Leptinotarsa decemlineata (Say 1824)
Colorado Potato Beetle
This notorious pest of various cultivated Solonaceae is native to the southwest Nearctic region where its natural host is buffalobur nightshade, Solanum rostratum Donal, but with the widespread cultivation of potatoes during the nineteenth century the beetle switched hosts and expanded rapidly; it is estimated the north and eastward expansion continued at about 85 miles each year, finally reaching the east coast in 1874. It was first recorded in Europe in 1877 but this colony, along with others, was eradicated. Around the time of the First World War it became established in France and soon spread throughout northern Europe, a further expansion occurred in the 1940’s and the species is now a pest across much of Europe and Asia. Various other Solonaceae also host the species e.g. capsicum, tomato and aubergine which makes control more difficult but two other factors contribute to its success; its high fecundity and the way it has evolved immunity to most commercial insecticides, various fungal and bacterial pathogens have been successfully used but ultimately practical methods e.g. crop rotation, substitution or even hand picking the beetles have been resorted to. Adults overwinter on field margins, among hedgerows or in the soil and under debris etc. and become active in the spring, generally around the time the host foliage begins to develop. Females lay batches of 10-30 eggs under the host leaves and may continue doing so for several weeks, ultimately producing up to 400 eggs. The larvae hatch within two weeks and the first instars tend to remain aggregated, feeding as a group, they grow rapidly and the first three instars take 2 or 3 days to develop, the fourth takes between 4 and 7 days depending on temperature etc. and the last few days are spent as a prepupal which does not feed and will burrow into the soil to pupate. The adults eclose after about two weeks. Both adults and larvae consume foliage but most damage is done by the fourth instar larvae; when they are present in numbers they quickly skeletonise the foliage and this seriously affects the developing tubers. Where they are prolific all stages of development may be present by midsummer and there may be two or three generations in a season depending on the climate. The species is occasionally recorded in the U.K. but has never become established, following world war two posters warning of the beetle were displayed in libraries etc. so that gardeners could recognize and report any occurrence, it remains a notifiable pest and any found must be reported to The Food & Environment Research Agency.
Among the European fauna this species is distinct and should not be confused with any other; the large size, around 10mm, and striking colouration are unmistakable.
The genus contains about 40 New World species, not all of which feed on Solonaceae. The present species occurs throughout the U.S. and southern Canada, and in the south there is a closely similar species, incorrectly called The False Colorado Potato Beetle, L. juncta Germar, 1824.