The biotype concept and its application to insect pests of agriculture

The use of the term biotype of insect pests of agriculture is discussed in the broad context of species, populations and individuals. There have generally been two quite distinct usages and thus two different concepts. The first is a general concept which applies, confusingly, both to individuals and to populations of a species which share certain biological characteristics, usually concerning virulence on different host varieties, with little or no knowledge of their genetic bases. This is generally synonymous with the term host race, used by many authors. The second is a very specific concept in which a particular gene or genotype for virulence in a pest is known to correspond with a particular gene for resistance in a host plant—the gene-for-gene relationship. We argue that the first concept is so general as to be of little value, and in some examples, such as the brown planthopper of rice, is potentially misleading. The specific concept depends on detailed genetic analyses which are available for very few examples and is thus of limited applicability. We conclude that the confusion of the two distinct concepts is dangerous. It is not possible to argue from the general to the specific. The term biotype has often been used to cover our ignorance of the detail of any particular insect/plant interaction.