g62-encyclopaedia-of-pests-and-natural-enemies-in-field-crops

Beetles (Coleoptera)Beetles occur in all types of habitats and are among the commonest insects onfarmland. A few beetle species are crop pests but the majority are harmless, whilesome are important predators of crop pests (see page 175).Life cycleBeetle young (larvae) do not lookAdultanything like the adults. Theirouter skin cannot grow and so Pupamust be shed in a series ofmoults as the beetle larva grows.The developmental stagesbetween each moult are called‘instars’. When the larva is fullygrown, it moults again, revealing aFully grown larvapupa. This is a non-feeding stage,inside which the larval body is broken down and reassembled in the adult form.EggsLarvaDefining featuresAdult beetles have a defined head andthorax and a distinct pair of hard wingcases covering the rest of their bodies,which meet in a line down the middle.Hard wingcasesAntennaeBiting mouthpartsHeadThoraxAbdomenBeetle larvae have hardened, oftendark, heads with biting mouthparts. Theyhave three pairs of legs and spiracles(the openings of the respiratory system)along the sides of the body.Weevils are a type of beetle. The adultshave a snout with angular antennae. Thelarvae do not have legs (see page 11).BitingmouthpartsLegsSpiraclesSnoutElbowedantennaeHeadThoraxBiting mouthpartsAbdomenHeadThoraxHard wing casesAbdomenPests: Beetles16