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Evaluation of efficacy of fumigants and natural product extracts for management of springtail Hypogastrura vernalis (Collembola: Hypogastruridae) and green peach aphid Myzus persicae (Hemiptera: Aphididae)

Ahmed, Qasim Hussein (2018) Evaluation of efficacy of fumigants and natural product extracts for management of springtail Hypogastrura vernalis (Collembola: Hypogastruridae) and green peach aphid Myzus persicae (Hemiptera: Aphididae). PhD thesis, Murdoch University.

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Vegetables are one of the most important crops in the world and especially in Australia. Under this research, three study cases were investigated for controlling vegetable pests, purple scum springtail Hypogastrura vernalis in export celery and green peach aphid Myzus persicae in Brassica crops. They are a serious quarantine and production pests of economically important celery and crucifer crops and hence were selected for the current study. This research investigates and assesses the impact of the use of various fumigants on infested celery with H. vernalis along with the use of plant volatiles and natural plant-based essential oils for control of M. persicae. Celery bunches become host to the Australian native springtail (Hypogastrura vernalis) (Collembola: Hypogastruridae). Springtails live inside the celery bunch and do not cause damage to the product. Springtails are, however, considered a quarantine pest and have had a significant impact on celery exports. On the other side, using chemical pesticides against aphids has led to resistant aganist chemical pesticides so that require further experiments on the prospective role of factors affecting M. persicae pest status, including plant volatile compound and essential oils are urgently needed.

Australia has widely grown celery Apium graveolens var. dulce for domestic and export markets. In the field, celery bunches become host to the Australian native springtail. These insects live inside the celery head, contaminating fresh celery but do not cause any visible damage. In chapter study, evaluation of ethyl formate (EF), phosphine (PH3) and their combination were used for celery fumigation against purple scum springtails that naturally infest celery. The selection of EF and PH3 was because both provide fast kill of insect within a few hours and are registered as fumigants in Australia. The material of EF breakdown is ethanol and formic acid, while the PH3 is slightly soluble in water and be broken down quickly into other products in the atmosphere. These are the first experiments that have used EF and PH3 for harvest celery fumigation.

In the laboratory experiments, three concentrations of EF 50, 60 and 90 mg L-1; four concentrations of PH3 1, 1.5, 2 and 2.5 mg L-1 and three concentrations of EF 20, 30 and 40 mg L-1 combined with 1 mg L-1 of PH3 were used for various exposure times at the laboratory temperature 25˚C. The result indicated that 100% mortality was achieved at 90 mg L-1 of EF for 2 h and 100% mortality was also achieved at 30 and 40 mg L-1 EF combined with 1 mg L-1 of PH3 for 2 and 4 h exposure time, however, phytotoxicity was observed in celery treated with EF at all concentrations both in combination and alone. PH3 at 2.5 mg L-1 achieved 100% mortality within 6 h, and no phytotoxicity was evident. From these data, we conclude that PH3 alone has potential as a fumigant for the pre-shipment treatment of celery infested with purple scum springtails.

In order to further develop natural or biological methods to manage the interaction between insect pests and host plants (three replicates per treatment) was studied using volatile organic compounds (VOCs). The VOCs from uninfested and infested Brassica plants with M. persicae were investigated by headspace solid microextraction (HS-SPME) combined with gas chromatography mass spectrometry (GC-MS). There is a need for chemical pesticides replacement with environmentally friendly alternatives because of chemical pesticides have been widely used against various pests including aphids have been shown a negative side of environments and an effect on non-target organisms and to understand the communication between aphid and the host plant. Understanding the biological and chemical basis of volatiles could lead to new approaches to the biocontrol of aphids. In Chapter two, the study was evaluated on VOCs from uninfested and infested Brassica plants with M. persicae. The results show that 29 compounds were detected in both infested and uninfested cabbage Brassica oleracea L. var. capitata, and 25 compounds were identified in both infested and uninfested broccoli Brassica oleracea L. var. italica plant samples. The HS-SPME combined with GC-MS analysis of the volatiles describes the differences between the infested and uninfested Cruciferous plant samples. Based on peak area from the GC-MS analysis, the VOCs from infested cabbage consisted of Propane, 2-methoxy, alpha- and beta-pinene, Myrcene, 1-Hexanone, 5-methyl-1-phenyl, Limonene, Decane, gamma-Terpinen and 2,4,4-trimethyl Heptane, all these volatiles were higher in the infested cabbage compared with their peak area in the uninfested cabbage. Similarly, the VOCs from infested broccoli were significantly greater than that from uninfested broccoli, such as D-limonene, Undecane, 3,4-dimethyl-, Heptane, alpha-Pinene, Oxalic acid, Citronellol, Tridecane, n-Decanoic acid, Cyclopentane, pentyl and n-Hexadecanoic acid compared with volatiles released from uninfested broccoli.

The results presented in this chapter three outline the response of aphids and parasitoids to plant volatiles by using Y-tube olfactometer. The results show that M. persicae were significantly attracted to infested and uninfested cabbage and broccoli plants compared with clean air; the percentage of aphid choice was 80% and 70% toward infested cabbage and broccoli, respectively, and 7% and 10% were attracted to the clean air choice. While 75.5% and 84% of aphids attracted to uninfested plants comparison with clean air 3% and 7%, for the cabbage and broccoli, respectively. Comparing infested and uninfested plants, the aphids were attracted by 63% and 26.6% for infested cabbage and broccoli respectively, versus 57% and 30% for uninfested cabbage and broccoli, respectively. The results indicate that using an olfactometer, tested parasitoids prefer and are attracted to, the cabbage plants infested with M. persicae compared with clean air. Parasitoids can discriminate the infested plant and significantly responsed to the infested plant odour and attracted by 86.6% and 100% for both parasitoids toward infested Brassica plants.

Another way to reduce chemical pesticides usage is with alternatives such as biopesticides for insect pest management. Therefore, chapter four describes the use of different essential oils (black pepper, eucalyptus, rosemary and tea tree), in combination and alone, against M. persicae. These essential oils have insecticidal activity and repellency against many insects including aphids and bioassay studies showed significant control of the green peach aphid through higher mortality. The results show that black pepper and tea tree pure essential oils were effective and caused 80% mortality of aphids for the contact treatment. However, the residual toxins were the most effective on aphids with 100% mortality for pure black pepper and tea tree oil and less than 96% for eucalyptus and rosemary. The combination of essential oils was tested with bioassay as contact and residual toxins. For the contact treatment, the mortality was 98.33% for black pepper + tea tree and rosemary + tea tree. While, in the residual treatment, the mortality was 100% for black pepper + eucalyptus, rosemary + eucalyptus and rosemary tea tree. The essential oil combinations exhibited synergistic, additive and antagonistic interactions for insecticidal activity. The combination of binary essential oils black pepper + tea tree oil showed enhanced activity, with a synergistic rate of 2.19. Essential oil formulation showed effective mortality of aphids, but phytotoxicity appeared on cabbage plants. The Fourier Transform Infrared Spectroscopy (FTIR) analysis of stability of a mixture of essential oils showed that it was not affected by store temperature (15, 25 and 35˚C) and all functional groups were not changed during the storage for three months. Based on the results, essential oils can be used as a commercial insecticide against M. persicae thereby reducing the use of chemical pesticides and their negative impact on the environment and human health. Natural products based on essential oils can be an excellent alternative to synthetic pesticides.

In summary, the use of EF fumigant in combination with PH3 and alone achieved high mortality on purple scum springtails, however, phytotoxicity on treated celery is a negative. Alternatively, PH3 alone achieved 100% mortality after 6 h without any observed phytotoxicity, therefore, PH3 has potential as a fumigant for the pre-shipment treatment of celery infested with purple scum springtails. Plant volatile organic compounds that release from the infested cabbage and broccoli can use as an indicator tool for the field infestation related to the differences between the infested and uninfested plant. Base on Y-tube olfactometer, Myzus persicae response to both infested and uninfested plants and parasitoids response to the infested plants. From the laboratory experiments, essential oils show high mortality on green peach aphids and could be used as an alternative to chemical pesticides. According to the FTIR analysis, essential oils can be stored at between 15 and 35˚C with no effect on the properties of the oil. Therefore, I suggest that tested essential oil constituents both pure and in combination could be screened as a potential natural insecticides. Further they could be involved in the chemical synthesis of new types of pesticides, based on essential oils and their constituents.

Item Type: Thesis (PhD)
Murdoch Affiliation: School of Veterinary and Life Sciences
United Nations SDGs: Goal 12: Responsible Consumption and Production
Supervisor(s): Ren, YongLin, Agarwal, Manjree and Emery, R.
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