Polydnaviruses (PDVs) are a group of insect viruses and symbiotic to some endoparasitoid wasps. Genome analyses of different PDVs provide a number of genes putatively associated with alteration of host insect physiological processes. Especially, PDV gene products assist host wasp development by suppressing immune responses and delaying larval development of parasitized lepidopteran hosts. Thus, PDV genes can be applied to control insect pests by incorporating them into crop genomes. This talk illustrates two examples of PDV genes: CpBV-CST1 and CpBV-ELP1. CpBV-CST1 has been known to inhibit insect cysteine proteases to suppress immune and development, while CpBV-ELP1 exhibits a high cytotoxicity to insect cells. Transgenic tobaccos expressing CpBV-CST1 or CpBV-ELP1 were constructed by using Agrobacterium-mediated transgenic system and exhibited antixenosis against chewing and sucking insect pests on tobacco.