Manjree Agarwal

Analysis of volatiles from stored wheat and Rhyzopertha dominica (F.) with solid phase microextraction–gas chromatography mass spectrometry

BACKGROUND Volatile organic compounds (VOCs) contribute significantly to food flavour and can be used as indicators of quality, age of storage, and hygiene condition of stored products. The VOCs in the headspace of three different samples - healthy wheat, Rhyzopertha dominica, and wheat with R. dominica - were analysed at 25°C by solid phase micro-extraction (SPME) coupled with gas chromatography-flame ionisation detection (GC-FID) and gas chromatography-mass spectrometry (GC-MS). All the experimental conditions were kept consistent except a polar column and a non-polar column were used to assess the differences in volatile fingerprints. RESULTS A total of 114 volatiles were identified by both the polar and non-polar columns, of which 48 were specific to one of the three samples tested. The volatiles were mainly carbonyl chemical compounds such as aldehydes, ketones and alcohols. GC-MS results showed slightly more VOCs were identified from the polar column. The total number for the three samples was 43 from the polar column compared to 39 from the non-polar column. Conversely, 30 VOCs unique to a given sample were identified from the non-polar column compared to 18 from the polar column. CONCLUSION The use of both polar and non-polar columns is essential to capture the full range of VOCs produced by the three specific sample types investigated. The data can form the basis of enquiry into the relationship between storage and grain quality, and insect infestation and grain quality by observing the impact that these circumstances have on the production of volatile organic compounds.

Ethyl Formate: A Potential Disinfestation Treatment for Eucalyptus Weevil (Gonipterus Platensis) (Coleoptera: Curculionidae) in Apples

ABSTRACT 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.

Headspace Solid-Phase Microextraction and Gas Chromatography-Mass Spectrometry for Analysis of VOCs Produced by Phytophthora cinnamomi

Volatile organic compounds (VOCs) from Phytophthora cinnamomi-infected lupin seedlings were collected by headspace solid-phase microextraction (HS-SPME). The sampling was done 28 to 44, 52 to 68, and 76 to 92 h after inoculation (HAI). The HS-SPME samples were analyzed by gas chromatography-flame ionization detector (GC-FID) to assess the differences in volatile compounds between the P. cinnamomi-infected lupin seedlings and the control. Three specific peaks were identified after 52 to 68 h with the infected lupin seedlings, at which time there were no visible aboveground symptoms of infection. Subsequently, the VOCs of five different substrates (V8A, PDA, lupin seedlings, soil, and soil + lupin seedlings) infected with P. cinnamomi and the corresponding controls were analyzed by gas chromatography-mass spectrometry (GC/MS). A total of 87 VOCs were identified. Of these, the five most abundant that were unique to all five inoculated substrates included: 4-ethyl-2-methoxyphenol, 4-ethylphenol, butyrolactone, phenylethyl alcohol, and 3-hydroxy-2-butanone. Therefore, these metabolites can be used as markers for the identification of P. cinnamomi in different growing environments. Some VOCs were specific to a particular substrate; for example, 2,4,6-rrimethyl-heptanes, dl-6-methyl-5-hepten-2-ol, dimethyl trisulfide, 6,10-dimethyl- 5,9-undecadien-2-ol, and 2-methoxy-4-vinylphenol were specific to P. cinnamomi + V8A; heptanes and 5-methyl-3-heptaneone were specific to P. cinnamomi + PDA; 3-methyl-1-butanol, ethyl acetate, 2-methyl-propanoic acid, ethyl ester, and ethyl ester 2-methyl-butanoic acid were specific to P. cinnamomi-inoculated lupin seedlings; and benzyl alcohol and 4-ethyl-1, 2-dimethoxybenzene were only detected in the headspace of inoculated soil + lupin seedlings. Results from this investigation have multiple impacts as the volatile organic profiles produced by the pathogen can be utilized as an early warning system to detect the pathogen from contaminated field soil samples. Data from this investigation have also illuminated potential metabolic pathways utilized by the oomycete during infection which may serve as potential targets for the development of specific control strategies.

Stable isotope labelling of the Mediterranean fruit fly Ceratitis capitata (Diptera: Tephritidae)

The use of stable isotopes to label an insect species, the Mediterranean fruit fly Ceratitis capitata (Diptera: Tephidae) (medfly) was investigated. Labelling allows mating and life history characteristics to be investigated experimentally. 13C6-glucose was incorporated into the diet of medflies at various stages of development by adding it to larval media or providing adults with sugar water. Data was collected from egg hatching until the death of adults. The results show that stable isotopes successfully labelled medflies in laboratory conditions. There were significant differences between labelled and unlabelled treatments in terms of eggs hatching rates, larval development, pupae emergence, adult survival, and mating behaviour. Labelling during larval development, and combined labelling at the larval and adult stages, resulted in detectable values. Labelling in the larval stage had no effect on mating behaviour, but that in the adult stage did. This study demonstrates that it is possible to label adult medflies and to detect the label after mating.

Evaluation of stable isotope 13C6-glucose on Volatile organic compounds in different stages of Mediterranean Fruit Fly (Medfly) Ceratitis Capitata (Diptera: Tephritidae)

The Mediterranean fruit fly (Medfly) Ceratitis Capitata (Diptera: Tephidae), as most of the Tephritidae species, is a pest of great economic importance around the world. For Integrated Pest Management (IPM) and biological pest management purposes, this research will investigate characterization of the broadest possible range of volatile organic compounds and the possible changing trends of volatile biological emissions during development stages of insect. During the last years, many types of research have been done to understand chemical communications between pest-pest interactions and about the insect responses to specific volatile organic compounds. An early comparison of the VOCs emitted from larvae, pupae and adult was performed. Our research focuses on the comparison of volatile compounds emitted from a different stage of Medfly using stable isotope 13C6-glucose. Gas Chromatography (GC) technique coupled with Flame Ionization Detection (FID) and gas chromatography with mass spectrometry (GC-MS) for identification of VOCs was employed. Head Space-Solid Phase Micro Extraction HSSPME method with Three-phase fiber 50/30 µm divinylbenzene/carboxen/ polydimethylsiloxane (DVB/CAR/PDMS) was used. The results showed that there are different chemicals emitted in a different stage of Medfly (Larvae, pupae, and adults M/F) especially in the adult stage. GC-MS detected 27 compounds from larvae, 23 compounds from pupae and 29 compounds from adults. These different VOCs emitted in different stages of Medfly were clearly displayed, and a broad range of emitted volatile compounds was successfully described. The characterization of release patterns could be useful tool for the selection of compounds and for further investigated in biological studies to understand of the key semi-chemicals involved in medfly behaviour.