T.L. Clayton1, G.M. Lorenz2, J.T. Hardke3, N. Bateman1, A.J. Cato4,
K. McPherson2, N.M. Taillon2, L. McCullars4, D.L. Frizzell3,
E. Castaneda-Gonzalez3, G.J. Lee3, W.J. Plummer3, W.A. Plummer2,and J.L. Black2
Abstract
The objective of this study was to determine the amount of damage that increasing densities of rice stink bug (RSB) could cause to different developmental stages of rice. Mesh field cages were used in established rice plots to contain introduced rice stink bugs which were infested at the following kernel development stages: flowering, milk, soft dough, and hard dough. Densities of 0, 17, 34, and 68 RSB per 10 sweeps were used for infestation densities. The first infestation timing was initiated at the flowering and milk stage. The second infestation timing was initiated at the soft and hard dough stages. No yield loss was observed for RSB density or infestation timing. Total peck and RSB peck observed on brown rice was greater with RSB densities of 68 per 10 sweeps and during the soft and hard dough infestation timing. Peck percentages never exceeded 1.5% peck even at the highest densities of RSB.
Introduction
The rice stink bug, Oebalus pugnax (F.), is a pest of rice that feeds on developing grains. Feeding by rice stink bug (RSB) during the flowering and milk kernel stages can cause kernels to become severely shrunken or be completely blank. When RSB feeding occurs during the soft dough and hard dough kernel stages, an area of chalky discoloration at the feeding site is often formed. This discoloration is known as ‘pecky’ rice and is caused by the invasion of fungi into developing rice kernels after the RSB has pierced the rice kernels during feeding (Swanson and Newsom, 1962; Hollay et
1 Program Associate I, Assistant Professor/Crop Entomologist, respectively, Department of Entomology,
Stuttgart.
2 Extension Entomologist, Program Associate, Program Associate, Program Associate, and Program
Technician, respectively, Department of Entomology, Lonoke.
3 Rice Extension Agronomist, Program Associate III, Program Associate I, Program Associate, and Pro-
gram Technician, respectively, Department of Crop, Soil, and Environmental Sciences, Stuttgart.
4 Graduate Assistant and Graduate Assistant, respectively, Department of Entomology, Fayetteville.
al., 1987). The rice inspection handbook allows for no more than 0.5% damaged grain, including pecky rice, in a 500-g sample to be considered U.S. grade 1 (USDA-FGIS, 2009). Grade reductions due to increased amounts of damaged kernels can lead to losses to the value of the harvested grain with drastic economic impacts occurring at grade 3 rice or 2.5% peck (USDA-FGIS, 2009). Clayton et al. (2016) observed more damage to milk stage rice at RSB densities of 3 RSB per 10 sweeps and above compared to the non-infested control and 1.5 RSB per 10 sweeps. Espino et al. (2007) also found significant amounts of RSB damage at the soft dough infestation timing; although, much greater RSB densities were used than in Clayton’s trials. The question of when RSB need to be controlled is still contested, with reports such as Espino et al. (2007) and Awuni et al. (2015) observing that increasing densities of RSB are able to cause damage to different kernel development stages of rice. The objective of this study was to determine the amount of damage that increasing densities of rice stink bug (RSB) could cause to different developmental stages of rice.
Procedures
Experiments were conducted at the University of Arkansas System Division of Agriculture’s Rice Research and Extension Center near Stuttgart, Ark. The cultivar Diamond was drill-seeded on 25 April 2017 and grown according to standard agronomic practices for Arkansas. Plots were 60 inches wide, 8 rows on 7.5-inch drill spacing, and 70 inches in length. This experiment was designed as a randomized compete block with four replications per infestation timing.
Mesh field cages were placed over plots prior to heading and an application of Karate Z at 2.56 oz/acre was used to prevent natural infestations of RSB and to remove any beneficial insects present. An application of Quilt Xcel 27 oz/acre was used to prevent multiple diseases. When approximately 50% of the plants in a plot reached the desired growth stage of kernel development, RSB infestations were initiated. Rice stink bug adults and late-instar nymphs were collected with standard 15 inch sweep nets in heading rice fields and weedy areas surrounding rice fields. Insects were kept in small cages with fresh plant material, a cotton ball soaked in sugar water, and a moist paper towel in a laboratory at 75 °F for 24 h prior to infestation in field cages to reduce mortality rate. Cage frames were 6 ft × 6 ft × 6 ft made from 1-inch PVC pipe with 6 ft × 6 ft amber fabricated coverings (Lumite, Inc., Alto, Ga.). The desired number of RSB were placed in small foam cups and placed in the rice canopy and allowed to move freely. Two infestation timings were used consisting of: flowering to milk growth stages; and soft to hard dough growth stages. A sequential infestation of RSB was made 7 days after the initial infestation with the same level of RSB. Infestations were terminated 7 days after the second infestation within a growth stage, and then terminated with a foliar insecticide application. Cages were kept in place until harvest. Infestation levels were 0, 42, 84, and 168 RSB/plot, or a density of 0, 17, 34, and 68 RSB per 10 sweeps, respectively.
Ten rice panicles were removed from each plot and placed in a brown paper bag, then stored in a grain dryer until moisture was 12%. These panicles were harvested by
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hand by separating whole kernels from blank kernels (unfilled kernels), with partially filled kernels counted as whole kernels. The center 4 rows of each plot were harvested with a plot combine, and harvested seed was stored in a cloth bag and placed in a grain dryer until moisture was 12%. A random 100-g sample of seed harvested with the plot combine was dehulled for examination of ‘peck’ using a light box. Seed was separated into undamaged, damaged, and RSB damaged seed. The seed in each category was weighed and the percentage of damage for each plot was calculated. After harvest, a random sample of 162-g of rough rice from each plot was used to evaluate grain milling quality. Rice was milled to obtain percent head rice (whole kernels) and percent total white rice (whole and broken kernels).
Results and Discussion
A trend of decreasing yield with increasing RSB populations was observed in the bloom and milk infestation timing, but there was no difference (P = 0.84, Fig. 1). No yield trend was observed for the soft and hard dough infestation timing (Fig. 1). Awuni et al. (2015) found uninfested plots yielded higher than plots infested with 10 and 20 RSB per 10 sweeps. Bowling (1963) observed a difference in yield between the non-infested cage and the highest infested cage of 50 RSB per 10 sweeps.
No interaction was observed for infestation timing by infestation density for total damage on brown rice (P = 0.17). Differences were observed for total damage on brown rice for RSB density, with the 68 RSB per 10 sweeps infestation density having higher total damage than the 0 and 17 RSB per 10 sweeps infestation densities (P < 0.01, Fig. 2). Clayton et al. (2016) found higher damage in plots infested with 3, 10, and 17 RSB per 10 sweeps than plots infested with 0 or 1.5 RSB per 10 sweeps. The soft and hard dough timing had higher total damage on brown rice than the bloom and milk timing (P < 0.01, Fig. 3). No interaction was observed for infestation timing by infestation density for RSB damage on brown rice (P = 0.18). An effect of RSB density was observed for RSB damage on brown rice (P < 0.01, Fig. 4). The 68 RSB per 10 sweeps infestation density had more RSB damage on brown rice than all other densities of RSB (Fig. 4). The 34 RSB per 10 sweeps infestation density had more RSB damage than the 0 RSB per 10 sweeps infestation level (Fig. 4). The soft and hard dough infestation timing had higher RSB damage on brown rice than the bloom and milk infestation timing (P < 0.01, Fig. 5). Espino et al. (2007) also found an increase in damage at soft dough in two experiments.
No interaction was observed for percent total rice (P = 0.81) or percent head rice (P = 0.36) between infestation timing and infestation density. No differences were observed for percent total rice or percent head rice. This agrees with Clayton et al. (2017), where there was no difference in milling yields across density or timing. There were no differ- ences observed for blank kernels for infestation timing or infestation density. Blackman (2014) also found no differences in unfilled kernels with RSB densities ranging from 2 to 37 RSB per 10 sweeps; although, Awuni et al. (2015) found an increase in blank kernels with an increase in RSB density.
Studies evaluating RSB damage potential have been conducted since the 1960s. In general findings are not consistent, with multiple studies observing yield loss and
high percentages of damage from RSB infestation and others observing little to no damage from RSB. This is likely due to outside factors including weather and disease occurrence. Further research is needed to evaluate these other factors to determine the damage potential of RSB.
Significance of Findings
The rice stink bug is an important economic pest of rice. Approximately 10 million dollars annually is spent on insecticide applications targeting rice stink bug in Arkansas. Current studies are suggesting that the threshold for RSB still needs to be evaluated. It is important that growers are provided with a threshold for control of this pest to avoid yield and quality losses, but equally important to avoid making unnecessary applica- tions for control to maximize profit for rice growers.
Acknowledgments
The authors would like to express our appreciation for funding and support from the Arkansas rice growers administered through the Rice Research and Promotion Board. We also wish to thank Chuck Pipkins for his assistance with this project. Support also provided by the University of Arkansas System Division of Agriculture.
Literature Cited
Awuni, G.A., J. Gore, D. Cook, F. Musser, A. Catchot, and C. Dobbins. 2015. Impact of Oebalus pugnax (Hemiptera: Pentatomidae) infestation timing on rice yields and quality. J. Econ. Entomol. 108(4):1739-1747.
Blackman, B.D. 2014. Evaluatin of economic injury levels and chemical control recommendations for rice stink bug (Oebalus pugnax) in Louisiana. Dissertation. Louisiana State University. Baton Rouge, La.
Bowling, C.C. 1963. Cage tests to evaluate stink bug damage to rice. J. Econ. Ento- mol. 56(2):197-200.
Clayton, T.L., G.M. Lorenz, J.T. Harke, G.J. Lee, E. Castaneda-Gonzalez, D.L. Friz- zell, and H.M. Chaney. 2016. Evaluation of rice kernel damage and yields due to rice stink bug, Oebalus pugnax, population and infestation timing. In: R.J. Nor- man and K.A.K. Moldenhauer (eds.). B.R. Wells Arkansas Rice Research Stud- ies. 2015. University of Arkansas Agricultural Research Station Research Series 634:137-145. Fayetteville.
Clayton, T.L., G.M. Lorenz, J.T. Hardke, A.J. Cato, G.J. Lee, H.M. Chaney,E. Castaneda-Gonzalez, D.L. Frizzell, N.M. Taillon, J.L. Black, and W.A. Plummer. 2017. Effect of rice stink bug, Oebalus pugnax, on Rice Quality and Yields. In: R.J. Norman and K.A.K. Moldenhauer (eds.). B.R. Wells Arkansas Rice Research Studies. 2016. University of Arkansas Agricultural Research Station Research Series 643:158-165. Fayetteville.
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Espino, L., M.O. Way, and J.K. Olson. 2007. Most susceptible stage of rice panicle development to Oebalus punax (Hemiptera: Pentatomidae). J. Econ. Entomol. 100(4):1282-1290.
Hollay, M.A., C.M. Smith, and J.F. Robinson. 1987. Structure and formation of feed- ing sheaths of rice stink bug (Heteroptera: Pentatomidae) on rice grains and their association with fungi. Ann. Entomol. Soc. Am. 80:212-216.
Swanson, M.C. and L.D. Newsom. 1962. Effect of infestation by the rice stink bug,
Oebalus pugnax, on yield and quality in rice. J. Econ. Entomol. 55(6):877-879.
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Fig. 1. Yield for multiple densities of rice stink bug at two infestation timings for studies conducted at the University of Arkansas System Division of Agriculture Rice Research
Fig. 2. Percent total brown rice damage for multiple densities of rice stink bug for studies conducted at the University of Arkansas System Division of Agriculture Rice Research and Extension Center, near Stuttgart, Ark., in 2017. Means followed by different letters are
significantly different at P = 0.05.
Fig. 3. Percent total brown rice damage for two infestation timings of rice stink bug for studies conducted at the University of Arkansas System Division of Agriculture Rice
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Fig. 5. Percent total rice stink bug damage on brown rice damage for two infestation timings of rice stink bug for studies conducted at the University of Arkansas System Division of Agriculture Rice Research and Extension Center, near Stuttgart, Ark., in 2017.
Fig. 4. Percent rice stink bug damage on brown rice damage for multiple densities of rice stink bug for studies conducted at the University of Arkansas System Division of Agriculture Rice Research and Extension Center, near Stuttgart, Ark., in 2017. Means