"The Cowpea is also a deterrent to a moth, the Spotted Stemborer (Chilo partellus ) which lays its eggs on the stems of maize and sorghum, then the developing caterpillar eats its way up the inside of the stem. This deterrence is helped by planting another companion or trap crop, around the maize which appears to be a better place for the moth to lay its eggs, but the plant, Napier Grass (Pennisetum purpureum) produces a gummy sap that kills the caterpillars. This growing method has been given the name "push-pull" as the Cowpea pushes the moth away while the Napier Grass pulls them towards it. This is a much more sustainable method of increasing crop yields than developing genetically modified plants"