Rhyzopertha dominica (Fabricius, 1782)

Thought to have been native to South-eastern Asia and spread to tropical regions worldwide, this naturally saproxylic species has become a serious pest of various stored products in temperate regions worldwide. It occurs frequently though sporadically across Europe with imported products and sometimes becomes temporarily established in the wild but permanent or long-term populations will probably survive the temperate climate only in the extreme south, in northern areas such as the UK it is infrequently reported and then mostly near areas processing imported goods, and sustained infestations can only occur under artificially heated conditions. In tropical climates its hosts include a range of hardwood trees and shrubs where the larvae develop under bark and within xylem, they develop quickly and may produce large populations, the adults fly-well and may disperse over long distances, they can bore into both natural and processed hardwoods and other materials and have a lifespan of between four and nine months, all of which equip them to become serious pest species under artificial conditions outside their natural range. Under artificial conditions their hosts include a very wide range of stored foods including wheat, barley, rye, rice, maize, millet, beans, flour, biscuits and a range of herbs and spices. The species is a primary pest, it can detect and bore into undamaged grains and therefore render products susceptible to secondary pests such as grain weevils etc., it can also introduce and spread fungal infections and the females are very fecund and so outbreaks in storage facilities can be very serious. Each female can produce between 200 and 500 eggs over a long period, they are small groups between 2 and 30 on the surface of host material, depending on the nature of the host most emerging larvae will bore into grains etc. and develop within, but they can also develop as free-living insects, feeding on debris and dust and developing at about the same rate. Under ideal conditions of about 12% r.h. and 30°C the life-cycle takes about 25 days and although adults fly readily they tend to remain and oviposit where the host is abundant so that very large populations can quickly build up. Larval development varies according to the host material, there may be between 2 and 7 instars and pupation occurs within the host unless the larvae are free-living. Both adults and larvae feed among the host, they leave empty grains with characteristic emergence holes, large amounts of frass and give the material a distinctive aroma and so, at least to the experienced, infestations can easily be detected.