The present invention relates to the field of controlling pests, such as insects, using a virus to express pest genes in hosts. More specifically, the present invention relates to a method for rapidly screening for pest genes which can lead to mortality of the pest when the pest has ingested host tissues expressing virus-linked pest gene sequences. The present invention also relates to a method for controlling pests by viral expression of target pest sequences to modify endogenous expression of pest genes in cells or tissues of the pest.