Leptinotarsa decemlineata Say Colorado beetle

The Colorado beetle is a notorious pest of potato. Infestations may also occur on related plants, including aubergine, tomato and common related weeds (Solanaceae) such as Solanum dulcamara and S. nigrum. The pest is of North American origin and was first noted in Europe in 1877, where it is now widely distributed; although often accidentally introduced, it is not established in the British Isles. The adults attack the leaves of host plants, but most damage is caused by the larvae. They feed ravenously and heavy infestations often lead to complete defoliation; infested plants are also contaminated by masses of black, wet frass excreted by both adults and larvae. Severe damage, often resulting in 50% yield loss, is most likely to occur in hot, dry summers. Direct feeding on potato tubers may occur, but usually only in store.

BIOLOGY

Adults hibernate deep in the soil, often up to half a metre below the surface. They emerge in the following year, usually in June, and then seek host plants on which to feed. In areas where the pest is well established and routine insecticidal sprays are applied to potato crops, infestations are usually most readily detected on volunteer potato plants that have emerged in crops such as cereals. Eggs are laid in batches of 20-80 on the underside of the leaves, each female being capable of depositing many hundreds of eggs over a month or more. The eggs hatch in about a week and the larvae then feed for about 3-5 weeks, passing through four instars. Fully grown larvae enter the soil to pupate in earthen cells. New adults emerge 2-3 weeks later. These beetles feed on potato foliage during the summer, and some may lay eggs to produce a second brood of larvae, before eventually overwintering. Any second-brood larvae that successfully complete their development before the potato haulm dies down in the autumn, pupate in the soil to produce new adults in the following year. Adults have a life span of up to 2 years. As a result of this and the protracted period of egg laying, the generations often overlap so that, during the summer months, all stages of the pest may be found together.

DESCRIPTION

Adult 10 mm long, distinctly hemispherical; head, thorax, legs and antennae orange, marked with black; elytra longitudinally striped alternately black and yellow (Plate 3f). Egg 1.2 mm long, yellowish-orange. Larva up to 12mm long; body sac-like, at first reddish-brown, later reddish-orange, with two rows of prominent black spots along either side; head, prothoracic plate and anal plate black; abdomen with several short, fleshy prolegs, including a well-developed pseudopod on the anal segment (see Fig. 75).

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