Impact of vector-expressed insecticidal peptides on the brown citrus aphid, Toxoptera citricidus

Transgenic crops expressing insecticidal peptide genes have been successful against a variety of insect pests; however identification of efficacious peptides and the development of genetically engineered crops is time consuming. To confront the rapid spread of citrus greening disease, a transient-expression vector based on citrus tristeza virus (CTV) has been developed to express foreign peptide genes. CTV offer faster alternative to transgenic plants because the vector can be graft-inoculated into existing plants. In addition, the CTV expression vector allows rapid screening of peptides with specific activity against phloem-feeding citrus pests. We conducted studies to evaluate the effectiveness of insecticidal peptides against the brown citrus aphid (BCA), Toxoptera citricidus (Kirkaldy) (Hemiptera: Aphididae). BCA is an important pest of citrus worldwide due to its status as a highly efficient vector of CTV. We evaluated lethal and sublethal effects of several CTV-expressed peptides, including the snowdrop lectin, Galanthus nivalis agglutinin (GNA), and indolicidin on the development of BCA. Aphids were fed on one of three host plants: 1) citrus inoculated with the CTV-expression vector containing foreign peptide gene, 2) citrus inoculated with the CTV-expression vector without a foreign peptide gene, and 3) citrus not inoculated with CTV. Fitness parameters examined included adult longevity, fecundity, and nymph development time. In addition, we examined insecticidal peptides resulting in feeding inhibition using a honeydew excretion assay. Results are discussed in relation to the potential for specific vector-expressed insecticidal peptides for control of BCA in the field as part of an integrated pest management program.