Azadirachtin, a triterpenoid chemical compound belonging to the limonoid group, is a secondary metabolite present in neem seeds. It is an insecticide used particularly in organic farming.
Occurrence
Azadirachtin is found in the neem tree, Azadirachta indica, from which its name is derived, as well as Azadirachta excelsa. It is found in all parts of the tree but the highest concentration is in the seeds (0.2 to 0.8 percent by weight). It was first isolated pure in 1968 following the antifeedant activity towards the desert locust (Schistocerca gregaria), but its chemical structure was finally established later in the 1980s.
Use
The neem tree has been used for > 2,000 years in India for the control of insect pests. It is categorised by the EPA as a biopesticide and is approved for organic farming. In California, a state with good usage data, 2585 kg were used in 2023. The list of azadirachtin containing products is long; It degrades rapidly in the environment. The risk to bees and other non-target arthropods is low.
- The substance acts as an insect growth regulator. It antagonizes both ecdysteroid (mainly 20E) and juvenile hormone activities by reducing secretion of prothoracicotropic hormone (PTTH) and allatotropins (neuropeptides with pleotropic [see pleotropy] functions) from the corpus cardiacum complex. This neuroendocrine disruption reduces pupation. It also causes degeneration of other neuroendocrine glands. It involves 71 reaction steps (48 steps in the longest linear sequence) with a yield of 0.00015%. Using transcriptome and genome mining and phylogenetic and homologous analysis, candidate genes were identified. They were heterologously expressed in Nicotiana benthamiana, and thus the metabolic steps were characterised and several of the purported intermediates isolated and characterised by NMR. Although the enzymes involved in the first part of the synthesis from 2,3-oxidosqualene to azadirone were characterised, it is not certain that the steps follow the order in the scheme.