CASE STUDIES INCLUDING COST BENEFIT ANALYSIS 1 COLORADO BEETLE STEP 1 PHYSICAL IMPACTS OF THE POLICY 1.1 Biology The Colorado Beetle is a pest of potato crops which has never become established in England. To be able to successfully manage the Colorado beetle, one needs a thorough understanding of its biology (XU G and Long GE, 1997). The pest is a leaf-feeding beetle. The adult is approximately 1.2 cm long and has characteristic longitudinal yellow and black stripes on its body. The adults hibernate deep in the soil and emerge in the late spring. These beetles walk or fly to potato crops. It is estimated that most beetles disperse up to about 1 km (Weisz et al. 1996). However, flight can be over very large distances when conditions are favourable, such as the crossing of the Baltic sea from Poland to Sweden in 1973 and of the English Channel in 1951. The females are mated in the autumn. In the spring one beetle is capable of laying up to 2400 eggs. The oval, 1.2 mm long yellow or light orange eggs are laid on the under-surface of potato leaves and take 4-12 days to hatch according to temperature. There are four larval stages, each feeding on potato leaves before once fully grown, digging in the soil and pupating. The number of generations depends on temperature. Thus in temperate countries such as the Netherlands, NW France and Germany there is one or one and sometimes a partial second generation whereas in hot climes there are three or four generations. In cold continental areas there may be partial generations with repeat overwintering by adults. Of particular interest to the England, Colorado beetle is endemic in France, The Netherlands and Germany. These are countries in the same climatic zone as England with the exception of S France. The pest is not yet established in Denmark, Finland, Norway and Sweden. It is endemic in a number of the former Eastern Block countries. In North America eastern provinces in Canada and Mexico are listed. A full list of countries is given in the data sheet on Colorado beetle produced by CABI and EPPO under contract 90/399003. The important thing to note is that Colorado beetle can breed in Canada and NW Europe in areas where the annual totals of accumulated temperatures above 10 degrees C are very similar to those in Britain. (Bartlett 1980). The Colorado beetle is constantly able to adapt to different climatic conditions (Ushatinskaya & Ivanchik 1992). The beetle is therefore ever moving into fresh areas and crossing international borders. (CABI/EPPO). This together with the potential amount of defoliation of potato crops makes Colorado beetle a pernicious pest. Colorado beetle remains a significant quarantine pest for much of the world where the bulk of potatoes are grown, for example China and Korea.
There are areas where the beetle survives over a greater range of temperatures and soil moistures than experienced in the UK.
A paper published in 1998 contains a prediction for the effect of climate change on Colorado beetle, using CLIMEX a computer program which estimates potential geographical distribution loaded with climatic scenarios. Thus in the UK the pest could extend its potential range by 120% with a 400 km shift of its northerly limit to include 99% of the ware and seed potato area. (Baker et al 1998). 1.2 Outbreaks and Interceptions The first outbreak took place at Tilbury, Essex, in 1901 when 70 beetles successfully overwintered. This outbreak was eradicated in 1902. There have been further outbreaks, all successfully eradicated giving a total of over 120 years of exclusion of this pest from this country. Looking wider at the European scene it is amazing that the entire European beetle population originated from the few individuals which arrived in Bordeaux in 1919. (CABI and EPPO Contract 90/399003) It is interesting to note that during the Second World War this pest became endemic in Jersey following the occupation of the island by the Germans. Colorado beetle...
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