Influence of Dual-Bt Protein Corn on Bollworm, Helicoverpa zea (Boddie), Survivorship on Bollgard II Cotton.

Similar Cry proteins are expressed in both Bt corn, Zea mays L., and cotton, Gossypium hirsutum (L.), commercial production systems. At least one generation of corn earworm, Helicoverpa zea (Boddie), completes development on field corn in the Mid-South before dispersing across the landscape into other crop hosts like cotton. A concern is that Bt corn hybrids may result in selection for H. zea populations with a higher probability of causing damage to Bt cotton. The objective of this study was to determine the susceptibility of H. zea offspring from moths that developed on non-Bt and VT Triple Pro (VT3 PRO) field corn to lyophilized Bollgard II cotton tissue expressing Cry1Ac and Cry2Ab. Offspring of individuals reared on VT3 PRO expressing Cry1A.105 and Cry2Ab had a significantly higher LC50 two out of the three years this study was conducted. Excess larvae were placed on artificial diet and allowed to pupate to determine if there were any inheritable fitness costs associated with parental development on VT3 PRO corn. Offspring resulting from males collected from VT3 PRO had significantly lower pupal weight and longer pupal duration compared with offspring of individuals collected from non-Bt corn. However, offspring from females collected from VT3 PRO were not different from non-Bt offspring. Paternal influence on offspring in insects is not commonly observed, but illustrates the side effects of development on a transgenic plant expressing less than a high dose, 25 times the concentration needed to kill susceptible larvae.

Efficacy of Selected Insecticides Applied to Hybrid Rice Seed.

Hybrid rice and insecticide seed treatments targeting rice water weevil, Lissorhoptrus oryzophilus Kuschel, have altered the landscape of rice production. The effect of reduced seeding rates on seed treatment efficacy in hybrid rice has not been studied. During 2011 and 2012, an experiment was conducted at seven locations to determine the relationship between low seeding rates used in hybrid rice and efficacy of selected insecticidal seed treatments as measured by rice water weevil densities and yield. Labeled rates of thiamethoxam, chlorantraniliprole, and clothianidin were compared with higher rates of these products to determine if labeled rates provide an acceptable level of control of the rice water weevil. Study locations were divided into low, moderate, and high groups based on rice water weevil larval densities. All seed treatments and seed treatment rates reduced rice water weevil densities. However, there was no observed yield or economic benefit from the use of an insecticidal seed treatment in areas of low pressure. Differences in yield were observed among seed treatments and seed treatment rates in moderate and high pressure locations, and all seed treatments yielded better than the untreated plots, but these differences were not always economical. All seed treatments showed an economic advantage in areas of high weevil pressure, and there were no differences among seed treatment products or rates, suggesting that currently labeled seed treatment rates in hybrid rice are effective for rice water weevil management.

Impact of Oebalus pugnax (Hemiptera: Pentatomidae) Infestation Timing on Rice Yields and Quality.

Sleeve and large field cage experiments were conducted in Stoneville, MS, in 2010 and 2011 to assess adult rice stink bug, Oebalus pugnax (F.), injury in rice. 'Cocodrie' and 'Wells' were infested at bloom, milk, and soft dough stages of panicle development. Twenty rice panicles were infested individually in the sleeve cage experiment as replicates with 0, 1, or 2 O. pugnax in a split-plot, completely randomized design. The large cage experiment had four replications infested with 9 or 18 O. pugnax per square meter over multiple rice panicles in a split-plot, randomized complete block design per cultivar. Caged uninfested controls were included in each experiment. Rough rice yield and percentage of clean, damaged, and blank kernels were evaluated. In both experiments, stage of panicle development impacted grain yield and quality. Yield loss was greatest during the bloom stage, while kernel damage was greatest during the milk and soft dough stages. Rice yield decreased with increased infestation density. Kernel damage increased with increased infestation density. Blank kernels affect yield, while kernel damage affects grain quality. While grain yield is the bottom line, grain quality affects marketability, which directly affects yield profitability. Based on these results, this study considers O. pugnax injury significant in all three stages of panicle development and concludes that a more aggressive threshold is recommended from panicle emergence through soft dough. More research is needed to determine the specific threshold, but it appears to be lower than the current threshold of 5 per 10 sweeps.

Impact of Water Management on Efficacy of Insecticide Seed Treatments Against Rice Water Weevil (Coleoptera: Curculionidae) in Mississippi Rice.

Two experiments were conducted at the Delta Research and Extension Center in Stoneville, MS, during 2011 and 2012 to determine the impact of water management practices on the efficacy of insecticidal seed treatments targeting rice water weevil, Lissorhoptrus oryzophilus Kuschel. Larval densities and yield were compared for plots treated with labeled rates of thiamethoxam, chlorantraniliprole, and clothianidin and an untreated control. In the first experiment, plots were subjected to flood initiated at 6 and 8 wk after planting. Seed treatments significantly reduced larval densities with the 8-wk flood timing, but not the 6-wk flood timing. Overall, the treated plots yielded higher than the control plots. In the second experiment, the impact of multiple flushes on the efficacy of insecticidal seed treatments was evaluated. Plots were subjected to zero, one, or two flushes with water. All seed treatments reduced larval densities compared with the untreated control. Significantly fewer larvae were observed in plots that received one or two flushes compared with plots that did not receive a flush. All seed treatments resulted in higher yields compared to the untreated control in the zero and one flush treatments. When two flushes were applied, yield from the thiamethoxam and clothianidin treated plots was not significantly different from those of the control plots, while the chlorantraniliprole treated plots yielded significantly higher than the control. These data suggest that time from planting to flood did not impact the efficacy of seed treatments, but multiple flushes reduced the efficacy of thiamethoxam and clothianidin.

The Impact of Simulated Corn Earworm (Lepidoptera: Noctuidae) Damage in Indeterminate Soybean.

Field experiments were conducted in Starkville and Stoneville, MS, during 2012 and 2013 to evaluate fruit removal level and timing on soybean growth, crop maturity, and yield. Fruit removal treatments consisted of 0, 50, and 100% of all fruit removed at specified growth stages (R2, R3, R4, and R5.5). Plant heights were determined at least biweekly from the time damage was imposed until R7. The impact of fruit removal level and timing on crop maturity was determined by estimating the percentage of naturally abscised leaves at 137 days after planting (DAP) when control plots were ∼10-15 d from harvest and the percentage of nonsenesced main stems at 139 DAP. There was no significant impact of fruit removal timing or fruit removal level on plant height or canopy width. Significant delays in crop maturity were observed when fruit removal was imposed at the R5.5 growth stage. Significant reductions in yield and crop value were observed as early as R3 and R4 when 100% of fruit was removed. Both fruit removal levels at R5.5 resulted in a significant reduction in yield and crop value compared with the nontreated control. Indeterminate soybeans appear to have the ability to compensate for some fruit loss during the early to middle reproductive growth stages without delaying maturity. However, severe fruit loss causes increasingly more yield loss as the plant approached maturity. Thresholds and economic injury levels therefore need to be adjusted accordingly to account for the dynamic nature of yield losses and crop maturity delays.

Lepidoptera (Crambidae, Noctuidae, and Pyralidae) Injury to Corn Containing Single and Pyramided Bt Traits, and Blended or Block Refuge, in the Southern United States.

Fall armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae); corn earworm, Helicoverpa zea Boddie (Lepidoptera: Noctuidae); southwestern corn borer, Diatraea grandiosella Dyar (Lepidoptera: Crambidae); sugarcane borer, Diatraea saccharalis F. (Lepidoptera: Crambidae); and lesser cornstalk borer, Elasmopalpus lignosellus Zeller (Lepidoptera: Pyralidae), are lepidopteran pests of corn, Zea mays L., in the southern United States. Blended refuge for transgenic plants expressing the insecticidal protein derivative from Bacillus thuringiensis (Bt) has recently been approved as an alternative resistance management strategy in the northern United States. We conducted a two-year study with 39 experiments across 12 states in the southern United States to evaluate plant injury from these five species of Lepidoptera to corn expressing Cry1F and Cry1Ab, as both single and pyramided traits, a pyramid of Cry1Ab×Vip3Aa20, and a pyramid of Cry1F×Cry1Ab plus non-Bt in a blended refuge. Leaf injury and kernel damage from corn earworm and fall armyworm, and stalking tunneling by southwestern corn borer, were similar in Cry1F×Cry1Ab plants compared with the Cry1F×Cry1Ab plus non-Bt blended refuge averaged across five-plant clusters. When measured on an individual plant basis, leaf injury, kernel damage, stalk tunneling (southwestern corn borer), and dead or injured plants (lesser cornstalk borer) were greater in the blended non-Bt refuge plants compared to Cry1F×Cry1Ab plants in the non-Bt and pyramided Cry1F×Cry1Ab blended refuge treatment. When non-Bt blended refuge plants were compared to a structured refuge of non-Bt plants, no significant difference was detected in leaf injury, kernel damage, or stalk tunneling (southwestern corn borer). Plant stands in the non-Bt and pyramided Cry1F×Cry1Ab blended refuge treatment had more stalk tunneling from sugarcane borer and plant death from lesser cornstalk borer compared to a pyramided Cry1F×Cry1Ab structured refuge treatment. Hybrid plants containing Cry1F×Cry1Ab within the pyramided Cry1F×Cry1Ab blended refuge treatment had significantly less kernel damage than non-Bt structured refuge treatments. Both single and pyramided Bt traits were effective against southwestern corn borer, sugarcane borer, and lesser cornstalk borer.

Impact of planting date and varietal maturity on tarnished plant bug (Hemiptera: Miridae) in cotton.

A field experiment was conducted in Stoneville, MS, during 2010 and 2011 to investigate the impact of varietal maturity, planting date, and insecticide application on tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), populations and damage in cotton. Four planting dates were selected to encompass the cotton-planting period in Mississippi. An early and late maturing variety were planted at each planting date, and each variety and planting date combination was either sprayed or unsprayed for tarnished plant bugs. Plots were sampled weekly from first square until physiological maturity. Plots were harvested at the end of the season. Early planting dates had lower densities of tarnished plant bug and required fewer insecticide applications than the later planting dates. Mid-April to early May planting dates sustained less yield loss from tarnished plant bug than mid-May to late-May planting dates. Tarnished plant bug had less impact on yield of the early maturing variety than on the late maturing variety. The sprayed plots yielded more than unsprayed plots. These data demonstrate that later plantings of cotton in the Mississippi Delta are likely to experience yield losses from tarnished plant bug and need to be sprayed more compared with early cotton plantings. As a result, growers should manage their crop for earliness through planting date and varietal selection.

Effects of aldicarb and neonicotinoid seed treatments on twospotted spider mite on cotton.

Twelve field experiments and one laboratory experiment were conducted to determine the effects of furrow applied aldicarb and seed treatments of thiamethoxam, imidacloprid, Avicta (thiamethoxam + abamectin), Aeris (imidacloprid + thiodicarb), and acephate on twospotted spider mite, Tetranychus urticae Koch, on cotton, Cossypium hirsutum L. For the field experiments, data were pooled across all experiments for analysis. Aeris, thiamethoxam, and imidacloprid treatments resulted in twospotted spider mite densities greater than those in the untreated check, aldicarb, and acephate treatments. However, cotton treated with Avicta (thiamethoxam + abamectin) had 34% fewer mites than other neonicotinoid seed treatments when infestations occurred near cotyledon stage. Untreated check and aldicarb treatments had the lowest mite densities. Only aldicarb reduced mite densities below that in the untreated check. In a laboratory trial, the fecundity of twospotted spider mite was measured. While neonicotinoid seed treatments increased mite densities in the field, they did not increase fecundity in the laboratory experiment. Foliar applied thiamethoxam slightly elevated average fecundity in the laboratory experiment. Increased use of neonicotinoid seed treatments instead of furrow applied aldicarb is likely at least partly responsible for recent increased twospotted spider mite infestations in seedling cotton across the mid-south.

Impact of twospotted spider mite (Acari: Tetranychidae) duration of infestation on cotton seedlings.

The yield response of cotton, Gossypium hirsutum L., to twospotted spider mite, Tetranychus urticae Koch, duration of infestation during the seedling stage was measured at Starkville and Stoneville, MS, during 2010 and 2011. The treatments included a noninfested control, infestations lasting for 7, 14, 21, or 28 d, and a season long infested control. Twospotted spider mites from a greenhouse colony were inoculated on all of the infested cotton plots during the three-leaf stage. Applications of miticides were made to terminate infestations at the desired timings for each treatment. Twospotted spider mite densities and injury ratings were determined for each treatment at the end of the infestation period and yield was measured at the end of the season. Twospotted spider mite densities and injury rating significantly increased as duration of infestation increased. Significant differences in yield were observed between treatments. These data suggest infestations initiated at the three-leaf cotton growth stage with population densities at a minimum of 0.39 mites/cm2 existing > 14 d could result in reduction of cotton yields.

Cotton aphid (Heteroptera: Aphididae) susceptibility to commercial and experimental insecticides in the southern United States.

Cotton aphid, Aphis gossypii Glover, has a history of developing resistance to novel insecticides. A program is needed to monitor cotton aphid susceptibility to new insecticides. Concentration-mortality bioassays were conducted from 2008 to 2011 to monitor the susceptibility of cotton aphids from fields across the midsouthern United States to thiamethoxam and sulfoxaflor. Flonicamid was included in 2010 and 2011. Bioassays followed the procedures described by the Insecticide Resistance Action Committee for testing neonicotinoids against cotton aphid. Mortality was rated at 48 and 72 h. These bioassays suggest that high levels of resistance to thiamethoxam occur in cotton aphid throughout the midsouthern United States. Resistance ratios ranged from 0.9 to 562.6 at 48 h, and from 0.9 to 29.1 at 72 h. Aphid colonies tested were considered susceptible to flonicamid and sulfoxaflor. The LC50 values ranged from 1.43 to 6.60 ppm for flonicamid. The LC50 values for sulfoxaflor ranged from 1.01 to 5.85 ppm and 0.92-4.13 ppm at 48 and 72 h, respectively. These values represent the baseline variability of the susceptibility of cotton aphid to flonicamid and sulfoxaflor. The moderate level of variability observed combined with the high level of efficacy at low rates and the high reproductive rate of cotton aphid suggests that an effective resistance management plan needs to be devised for these insecticides. Flonicamid and sulfoxaflor should provide effective control of cotton aphid in areas where thiamethoxam resistance occurs. However, these insecticides need to be incorporated into a rotation strategy to preserve their efficacy against cotton aphid.

Determination of Residual Control and Concentration of Chlorantraniliprole in Soybean.

Studies were conducted in 2020 and 2021 at the Delta Research and Extension Center in Stoneville, MS to determine concentrations of chlorantraniliprole (Prevathon, FMC Corporation, Philadelphia, PA) in soybean (Glycine max L.) leaves and florets. Chlorantraniliprole was applied as a foliar spray at four rates (0.028, 0.053, 0.078, 0.103 kg ai ha-1) for leaves and two rates (0.053, 0.078 kg ai ha-1) for florets. Leaf bioassays with corn earworm, Helicoverpa zea (Boddie), were conducted concurrently to determine mortality within three plant zones to evaluate chlorantraniliprole distribution throughout the canopy. For the leaf study, plants were partitioned into three zones consisting of a top (18th node), middle (13th node), and bottom (9th node) zone. Leaf samples from each zone were analyzed for chemical concentrations and bioassays were conducted at 1, 7, 14, 21, and 28 days after treatment (DAT). Floret samples were analyzed at 4, 7, 10, and 14 DAT. Concentrations of chlorantraniliprole, though variable, provided >71% control through all sampling dates, application rates, and canopy zones tested. Chlorantraniliprole was viable up to 28 DAT. Results from the soybean floret study suggested chlorantraniliprole was detected in florets up to 14 DAT. An additional leaf bioassay was conducted using concentrations detected in the floret study. Concentrations in florets provided mortality of corn earworm up to 48% out to 14 DAT. With a long residual expected, chlorantraniliprole applications should continue to be used to control corn earworm infestations in soybean and some additional control could be expected in florets.

Development of a plant-based threshold for tarnished plant bug (Hemiptera: Miridae) in cotton.

The tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), is an important pest of cotton, Gossypium hirsutum L., in the mid-southern United States. It is exclusively controlled with foliar insecticide applications, and sampling methods and thresholds need to be revisited. The current experiment was designed to establish a plant-based threshold during the flowering period of cotton development. Experiments were conducted in MisSissippi in 2005 and 2006, Arkansas in 2005, and Louisiana in 2005 through 2008. Treatments consisted of various combinations of thresholds based on the percentage of dirty squares that were compared with the current threshold with a drop cloth or automatic weekly applications. Dirty squares were characterized as those with yellow staining on the developing bud resulting from tarnished plant bug excrement. Treatments consisted of 5, 10, 20, and 30% dirty squares. Each plot was sampled weekly, and insecticides were applied when the mean of all replications of a particular treatment reached the designated threshold. At the end of the season, plots were harvested and lint yields were recorded. Differences were observed in the number of applications and yields among the different treatments. The 10% dirty squares threshold resulted in a similar economic return compared with the drop cloth. A threshold of 10% dirty squares resulted in a similar number of insecticide applications, yields, and economic returns compared with that observed with the drop cloth. These results suggest that a threshold of 10% dirty squares could be used to trigger insecticide applications targeting tarnished plant bugs in flowering cotton.

Feeding Behavior and Fruiting Form Damage by Bollworm (Lepidoptera: Noctuidae) in Bt Cotton.

Bt technologies have played a major role in the control of bollworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae), in cotton. Variation in expression levels among varieties and plant parts, along with selection pressure on bollworm populations, has led to the development of resistance to some Bt proteins. Trials were conducted to evaluate how cotton varieties expressing different Bt proteins affect bollworm larval behavior and their damage in flowering cotton. Differences in larval recovery were observed among cotton varieties at 3 d with 3-gene Bt cotton having the lowest recovery and non-Bt cotton having the greatest recovery. Loss of bloom tags and abscission of small bolls at the site of infestation affected bollworm larval recovery among varieties. Day after infestation was the main factor that affected bollworm movement across all varieties. Number of total damaged fruiting forms by an individual bollworm larva was different among all varieties. Overall, flower bud (square) and fruit (boll) damage by an individual larva was lower on 3-gene cotton than 2-gene cotton and non-Bt cotton. An individual larva damaged fewer squares on 2-gene cotton than non-Bt cotton, but boll damage from bollworm was similar among 2-gene cotton and non-Bt cotton. The level of square and boll damage in 2-gene cotton has increased compared to previous research further supporting the occurrence of bollworm resistance to Cry proteins. The 3-gene cotton containing the Vip3A gene experienced low levels of damage and survival. These results will be important for improving management recommendations of bollworm in Bt cotton technologies.

Impacts of Winter Annual Cover Crops and Neonicotinoid Seed Treatments on Arthropod Diversity in Mississippi Soybean.

Winter annual cover crops can be planted before soybean in Mississippi for many agronomic reasons. Incorporating winter annual cover crops into soybean production changes the seasonal hosts within fields. Some studies suggest that reducing tillage and using diverse species of cover crops can increase arthropod diversity and predator activity. Neonicotinoid seed treatments are often implemented to combat early season insect pests in soybean that follow cover crops, but negative effects on the environment such as reductions in biodiversity are often attributed to these compounds. We conducted an experiment to measure the effects on the diversity of the soybean epigeal and foliar communities when incorporating cover crops as well as insecticidal seed treatments into Mississippi soybean growing systems. Our results showed that legume cover crops had significant impacts on the epigeal community diversity of soybean planted behind them. These cover crops, especially hairy vetch, supported a more diverse foliar community before termination. To prevent increases in herbivorous arthropods, neonicotinoid seed treatments can be used without affecting epigeal predators such as beetles, ants, and spiders. The neonicotinoid seed treatments affected arthropod diversity, but the reductions were mainly caused by decreases in herbivorous pest insects that fed on treated soybean plants.

Influence of Soil Moisture Zones on Rice Water Weevil (Coleoptera: Curculionidae) Populations in Furrow Irrigated Rice.

Water conservation is an important factor for production of rice in the United States because of declining aquifer levels, but little research has been done to evaluate insect management in rice systems integrating water conservation practices. Rice water weevil, Lissorhoptrus oryzophilus Kuschel, is an important insect pest of rice in the U.S. Rice water weevil is a semiaquatic species that relies on flooded conditions to complete larval development, so water conservation practices are likely to impact their pest status. The study was conducted across the Mississippi River alluvial floodplain to compare rice water weevil population densities in different zones of a furrow irrigated rice field to a conventionally flooded rice field. All locations were sampled at 3, 4, and 5 wk after the initial irrigation. Larval densities were greatest in the lower end of furrow irrigated fields and in the adjacent flooded rice field compared with the upper and middle sections that did not hold standing water when averaged across three sample dates. Also, rice water weevil densities were greater during week five than week three. In terms of rice yields, the top third of furrow irrigated rice fields, the section that remained mostly dry, produced lower rough rice yields than all other sections and the flooded field. These results suggest that rice water weevil populations can be lower in a furrow irrigated rice system. As a result, more research is needed to determine whether a spatial management plan can be developed based on soil moisture zones in furrow irrigated rice.

Quantifying the Contribution of Seed Blended Refugia in Field Corn to Helicoverpa zea (Lepidoptera: Noctuidae) Populations.

Helicoverpa zea (Boddie), a pest of cotton that also occurs in field corn, is commonly controlled through the use of foliar-applied insecticides or transgenic crops expressing Bacillus thuringiensis (Berliner) (Bt) genes. To minimize the risk of Bt resistance in pest populations, refuge systems have been implemented for sustainable agroecosystem management. Historically, structured refuge compliance among growers has been low, leading to the commercialization of seed blended refugia. To test the viability of seed blended refugia in southern U.S. field corn, field studies were conducted in Mississippi and Georgia during 2016, 2017, and 2018 growing seasons. To quantify adult H. zea emergence from structured (non-Bt corn) and seed blended refuge options, emergence traps were utilized. Kernel damage among seed blended refuge and structured refuge corn ears were recorded and compared. The timing of moth emergence was recorded. When compared to a structured refuge, H. zea adult moth emergence from seed blended refugia did not significantly differ. Kernel damage of non-Bt plants in the seed blended treatments was not significantly different than non-Bt plants in the structured refuge treatments. Moth emergence timing was not significantly delayed between the structured refuge and seed blended refuge treatments. Results of this study suggest that a seed blended refuge may provide an effective insecticide resistance management alternative for H. zea in areas where structured refuge compliance is low.

Sublethal Impacts of Novaluron on Tarnished Plant Bug (Hemiptera: Miridae) Adults.

Tarnished plant bug, Lygus lineolaris Palisot de Beauvois (Hemiptera: Miridae), has become a primary pest of cotton in the Midsouthern United States. Insect growth regulators such as novaluron are an important part of L. lineolaris management. While novaluron is lethal to nymphs, it does not kill adults, so it has been used when nymphs are the primary stage present. However, cotton yield protection was observed from an application of novaluron when adults were the predominant stage present. To explain this, a series of studies were conducted to examine sublethal impacts of novaluron to L. lineolaris adults. Novaluron ingestion by adults reduced hatch rate and sometimes reduced oviposition rate. Ingestion by either males or females reduced hatch rates, but the reduction was greater from female exposure. Contact exposure of adults with novaluron residues within 1 d of application reduced hatch rate by about 50%, but the impact on oviposition was inconsistent. A field study showed reduced hatch rate from contact exposure to mixed-age natural populations, but the overall net reproductive rate was not reduced. Surface exposure of eggs to novaluron did not reduce hatch rate. Overall, exposure of tarnished plant bug adults to novaluron, regardless of adult age or exposure route, reduced egg viability. However, the impact on oviposition rate and net reproductive rate varied with adult age and exposure route. This understanding of sublethal impacts of novaluron, in addition to lethal impacts on nymphs, should be considered when choosing application times to maximize effects on L. lineolaris populations.

Evaluation of Current Tarnished Plant Bug (Hemiptera: Miridae) Thresholds in Transgenic MON 88702 Cotton Expressing the Bt Cry51Aa2.834_16 Trait.

The tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), is an important pest of cotton in many areas of the southern United States. An experiment was conducted at two locations in Mississippi during 2016 and 2017 to evaluate action thresholds for tarnished plant bug on a novel Bacillus thuringiensis cotton that expresses the Cry51Aa2.834_16 toxin. Treatments included the current action threshold, a 2× threshold, and treatments where insecticides were only applied during the early season (preflower) or only during late season (during flowering) based on the current action thresholds. These were compared to an untreated control and a weekly insecticide use regime that received weekly insecticide sprays. All treatments were imposed on both Bt Cry1Aa2.834_16 cotton and a nontraited cotton. The Bt Cry1Aa2.834_16 trait reduced the number of tarnished plant bugs and injury, and improved yields compared to nontraited cotton. For all spray treatments except the weekly insecticide use regime, yields were greater for the Bt Cry51Aa2.834_16 cotton than the nontraited cotton. In terms of thresholds, Bt Cry1Aa2.834_16 cotton sprayed based on current action thresholds resulted in similar yields to the weekly insecticide use regime of both cotton types. In contrast, the 2× threshold resulted in lower yields than the current threshold for both cotton types. Though thresholds intermediate to the currently recommended action threshold and the 2× threshold were not tested, these data suggest that currently recommended action thresholds appear appropriate for Bt Cry51Aa2.834_16 cotton. These results suggest that this trait will be an important component of current IPM programs in cotton where tarnished plant bug is an important pest.

Assessing Soybean Genotypes for Resistance to Helicoverpa armigera (Lepidoptera: Noctuidae).

Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) is an important pest capable of colonizing several species of cultivated plants, including soybean [Glycine max (L.) Merrill]. The primary management strategy for this insect is chemical control and adoption of Bt plants. However, alternative environmentally friendly strategies should be investigated and adopted as available for sustainable management of this insect pest. One potential underutilized method for insect control is plant resistance. The objective of this study was to categorize resistance (antixenosis and antibiosis) of 22 soybean genotypes on H. armigera in a laboratory setting. A preliminary experiment was conducted using soybean leaves and pods to determine the most promising genotypes for resistance. For each selected genotype, we collected biological parameters, leaf intake, and performed confinement tests. The genotypes PI 227687, PI 274453, PI 274454, PI 229358, PI 171451, 'IAC 17', and 'IAC 19' expressed resistance against H. armigera. Each genotype lowered larval survivorship. The genotypes PI 229358, PI 227687, PI 274453, and PI 274454 expressed resistance by prolonging larval development and reducing fifth-instar larvae weight. 'IAC 19' reduced leaf consumption and lowered the weight of fifth-instar larvae. Antixenosis was found in genotypes PI 227687, PI 274454, and 'IAC 19'. These genotypes might be used in breeding programs focusing on soybean resistance to lepidopterans.

Evaluation of Flood Removal in Combination with Insecticide Seed Treatment for Rice Water Weevil (Coleoptera: Curculionidae) Larval Management in Rice.

An experiment was conducted at the Delta Research and Extension Center in Stoneville, MS during 2017 and 2018 to determine whether removal of the flood is an economical method of control for rice water weevil, Lissorhoptrus oryzophilus Kuschel. This experiment compared a continuous flood production system to draining a rice field completely and reestablishing a flood for the remainder of the growing season. In addition, two insecticide seed treatments, thiamethoxam and chlorantraniliprole, were compared with an untreated control within each system. Rice water weevil densities were measured prior to draining at 3 wk after flood and again after the flood was reestablished in drained plots. Rice water weevil densities were greater in 2017 than 2018. Chlorantraniliprole at the predrainage and postdrainage sample timing reduced larval numbers compared with the untreated control. The plots where water was removed until soil cracking then re-flooded had significantly lower weevil populations than plots that were continuously flooded during 2018 only. Draining of plots resulted in lower yields in 2018, but not in 2017. Additionally, both of the insecticide seed treatments resulted in greater yields and economic returns than the untreated control. Draining of flooded rice when rice water weevil larvae were present did not provide a consistent benefit, and may result in yield and economic penalties. Insecticide seed treatments consistently provided greater yield benefits in flooded rice. Based on these results, draining of flooded rice is not recommended to manage rice water weevil and insecticide seed treatments should be used to minimize economic losses.