Sap beetles (nitidulids; family Nitidulidae)

Sap beetles (Nitidulidae) are small, dorsoventrally flattened, oval beetles, light brown to black, measuring 2–4 mm. The elytra are often shortened, exposing the last two or three abdominal segments (tergites), a characteristic family trait. Elytra commonly show contrasting maculation, with one or two yellow to rufous-brown spots. Antennae terminate in a compact, three-segmented club. Adults are highly mobile.

In stored grain, both larvae and adults are opportunistic mycetophages/saprophages; injury is secondary and often non-distinctive. Larvae excavate short galleries in mold-caked fines, broken kernels, and moist residues, leaving frass and body fragments that contaminate lots. They rarely penetrate sound, dry kernels, but they degrade already compromised grain and contribute to caking. Through constant movement, adults disseminate spores of molds, bacteria, and yeasts on their integument and in feces, amplifying spoilage microflora across the bin. This accelerates hot spots, off-odors, discoloration, and quality downgrades, and may elevate mycotoxin risk where toxigenic fungi are present. Typical infestations cluster around moisture pockets, leaks, and areas with fermentation or heating. Economic impact arises less from direct consumption and more from contamination, spread of microbial decay, and the downgrading of grain quality and storability.

Signs of Nitidulidae (sap beetles) infestation in stored grain: - Pinholes and shallow feeding perforations in kernels; ragged edges on cracked or germ-damaged grain. - Numerous active adults on the grain surface and in the headspace, sometimes in very large numbers, often aggregating near lights and warm spots. - Cream to tan larvae and shed exuviae within fines, especially in damp, caked, moldy pockets. - Frass and fine dust beneath crusts and around feeding sites. - Localized “hot spots” with caking, moisture condensation, and visible mold/yeast growth, accompanied by a sweet, fermentative, fruity odor. - Elevated captures in pitfall/probe traps near leaks, spills, and accumulations of broken kernels. - Rapid “surface swarming” of beetles after disturbance or when grain is exposed.

Sap beetles (Nitidulidae) are holometabolous pests of stored grain. After mating, females oviposit directly on or within the commodity; fecundity is very high, with up to 1,000 eggs per female over 3–4 months. Eggs hatch into active, mobile larvae that disperse through the infested lot and burrow into the product to feed. Development is rapid, proceeding through larval stages to pupation and emergence of adults. Newly emerged adults are strong fliers, readily colonizing storage sites and spreading between lots. The combination of high oviposition rate, good flight capacity, and short generation time drives explosive population growth under favorable storage conditions.

Preferred environment: warm, humid sites with fermenting, sugar-rich substrates where yeasts and molds flourish—ripening fruit or damp, moldy grain hotspots—whose fermentation volatiles attract these saprophagous, mycetophilous beetles.

Other species of the genera Carpophilus and Glischrochilus.