THE CLOVER ROOT BORER ¥S 
they alight but usually maneuver to the highest point on the plant 
and again essay to fly, not always sucessfully, as they are clumsy in 
taking off. Negative geotropism is very pronounced at this time, so 
much so that if two root borers happen to climb the same grass blade, 
the second will climb upon the back of the first as the highest available 
point. This tendency is closely related to the temperature; and even 
the obscuration of the sun by a. cloud will often cause borers which 
have climbed plants to turn and descend to the ground. Observa- 
tions indicate that borers commonly fly from 6 to 10 feet above clo- 
ver fields, usually against the wind. Their flight is fairly straight 
and not rapid. 
Females predominate in the early days of flight, being frequently 
85 to 95 per cent of those collected. Of these, more than 90 per 
cent were found to have been fertilized before capture. In 1921, 
when a careful count by sexes of those collected was made, males 
Fig. 8.—Small bannerlike screen covered with sticky tree-banding material and used in flight 
experiments 
became more numerous (68. 6 per cent of the total catch) than fe- 
males on May 13, near the time of maximum flight. 
FLIGHT EXPERIMENTS 
As flight is the principal means of interfield dissemination of root 
borers, and as the time and extent of infestation of clover fields in the 
first crop year are therefore almost entirely dependent on habits of 
flight, this phase of root-borer activity was given special attention. 
Experiments with flight screens coated with sticky tree-banding 
material were conducted near Forest Grove, Oreg., in the humid 
Willamette Valley, and near Wapato, Wash., in the irrigated Yakima 
Valley. Screens of two types were used, the first being small and 
bannerlike (fig. 8), 18 or 24 inches wide by 3 feet long, placed on 
poles stuck in the ground and anchored by guy wires or nailed to 
