Brentidae sp. (Coleoptera: Curculionoidea)
Brentidae (straight snouted beetles) are one of ten families in the superfamily Curculionoidea (weevils), eight of which are extant. One of these eight families (Attelabidae) was featured in week 73 of the Insect of the Week series. The Curculionoidea comprise nearly 100,000 species and is the largest superfamily of animals on earth. The earliest appearance of Brentidae in the fossil record is between the Aptian and Albian ages in the lower Cretaceous (sometime between 121-100 million years ago). With their long snouts species are easy to recognize. Brentids are mostly dark in colour, black, brown or dark red. Adults lack geniculate (elbowed) antennae, present in most curculionoids. Instead, brentids have the antennae straight and filiform, and never ending in a club. Labial and maxillary palpi are absent. Most species of the family are confined to forest habitats where they find their preferred food, the wood of recently dead trees, xylem, and the fungi growing under bark. Adult brentids are much longer than broad and are more or less tubular (see image) which provides a clue as to their behaviour. The adult females drill holes in the wood into which they lay their eggs. Some brentids have evolved specialized relationships with other species. Members of the tribe Eremoxenini develop exclusively in ant nests!
Depending on the subfamilies that different taxonomists place in the family, estimates of the diversity of Brentidae range from 1800 to nearly 4000 species. Most brentid adults are between 4-20 mm long. However, with so many species you would expect there to be great variation, and the individuals of one species (Eutrachelus temmincki) are spectacularly long, with males reaching as much as 80 mm in length, about the size of your forefinger!
Cycads, Brentidae, and Dinosaurs
Cycads are ancient plants with their earliest appearance in the fossil record during the Pennsylvanian era, ca. 354-290 million years ago. In Africa several brentids have an interesting relationship with cycads. Currently, 12 species of Afrotropical Brentidae are known to pollinate cycads of the genus Encephalartos. The two groups exhibit brood site-pollination mutualism (BSPM), whereby the larvae of the Brentidae develop in the tissues of the male cycad and, after emerging, the adults become dusted with pollen which they transfer to female cones. With the appearance of phytophagous dinosaurs millions of years later it is thought that cycads were their principal source of food. It is very satisfying to suspect that during the Cretaceous period Brentidae were critical to the growth of cycads that, in turn, nourished the giants that walked the earth so long ago. Of late, BSPM has become recognized as an important pollination mechanism in many insect-plant associations.
Credits: Dr Robert Copeland