Maize billbugs and billbug grubs (extended information)

Nicentrites testaceipes - lesser maize billbug
Geraeus senilis - large maize billbug

Description and life cycle

From the early or midwhorl stage to near tasseling, one can observe in the whorl abundant, grayish, lesser billbugs 3mm to 4mm long and large billbugs 5mm to 7mm long. When disturbed these drop into the whorl or onto the ground and remain motionless for some time. These insects pass through complete metamorphasis: egg (white and bean-shaped), larva (white, legless, humpbacked grubs with brown heads), pupa (white and soft), and adult (referred to as weevil, snout beetle or billbug).

Mechanism of damage

Leaves show white specks, which grow together under severe infestations. The specks are an indication of feeding by billbugs in the whorl, where they scratch small, irregular sections of the epidermis without puncturing it. As the leaves unfold, the specks become visible. The grubs feed on the roots of maize plants, which as a result, become prone to lodging. Damage in fields where maize is preceded by forage or cover crops may be particularly severe.

Geographic distribution

Damage by these insects can have economic significance mainly in the highlands of the Neotropics (which include northern South America, the West Indies, and tropical North America).