CORN STEM WEEVIL: Listronotus humilis, Curculionidae
ADULT: Beetles are tiny (5/32 in.) with mottled medium to dark brown bodies speckled with minute white scales. Their mouthparts are produced downward in front of eyes into a narrow snout. Adults quickly jump or fall from plants when approached. Their coloring and small size makes them difficult to find once they fall to the soil.
EGG: Creamy white eggs (becoming darker with age) 1/32 in. long are deposited in leaf sheaths or stalks. Larvae emerge into the plant stem in 3 to 6 d.
LARVA: The legless, translucent larvae have dark brown heads and long setae. They reach 1/4 in. long at maturity. Larvae develop to pupa in 20 to 25 d.
PUPA: Larvae pupate within plant and pupal stage lasts 4 to 9 d. The white pupae have exposed appendages.
GENERATION TIME: 27 to 40 d.
DAMAGE: This pest is most abundant in late spring and early fall. Larvae mine lower stems of young plants near soil line and cause stunting, wilting, and lodging. Mining near the leaf surface looks like damage from leaf mining flies. Adult feeding and egg puncture holes cause some damage. Eggs are also deposited in sorghum, Cyperus rotundus and goosegrass in corn and surrounding fields. These beetles also attack wheat, tomato and onion. It was a major pest in the Everglades in the Spring and Fall crops during the 1960's. Foliar treatments for fall armyworm and corn earworm often hold this insect under control. There are no pesticides specifically labeled to control this insect.