-infested celery has led to rejection for export with an impact on market value for fresh produce. In this study, fumigation with ethyl formate (EF), phosphine (PH3), and their combination on mortality of purple scum springtails in naturally infested celery was evaluated. Laboratory experiments were conducted using concentrations of 50, 60, and 90 mg·L−1 of EF for 1, 2, and 4 hours; 1, 1.5, 2, and 2.5 mg·L−1 of PH3 for 2, 4, and 6 hours; and 20, 30, and 40 mg·L−1 of EF combined with 1 mg·L−1 of PH3, for 2 and 4 hours at the laboratory temperature 25 °C. Complete control was achieved at 90 mg·L−1 of EF for 2 hours; however, phytotoxicity was observed in celery treated by EF at all concentrations. PH3 at 2.5 mg·L−1 achieved 100% mortality within 6 hours, and no phytotoxicity was evident. Mortality of 100% was achieved also at 30 and 40 mg·L−1 EF combined with 1 mg·L−1 of PH3 for 2 and 4 hours exposure time; however, phytotoxicity occurred with EF alone treatments and with the combination. From these data, we conclude that PH3 alone has potential as a fumigant for the preshipment treatment of celery infested with purple scum springtails.

Introduction Australia has an important role in citrus (Citrus spp., Rutaceae) production in the world, and this production has increased (FAO, 2017). Many pest species such as Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), Aonidiella aurantii, Sasseita oleae (Gomez-Menor Ortega) (Hemiptera: Coccidae), Toxoptera citricada (Kirkaldy) (Hemiptera: Aphididae), Phyllocnistis citrella Stainton (Lepidoptera: Gracillaridae), et al. were observed in WA (Western Australia) citrus orchards (Sonia, 2006). Growers have followed various methods to avoid damage caused by these pests. Biological control is one of these methods (FAO, 2017; Pekas, 2011a; Uygun and Satar, 2008). There are 32 species in the genus Aonidiella Berlese & Leonardi, which is a genus of scale insects in the family of Diaspididae (Hemiptera), the armoured scale insects (Ben-Dov, 2006). California red scale Aonidiella aurantii (Maskell) occurs on numerous host plants throughout the world. They attack different crops such as fruit trees and ornamental plants all over the world, and cause heavy damage to the plants. Individual species infest leaves, fruits, branches, main stems, trunks, and roots. They are distributed throughout the world except in the cold extremes of the Arctic and Antarctic regions (Miller, 2005). California red scale Aonidiella aurantii is one of the most important pests infesting citrus trees in different parts of the world (

An optimum method has been developed for extracting volatile organic compounds (VOCs) which contribute to the aroma of different species of citrus fruit (orange, lemon, lime, and mandarin). Headspace solid phase microextraction (HS-SPME) combined with gas chromatography (GC) coupled with flame ionization detection (FID) is used as a very simple, efficient and nondestructive extraction method. A three phase 50/30 µm PDV/DVB/CAR fibre was used for the extraction process. The optimal sealing time for volatiles reaching equilibrium from whole fruit in the headspace of the chamber was 20, 16, 8 and 16 hours for lemon, lime, mandarin, and orange respectively. Optimum fibre exposure times for whole fruit were 2, 4, 2 and 2 hours for lemon, lime, mandarin, and orange respectively. Three chamber volumes (500, 1000 and 2000 ml) were evaluated for the collection of VOCs with the 500 ml chamber being selected. The 500ml chamber produced the highest quality peak areas and quantity of extracted volatiles. As a result of fruit respiration, the percentage of oxygen (O₂) of all citrus fruit species in 500 ml chamber decreased from 21.8% to 18.8% in the 20 hours sealing time, while carbon dioxide (CO₂) contents increased to 2.9% also in the 20 hours sealing time. The results of this study showed the feasibility of this technique for identifying VOCs from four of the citrus fruit species and its potential as a routine method for physiological studies on citrus fruit or on other fruit species.

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