The following is the most notorious polyphagous pest

The most notorious polyphagous pest is Helicoverpa armigera.
Helicoverpa armigera is a species of Lepidoptera in the family Noctuidae. It is known as the cotton bollworm, corn earworm, Old World (African) bollworm, or scarce bordered straw. The larvae feed on a wide range of plants, including many important cultivated crops.
It is a major pest in cotton and most polyphagous and cosmopolitan pest species.
The cotton bollworm is a highly polyphagous species. The most important crop hosts are tomato, cotton, pigeon pea, chickpea, rice, sorghum, and cowpea.