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Stegobium paniceum (Linnaeus, 1758)

Synonym(s) : 

Sitodrepa panicea Linnaeus 1758, Dermestes paniceus Linnaeus 1758
Anobium ferrugineum Herbst 1783, Ptinus testaceus Thunberg 1784
Ptinus upsaliensis Gmelin 1790, Anobium minutum Fabricius 1792
Ptinus rubellum Marsham 1802, Ptinus tenuicorne Marsham 1802
Anobium tenuestriatum Say 1825, Anobium ireos A. Villa & G. B. Villa 1833
Anobium villosum Melsheimer 1845, Anobium obesum Melsheimer 1845
Anobium nanum Kuster 1849, Cis bonariensis Steinheil 1873
Cis striatopunctatum Steinheil 1873

Common names

  • Vrillette du pain; Vrillette boulangère; Stégobie des pharmacies
  • Drugstore beetle; Biscuit beetle; Bread beetle
  • Carcoma del pan (de las drogas)
  • Brotkäfer

Classification:

  • Order:  Coleoptera
  • Family:  Ptinidae
  • Genus:  Stegobium
  • Species:  paniceum

Frequency index:

5
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Overview

The Anobiidae family (the name derives from the fact that most adults pretend to be dead and can remain motionless for several hours when they feel endangered) is mainly composed of xylophagous insects (cf. General features about that family).

Yet, Stegobium paniceum (once called Sitodrepa panicea), along with tobacco beetles or Ptinus (cf. Mezium affine and Gibbium psylloides fact-sheets) are polyphagous.

Bread beetles are common coleoptera in natural environments. Their activity period lasts from April to September; at that time they frequently get into houses, warehouses, museums, where they can settle if they find food that suits them.

In natural environments, Stegobium paniceum can be found in numerous habitats and places, including apiaries.
They can feed to the expense of matters of animal origin as well as of plant origin, and few materials are spared.

They are particularly fond of starchy products (they are amylophagous); they can occasionally infest wood, but it is only second-choice food. Although larvae and adults shy away from light, they are attracted to ultra-violet light and can therefore be trapped that way. 

Recognition criteria

Adult

Size

2 to 3.7 mm long.


Aspect

Cylindrical, oblong body, covered in a pubescence of very fine flat bristles.

Sharply domed thorax, wider on the sides, with a finely grainy, thickly pubescent surface, like the upper part of the elytra; elytra are ornamented with rows of lengthwise pits (striations).
Eleven-articled antennae, the last 3 articles form an elongate club (antennae are serrate and club-less in Lasioderma serricorne (see fact-sheet)).
Two rows of small spines (spinulae) on the ventral face of the first 6 abdominal segments.

Head partly covered by the pronotum which forms a kind of hood.


Colour

Entirely yellowish brown to deep dark brown, legs included.
Yellowish to greyish dorsal pubescence.

 

Larva

Size

4 to 5 mm at the last developmental stages


Aspect

Look like small arched white grubs.


Colour

Shiny whitish, with a thick hairiness formed of fine erect golden bristles ; brownish head. Larvae grow slightly darker as they get older.

 

Development cycle

It very much depends on thermo-hygrometric conditions. For example, the cycle is fairly short, i.e. about 2 ½ months at temperatures between 22° and 25°C, but it is longer (7 months) at 17°C. Below 15°C and above 34°C, development is no longer possible; adults are killed at temperatures below – 10°C. Like their larvae, they fear light but can stand very dry conditions for 3 weeks.
Mating starts 48 hours after adult emergence. It mostly takes place in the open air and more rarely in old larval galleries.

Fecundity varies between 23 and 114 eggs (between 40 and 60 on an average). Eggs are usually laid in small bunches of 4 or 5 on the nutrient substrate. Egg-laying lasts about 20 days. Eggs do not develop below 4°C and are killed below – 5°C. They hatch after 1 or 2 weeks. New-born larvae feed on debris and crumbs. They are very small and can thus get into tiny cracks, e.g. foodstuff wraps, where they can contaminate many products. They immediately tunnel deep into the substrate.

They display the particular feature of moving around (which is not the case for other Anobiidae species) on short distances thanks to a kind of abdominal sucker that they use as a fixation point
As soon as they find a suitable (highly nutritive) place, larvae remain within a big enough space where they develop, which requires between 50 days (in optimal conditions) and 140 days. At the end of their development, they build themselves a cocoon made from tiny food particles. Nymphosis occurs in that cocoon and lasts between 3 and 14 days, depending on ambient temperature.
Depending on thermo-hygrometric conditions and nutrient richness, there can be up to 4 generations per year.

Males can live for up to 20 days, and females an average 30 days, with extremes ranging from 13 to 85 days depending on ambient temperatures.
Unlike their larvae, which are quite voracious, adult bread beetles do not feed and do not cause any damage. Such is not the case for Lasioderma serricorne, for example.

Infected materials

  • Papier

The species has been living in the vicinity of humans for thousands of years, and specimens have even been found in Egyptian mummies dating back to more than 3,500 years.

They are above all dangerous pests of foodstuffs, especially starchy ones.

As their common name indicates, they are particularly fond of bread and its by-products, all kinds of paper bases, wheat, rice, processed cereal (tapioca, flour), beans, peas, spices (peppers, ginger, curcuma, coriander, safran), ginger-bread, pastries, pasta, dried plants (rhubarb, liquorice), seeds (aniseed, fennel, coriander, cumin), almonds, chocolate, tea, coffee, cocoa, tobacco, bamboo, wicker, wool, hairs, hair, herbaria, cork, and many other products in storerooms and warehouses. 

They are also common guests in museums where they infest insect collections, stuffed animals, leather, book-bindings (especially those made of pigskin), archives, parchments…They are particularly harmful to old pictures whose canvasses have been remounted using starch- or flour-based pastes.

The very small round holes they bore in infested materials before taking flight are a clue of their presence.
When they move around or if needs be, they can even bore through thin lead sheets.

Geographical distribution

They are distributed worldwide, but they mostly live in the hot regions of the globe.