Interaction between larval alpha-amylase of the tomato leaf miner, Tuta absoluta Meyrick (Lepidoptera: Gelechiidae) and proteinaceous extracts from plant seeds

The tomato leaf miner, Tuta absoluta Meyrick (Lepidoptera: Gelechiidae), is one of the most destructive pest of solanaceae and it prefers tomato (Solanum lycopersicum L.). The aim of the current study was to investigate the effects of a wide range of seed proteinaceous extracts from different plant families against T. absoluta α-amylase activity. The effect of pH on the inhibitory activity of seed extracts showed that seed extracts of amaranth along with a wheat cultivar (Alvand, Aflak, Sarvdasht, Alborz, and Kavir) produced more than a 50% inhibition of the insect amylase. Aflak wheat seed extract at 10 μg, inhibited 81% of the insect amylase. This percent was the highest inhibition achieved. The other proteinaceous seed extracts had a lower effect on the enzymatic activity. Probit analysis showed that Aflak, Kavir, Alborz, Alvand, Sarvdasht, and amaranth inhibited the amylase activity with an I50 of 1.94, 3.24, 3.46, 3.31, 4.97, and 15.39 μg, respectively. The effect of pH on the inhibition of the α-amylase showed the highest inhibition of Amaranth and wheat, at a pH value of 8.0, which corresponds to the pH of the insect’s gut. Gel electrophoresis assays confirmed the spectrophotometric assays showing that the α-amylase of the insect gut was affected by the presence of the seed extracts. In the gel assay, a high concentration (14 μg protein) of amaranth proteinaceous seed extract greatly decreased the intensity of the α-amylase band. A high concentration of the Aflak wheat cultivar (10 μg protein) caused the disappearance of the amylase band in the gel. Thus, it is concluded that the physiochemical environment of the insect gut affects the interaction between digestive α-amylase and the metabolites. The experiments showed that seed proteinaceous extracts from non-host plant species, produced more inhibition of the insect amylase when compared to the host plant species. It appears that with evolution, adaptation took place so that insect/s could overcome the plant metabolites.