584 A CENTURY OF PROGRESS IN THE NATURAL SCIENCES 



SystematiscJie Hymenopterologie und Bipterologie (1901-1908), Konowia (1922- 

 1931), and Insecutor Inscitiae Menstruus (1913-1926). 



Modern Control of Dipterous Pests: The Diptera are of economic importance 

 chiefly through their attacking man and animals and by the transmission of 

 various diseases, as discussed earlier. A further group of species destroy various 

 crops, among such being certain gall midges, Cecidomyidae, as the hessian fly, 

 pear midge, cloverseed midge, chrysanthemum midge, and others (Barnes, 1946- 

 date) ; the fruit flies, notably the apple maggot, Mediterranean fruit fly, Mexi- 

 can fruit fly, and many others; and a variety of pests that attack garden and 

 forage crops, as the frit fly, cabbage maggot, and many others. Before the ad- 

 vent of modern sj^nthetic insecticides (about 1945) a system of control had been 

 established against most of these pests, based partly on chemicals, but also utiliz- 

 ing biological and cultural methods. With the discovery of DDT and other well- 

 known chemical compounds, very effective controls for many of these pests were 

 obtained and it appeared that for certain of these, at least, the problem of hold- 

 ing them in check had been solved. However, at the present moment it has 

 become apparent that certain of these insects have built up a strong resistance 

 to all such types of chemicals and it appears that it is only a question of time 

 before we will have to revert, at least in part, to former methods of control. 

 Such statements apply specifically to the housefly and mosquitoes but appar- 

 ently it eventually will apply also to most if not all of the other forms against 

 which such chemicals are now used. 



The Future 



The vast increase in our knowledge of the Diptera during the past century 

 seems certain to continue in every field of study. As regards taxonomy, it is 

 certain that far less than one half of the species in the order have been described 

 and, as indicated previously, it seems very possible to me that perhaps only some 

 20 per cent may have been made known to this date. The airplane and other 

 methods of modern transportation will enable collectors to visit the remote spots 

 of the earth and the great museums will continue to grow apace. The value of 

 the type specimen has become increasingly apparent and every possible precau- 

 tion should be taken to safeguard such unusually valuable specimens against 

 loss from fire, atomic destruction, or from any other cause. As an added pre- 

 caution, wherever possible, such types should be photographed or so illustrated 

 that there remains no possible question as to the identity of the species. As the 

 number of described Diptera increases, students of the world fauna will of neces- 

 sity be compelled to restrict their studies to individual families or perhaps 

 even to lesser categories, such as genera. Already there are certain genera in 

 the order with more than 1,500 described species, with many more awaiting 

 discovery. 



Until very recently work on the taxonomy of any major group of insects 

 was possible only lo students who were connected with leading museums or uni- 

 versities that possessed unusually complete library facilities. The development 

 of the microfilm and photostat processes, with other methods of reproducing 

 literature quickly and economically, has changed this picture and it is now pos- 

 sible to procure copies of papers in rare or otherwise virtually unobtainable 



