10 CIRCULAR 2 41, U. S. DEPARTMENT OF AGRICULTURE 



for the purpose of introducing them into the Hawaiian Islands in 

 hopes that they might prove of service in control of the sugarcane 

 leaf hopper (Perkinmella sacchwicida Kirk.). 



An extended study by Fenton (5) upon the dryinid parasites of 

 leaf hoppers has shown that these insects are Of very common oc- 

 currence, that many species have no other hosts, and that they are 

 very widely distributed in the meadow and pasture lands of many 

 regions. 



Among the Diptera a genus, Pipunculus, is recorded as parasitic 

 upon leaf hoppers, and Giard (10) is authority for the opinion that 

 these are in general parasites, especially of the family Jassidae (Tet- 

 tigoniidae). These have not been recognized to any great extent in 

 this country, and it can not be said to what extent they may be of 

 service here, although a species in this genus has been taken by Pro- 

 fessor Knowlton in considerable numbers from the sugar-beet leaf 

 hopper, Eutettix tenellus. 



The order Strepsiptera, or the twisted-winged insects, includes 

 some very peculiar and remarkable parasites, numbers of which 

 have been recognized as occurring on leaf hoppers. These parasites 

 are so minute and inconspicuous that they are very seldom observed, 

 and there are no very positive data as to the numbers in which they 

 may occur, so although they may be a very constant factor in con- 

 trol, it is doubtful if they can be credited with very much influence 

 in reducing the numbers of the hoppers. 



REMEDIAL MEASURES 



The usual methods of control for leaf hoppers may be discussed 

 here under the general head of remedial measures, but some of the 

 particular modes of treatment, applicable to certain species and to 

 particular conditions of culture, must be discussed in connection with 

 the species concerned. Practically all of the measures available 

 must be adapted to the seasons or conditions of crop, and, conse- 

 quently, to advise any general method which would be applicable 

 in all cases is impossible. 



CULTURAL METHODS 



Under the head of cultural methods the effect of different plans 

 of cropping or the rotation or alternation of different crops may be 

 discussed. This is, in many cases, one of the most effective means 

 in keeping leaf hoppers in check. The general immunity of spring 

 wheat in the northwestern wheat-growing regions is quite certainly 

 clue to the effect of the methods of culture prevailing there, which do 

 not permit of a general infestation of the wheat fields; for during 

 the time when the insects would scatter for oviposition, most of the 

 fields to be planted in wheat are bare and furnish no attraction. In 

 the case of the northern wheat regions, as in Pennsylvania, another 

 condition is evidently responsible for the lack of infestation, and this 

 is the extreme cleanliness of the culture, the fields being cultivated 

 so close to the fences that scarcely any grassland remains, and the 

 source from which the dispersal of the leaf hoppers generally takes 

 place is thus done away with. 



A very different condition is presented in fields which have been 

 continually in grass for a number of years. In such cases the hop- 



