24 Mar 2020
The black weevil with the 2 mm spots in bright red or orange climbs up the stem of a Sandhof lily (Crinum paludosum) without haste and starts to feed on the pedicel. A few metres away another red-spotted lily weevil (Brachycerus ornatus) sits on the dark green elongated leaf of a lily and eats contentedly. The lilies appear within days after heavy rains, and so does the red-spotted lily weevil because it depends on these flowers. At almost 60 millimetres long, this weevil is one of the largest types there is.
Most weevils depend on just one or only several different types of plants, i.e. they cannot exist without this plant or plants. At Sandhof farm near Mariental in southern Namibia the red-spotted lily weevil eats nothing but the Sandhof lily. This beetle does occur in large parts of southern Africa, however, among others in former Bushmanland. In the Nyae Nyae Conservancy in the Otjozondjupa region I discovered the beetle in a pan where it was munching on a vlei lily (Crinum carolo-schmidtii) which is related to the Sandhof lily. In South Africa these weevils have been studied by Prof. Schalk Louw, a Namibian by birth. Their host plant was the ground lily (Ammocharis coranica).
The red-spotted lily weevil is completely dependent on its host plants, which only grow under certain weather conditions. As they make their appearance the weevil will also ‘wake up’, eat, reproduce and lay eggs. When the plant withers away, the adult weevil, its eggs and/or the larvae or pupae must hibernate as well. According to weevil expert Dr Rolf Oberprieler very little is known about the life cycle of the weevil, especially the red-spotted lily species found at Sandhof. Dr Oberprieler is a former student of the German private school in Windhoek who studied and conducted research in South Africa and now lives in Australia. He says that all Brachycerus species and other soil-loving weevils live for several years and hibernate in the soil under stones, or perhaps dig themselves directly into the ground. Their exact lifespan is not known yet. Weevils in a terrarium in Pretoria survived for three years, Dr Oberprieler says, adding that perhaps they were not kept under the best conditions. The expert reckons that these beetles live longer in nature.
Ants are probably among the few enemies that the large red-spotted lily weevils have, because ants can apparently ‘scoop out’ the eggs which the beetles deposit in the ground next to a host plant. No animals have ever been seen eating adult weevils or larvae. When the larvae hatch they dig deeper until they are below the lily’s bulb, Prof. Schalk Louw says. They get into the bulb and eat their way through this ‘pantry’. During the larval stage the growing larva sheds its skin several times. When it is fully grown and the bulb hollowed out, the larva digs itself back into the ground and pupates. This is the stage where the larva ‘transforms’ into a beetle, which then hatches as an adult when circumstances are favourable.
According to Prof. Louw and Dr Oberprieler, the eggs, larvae, pupae and/or adult beetles hibernate in the period between abundant rainy seasons which cause the appearance of the host plants. Oliver Morgan, the owner of Sandhof farm, says that every so often beetles are found in damp places in buildings, for example under bags of feed in the storage shed or in the engine room. They are still alive and probably hibernate there.
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