Potentials of plant-derived sterol carrier protein inhibitors in insect management

Cholesterol- a type of sterol has a crucial role in development and many physiological processes of insects. It acts as a precursor for insect moulting hormones, namely ecdysone and 20-hydroxyecdysone. The hydrophilic environment inside the insect body restricts intracellular transfer of cholesterol. Therefore, its transport is facilitated by sterol carrier proteins (SCP). Sterol carrier proteins belong to the SCP-2 gene family, with two main members, SCP-X and SCP-2. Blocking sterol carrier proteins results in decreased availability for cholesterol binding and transport within the insects; this may affect the cholesterol metabolism in insects. Sterol carrier proteins inhibitors (SCPIs) are the potential inhibitors of the biological activity of sterol carrier proteins in insects. There are several plant-derived SCPIs, viz. quercetin isolated from Saxifraga stolonifera, and alpha-mangostin and panthenol, extracted from Garcinia mangostana. Calotropis gigantean also contains two SCPIs, namely terpene, and alpha-amyrin. The potential of synthetic and plant-derived SCPIs for blocking SCP-2 protein to prevent cholesterol binding has been documented in various insects such as Aedes aegypti, Helicoverpa armigera, Manduca sexta, Spodoptera littoralis, and Spodoptera litura. The SCPI binds with the SCP-2 by competitive inhibition, which results in mortality at the early stages of larvae and also impairs insect growth and development. Decreased cholesterol absorption in insects shows significant lethal and sub-lethal effects in insects. Therefore, these plantderived SCPIs could potentially be used in integrated pest management.