Maize weevil (Sitophilus zeamais), also called the corn weevil.

Adult maize weevil (Sitophilus zeamais Motschulsky), also called corn weevil, is reddish-brown with four yellow to reddish maculae on the elytra. It bears the characteristic elongate rostrum of weevils. Externally, it is indistinguishable from the rice weevil (Sitophilus oryzae); reliable diagnosis requires dissection to assess internal characters. The visible combination of a long rostrum and a four-spot elytral pattern is typical for this species group but is not sufficient to separate S. zeamais from its congener.

A primary internal feeder of stored cereals, this pest causes both quantitative and qualitative losses. Larvae develop concealed within kernels, tunneling through endosperm and embryo and hollowing the grain. Adults and larvae feed directly on sound kernels; adults also exploit previously damaged grain. On emergence, adults bore diagnostic exit holes with notched edges, accompanied by frass and seed dust. Infestations generate respiration hotspots that warm the grain mass and elevate intergranular humidity and moisture levels. The outcome is perforated, weakened, and fragmented kernels with diminished integrity and quality.

Signs of infestation by the maize weevil (Sitophilus zeamais Motschulsky) in stored grain: - Weevil‑damaged kernels: round emergence holes with slightly notched, uneven margins; kernels feel hollow and crush easily; increased fines and powdery frass. - Oviposition marks: tiny pits on kernels sealed with a translucent gelatinous plug (operculum), indicating an internal feeder developing within. - Hot spots: localized grain heating from insect metabolism, evident on temperature cables or as warm pockets when probed. - Moisture pockets: elevated intergranular humidity, caking, and often secondary mold growth driven by insect respiration and damaged grain. - Surface activity: live adults on the grain surface, concentrated near warm zones and spouts; adults may fly when disturbed. - Odor and segregation: musty odor, accumulation of fines and frass at the surface, under perforated floors, and in handling equipment; reduced test weight and “weevil‑damaged kernels” in grading.

Maize weevil (Sitophilus zeamais Motschulsky) is holometabolous. Long‑lived, volant adults (3–6+ months) disperse readily among grain stores. After a short pre‑oviposition period, the female uses her rostrum to bore into a kernel, lays a single egg, and seals the site with a mucilaginous plug. The endophytic larva, through successive instars, feeds concealed within the grain. Pupation occurs inside a cavity in the kernel. The teneral adult hardens and emerges by chewing a round exit hole, leaving frass and weakened grains. In warm, humid stores, generations overlap and populations rise quickly.

Maize weevil thrives in granaries, warehouses, and silos, within bulk stored grain. Its gregarious, aggregative behavior deep in the grain mass renders infestations cryptic, hindering early detection.

Granary weevil (Sitophilus granarius), Rice weevil (Sitophilus oryzae) – practically identical.