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

Rape winter stem weevil (Ceutorhynchus pictarsis)Rape winter stem weevil (Ceutorhynchus pictarsis)Crops affectedCereals✔ OilseedsVegetable brassicasPotatoesCarrotsAlliumsPeasField beansSugar beetLettuceImportanceRape winter stem weevil is an occasional pest ofoilseed rape. It first came to attention in 1982, when anumber of severe infestations were experienced inthe east and south east. The main damage is causedby the larvae feeding within stems; adult feeding inthe autumn is not considered important.Risk factorsInitially limited to Lincolnshire and Cambridgeshire,the pest has now spread to other areas. Attacks areoften worse near wooded areas.Identification and symptomsAdults are 2.5–4 mm long, metallic black beetles, withelongated snouts, branched antennae and reddishbrownleg tips.Eggs are laid in leaf petioles and other crevices on theplant.Hatching larvae are white, plump and legless, with anorange-brown head end. After hatching, they burrowinto the leaf petiole and from there into the stem anddown to the crown of the plant, where numerouslarvae can congregate in clusters. At maturity, theycan reach 5 mm in length, at which point they leavethe plant and drop to the soil to pupate.© ADASAdult rape winter stemweevilLife cycleJan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec12334Adults emerge from the soil and disperse towoods and hedges, where they enter a restingphase.Adults invade autumn-sown oilseed rape crops,feeding on leaves.1 2Eggs are laid in punctures and crevices in the leafstalk and plant crown. Hatching larvae bore intothe stem to feed.4 Fully fed larvae descend to the soil to pupate.© ADAS3Adult rape winter stemweevilThe impact of larval feeding can vary widely,depending on the number of eggs laid on the plant.The larvae can destroy the terminal shoot, with theresult that some plants may die during the winterwhile others survive by developing secondary shoots,producing a stunted plant with a rosette-likeappearance. Attacked crops tend to be irregular andpatchy with uneven flowering and ripening.MonitoringAs adults are difficult to spot and larvae arechallenging to find, monitoring this pest can bedifficult. Where crops have previously been attacked, itis worthwhile inspecting the crop for young larvaefrom late October.ThresholdsNone established.Non-chemical controlNatural enemies include spiders, ground beetles, rovebeetles and several parasitoid species.Insecticide resistanceNone known.© Dewar Crop ProtectionRape winter stemweevil larva© SyngentaRape winter stemweevil damage31Pests: BeetlesPests: Beetles32