PLANTÐINSECT INTERACTIONS Sorghum as a Trap Crop for Nezara viridula L. (Heteroptera: Pentatomidae) in Cotton in the Southern United States

The southern green stink bug, Nezara viridula L., may disperse from alternate host plants, especially corn,ZeamaysL., andpeanuts,Arachis hypogaeaL., into cotton,Gossypiumhirsutum L. Trap crops may be useful to intercept dispersing stink bugs. Therefore, the ability of sorghum, Sorghum bicolor L. Moench, to trap N. viridula adults in cotton was studied for 3 yr. The 2002 experimentwas designed to compare the ability of small plots of sorghumandcotton to trapN. viridula along the interface, or common boundary, of a corn and cotton Þeld. In the 2003 experiment, cotton Þelds with sorghum and cotton plots planted along the interface of a cornÐcotton farmscape were compared with cotton Þelds without these interface plots. In both experiments, N. viridula adults strongly preferred sorghum to cotton, and marking studies revealed that most N. viridula adults that dispersed into sorghum remained in sorghum instead of moving into cotton. Overall, percent parasitismofN. viridula adults byT. pennipeswas higher in sorghum trap cropplots than in interface cotton control plots. In 2003, density of N. viridula adults was lower in cotton Þelds adjoining sorghum trap crop plots than in control cotton Þelds. Furthermore, economic threshold for N. viridula was not reached along the interface of the cornÐcotton farmscape in any cotton Þeld with sorghum plots. In contrast, economic threshold was reached in 61.5% of the control cotton Þelds. In the third season, a full-scale Þeld experiment was conducted to determine the effectiveness of sorghum, planted in a strip along the length of the interface of a peanutÐcotton farmscape, as a trap crop in cotton. Before the test, each cotton Þeldwas partitioned into eight side-edge and three interior block locations. Each Þeld had four sides with side A occurring along the interface of the Þeld. Edge 1 was 0Ð3.66 m from the outside edge of the Þeld, and edge 2 was 3.66Ð7.31 m from the outside edge of the Þeld. In control cotton Þelds, density of N. viridula adults was much higher in the interface side in edge one than in any other side-edge location, strongly indicating that N. viridula adults dispersed from peanuts into these cotton Þelds. Control cotton Þelds had higher numbers ofN. viridula adults in the interface side inedgeonecomparedwithcottonÞeldswith sorghumtrapcrops.Overall, in 2004, control cottonÞelds were treated with insecticides for control ofN. viridula 1.4 times, whereas cotton Þelds with sorghum trap crops were treated for control of this stink bug only 0.2 times. These results show that sorghum can serve as a trap crop for N. viridula adults in cotton Þelds.