Lasioderma serricorne (Fabricius, 1792)
POLYPHAGA Emery, 1886
BOSTRICHOIDEA Latreille, 1802
XYLETININAE Gistel, 1848
LASIODERMINI Böving, 1927
LASIODERMA Stephens, 1835
This is the principal pest of stored tobacco and tobacco products worldwide, it has a cosmopolitan distribution but the adults cannot tolerate low temperatures, exposure to 4°C for 6 days is lethal, and so they cannot survive unheated conditions in temperate areas. The species is thought to have originated in the Middle East as specimens have been found in ancient Egyptian tombs, and it is now abundant in tropical regions worldwide including even remote islands, in fact any area to which tobacco products (etc.) have been transported. They thrive and breed quickly at temperatures above 17oC, the adults disperse by flight and the earlier stages are transported with host products and so they may colonize and spread quickly, the only requirements seem to be moderately high temperatures and at least some humidity. As well as being transported with tobacco and its products they are extremely versatile regarding nutrition and behaviour; the adults may consume liquids but they do not feed, they host a symbiotic yeast, Symbiotaphrina kockii, which is passed on to the larvae via the eggs and this produces sterols and B-vitamins which allow the larvae to develop on a very wide range of foods of variable nutritional quality; they have been reared on all types of seeds, grains, cereals, nuts, herbs, spices, dried fruit and fishmeal etc. as well as dried flowers, leather, woollen products, bamboo, furniture stuffing, book-binding adhesives and packaging material but despite having a strong preference for tobacco they reach the largest body size and highest fecundity when reared on wheat-flour. Optimal development conditions 30-37°C and 70-75%r.h. and so the occurrence in temperate areas is sporadic and seasonal; in the U.K. they are occasionally recorded with imported products in the south of England. Exceptionally some females can overwinter in crevices or among stored products in warehouses etc. and become active in the spring and summer, but only a single generation is produced each year and populations are short-lived, their presence in domestic premises is similarly sporadic and they are easily controlled with good housekeeping. Adults are generally short-lived, between 3-8 weeks but under exceptional conditions may survive for up to a year, in temperate areas the life-cycle takes at least 7 weeks but development in all
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stages may be prolonged by adverse conditions; in warmer climates they breed continuously and there may be 5 or 6 overlapping generations annually with all stages present in the same host material. Adults become sexually mature during pupal development, may mate within hours of eclosion and begin ovipositing after a day or so. Between 10 and 100 eggs are laid directly onto the food source over a period of about 3 weeks; dry and packaged material is preferred and females may work their way through packaging to reach suitable sites, after depositing the eggs a pheromone is applied to the site which will prevent other females ovipositing. Larvae emerge between 5 and 10 days later and in good conditions will develop rapidly; 4 instars are passed and they are fully grown within 5 to 10 weeks, they remain in the host during development and are strongly photophobic, leaving only to find a suitable site for pupation; chewing their way through packaging etc. and choosing a dark crevice remote from other larvae. The pupal stage generally lasts between 1 and 3 weeks and freshly emerged adults will quickly find a nearby food source and pass their lives within, but if this is not availably they will disperse by flight; in temperate regions they tend to swarm in the spring and again in the warmest part of the summer. In tropical regions the life-cycle takes between 50 and 90 days, and rapid generations will be produced for as long as conditions allow.
Among the U.K. fauna Lasioderma is distinguished by the serrate antennae which lack any modified terminal segments and the smooth, non-striate elytra.
2-3.5mm. entirely pale to medium reddish-brown with lighter appendages, short-oval and convex, the dorsal surface with dense, short and pale pubescence. Head strongly deflexed (hypognathous) and usually not visible from above, when at rest the mandibles lie against the base of the prosternum. Eyes large, round and convex. Antennae inserted laterally in front of the eyes, the insertions therefore widely separated, much more so than the length of the first segment; 11-segmented, the basal segment large and curved, 2 and 3 quadrate, 4-10 serrate and the terminal segment elongate and rounded apically. Pronotum convex and smooth; without elevated areas or depressions, finely and densely punctured, the lateral margins are almost straight when viewed from the side, anterior angles acute, and the posterior angles indistinct. Scutellum distinct. Elytra convex and completely covering the abdomen, the punctation sparse and fine. Abdomen with 5 visible sternites, all free, the basal sternite without furrows to receive the legs when retracted. Legs slander and relatively long, the anterior tibiae gradually widened to an obliquely truncate apex. Tarsi 5-5-5, the first segment long, segments 2-4 lobed below.