BIODIVERSITAS ISSN: 1412-033X Volume 23, Number 7, July 2022 E-ISSN: 2085-4722 Pages: 3355-3363 DOI: 10.13057/biodiv/d230706 Amethyst leaf extract as pest control and fertilizer for soybean plants OPIR RUMAPE 1,2,♥ , AKRAM LA KILO 1,2 , NETTY INO ISCHAK 1,2 1 Department of Chemistry, Faculty of Mathematics and Natural Sciences, Universitas Negeri Gorontalo. Jl. Jendral Sudirman No. 6, Gorontalo 96128, Gorontalo, Indonesia. Tel./fax.: +62-435-821125,  email: rumapeo@gmail.com 2 Department of Chemistry Education, Faculty of Mathematics and Natural Sciences, Universitas Negeri Gorontalo. Jl. Jendral Sudirman No. 6, Gorontalo 96128, Gorontalo, Indonesia Manuscript received: 3 March 2022. Revision accepted: 17 June 2022. Abstract. Rumape O, Kilo A, Ischak NI. 2022. Amethyst leaf extract as pest control and fertilizer for soybean plants. Biodiversitas 23: 3355-3363. Amethyst (Datura metel L.) is a plant that grows and develops in the Gorontalo area, and people use it as traditional medicine. This plant has a natural insecticidal activity that is not yet known by the general public. So far, the results of research on natural insecticides from amethyst have only been tested on a small scale in the laboratory, not yet applied on a large scale in the garden. The purpose of this study was to extract amethyst leaves and apply it as an inhibitor of feeding activity and insect mortality in both the laboratory and soybean gardens. Amethyst leaves were extracted in the laboratory using methanol, n-hexane, and ethyl acetate. The extracts were tested phytochemically to determine the type of secondary metabolite, before applying it. Phytochemical test showed amethyst leaves contain alkaloid, flavonoid, terpenoid, and saponin. The application treatment for the bioactivity used variations in the concentration of amethyst leaf extract of the fractions (methanol, ethyl acetate and n-hexane), namely 1.0, 2.5, 5.0, 7.5, 10%; and 0% as control. In the laboratory, the treatment was applied by contact to 5 insects Spodoptera litura instar III for each concentration treatment with 3 replications. Observation parameters were the percentage decrease in feeding activity and mortality of S. litura larvae. In the garden, the extracts with varying concentrations of the same as in the laboratory, were applied to soybeans treated with the pest S. litura in a closed container, and the other was sprayed on plants that were left exposed. The results showed that the three extracts could kill pests, but n-hexane extract was the most effective compared to ethyl acetate and methanol extracts. Amazingly, soybean plants whose yellow leaves turn green after being given the extract. This indicates that the secondary metabolites of amethyst are not only used as insecticides to control pests, but also as plant fertilizers. Keywords: Antifeedant, Datura metel, natural fertilizer, natural insecticide, soybean, Spodoptera litura INTRODUCTION The use of synthetic pesticides is the main choice of farmers in controlling plant pests, even though they know the bad impact on human health and the environment (Rijal et al. 2018; Rani et al. 2021). They are also aware that chemicals from synthetic pesticides can be exposed to humans through consumption of agricultural products contaminated with pesticides (Ahmed et al. 2000). Only for practical reasons and quickly obtain yields and low costs, farmers ignore the negative effects of these synthetic chemicals (Damalas and Koutroubas 2018). In developing countries, the use of synthetic pesticides occurs in smallholder farmers who tend to have relatively unsatisfactory of education and restricted access to agricultural edification (Meemken and Qaim 2018), although in rural areas there are still farmers who use natural pesticides only a few types of plants are used and these activities are also starting to be degraded (Cahyaningsih et al. 2022). This has shown that the implementation of synthetic pesticides in the field is carried out systematically and widely (Deguine et al. 2021). The use of this pesticide is inevitable, with the production of synthetic pesticide increasing every year globally (Gyawali 2018). According to the Food and Agriculture Organization (FAO), consumption of chemical pesticides has almost doubled, increasing from 2.3 to 4.1 million tonnes between 1990 and 2018 worldwide where China is the main contributor, followed by the United States, Brazil, Argentina and Canada (Deguine 2021; Fernández 2021). This increase is in line with the industrialization of the agricultural sector which continues to add chemicals to natural ecosystems (Nicolopoulou- Stamati et al. 2016). This is also exacerbated by the production of very large subsidized fertilizers and is obtained at low prices by farmers. Production of synthetic fertilizers in Indonesia in 2021 has reached 12,235 million tons (Nasution 2022), with subsidized fertilizers of 8,777 tons (Ramadhan 2022). The fertilizer is distributed throughout Indonesia, including Gorontalo which gets a quota of 64.162 tons. The allocation of subsidized fertilizer in one Gorontalo district alone has increased to 13,991 tons in 2021 (Eross 2021). The use of these pesticides increases agricultural productivity by up to 60% (Gresik 2020). This shows that farmers' dependence on the use of pesticide fertilizers is very high, and continues to increase the contamination of agricultural products with harmful chemicals of synthetic pesticides. Therefore, it is necessary to find alternative insecticides that are natural and safe for the environment. The development of natural insecticides is currently more directed at the discovery of secondary metabolite compounds that are not only effective in controlling pests but also have selective activity against certain pests that damage plants. Indonesia has abundant plant resources that