The Azadirachtins: potent insect growth inhibitors

Abstract

In the course of their coevolution with insects, plants have learnt to protect themselves by chemical means. Semiochemical act as antifeedants or deterrents, others by disrupting growth and development. By use of the Epilachna varivestis bioassay we isolated from Azadirachta indica seed a group of triterpenoids which interfee with larval growth and development in ppm range. Main components are the azadirachtins A and B with identical biological activity. Various other azadirachtins were obtained, either as minor seed components or by chemical modification of the naturally occuring compounds. Structure vs. activity relation studies enabled us to postulate a basic structural element that should still be biologically active and with much simpler chemical structure than natural compounds. What underlies the biological activity of these insect growth inhibitors? Their interference with the hormonal regulation of development and reproduction has been studied in Locusta migratoria and Rhodnius prolixus. In addition, tritiated dihydroazadirachtin A was used. With this approach, a precise correlation between administered dose, resulting effects, and retention of the compound was established. The azadirachtins either interrupt, delay, or deviate whole developmental programs. Results from these studies provide another chemical probe for studies in insect endocrinology and physiology

Effects of azadirachtin on mortality rate and reproductive system of the grasshopper Heteracris littoralis Ramb. (Orthoptera: Acrididae)

“…Schmutterer et al (1981Schmutterer et al ( , 1993 reported severe damage to the female ovarian follicles of Locusta, Nomadacris, and Schistocerca after treatment with azadirachtin. Also, Rembold (1987) reported delayed vitellogenin synthesis in azadirachtin-treated L. migratoria, causing severe damage to the oocytes. Shalom et al (1988) showed inhibition of oocyte development and oocyte resorption in female L. migratoria after treatment with azadirachtin The inhibition of ovarian follicle development was also reported by Ghosh et al (1999) on Gesonula punctifrons (Orthoptera: Acrididae) treated with azadirachtin.…”

“…Vitellogenesis is a rather complicated process, involving the deposition of yolk in the oocyte, resulting in a very rapid increase in size. Azadirachtin may inhibit vitellogenin synthesis or absorption which eventually leads to: inhibition of both oogenesis and ovarian ecdyosteroid synthesis (Rembold & Sieber 1981), inhibition of ovarian development (Karnavar 1987), delaying of the vitellogenin synthesis process (Rembold 1987) and interference with vitellogenin synthesis and its absorption by the follicles (Schmutterer et al 1981(Schmutterer et al , 1993Ghosh et al 1999 Table 2. Effect of different doses of azadirachtin on the longevity and egg production of H. littoralis (mean ± SD).…”

Insecticidal Triterpenes in Meliaceae: Plant Species, Molecules and Activities: Part Ⅰ (Aphanamixis-Chukrasia)

“…Of note, there are more than 2000 references focusing on azadirachtins and several reviews on azadirachtins. Further information can be referred to in the papers by Mordue (1993), Kraus (1993), Ley (1994), and Devakumar (2009) [21,41,[76][77][78][79][80][81][82][83][84][85][86][87].…”

Azadirachta indica

“…Azadirachtin inhibited oogenesis and ovarian ecdysteroid synthesis in Locusta migratoria migratorioides (Rembold and Seiber 1981 ). All azadirachtins (A-G) were reported to be potent insect growth inhibitors with high toxicity below <10 ppm in the Epilachna varivestis bioassay (Rembold 1987 ). Isonimolicinolide and nimolicinoic acid, two triterpenoids from neem fruits, showed insect growth-regulating properties against the pulse beetle ( Callosobruchus analis ) (Siddiqui et al 1987a ).…”