The ladybug (also called ladybeetle or ladybird beetle) was designated an official state insect of Tennessee in 1975 (as was the firefly). The honeybee was adopted in 1990 as Tennessee's agricultural insect, and in 1995 the zebra swallowtail was recognized as the official state butterfly.

Ladybugs help gardeners and farmers by eating tiny insect pests that damage plants. A ladybug can consume up to 60 aphids per day, and will also eat a variety of other harmful insects and larvae (including scales, mealy bugs, leaf hoppers, mites, and other types of soft-bodied insects), as well as pollen and nectar. Ladybugs produce a chemical that smells and tastes terrible as protection from predators. Ohio, Massachusetts, New Hampshire, New York, and Delaware also designate the ladybug as an official state symbol (see list of state insects for all 50 states).

According to John Losey, a Cornell University entomologist who leads the Lost Ladybug Project. (a project funded by a National Science Foundation grant recruiting citizen scientists, particularly children, to search for nine-spotted ladybug and other ladybug species and send photos of them to Cornell for identification and inclusion in a database), there are about 5,000 species of ladybugs, also known as ladybird beetles, with about 450 species in the United States.

Source:

Tennessee Symbols: Tennessee Blue Book (PDF)
Ladybug, Ladybug, Where Have You Gone? - msnbc

Links:

State Insects - 50 States List