The original stimulus which started KENNETH SPENCER on a study of the Agro myzid flies was an invitation, which he accepted, to translate from the German the monograph on Leaf Miners by Professor E. M. HERING. From this developed nearly 20 years of collaboration until Professor HERING's death in 1967. Dr. SPENCER has himself described over 600 new species in the family, many of which he collected and reared from known host plants during his extensive travels to all the five main continents. Largely as a result of his work, the number of species known in Britain has increased from 90 in 1945 to 313 today. He is thus uniquely qualified to write this book about the hundred and fifty or so species which are regularly associated with cultivated plants. Much of the taxonomic detail provided here will be of value primarily to specialists; but with the help of a microscope and the botanical host list (Chapter 2) and the numerous illustrations (mostly prepared by ANN SPENCER) those in agri cultural institutes and elsewhere should now be able to identify the majority of species found attacking crops in any part of the world.

Phytophagous insects represent a very particular not really belong to their host plant range. This may group of organisms. Firstly, their number amounts lead to mistaken conclusions especially in regions to more than one quarter of all recent species (ex where only few observations were possible, as well cluding fungi, algae and microbes) and together with as in the case of uncommon insect species. Fourthly, the green plants on which they feed they form al the great majority (99. 4%) of the agromyzid species most one half of all living species described so far. studied show a high degree of host specialization Secondly, their overwhelming majority shows very which makes these insects especially suitable for narrow host plant specialization, that is they feed taxonomic-phylogenetic considerations. only on one or a few, mostly closely related plant With such an enormous amount of data, it may species, a characteristic that led J. H. Fabre to elab have been tempting to draw far-reaching conclu orate the notion of the 'insects' botanical instinct' a sions. However, the author has been very careful in century ago. doing this.