Abstract
The sustainability of agroecosystems are maintained with agro-chemicals. However, after more than 80 years of intensive use, many pests and pathogens have developed resistance to the currently used chemistries. Thus, we explored the isolation and bioactivity of a chemical compound, Precocene I, isolated from the perennial grass, Desmosstachya bipinnata (L.) Stapf. Fractions produced from chloroform extractions showed suppressive activity on larvae of Spodoptera litura (Lepidoptera: Noctuidae), the Oriental armyworm. Column chromatography analyses identified Precocene I confirmed using FTIR, HPLC and NMR techniques. The bioactivity of the plant-extracted Dp-Precocene I was compared to a commercially produced Precocene I standard. The percentage of mortality observed in insects fed on plant tissue treated with 60 ppm Db-Precocene I was 97, 87 and 81, respectively, for the second, third and fourth instar larvae. The LC50 value of third instars was 23.2 ppm. The percentages of survival, pupation, fecundity and egg hatch were altered at sub-lethal concentrations of Db-Precocene I (2, 4, 6 and 8 ppm, sprays on castor leaves). The observed effects were negatively correlated with concentration, with a decrease in effects as concentrations increased. Distinct changes in feeding activity and damage to gut tissues were observed upon histological examination of S. litura larvae after the ingestion of Db-Precocene I treatments. Comparative analyses of mortality on a non-target organism, the earthworm, Eisenia fetida, at equal concentrations of Precocene I and two chemical pesticides (cypermethrin and monocrotophos) produced mortality only with the chemical pesticide treatments. These results of Db-Precocene I as a highly active bioactive compound support further research to develop production from the grass D. bipinnata as an affordable resource for Precocene-I-based insecticides.
Highlights
Agricultural productivity is drastically reduced due to insect pests, with an estimated annual post-harvest loss of about 10–30% of major agricultural crops [1]
The bioactive compound Db-Precocene I was isolated from chloroform extract of
S. litura when they were exposed to the isolated Db-Precocene I (Figure 1A)
Summary
Agricultural productivity is drastically reduced due to insect pests, with an estimated annual post-harvest loss of about 10–30% of major agricultural crops [1]. Climatic conditions in a tropical country such as India favor the growth of agriculture pests, which in turn affect the productivity [2]. Growing economic and environmental concerns have increased interest in the use and development of less persistent, botanical-based insect pest management products. The unselective usage of chemical pesticides results in the development of pests with genetic resistance to insecticides [3], while posing potential hazards with toxic residues, environmental health hazards and a negative impact on beneficial insects, such as predators, parasitoids and pollinators [3]. Phytochemicals in plants offer a huge, untapped variety of chemicals that have potential use to defend crops against agricultural pests [4].
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