Overwintering site selection and associated microclimates for the redbanded stink bug (Hemiptera: Pentatomidae), a non-native pest of soybean.

Cold winter temperatures govern the distribution and abundance of many insect species, but refugia that provide microclimates can moderate temperature-driven mortality. Winter temperatures have been implicated in limiting the survival and range of Piezodorus guildinii (Westwood) (Hemiptera: Pentatomidae; redbanded stink bug), an economically damaging invasive pest in the southeastern United States, but the role of refugia in overwintering survival of this pest is poorly understood. We conducted 2 studies in successive years to evaluate how leaf litter from hardwoods, pines, and soybeans modulate overwintering site selection and survival of P. guildinii. In the second-year study, we also quantified the buffering effect of the 3 leaf litter types compared to ambient conditions and assessed diapause. In the first-year study, we found that stink bugs preferentially dispersed into leaf litter compared with remaining unsheltered on bare soil; no clear preference among leaf litter types was found. In the second year, however, no clear differences were found among leaf litter types and bare soil. Means of daily minimum temperatures under leaf litter were at least 3.0 ±â€…0.9 °C (SE) warmer and generally less variable than ambient conditions. While high mortality in both studies illustrates that more work must be done to fully understand overwintering survival, limited survival through potentially lethal conditions in the first-year study nonetheless emphasizes the possibility of populations persisting and rebounding in the following spring. Furthermore, our study highlights the potential for stink bugs to persist in areas with lethal ambient temperatures by dispersing into widely available substrates.

Molecular characterization and expression patterns of a ryanodine receptor in soybean looper, Chrysodeixis includens.

Diamide insecticides, such as chlorantraniliprole, have been widely used to control insect pests by targeting the insect ryanodine receptor (RyR). Due to the efficacious insecticidal activity of diamides, as well as an increasing number of resistance cases, the molecular structure of RyR has been studied in many economically important insects. However, no research has been conducted on diamide resistance and RyR in the soybean looper, Chrysodeixis includens, a significant crop pest. In this study, we found moderate resistance to chlorantraniliprole in a field population from Puerto Rico and sequenced the full-length cDNA of the C. includens RyR gene, which encodes a 5124 amino acid-long protein. Genomic analysis revealed that the CincRyR gene consists of 113 exons, one of the largest exon numbers reported for RyR. Alternative splicing sites were detected in the cytosolic region. The protein sequence showed high similarity to other noctuid RyRs. Conserved structural features included the selectivity filter motif critical for ryanodine binding and ion conduction, as well as various domains involved in ion transport. Two mutation sites associated with diamide resistance in other insects were screened but not found in the Puerto Rico field populations or in the susceptible lab strain. Gene expression analysis indicated high expression of RyR in the third instar larval stage, particularly in muscle-containing tissues. Furthermore, exposure to a sublethal dose of chlorantraniliprole reduced RyR expression levels after 96 h. This study provides a molecular basis for understanding RyR structure and sheds light on potential mechanisms of diamide resistance in C. includens.

Investigating the Migratory Behavior of Soybean Looper, a Major Pest of Soybean, through Comparisons with the Corn Pest Fall Armyworm Using Mitochondrial Haplotypes and a Sex-Linked Marker.

The Noctuid moth soybean looper (SBL), Chrysodeixis includens (Walker), is an economically important pest of soybean (Glycine max (Linnaeus) Merrill). Because it is not known to survive freezing winters, permanent populations in the United States are believed to be limited to the southern regions of Texas and Florida, yet its geographical range of infestations annually extend to Canada. This indicates annual migrations of thousands of kilometers during the spring and summer growing season. This behavior is like that of the fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith), also a Noctuid that is a major global pest of corn. SBL and FAW are projected to have very similar distributions of permanent populations in North America based on climate suitability modeling and the overlap in the distribution of their preferred host plants (corn and soybean). It therefore seems likely that the two species will display similar migratory behavior in the United States. This was tested by identifying genetic markers in SBL analogous to those successfully used to delineate FAW migratory pathways and comparing the distribution patterns of the markers from the two species. Contrary to expectations, the results indicate substantial differences in migratory behavior that appear to be related to differences in the timing of corn and soybean plantings. These findings underscore the importance of agricultural practices in influencing pest migration patterns, in particular the timing of host availability relative to mean seasonal air transport patterns.

Evidence for Two Soybean Looper Strains in the United States with Limited Capacity for Cross-Hybridization.

The noctuid moth soybean looper (SBL), Chrysodeixis includens (Walker) is an economically important pest of soybeans (Glycine max (L.) Merr.) in the southeastern United States. It has characteristics that are of particular concern for pest mitigation that include a broad host range, the capacity for annual long-distance flight, and resistance in some populations to important pesticides such as pyrethroids and chitin synthesis inhibitor. The biology of SBL in the United States resembles that of the fellow noctuid fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith), a major pest of corn and several other crops. FAW exhibits a population structure in that it can be divided into two groups (host strains) that differ in their host preferences but are broadly sympatric and exhibit incomplete reproductive isolation. In this paper, strategies used to characterize the FAW strains were applied to SBL to assess the likelihood of population structure in the United States. Evidence is presented for two SBL strains that were defined phylogenetically and display differences in the proportions of a small set of genetic markers. The populations exhibit evidence of reproductive barriers sufficient to allow persistent asymmetry in the distribution of mitochondrial haplotypes. The identified molecular markers will facilitate studies characterizing the behaviors of these two populations, with relevance to pest mitigation and efforts to prevent further dispersal of the resistance traits.

Standardized Field Trials in Cotton and Bioassays to Evaluate Resistance of Tobacco Thrips (Thysanoptera: Thripidae) to Insecticides in the Southern United States.

Foliar-applied insecticide treatments may be necessary to manage thrips in cotton (Gossypium hirsutum L.) under severe infestations or when at-planting insecticide seed treatments do not provide satisfactory protection. The most common foliar-applied insecticide is acephate. Field observations in Tennessee suggest that the performance of acephate has declined. Thus, the first objective was to perform leaf-dip bioassays to assess if tobacco thrips, Frankliniella fusca (Hinds) (Thysanoptera: Thripidae), in cotton production regions have evolved resistance to foliar-applied insecticides. A second objective was to assess the performance of commonly applied foliar insecticides for managing thrips in standardized field trials in Arkansas, Tennessee, Mississippi, and Texas. For both objectives, several insecticides were evaluated including acephate, dicrotophos, dimethoate, lambda-cyhalothrin, imidacloprid, and spinetoram. Field trials and bioassays were completed from 2018 to 2021. Dose-response bioassays with acephate were performed on tobacco thrips field populations and a susceptible laboratory population. Bioassay results suggest that tobacco thrips have developed resistance to acephate and other organophosphate insecticides; however, this resistance seems to be most severe in Arkansas, Tennessee, and the Delta region of Mississippi. Resistance to other classes of insecticides were perhaps even more evident in these bioassays. The performance of these insecticides in field trials was variable, with tobacco thrips only showing consistent signs of resistance to lambda-cyhalothrin. However, it is evident that many populations of tobacco thrips are resistant to multiple classes of insecticides. Further research is needed to determine heritability and resistance mechanism(s).

Effects of Soybean Plant Population on Yield Loss From Defoliation.

Plant densities in Mid-South U.S. soybean, Glycine max (L.) Merr., fields can vary greatly due to a wide range of factors, although soybean yields are generally insensitive to variations in density. Currently, it is unknown if yield loss from insect-related defoliation varies across different soybean stand densities. Soybean was planted in Starkville and Stoneville, MS, in 2016 and 2017 at five seeding rates ranging from 123,500 to 420,070 seed/ha in 74,130 seed/ha increments. Each seeding rate contained a nondefoliated plot and a plot that was defoliated 67% at the R1 growth stage. Defoliated plants had a greater leaf expansion rate from R1 to R3 than nondefoliated plants. Defoliation reduced yield where plant densities were <192,800 plants/ha, but greater densities were not affected. Reduced yield in defoliated plots when compared with nondefoliated plots at equivalent R3 leaf area index values indicated that some resources were used to replace the removed leaf area instead of seed production. These results suggest that fields with substandard plant densities might benefit from a reduced treatment threshold for defoliating pests.

Effects of Soybean Planting Date on Yield Loss From Defoliation.

Soybean, Glycine max (L.) Merr., is planted during 3.5-4 mo across the Mid-South United States. Currently, no information exists regarding the effects of planting date on soybean yield loss from early season defoliation. In 2015 and 2016, to evaluate the effects of planting date on yield loss from defoliation, soybean were planted in field plots 2 wk apart from early April to mid-June, for a total of six planting dates. Each planting date included a nondefoliated control and a 100% defoliation treatment where leaves were manually excised at the V4 growth stage. Mean yield loss from defoliation varied across planting dates, with mid-April plantings having the least amount yield reduction, 573 kg/ha, and early-June plantings having the greatest yield reduction, 904 kg/ha. Percent yield reduction from defoliation increased as planting was delayed, suggesting that defoliation thresholds might need adjustment based on planting date and yield potential. However, more research is needed at lower levels of defoliation to accurately delineate such thresholds.

Resistance monitoring to four insecticides and mechanisms of resistance in Lygus lineolaris Palisot de Beauvois (Hemiptera: Miridae) populations of southeastern USA cotton.

BACKGROUND: Economically damaging infestations of the tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), have become more frequent in Virginia and North Carolina cotton since 2013 and 2010, respectively. Foliar insecticide use has increased dramatically in response. Efficacy data (LC50 ) are needed to evaluate L. lineolaris susceptibility and resistance levels (RR50 ) to commonly used and recommended insecticides for managing this pest in the southeastern USA. RESULTS: Elevated resistance levels to acephate and bifenthrin were measured in L. lineolaris populations collected from wild and cultivated hosts in Virginia, North Carolina and northern Alabama when compared to a susceptible laboratory population. High levels of bifenthrin resistance were observed in 2018 and 2019. Mixed-function oxidase and esterase (EST) inhibitors, piperonyl butoxide and S,S,S-Tributyl phosphotrithioate, respectively, had a synergistic effect on bifenthrin with resistant populations of L. lineolaris. Bifenthrin-resistant L. lineolaris populations expressed elevated levels of cytochrome P450 (CYP450 ) monooxygenase and general EST activity. Results suggest that insecticide resistance is present in some locations and that CYP450 and EST activity in L. lineolaris contribute to pyrethroid resistance in the southeastern USA. CONCLUSIONS: Results can serve as a baseline for continued monitoring of L. lineolaris insecticide resistance and inform insecticide resistance management strategies that help southeastern USA cotton producers to minimize inputs and slow resistance development. © 2020 Society of Chemical Industry.

Quantifying the Impact of Excluding Insecticide Classes From Cotton Integrated Pest Management Programs in the U.S. Mid-South.

Current assessments from the U.S. Environmental Protection Agency suggest that some current insecticides may be lost or severely restricted in the near future. An experiment was conducted from 2014 to 2015 at two locations in Mississippi to determine the impact of losses of insecticide classes on integrated pest management of insect pests in cotton. The treatments included cotton treated with all available classes of insecticides, cotton treated with all classes except neonicotinoids, cotton treated with all classes except pyrethroids, cotton treated with all classes except carbamates and organophosphates, and an untreated control. Plots were scouted weekly and insecticide applications were made with the most efficacious and economical insecticides for each treatment when that treatment reached threshold for a particular insect pest(s). The primary insects at both locations were tobacco thrips and tarnished plant bugs. Thrips pressure was similar at both locations and generally showed that all insecticide treatments provided a similar level of protection compared with the untreated control. At the Stoneville location where tarnished plant bug pressure was greatest, cotton yields and economic returns differed between plots where all classes of insecticides were applied compared with the untreated control and where neonicotinoids were excluded. However, in Starkville where tarnished plant bug pressure was less, there were no differences among treatments. Although yield and economic returns were similar in high tarnished plant bug pressure areas when using all classes compared with managing without pyrethroids or organophosphates, a rotation among all insecticide classes should be beneficial for resistance management in Mid-South cotton production.

Influence of Temperature on the Efficacy of Foliar Insecticide Sprays Against Sugarcane Aphid (Hemiptera: Aphididae) Populations in Grain Sorghum.

The use of foliar insecticide sprays at low temperatures may result in decreased efficacy in grain sorghum, Sorghum bicolor L. Moench, for control of sugarcane aphid, Melanaphis sacchari (Zehntner). Sulfoxaflor and flupyradifurone were evaluated to determine the impact of temperature on their efficacy against sugarcane aphid in grain sorghum. Sorghum was treated at the soft dough growth stage with sulfoxaflor and flupyradifurone, as well as an untreated check. Leaf discs were pulled at various intervals from 0 to 10 d after treatment, placed in water agar plates, infested with aphids, placed in growth chambers at 15.5°C or 29.4°C, and evaluated 48 h after each interval. In 2015, both insecticides resulted in similar levels of sugarcane aphid mortality and efficacy decreased at a similar rate at 15.5°C. At 29.0°C, flupyradifurone resulted in greater mortality of sugarcane aphid than sulfoxaflor as length of time after treatment increased, suggesting that it provides longer residual control than sulfoxaflor. In 2016, both insecticides provided poor control of sugarcane aphid at 15.5°C for all time intervals. At 29.0°C, flupyradifurone provided overall better control than sulfoxaflor. These data suggest that lower temperatures can reduce the efficacy of both sulfoxaflor and flupyradifurone. In addition, flupyradifurone appeared to provide longer residual control and overall better control of sugarcane aphid than sulfoxaflor. If lower temperatures occur when sugarcane aphid populations exceed current thresholds, weather forecast should be considered in pest management decision-making process.

Neonicotinoid Insecticide Resistance in Tobacco Thrips (Thysanoptera: Thripidae) of Mississippi.

Insecticidal efficacy of neonicotinoid insecticides used against tobacco thrips, Frankliniella fusca (Hinds) (Thysanoptera: Thripidae), in cotton, Gossypium hirisutum L. (Malvales: Malvaceae), was evaluated for field populations collected in Mississippi during 2014-2016. Resistance was documented in 16 and 57% of populations to imidacloprid and thiamethoxam, respectively. Resistance levels did not vary by host plant for any neonicotinoid, but resistance levels varied between the two main agricultural areas (Delta and Hills) of Mississippi and among years for some neonicotinoids. In spite of documented resistance, neonicotinoid seed treatments are still used on cotton in the midsouthern United States due to the lack of reliable alternative management strategies. The development of alternative thrips management strategies is critical to the sustainability of cotton production in the midsouthern United States.

Effects of Bt Corn on the Development and Fecundity of Corn Earworm (Lepidoptera: Noctuidae).

The corn earworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae), is only moderately susceptible to most toxins from the bacterium Bacillus thuringiensis (Bt) expressed in transgenic corn. To better understand the impact of Bt corn on the life cycle of H. zea, we collected pupae of H. zea during 2014-2016 in North Carolina, South Carolina, and Mississippi from corn hybrids expressing Cry1Ab, Cry1F, Cry1F + Cry1Ab, Cry1F + Cry1Ab + Vip3Aa20, Cry1A.105 + Cry2Ab2, and Cry1A.105 + Cry2Ab2 + Cry1F, as well as from non-Bt near-isolines. We investigated the effect of Bt corn on pupal weight, fecundity, and egg viability of H. zea. Pupal weights were significantly reduced for males and females from all Bt hybrids compared with non-Bt near-isolines. Female pupae from the hybrid expressing Cry1F + Cry1Ab were also significantly lighter relative to those from the near-isolines expressing only Cry1F. Reductions in pupal weight did not result in any detectable effects on fecundity or egg viability. The reduction in pupal weight in the hybrids expressing Cry1F and Cry1F + Cry1Ab significantly declined over time in South Carolina, possibly indicating developing resistance to these Bt toxins. These data can be incorporated into insect resistance management models used to improve risk management decisions regarding H. zea in Bt crops in the complex landscapes of the southern United States.

Susceptibility to insecticides and activities of glutathione S-transferase and esterase in populations of Lygus lineolaris (Hemiptera: Miridae) in Mississippi.

BACKGROUND: Lygus lineolaris (Palisot de Beauvois) is a serious pest of cotton (Gossypium hirsutum L.) in Mississippi, particularly in the Delta region. This may be due to decreased insecticide susceptibility in that region. Research has revealed populations of L. lineolaris in the Delta region with high levels of insecticide resistance; however, comparisons with populations in the remainder of the state are limited. RESULTS: Experiments were undertaken to compare the LC50 values and activities of detoxification enzymes of L. lineolaris populations. The results of these studies indicated that the LC50 values were not different between the Delta and Hills regions, but differences were significant between populations within and across regions. Results of the detoxifying enzyme activity assays revealed significantly higher esterase activity in the Delta region when compared with the Hills. Glutathione S-transferase activity was not different between regions, but differences within and across regions were significant. CONCLUSION: The results indicated that glass-vial assays to determine and compare LC50 values may be less accurate than enzymatic assays for detecting insecticide susceptibility differences. Higher esterase activity is likely a contributing factor to the difficulties with managing L. lineolaris in the Mississippi Delta region. © 2015 Society of Chemical Industry.

Risk assessment for Helicoverpa zea (Lepidoptera: Noctuidae) resistance on dual-gene versus single-gene corn.

Recent Environmental Protection Agency (EPA) decisions regarding resistance management in Bt-cropping systems have prompted concern in some experts that dual-gene Bt-corn (CrylA.105 and Cry2Ab2 toxins) may result in more rapid selection for resistance in Helicoverpa zea (Boddie) than single-gene Bacillus thuringiensis (Bt)-corn (CrylAb toxin). The concern is that Bt-toxin longevity could be significantly reduced with recent adoption of a natural refuge for dual-gene Bt-cotton (CrylAc and Cry2Ab2 toxins) and concurrent reduction in dual-gene corn refuge from 50 to 20%. A population genetics framework that simulates complex landscapes was applied to risk assessment. Expert opinions on effectiveness of several transgenic corn and cotton varieties were captured and used to assign probabilities to different scenarios in the assessment. At least 350 replicate simulations with randomly drawn parameters were completed for each of four risk assessments. Resistance evolved within 30 yr in 22.5% of simulations with single-gene corn and cotton with no volunteer corn. When volunteer corn was added to this assessment, risk of resistance evolving within 30 yr declined to 13.8%. When dual-gene Bt-cotton planted with a natural refuge and single-gene corn planted with a 50% structured refuge was simulated, simultaneous resistance to both toxins never occurred within 30 yr, but in 38.5% of simulations, resistance evolved to toxin present in single-gene Bt-corn (CrylAb). When both corn and cotton were simulated as dual-gene products, cotton with a natural refuge and corn with a 20% refuge, 3% of simulations evolved resistance to both toxins simultaneously within 30 yr, while 10.4% of simulations evolved resistance to CrylAb/c toxin.

Impact of Nosema (Microsporidia) infection and fumagillin treatment on Lygus lineolaris (Hemiptera: Miridae).

A consistent supply of healthy tarnished plant bug, Lygus lineolaris (Palisot de Beauvois) (Hemiptera: Miridae), is necessary for the development of novel management strategies targeting this pest. After being in culture for several years, a substantial portion of a tarnished plant bug colony was found to be infected with a Nosema (Microsporidia) species. Studies were subsequently undertaken to evaluate the impact of Nosema infection on tarnished plant bug productivity and to test the efficacy of fumagillin to treat this infection. Using buffalo black stain, infections could not be reliably detected in adult tarnished plant bugs until adults were 6-8 days post eclosion. Nosema infections reduced adult longevity and fecundity. Maximum fecundity was restored using a concentration of 16.8 ppm fumagillin while maximum longevity for females was at a concentration of 33.6 ppm fumagillin incorporated into the tarnished plant bug diet. Minimum infection scores were obtained at 67.2 ppm, the highest concentration tested. A field survey of tarnished plant bugs in Mississippi found Nosema infections in 3% of wild tarnished plant bugs.

Pyrethroid insecticide tolerance in bean leaf beetle, Cerotoma trifurcata, in the Mississippi Delta.

BACKGROUND: Pyrethroid insecticides have historically been effective for controlling bean leaf beetles in soybeans. Perceived field efficacy in the Mississippi Delta region has been lower over the past several years. Laboratory and field data were collected to determine whether there has been a reduction in pyrethroid insecticide susceptibility. RESULTS: Laboratory and field data both confirmed that control of bean leaf beetles with pyrethroid insecticides is poorer in the Delta regions of Mississippi and Louisiana than in all other regions tested. However, it was not possible to show that this reduced susceptibility changed over time. Furthermore, insect movement appeared to make insecticide susceptibility regional, so that localized insecticide applications had little impact on the susceptibility of successive generations. CONCLUSION: Lack of field control owing to low efficacy of pyrethroid insecticides against bean leaf beetle populations in the Delta region should be expected. Selection pressure on a regional basis may further decrease efficacy. Carbamate insecticides generally still provide high levels of control.

Tarnished plant bug (Hemiptera: Miridae) thresholds and sampling comparisons for flowering cotton in the midsouthern United States.

The tarnished plant bug, Lygus lineolaris (Palisot de Beauvois) (Hemiptera: Miridae), has become the primary target of foliar insecticides in cotton, Gossypium hirsutum L., throughout the Midsouth over the past several years. This prompted a reevaluation of existing action thresholds for flowering cotton under current production practices and economics. A trial was conducted at 19 locations throughout the Midsouth during 2006 and 2007. Threshold treatments ranged from a weekly automatic insecticide application to a very high threshold of 10 tarnished plant bugs per 1.5 row-m on a black drop cloth. Individually, all locations reached the lowest threshold, and eight locations had a significant yield loss from tarnished plant bugs. Across all locations, lint yield decreased 0.85 to 1.72% for each threshold increase of one tarnished plant bug per 1.5 row-m. Yield loss was most closely correlated to pest density during the latter half of the flowering period. The relationship between plant bug density or damage and yield was similar for drop cloth, sweep net, and dirty square sampling methods, but the correlations among these sampling methods were not high. Incorporating actual insecticide application data from the trial and average production and economic factors for Midsouth cotton, the economic threshold, if monitoring once per week, should be between 1.6 and 2.6 tarnished plant bugs per 1.5 row-m during the flowering period. More frequent monitoring or situations where insecticide applications are more efficacious may alter this threshold.

Tarnished plant bug (Hemiptera: Miridae) thresholds for cotton before bloom in the Midsouth of the United States.

Insecticide applications to control tarnished plant bug, Lygus lineolaris (Palisot de Beauvois) (Hemiptera: Miridae), during cotton, Gossypium hirsutum L., bud formation are common throughout the Midsouth of the United States. Cultivation practices and the pest complex have changed since action thresholds were established for this pest. A trial was conducted at 33 locations over 3 yr throughout the Midsouth to evaluate tarnished plant bug damage to cotton during the prebloom period. There was no consistent yield response to action thresholds, but average tarnished plant bug density and average square loss were both significant factors impacting lint yield. Based on the yield responses and application frequency of the various action thresholds, the best economic scenario occurred when tarnished plant bug density during the prebloom period averaged eight per 100 sweeps and square retention averaged 90%. The action thresholds required to achieve these averages are expected to be higher than these levels because pest pressure is not normally constant during the prebloom period. When insecticides are required, an application interval shorter than one week may be needed to obtain satisfactory control.

Integrating biological and chemical controls in decision making: European corn borer (Lepidoptera: Crambidae) control in sweet corn as an example.

As growers switch to transgenic crops and selective insecticides that are less toxic to natural enemies, natural enemies can become more important in agricultural pest management. Current decision-making guides are generally based on pest abundance and do not address pest and natural enemy toxicity differences among insecticides or the impact of natural enemies on pest survival. A refined approach to making pest management decisions is to include the impact of natural enemies and insecticides, thereby better integrating biological and chemical control. The result of this integration is a dynamic threshold that varies for each product and the level of biological control expected. To demonstrate the significance of conserved biological control in commercial production, a decision-making guide was developed that evaluates control options for European corn borer, Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae), in sweet corn, Zea mays L., where the primary natural enemies are generalist predators. Management options are lambda-cyhalothrin (broad-spectrum insecticide), spinosad (selective insecticide), Trichogramma ostriniae (Peng and Chen) (Hymenoptera: Trichogrammatidae) (parasitoid), and Bacillus thuringiensis (Bt) sweet corn (transgenic variety). The key factors influencing thresholds for all treatments are the intended market, predator populations, and the presence of alternative foods for the predators. Treatment cost is the primary factor separating the threshold for each treatment within a common scenario, with the lowest cost treatment having the lowest pest threshold. However, when the impact of a treatment on natural enemies is projected over the 3-wk control period, the impact of the treatment on predators becomes the key factor in determining the threshold, so the lowest thresholds are for broad-spectrum treatments, whereas selective products can have thresholds > 6 times higher by the third week. This decision guide can serve as a framework to help focus future integrated pest management research and to aid in the selection of pest management tools.

The influence of post-exposure temperature on the toxicity of insecticides to Ostrinia nubilalis (Lepidoptera: Crambidae).

The influence of post-treatment temperature on the toxicities of two pyrethroids (lambda-cyhalothrin and bifenthrin), a carbamate (methomyl) and a spinosyn (spinosad) to Ostrinia nubilalis (Hubner) larvae was evaluated in laboratory assays. From 24 to 35 degrees C, the toxicities of the pyrethroids decreased 9.5- and 13.6-fold while spinosad toxicity decreased 3.8-fold. The toxicity of methomyl did not change significantly. The results demonstrate that the most effective insecticide against a pest may vary with environmental conditions. In situations where comparable products from multiple insecticide classes are available, temperature should be included as a factor in the decision-making process.