Common Name: Mold or Plaster Beetles
Scientific Name: Various
The common name of mold refers to the fact that these beetles feed on mold and that of plaster because new plaster which remains damp too long will often support a growth of mold which attracts these beetles. Mold beetles are primarily a nuisance pest but can be of considerable importance in food-processing, canning, glass, pharmaceutical, and bottling plants. They are worldwide in distribution with about 120 species occurring in the United States and Canada.
Adults about 1/32-1/8″ (1-3 mm) long; body form distinctive with elytra (wing covers) elongate-oval, widest at middle, usually rounded at humeri (front corners/shoulders), pronotum narrower than elytra, often nearly round in dorsal view but in some species sides nearly parallel or widest at front, head prominent, often nearly as wide as pronotum. Color reddish brown to brown, rarely black. Antenna 8-11-segmented with a 1- to 3-segmented, elongate club. Elytra usually striate (with punctures/pits in longitudinal rows). Dorsal surface sometimes hairy. Legs with tarsi 2-segmented (2-3-3 or 2-2-3 respectively).
(1) Silken fungus beetles (Cryptophagidae) with elytra (wing covers) lacking striae (grooves/lines of punctures/pits), pronotum often with depressions at its base and as wide as base of elytra, and tarsi 5-5-5 or 5-5-4 (some males).
(2) Hairy fungus beetles, including Typhaea stercorea, (Mycetophagidae) have pronotum often with 2 basal depressions (absent in T. stercorea) and pronotum wide as base of elytra, and often larger (1/32-1/4″ or 1-6.3 mm) long but T. stercorea 1/16=1/8 (2.2-3 mm) long.
(3) Toothnecked fungus beetles (Derodontidae) with antennal club weak, not pronounced, elytra with large punctures, some species with prominent “teeth” along pronotal margins, and often larger 1/16-1/4″ (1.8-6 mm).
(4) Black (alphitobius laevigatus) and twobanded (Alphitophagus bifasciatus) fungus beetles (Tenebrionidae) with tarsi 5-5-4 and compound eyes notched; in addition, black fungus beetle is black above and brown or rust red underneath, and twobanded fungus beetle is reddish brown with 2 black bands across elytra.
1. Plaster beetle, Cartodere constricta Gyllenhal. Adults pale brown to dark reddish brown with antennae and legs paler; antennal club 2-segmented; pronotum distinctly constricted; elytra near base with a prominent ridge (carina) between 7th and 8th row of punctures/pits (counting from midline); length about 1/32-1/16″ (1.2-1.7 mm) long; found worldwide.
2. Dienerella arga (Reiter). Adults similar to D. filum below but antennal club 3-segmented and pronotum with median depression in basal (posterior) half, not anterior half; occurs in Europe, North Africa, and in Oregon, Ohio, Pennsylvania, and Texas.
3. Dienerella filum (Aube). Adults brownish; head with median depression widened towards rear; antenna with 2-segmented club; pronotum with a broad, moderately deep depression along midline in anterior/front half; hind wings absent; length about 1/16: (1.7-2 mm) long: found in Europe, and widespread in North Africa and North and South America.
The information summarized here is for the plaster beetle, Cartodere constricta. Eggs are laid singly among the fungi, for a total of about 10 eggs over 2 months. In cultures kept at 75F (24C), the eggs hatched in 6-7 days. The 3 larval instars required 5 days for the 1st, 7 days for the 2nd, and 12 days for the 3rd. The 3rd instar fed for 9 days. It then stopped feeding and attached itself to a surface by means of an anal secretion.
After 3 days it pupated. The pupal stage lasted 7-8 days. Developmental time (egg to adult) required at least 36 days at 75F (24C), 54 days at 65F (18C), and as long as 5 months at lower temperatures.
Both larvae and adults apparently feed only on mold spores. They are commonly found in moldy plant and animal substances, in fungi, in vegetable debris, under bark and stones, and sometimes in ant and termite nests. They are commonly found in moldy stored food products but cause no direct damage to the food material. With large infestation, deposition of their fecal material may further reduce the product’s valve. Mold beetles can be a problem within the first year of a newly built home. This can occur when the plaster or sheetrock walls are slow in drying. The dampness associated with the plastering temporarily supported mold growth, especially in wall voids.
They can also infest mounted plant specimens in herbaria. Often newly collected plant specimens are not properly dried or kept dry before mounting and, therefore, get mold growth on them. This can also occur with other museum specimens. Some other situations where they have been found include damp basements on various articles such as old boots, hats, etc., or moldy wallpaper, under linoleum in kitchens and bathroom, on moldy paper and newsprint, in old bird nests, etc. Some species can fly.
The key to control is drying out the problem area enough to stop mold growth; in general, reduce RH below 20%. Heat and/or ventilation can be used to lower the humidity. Temperatures above 110F/43C kill adult beetles in about 24 hours or less. Wall void injection may be desirable for quicker results or in areas of continual high moisture which cannot be satisfactorily reduced.
A non-residual aerosol with 4-way tip should be applied first for a quick contact kill. This is followed by application via a 4-way tip of a positively-charged boron-based duct, which acts both as an insecticide and fungicide for long-term control. Adults in the living space can be removed with a vacuum. Rarely is an ULV application of a non-residual pesticide required.