Oviposition preference and sex ratio of redbanded stink bug, Piezodorus guildinii (Westwood) in Louisiana soybean

The redbanded stink bug, Piezodorus guildinii (Westwood), is a significant soybean pest across the Mid-South Region of the U.S. First documented in Louisiana soybean during 2000, it has become the dominate stink bug pest throughout the state, comprising 50 to 74% of total stink bugs collected. The objective of this study was to characterize redbanded stink bug oviposition in soybean and estimate adult sex ratios throughout the 2008 and 2009 soybean production season in Louisiana. Over 650 egg masses (clusters) from redbanded stink bug native populations were collected in field surveys of 2400 plants during June through September. The mean number of eggs within a cluster was 17.6 ± 0.26. Across all samples and years, egg clusters were more common on soybean pods (45%) and leaves (52%) compared to that on main stems (3%). However, egg masses were primarily recorded on leaves during the earlier soybean reproductive stages (R1-R3). During the pod filling stages (R4-R7) female oviposition was similar between pods (46%) and leaves (52%). Within the soybean plant, oviposition was distributed among the lower (43%), middle (37%) and upper (20%) canopies. During the two years, over 2,000 redbanded stink bug adults were collected with a sex ratio of 1.2 females to 1 male. A high frequency (80%) of eggs found in the lower two-thirds of the plant canopy could reduce redbanded stink bug nymph exposure to insecticide sprays. The slightly higher female to male ratio ensures that females are available to selected males during mating.