Transgenic tobacco plants expressing the Allium porrum L. (leek) agglutinin (called APA) under the control of the 35S constitutive promoter were tested for their insecticidal activity against the cotton leafworm, Spodoptera littoralis (Lepidoptera: Noctuidae). Southern blot and PCR analysis confirmed that the APA gene was integrated into the plant genome. Northern and Western blots as well as semi-quantitative agglutination assays revealed lectin expression at various levels in the transgenic lines. Biochemical analyses indicated that the recombinant APA has the same molecular structure as the native lectin. Native and recombinant lectin have the same N-terminal amino acid sequence. Bioassays using detached leaves from transgenic tobacco plants demonstrated that the ectopically expressed APA significantly (p < 0.05) reduced the weight gain of 2nd-instar larvae of S. littoralis. This inhibitory effect was observed throughout the experiment and on day 11 the caterpillars fed on transgenic tobacco leaves were 25–30% lighter in weight than the control caterpillars fed on wild type plants. In addition the lectin retarded the development of the larvae and metamorphosis, reduced pupal weight and increased mortality rate. These findings suggest that APA is a suitable insect resistance protein for integrating into plant genomes for controlling S. littoralis.
