Tenebroides mauritanicus (Linnaeus, 1758)
POLYPHAGA Emery, 1886
CLEROIDEA Latreille, 1802
TROGOSSITINAE Latreille, 1802
TENEBROIDES Piller & Mitterpacher, 1783
A cosmopolitan species, originally from Africa, and in some regions a significant pest of stored products. They occur especially in grain silos, granaries, warehouses and other commercial sites but also in houses where both adults and larvae feed on a wide variety of foodstuffs; cereals, processed breakfast products, potatoes, nuts and fruit etc, the adults are opportunistic and will often lay eggs under flaps of cartons or among packaging within storage boxes. The species occurs only occasionally in the U.K. but is never a pest. Adults and larvae can chew through sacking, card and wood so allowing other pest species access to products, and unlike other grain pests they feed on both whole grain and flour. They are also predatory and actively hunt and feed on other pest species e.g. Oryzaephilus spp. Both stages are notorious for being able to burrow into wooden structures and remain dormant for long periods if food is unavailable, and these burrows are also used by other insects. They can also be a serious pest of stored tobacco; here both stages bore through bales in search of prey, consuming the product as they go. These habits may be an adaptation of their natural lifestyle; in Europe the genus occurs in the wild (although such specimens are often thought to be a subspecies of the present species or even conspecific), living under bark and predating other wood boring insects. Females lay eggs in groups of about 50 loosely among stored products which hatch, depending on temperature, in around 10 days and each female will lay around 1000 eggs. Larval development depends upon the type of food, e.g. on tobacco they may take 2 or 3 years, and temperature; in unfavourable conditions they can go without food for prolonged periods, more than 50 days for adults and more than 120 days for the larvae. In general the larvae consume only the soft parts of grains such as wheat and oats and so may destroy large amounts of material; a single larva has recorded destroying a hundred thousand grains. The larvae grow to 20mm and so are among the largest to be found among stored grains; they are greyish white with a dark head and pronotal plates. The dorsal surface of the terminal abdominal segment is dark with two robust upturned urogomphi. They migrate away from the food source to pupate and pupal chambers have been found in some unusual places e.g. in books, within corks inserted in bottles and inside a bottle of milk. Adults eclose between 1 and 3 weeks after pupation. In temperate regions there may be 2 generations a year with a partial third, in tropical regions there are three.
Tenebroides mauritanicus 1
Tenebroides mauritanicus 2
6-19mm. A very distinctive species suggestive of a carabid but the form of the antennae and the pronotum should make it obvious. Elongate and rather flattened, entirely dark brown or with the appendages lighter. Head and pronotum coarsely punctured. Head very large with broad temples behind almost flat eyes. Mandibles prominent and produced forward. Antennae 11 segmented; second segment very short and transverse, last 4 or 5 expanded inside to form a distinct club. Pronotum distinctive; lateral and basal margins bordered, hind angles sharp and obtuse, front angles protruding. Pediculate; base of the scutellum forward of the elytral base so that there is a space between the elytra and the pronotum. Elytra elongate and evenly rounded; with well impressed striae and finely punctured interstices. Interstices on disc with transverse wrinkles. Scutellary stria absent. All tibiae widened towards apex and smooth on the outer side. Front tibiae with two apical spurs, mid and hind tibiae with one. Tarsi 5-5-5 with the claw segment as long as the rest combined. Claws prominent; curved and smooth. Empodium short, but obvious at x30, with two setae that are almost as long as the claws. The sexes can be distinguished by the form of the punctation on the sternites; in the male it is fine and dense whereas in the female it is much stronger and sparse.
Teneboides fuscus (Goeze, 1777)
The name Teneboides fuscus (Goeze, 1777) was formerly considered to be a synonym of T. mauritanicus (Linnaeus, 1758) but many authors now agree that it is a valid species. It is thought to be partitioned ecologically from the synanthropic T. mauritanicus, and exclusively wild in occurrence; it is widespread and generally common across southern and western Europe from Morocco and Spain to Hungary but further east it is more sporadic and rare, being recorded as far as Ukraine. It is rare in Germany and absent from most of Northern Europe including the U.K. The species is saproxylic; occurring under the bark or among dead wood of a range of deciduous trees; in France it is recorded from oak and beech, in Spain from sweet chestnut, beech, olive, oak, lime and willow. Both larvae and adults predate other subcortical insects. They occur in a wide range of habitats; parks, wooded pasture, woodland and appropriate gardens etc.
Modern opinions consider both species as valid based on ecological criteria but Kolibac,1993 also gives some morphological characters for their separation:
Antennae dilated from the sixth segment. Elytra weakly shiny and with dense transverse wrinkles. Frons comparatively narrower.
Antennae dilated from the eighth segment. Elytra rather dull and with only weak transverse wrinkles. Frons comparatively wider.