Bruchus rufimanus Boheman, 1833
Originally native through much of Africa this species is now more or less cosmopolitan in distribution and common or abundant throughout most of its range; having been transported worldwide along with food products it is now considered to be a serious pest of a wide range of legume crops in Europe, North Africa and North America. In the U.K. it is widespread and generally common through England but local and sporadic in Wales and southern Scotland. Adults feed on pollen while the larvae feed within seeds, both in the field and among stored products, the main host is Vicia faba L., broad bean, but other hosts include species of vetch, Vicia L. sp., sweet peas, Lathyrus L. sp., lupins, Lupinus L. sp., Pisum L. sp., peas, Lens L., sp. and Astragalus L., milk vetches. Among dry seed produce stored under artificial conditions the beetle may breed continuously and huge populations quickly build up with individual seeds hosting 5 or 6 larvae, and larvae move between seeds as they are consumed or dry out. In the wild the adults overwinter among leaf litter, moss or under bark etc. generally near the host plant; they spend the winter in reproductive diapause which is broken in the spring with increased day length, temperature and the ingestion of pollen. They move to the host early in the year by flight during the day and spend the nights under leaves or on flowerheads, in temperate regions they are sexually mature from late April or May when oviposition begins. Eggs are laid on the outside of seed pods, up to 10 per pod and each female will produce up to 100 eggs. Larvae emerge after 1-3 weeks, bore into the pod, and begin feeding upon the seeds, they pass through three instars and are fully developed within about three months, at this time the pods may be crammed with larvae and the seeds destroyed or hollow. The fully grown larva cuts a circular cap in the pod from which the adult will emerge and then pupates, this stage lasts between 10 and 15 days and emerging adults disperse to feed on pollen and tender foliage. Most adults will spend a period feeding and then may enter a diapause during the warmest part of the summer prior to overwintering, but slowly developing larvae and late season pupae will enter a diapause and overwinter inside the pods, producing adults in the spring. All overwintering adults become sexually mature in the spring. The adults will become quite suddenly abundant in the
Bruchus rufimanus ♂
Bruchus rufimanus ♀
Bruchus rufimanus ♂
spring and may be swept from grassland or vegetation in almost any situation where the host thrives, and they will vanish equally suddenly during June or early July depending on the season although the odd specimen will turn up through the summer and they may appear again briefly in the autumn.
At 3-5.5mm this distinctive species is one of the largest of the genus and is not likely to be confused with any other U.K. species. Head hypognathous, densely punctured and covered with pale scales, rostrum short and broad, and with very deeply notched eyes that are almost crescent-shaped and strongly protruding behind the antennal insertions. Temples strongly contracted behind the eyes to a short and narrow neck. Apical segment of palps cylindrical. Antennae 11-segmented and robust; black with segments 1-4 usually orange. Pronotum transverse and rounded anteriorly from a small but distinct lateral tooth, densely punctured and moderately densely covered with pale scale-like pubescence which is dense at the middle of the base and over the acute hind angles. The hind margin is broadly produced backwards medially. Scutellum with dense pale scales. Elytra broadly oval and distinctly wider than the pronotum, with distinct, convex shoulders and separately rounded apices which leave the pygidium exposed. Each with 10 well impressed striae which end before the apex. Interstices flat and variously scaled; when fresh overall with a mixture of grey and cream scales and paler patches forming two transverse bands, one before and one after the middle, and the pattern of pale scales on the pronotal base and scutellum generally continues along the bases of interstices 1 and 2, and there is usually a prominent pale patch on interstice 3 before the middle. Specimens quickly become worn. Abdomen with 5 visible sternites, the first much longer than the others, and the pygidium is covered with dense pale, almost white, scales. The front legs are pale, red to yellow, and the middle and hind legs are dark although this may vary. Male middle tibia curved and strongly toothed inside at the apex, this tooth is very much weaker or even missing in the female. Hind tibiae almost straight, with two unequal teeth below the apex, the inner one much larger. The first segment of the hind tarsus is very long and curved. Fully winged, specimens fly strongly and may do so readily when disturbed.