Tuesday, 21 May 2013

Something weevil this way comes

When it comes to global dominance, it may surprise you to discover that the weevils form the largest known family (the Curculionoidea) within the animal kingdom. Roughly one in every four beetle species is a weevil and even here, in the cooler climes of north-western Europe, they are still remarkably well represented. Many weevils feed on particular plants, either a single species or several that belong to the same family, and it is this close association that supports the sheer diversity seen within the weevil family. Weevils are sometimes referred to as botanists’ insects because of this and being good at botany is particularly useful when it comes to attempting an identification.

Weevils show variation in terms of size, colour and structure, though all the true weevils have a distinct snout to the head. In some species this snout (known as the rostrum) is broad, while in others it is extremely fine and narrowed. All of our weevils feed on plant material. Some feed on the roots, including Ferreria marqueti a blind, eyeless species only recently discovered in south-east England. Others feed on the stems, leaves or flowers and some feed on plant seeds. There are also species that feed on dead and decaying wood, some of which are regarded as economic pests as they can also damage the living wood of commercial timber. Perhaps most remarkable of all are the weevils that feed on aquatic vegetation, some of which feed below the water’s surface.

Adult weevils can be found throughout the spring and summer months and most species have a single generation each year, although this may be modified by the seasonality of the plant material upon which they depend. Some of the easiest weevils to track down are those to be found feeding on stinging nettles. These include the green weevil Phyllobius pomaceus, some of whose relatives are pests of fruit trees. Perhaps the most familiar weevils, however, are the vine weevils, notably Otiorhynchus sulcatus (the vine weevil) and O. singularis (the clay-coloured weevil), both of which are important pests of pot plants (indoor or outdoor). In fact, many readers will probably only think of weevils in terms of their pest status, unaware of the many hundreds of other species feeding on wild plants and dead wood.

Perhaps the most famous of all weevils is the cotton or ‘boll’ weevil, a species that effectively halted the cotton monocultures of the southern United States. While the response of this weevil to an abundance of food may have been disastrous at the time, leading to widespread failure in the cotton crop, it has since been recognised by some economists as being the stimulant behind diversification in American agriculture. 

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