Oryzaephilus Ganglbauer, 1899






POLYPHAGA Emery, 1886

CUCUJOIDEA Latreille, 1802

SILVANIDAE Kirby, 1837

SILVANINAE Kirby, 1837

O. mercator (Fauvel, 1889)

O. surinamensis (Linnaeus, 1758) 

This small genus includes about 16 species and is native to tropical and subtropical regions worldwide, in nature they develop on a wide range of vegetable and fungal matter, including fruits, grains and seeds, and several have been transported with the trade and storage of foodstuffs and become cosmopolitan. The two species outlined below are now cosmopolitan and have become very serious pests of stored food products, destroying produce by direct feeding, rendering it vulnerable to further attack by other pests and by introducing fungal and bacterial infections. Both are regularly introduced to Europe and both become regularly though usually temporarily established, a third very widespread species, O. abeillei (Guillebeau, 1890) has been recorded from Greece. Adults have a very distinctive elongate and flattened appearance, the body is constricted between the head and pronotum and the pronotum and elytra and the head is widely produced in front of the eyes. The form of the pronotum will identify the genus; the surface is divided into four distinct areas, the central two flat and the outer two sloping to the lateral margins, by three longitudinal ridges, one median and one either side on the disc, and the lateral margins each have six strong teeth, two towards the anterior and posterior margins being more strongly developed. The eyes and temples are prominent and the antennae have a variously-developed three-segmented club.

Oryzapehilus surinamensis

Oryzapehilus surinamensis

Oryzapehilus mercator

Oryzapehilus mercator

Oryzapehilus surinamensis larvae

Oryzapehilus surinamensis larvae

O. mercator (Fauvel, 1889)

Native to various tropical regions and now cosmopolitan due to human transportation this species regularly occurs throughout Europe although is only rarely detected in the UK. Worldwide it is a serious pest of a wide range of stored and processed products including chocolate, tobacco, drugs and spices etc, both larvae and adults feed primarily on cereal products; oatmeal, bran and various seeds and rice products, it is often associated with cereals with a high oil content and will also feed on seed-borne fungi, many of the European records have been from imported peanuts. In temperate regions it survives in heated premises, usually commercial storage depots but also in domestic dwellings and restaurants etc, outbreaks tend to be sporadic but the species may turn up just about anywhere; it occurs in apartments and multiple dwellings in Canada and a breeding population has been recorded in a kitchen on Svalbard. The biology is much the same as that of O. surinamensis but unlike that species the adults are good fliers, coupled with the high fecundity; each female may produce up to 300 eggs, the potential for infestation is very high. Populations always occur around or very close to stored foodstuffs and under artificially heated conditions the life cycle from egg to adult may take as little as four weeks, adults are attracted to damaged grains, upon which they will readily oviposit, but they are also primary pests, capable of penetrating whole grains and nuts. In situations where there is continuous movement of the food source, e.g. in busy depots, adults will resort to ovipositing on almost any organic matter, the larvae are capable of developing on just about any vegetable or fungal matter, and so populations may be extremely persistent. In domestic premises the beetles are little more than a nuisance and control is usually a matter of good hygiene but control in commercial operations is very difficult and usually involves fumigation or pesticide applications because, as with O. surinamensis, the species is very cold-tolerant over short periods and a temperature of -18C must be maintained for at least six days in order to kill all stages of the life-cycle.

Compared with O. surinamensis, O. mercator (Fauvel, 1899) is on average smaller, 2.5-3.0mm, the eyes are larger and the temples, about a quarter of the diameter of the eyes in length, are sharply pointed. Antennal segments nine and ten are distinctly transverse. Males lack the toothed hind femora and tuberculate clypeus seen in O. surinamensis.

Oryzapehilus mercator.jpg
O. surinamensis (Linnaeus, 1758) 
Oryzapehilus surinamensis 1.jpg

With the exception of high northern latitudes this generally common stored product pest has a cosmopolitan distribution, being most prolific in humid tropical regions, its origins are unclear and the name refers to specimens from Surinam upon which Linnaeus based his original description. The beetle develops in a wide range of stored products; especially grains and flour but also biscuits, cereals, sugar and sugar products, nuts, dried fruit, yeast and tobacco, and it has also, albeit rarely, been found developing in dried meats. Among stored grains it is a secondary pest, unable to penetrate the seed coats, but readily attacking grain that has been damaged or infested by other pests e.g. Sitophilus. It is regularly imported into the U.K. with bulk grains and unprocessed cereals and is considered one of the most important pests of domestic grain. Adult beetles cannot fly and are dispersed through trade; they can survive a wide range of conditions, including sub-zero temperatures for several days, and can persist in unheated warehouses in temperate regions. Protecting bulk products with packaging is rarely successful as the narrow and flat form of the adults allows them to access the smallest openings; conversely they are rarely a pest in domestic situations. The adults are elusive; when disturbed they move rapidly into the food or hide in the smallest crevices and are able to run quickly up the smoothest surfaces including clean and dry grass. Infestations usually occur among the surface few inches of stored grain, the beetles are fecund and long-lived and so large populations soon build up and severe attacks may cause grain to heat up and so cause extensive damage. Adults generally live between six and ten months although they have been recorded living up to three years under laboratory conditions, and the females have a long egg-laying period; up to ten eggs are laid each day and the total may exceed three hundred. The eggs are laid among loose grain or simply placed on the surface of suitable food, and the larvae emerge after between three and fifteen days, depending upon temperature etc. The larvae develop rapidly and are usually full-grown within a week or two, now they construct a pupal cell by sticking together food fragments etc. either within the food mass or among packaging, and here the prepupal and pupal stages are passed, this lasts between one and four weeks and, under optimum conditions, the entire cycle from egg to adult may be completed in twenty four days. In unheated conditions where the food supply is erratic the cycle may be greatly prolonged; an egg to adult period of 315 days has been recorded; all stages can tolerate wide temperature fluctuations and low humidity and so they can be very persistent and difficult to eradicate. In warm and humid climates populations may explode; there may be four to six generations each year and infestations may contain large numbers of life stages. Adults may be carnivorous, preying upon other pest species among the food.

Although small, 2.5-3.5mm, the form of the temples and lateral pronotal margins is distinctive, the only confusion might be with another member of the genus, O. mercator (Fauvel, 1889).

Entirely reddish-brown. Head quadrate, prognathous and flattened with the clypeus narrowed anteriorly, and with dense, coarse punctation and fine pale pubescence throughout. The eyes are small and finely pubescent, the temples protruding and rounded; about as long as half the diameter of the eyes.  Antennae inserted on the lateral margin well in front of the eyes; 11-segmented, the basal segments slightly elongate, 5-8 quadrate to transverse, and 9-11 forming a distinct club.  Pronotum elongate and very characteristic; with 6 large and sharp teeth on each lateral margin, those at the anterior and posterior angles longer and more acute. Disc with 3 longitudinal raised lines which are usually emphasized with pale setae, the entire surface is coarsely punctured. Elytra elongate-oval, broadest at or behind the middle, flattened anteriorly and convex in the posterior half. The striae are strongly punctured, the interstices mostly obscured by transverse wrinkles, the entire surface with well-defined rows of recumbent pale setae. Legs long and slender; femora clavate, tibiae weakly curved and angled on the outer edge towards the apex. In the male the hind femora have fine teeth and the clypeus has fine lateral tubercles. Tarsi 5-segmented, the basal segments bilobed and the terminal segment elongate; as long as the basal segments combined.