A method of screening insect pest genes to identify insect pest genes which can lead to mortality of the insect pest when expression of the insect pest genes is silenced in the insect pest, the method comprising: (a) inserting a first nucleic acid comprising a sequence of an insect pest gene to be screened and a second nucleic acid comprising a sequence of an insect pest small RNA biosynthesis gene into a virus-induced gene silencing (VIGS) vector of a virus that can infect a desired plant host to produce a modified VIGS vector, wherein the insect pest gene is selected from the group consisting of a gene in a metabolic pathway, a gene in an energy metabolism pathway, a gene encoding a detoxification protein, a gene involved in organ or tissue differentiation, a gene involved in development regulation, a gene involved in molting processing and a gene encoding a cytoskeleton protein; wherein the insect pest small RNA biosynthesis gene is selected from the group consisting of Dicer-1 gene, Pasha gene, Loquacious gene ( Loqs), ARGONAUTE1 gene, ARGONAUTE2 gene, ARGONAUTE3 gene, Piwi gene, Stellate gene and Aubergine gene (Aub); (b) inoculating the plant host with the modified VIGS vector to produce an infected plant host; (c) growing the infected plant host under conditions in which the modified VIGS vector is replicated to produce RNA which accumulates in tissue of the plant host; (d) feeding the plant host tissue with RNA to insect pests; and (e) determining whether the RNA is toxic to the insect pest, wherein insect pest toxicity identifies the insect pest genes as insect pest genes that lead to mortality of the insect pest when the insect pest gene expression and the insect pest small RNA biosynthesis gene expression are co-silenced in the insect pest. (a) inserting a first nucleic acid comprising a sequence of an insect pest gene to be screened and a second nucleic acid comprising a sequence of an insect pest small RNA biosynthesis gene into a virus-induced gene silencing (VIGS) vector of a virus that can infect a desired plant host to produce a modified VIGS vector, wherein the insect pest gene is selected from the group consisting of a gene in a metabolic pathway, a gene in an energy metabolism pathway, a gene encoding a detoxification protein, a gene involved in organ or tissue differentiation, a gene involved in development regulation, a gene involved in molting processing and a gene encoding a cytoskeleton protein; wherein the insect pest small RNA biosynthesis gene is selected from the group consisting of Dicer-1 gene, Pasha gene, Loquacious gene ( Loqs), ARGONAUTE1 gene, ARGONAUTE2 gene, ARGONAUTE3 gene, Piwi gene, Stellate gene and Aubergine gene (Aub); (b) inoculating the plant host with the modified VIGS vector to produce an infected plant host; (c) growing the infected plant host under conditions in which the modified VIGS vector is replicated to produce RNA which accumulates in tissue of the plant host; (d) feeding the plant host tissue with RNA to insect pests; and (e) determining whether the RNA is toxic to the insect pest, wherein insect pest toxicity identifies the insect pest genes as insect pest genes that lead to mortality of the insect pest when the insect pest gene expression and the insect pest small RNA biosynthesis gene expression are co-silenced in the insect pest.