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 ET-169 December 1940 
 
 United States Department of Agriculture 
 Bureau of Entomology and Plant Quarantine 
 
 IMPROVEMENTS IN THE STANDARD INSECT SWEEP NET 
 
 By W. C. Cco'.i and E. W. Davis, Division of Truck Crop 
 and Garden Insect Investigations 
 
 The standard sweep net, with a circular opening about 15 
 inches in diameter, has been used for collecting leafhoppers on the 
 beet leaf hopper project ever since the work was started. Various 
 workers have recognized the drawbacks of net collection as an 
 indicator of leafhopper populations, and other quantitative methods 
 have been devised and used extensively, but the sweep net still 
 remains the most rapid method available, and efforts have been made 
 to increase its efficiency and reliability. Two improvements in 
 the sweep net which have been made at this laboratory during the 
 past two years are described below. 
 
 I. Modification of the Net Frame for Sweeping Low Vegetation 
 
 The standard insect net has a round opening, and when vege- 
 tation a few inches in height is swept, only a small part of the 
 circumference of the net opening comes in contact with the vege- 
 tation. During the winter of 1938-39 the senior writer experimented 
 with various modifications of this round opening, finally producing 
 a net frame that was nearly semicircular. It was found that this 
 type of opening regularly secured larger numbers of leafhoppers 
 than the ordinary circular net, and that the collections tended to 
 be more uniform, because of the greater disturbance of the vege- 
 tation. 
 
 The semicircular frame is constructed by bending the two 
 members of the frame at right angles approximately T-g- inches from 
 the tips. The bending is facilitated by heating the frame with a 
 blowtorch at the point where the bend is to be made. The temper of 
 the steel is altered at this point, but this seems to make little 
 difference in the strength of the frame, as such frames have been 
 in constant use for over a year without giving evidence of weakness. 
 
 Figure 1 shows the modified net frame and a standard round 
 frame without nets. The greater efficiency of the modified net 
 frame for use on low-growing vegetation can be easily seen froa 
 the photograph. 
 
- 2 - 
 
 II. An Improved Net Bag 
 
 The cloth bag originally used for sweeping work was made of 
 heavy cotton or light canvas material. Experiments with lighter 
 materials, performed by the senior writer and F. R. Lawson during 
 1930 and 1931, showed that some of these lighter materials could be 
 used to good advantage, and in recent years most of the nets used 
 have been made from cotton scrim or marquisette, which allows the 
 air to flow through the net. Air flow is of considerable import- 
 ance, as comparative tests have shown that a porous net will 
 capture at least twice as many leafhoppers as one made of material 
 so tightly woven that it seriously obstructs air flow. The chief 
 disadvantage of the more open materials is their tendency to catch 
 upon twigs and thorns, which tear the net or open up the threads 
 of the weave so that leafhoppers escape. This makes it necessary 
 to replace the net bags frequently, as one bag will seldom last for 
 more than two or three days of active service. The junior writer 
 suggested that net bags be constructed of two materials, the outer 
 or lower half of heavy cotton sheeting, and the upper or inner half 
 of marquisette. The half made of heavy cotton sheeting would come 
 in contact with the rough vegetation and the ground, while the 
 half made of marquisette would permit the free passage of air. 
 Such nets have been used for over a week of heavy duty without 
 showing any signs of wear, and they capture as many leafhoppers 
 as nets constructed entirely of open-weave material. 
 
 In constructing these nets the two materials are sewed to- 
 gether with a flat or "felled" seam, so that the net is reversible. 
 Figure 2 shows one of the net bags, and figure 3 shows the bag in 
 position on one of the modified net frames. 
 
Figure 1. — The standard round sweep net frame and the 
 new eemicircular frame. 
 
 Figure 2. — The new net b^g, made half of 
 cotton sheeting and half of marquisette. 
 
 Figure 3. — The new net bag, in po- 
 sition on a semicircular frame. 
 
UNIVERSITY OF FLORIDA 
 
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 3 1262 09082 5034