Why the Mulberry Silkworms (Bombyx mori) are Monophagous and the Cotton Leaf Worms (Spodoptera littorallis) are Polyphagous?

Abstract

Larvae of order Lepidoptera have biting mouth parts and almost fed on leaves. The insects of Lepidopterous were divided into three groups depended on number of the host plants, the monophagous, the oligophagous and the polyphagous. Sense organs are responsible for the number of host plants and insects select for hosts to fed on. In this study, the head capsule of larvae was cut at the end of larval stage of the mulberry silkworms and the cotton leaf worms to examine by scanning electron microscope for the number and type of sense organs on head capsule of larvae of both insects. The total number of sense organs on the head capsule of the mulberry silkworm was 82 where they were more than that of the cotton leaf worm where they were only38 sense organs. In addition, When mouth parts of the mulberry silk worm were covered with nail polish then the larvae were offered five different species of plant leaves ,Abelmoschus esculentus (okra), Vitis vinifera (grapes), Ricinus communis (castor bean plant),Cucurbita moschata (Pumpkin) and Morus alba (mulberry) to fed on. The treated larvae couldn't recognize mulberry leaves to feed on. The larvae fed on small part of grapes and okra leaves then stopped to continue feeding. Vomiting and diarrhea were happened to larvae then died.