Sap-feeding insects of the suborder Sternorrhyncha cause significant damage to agriculture by feeding on plants and transmission of plant pathogens. They encounter two main obstacles from their specialized diet: low concentrations of essential amino acids and high osmotic pressure. The latter is overcome by production of oligosaccharides from sucrose, thereby decreasing the osmotic pressure per sugar unit. Sucrase, a crucial enzyme in this process, cleaves sucrose into glucose and fructose. Previous studies have shown that feeding acarbose, a sucrase inhibitor, to pea aphids (Acrythosiphon pisum) at concentrations as low as 5 µM leads to increased mortality from starvation and constant loss of water from tissue. Acarbose is approved for medical use in human patients with type 2 diabetes and its toxicity and potential impact on the environment is low: its oral LD50 in rats is 24 g kg-1, several times higher than that of commercial insecticides.
Screening potential inhibitors against specific enzymes allows the identification of compounds that show high activity against a narrow group of insects, thereby minimizing the impact on non-target species (e.g. honey bees). Such inhibitors may be suitable for use as insecticides by themselves, or as additives in conventional pest-control, i.e. decreasing overall fitness and survivability of target species, thus making them susceptible to lower concentrations of commercial insecticides.
The coding sequence for the sucrase enzyme from the tomato potato psyllid Bactericera cockerelli was identified from transcriptome sequence data. The corresponding enzyme was isolated after expression in Escherichia coli. The activity and kinetics of the purified enzyme were characterized and a set of potential inhibitors were tested for their effectiveness. As a control, the effect of the compounds on α-glucosidase was also measured. Additionally, the feasibility of applying sucrase inhibitors through spraying was investigated.