Parasitic wasp cocoons and stem borers. Cocoon of the parasitic wasp Cotesia sesamiae that have formed after eggs were laid in African pink stem borers (Sesamia calamistis). The larvae of the Sesamia calamistis moth feed on a wide range of plants, boring into the plant stems. The crops affected include rice, millet, sugar cane, wheat and maize. It is found in many tropical and subtropical regions of Africa. Its numbers can be reduced by use of the parasitic wasp Cotesia sesamiae, a form of biological pest control. The wasp lays its eggs in the larva and the hatching and development of the wasp (including the formation of the cocoons seen here) kills the larva.