Bad Bugs… Fungus Feeding Grain Beetles

by Alain VanRyckeghem, BCE Technical Director

That time of the year has arrived when the combination of heat, humidity and harvest time creates the perfect environment for molds to develop on maturing field crops and in flat grain storages. Foreign grain beetles Ahasverus advena, and hairy Fungus beetles Typhaea stercorea are developing on the corn smuts and molds of maturing corn plants in the fields, as well as the spilled grains and residues around storage bins. Flat and rusty grain beetle, Cryptolestes, pusillus; C. ferrugineus, populations are exploding in numbers in grain piles sitting on cool damp ground, or in bins of summer wheat or corn that are being moved to make room for the new crop.

bad bugs fungus feeders

While the name ‘grain beetle’ suggests they are feeding on stored grains, there are some differences. The foreign grain beetles and hairy fungus beetles actually feed on the molds and fungi (Penicillium sp. and Aspergillus sp.) that grow on the wheat or corn in poor storage conditions. Poor aeration programs and high moisture content contribute to the storage conditions that allow the molds to proliferate. Flat and rusty grain beetle larvae prefer to feed on the germ, but also eat on broken kernels and grain dust.

Adult foreign grain beetles are about 3 mm long. They are reddish brown having three distinct clubs on antennae, and a thorax with small rounded nubs on the front corners. These are very distinctive and diagnostic features for this species.

The hairy fungus beetle is 3-4 mm long, hairy, reddish brown with antennae having three distinct clubs, but the thorax does not have the rounded nubs like the foreign grain beetle.

The flat and rusty grain beetles are very similar to each other; with both species being about 1.5 – 2 mm long, reddish brown and have very long thin (filiform) antennae. The back of the head of the flat grain beetle has a tiny ridge running completely across, while the rusty grain beetle does not run completely across. Other features are less distinctive as there are differences in antennal lengths of males and females.

All four species live about 9 months as adults. The adult females lay about the same number of eggs (100-300). The life cycle of the foreign grain beetle requires 15-24 days while that of the rusty grain beetle and the flat grain beetle requires 27-40 days. The rusty grain beetle develops faster than the flat grain beetle at similar temperatures.

All the adult beetles are great fliers and are attracted to lights including insect light traps. Using grain probe traps set just below the surface of the wheat or corn can provide data that gives you advanced notice of increasing populations. Aeration and/ or fumigations when populations are low will provide greater control and prevent losses in grain weight and low grades. Rusty and flat grain beetles show high resistance to phosphine and require high doses of sulfuryl fluoride for control.

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