Location: Southern Insect Management Research
2017 Annual Report
Objectives
Objective 1: Develop new approaches for the control of noctuid and hemipteran pests of southern row crops, integrating multiple control tactics into integrated pest management systems.
Sub-objective 1.A: Develop new strategies that reduce numbers of insecticide applications on soybean and cotton that are not economically justified.
Sub-objective 1.B: Develop new approaches for the control of insect pests of sweet potato.
Objective 2: Minimize negative effects of integrated pest management systems on pollinators and other beneficial arthropods.
Sub-objective 2.A. Determine the impact of current insect management strategies in corn, cotton, sweet potatoes, and soybean on populations of pollinators and beneficial insects.
Sub-objective 2.B. Examine the acute toxicity, synergistic/antagonistic interactions, and sub-lethal impacts of commonly used pesticides on honey bees using bioassay, biochemical, and molecular approaches.
Objective 3: Improve pest risk assessment by determining environmental influences that affect populations of important insect pests of southern row crops with emphasis on bollworms, tobacco budworms, tarnished plant bugs, stink bugs, and soybean loopers.
Objective 4: Develop methods to measure and manage insecticide resistance of pest populations of southern row crops with emphasis on bollworm, tobacco budworm, tarnished plant bug, and stink bugs.
Sub-objective 4.A. Measure levels of insecticide susceptibilities of tarnished plant bugs, bollworms and other important insect pests of southern row crops through laboratory bioassays.
Sub-objective 4.B. Develop within-field bioassays to determine insecticide susceptibilities of key pests of southern row crops.
Sub-objective 4.C. Examine the impact and sensitivity of resistance management options for major insect pests of southern row crops through simulated modeling.
Approach
Insect management guidelines are generally static from year to year regardless of crop prices, costs of insecticides and yield potential of the crop. We plan to summarize published information for bollworm, tarnished plant bug, and stink bugs and develop economic injury level probability distributions using Monte Carlo simulations. On-farm field evaluations across the Mississippi Delta will evaluate economic returns and environmental sustainability of different insecticidal control strategies in soybean and cotton. Commercially available and experimental sweet potato varieties will be planted annually and the economic impact of insect and nematode control in sweet potato will be examined. The impact of current insect management strategies in southern row crops on populations of pollinators and beneficial insects will be examined in production fields. The surrounding habitats of each field will be documented for plant community composition, focusing on blooming plants that may be of interest to pollinators. Each of these fields will be sampled using a combination of sampling techniques. Community structure will be compared between cropping systems, and related to insecticide applications. We plan to evaluate acute and sub-lethal toxicities and synergistic/antagonistic interactions of honey bees to commonly used pesticides. An examination of gene regulation in honey bees associated with immunity, adaptation, detoxification, digestion/metabolism, and stress-related genes will be conducted after exposure to pesticides with techniques such as real-time PCR , RNAseq or microarrays. Hemipteran and lepidopteran phytophagous pest populations are highly mobile within the landscape and use a variety of weeds and crops as host plants. To examine landscape influences on these insects, the landscape composition surrounding historic and current collection locations will be quantified using Cropland Data Layers (CDLs). Using these CDL layers, buffer zones will be generated around locations. Output data will be tabulated to produce total area of habitat type included within each buffer area and will be related to data collected on insect populations using appropriate statistical analyses. SIMRU will continue to examine susceptibilities of hemipteran and lepidopteran insect pests collected from locations across the Mississippi Delta with a variety of assay methods which may include topically treated diet, residual contact bioassays, glass vial bioassays and a feeding contact assays using floral foam. Insects from original collections will be preserved for molecular analysis using genetic markers. When colonies of any of the pest groups have reduced susceptibility to the tested insecticides, efforts will be made to preserve the colony under a selected and non-selected sequence of exposures to the insecticides of interest We propose to develop rapid bioassays to predict the effectiveness of an insecticide application on a real field population of insects. To examine predictive values of laboratory assays on actual field populations, a plot sprayer will be used to deliver a range of formulated product rates on targeted insects.
Progress Report
Published literature has been examined to develop databases of economic injury levels of bollworms and other caterpillar pests on Bt and non-Bt cotton. Data from peer-reviewed papers and unpublished data have been compiled. Additionally, economic injury levels of stink bugs and bollworms from published reports on soybean have been compiled. Cotton and soybean field plots were established during 2016 to examine economic returns for insecticide applications at different densities of bollworms and stink bugs on these plots.
Participated in the 2016 sweet potato variety trials at the Alcorn State University Research Farm in Mound Bayou, Mississippi. The yield and quality of ten sweet potato varieties grown in the Mississippi Delta were compared. The varieties included lines from Louisiana and North Carolina to examine their compatibility to the growing conditions of the Mississippi Delta. Three varieties were identified that yielded more #1 sweet potatoes than other varieties tested. This information is being used by local sweet potato producers and others in the southern U.S.
Collections of native bees were continued in a variety of agricultural produced commodities including commercial fields of corn, cotton, sorghum, sunflowers and soybean located across the Mississippi Delta. Additional specimens were collected from selected non-agricultural areas including fallow fields, roadside ditches, and National Wildlife Refuges in the Mississippi Delta. Samples were collected with a combination of collection techniques including bee bowl units, malaise traps and sweep net sampling to document species richness and abundance. Additional specimens were added from bycatch of other studies including moth pheromone traps. Over 15,000 specimens have been cleaned, pinned, and mounted, and entered into a database. There is little or no existing information pertaining to the native bees present in these agricultural commodities in the Mississippi Delta. This baseline information is being used to examine potential impacts of local agricultural production practices on these insects.
The toxicities of honey bees to mixtures of imidacloprid with pesticides from seven different classes were examined. Spraying methods were used that simulated field exposure to the bees. Synergistic activities were detected for mixtures of imidacloprid with three different pesticides (tetraconazole, sulfoxaflor, and oxyamyl). Mixtures of imidacloprid with acephate and lambda-cyhalothrin showed additive interactions, while imidacloprid mixed with clothianidin or glyphosate had no additive/synergistic interaction. Acephate significantly suppressed the enzyme activities of acetylcholinesttearse and esterase, but all other mixtures did not suppress levels of the enzymes that were tested. This study provides valuable information for guiding pesticide selection in premixing or tank mixing in order to alleviate toxicity risk to honey bees.
Feeding assays were used to simulate in-hive exposures of formulated imidacloprid alone and mixed with six representative pesticides from different classes. Additive/synergistic toxicity was not detected from mixtures of imidacloprid with the pesticides examined at residue levels. Enzymatic data showed that activities of treated survivors were mostly similar to those found in control treatments. This study showed that residue levels of six pesticides in pollens/hive may not adversely affect honey bees, but long term exclusive ingestion of maximal residue levels of imidacloprid and sulfoxaflor may induce substantial bee mortality. Rotating with other insecticides is a practical way to reduce the residue level of any given pesticide.
Two laboratory bioassay methods were used to examine susceptibilities of field populations of tarnished plant bugs to four different classes of insecticides commonly used in the Mississippi Delta. Forty-two field populations were tested using either a diet-overlay method or exposure to an insecticide in a glass vial. Insecticides tested included: acephate, permethrin, imidacloprid, thiamethoxam, and sulfoxaflor. All technical grade insecticides were diluted in acetone, with the exception of thiamethoxam which was diluted in honey water. In general, high variation was observed in the lethal concentration needed to cause mortality in 50% of a tested population (LC50). These methods are being examined to determine the best predictor of tarnished plant bug field control on cotton.
Current insecticide susceptibilities of lepidopteran pests of the Mississippi Delta, including bollworm and tobacco budworm, to synthetic insecticides were evaluated. Assays included insecticide mixed with artificial diet (diet-incorporated), and direct applications of one ul droplets to 3rd instar larvae (topical). Insecticides tested included lambda-cyhalothrin, chlorantraniliprole, and acephate. Insect populations were collected from wild and cultivated host plants. Nine populations of bollworm and three populations of tobacco budworm were examined. Populations of tobacco budworm and bollworm responded similarly to tests conducted with chlorantraniliprole. Tobacco budworm populations were at least 40-fold more tolerant to lambda-cyhalothrin in diet-incorporated assays compared with tested bollworm populations. Additionally, many of these same populations were tested to a commercially available product of Bacillus thuringiensis (Dipel®) and excised non-Bt and Bt plant tissue in the laboratory. Using measured LC50 values, ratios (field colony/susceptible lab colony) field populations of bollworm and tobacco budworm were 0.75–26.1 and 0.34–2.35 more tolerant than comparable laboratory susceptible populations to Dipel®. Ratios of first generation larvae from field-collected insects surviving on excised Bt cotton tissue relative to USDA laboratory colony ranged from 0.1-2.7 for bollworm and 0-0.2 for tobacco budworm, and increased relative to collection date throughout the growing season. The goal of this research was to determine the relationship between variable measurements of susceptibility in laboratory assay methods, insect survival in the field, and damage to Bt crops and to identify resistance events as they occur.
Accomplishments
1. Impact of various pesticide classes on honey bee survival. Information regarding the impact of direct sprays and residues from different pesticide classes on honey bee populations is needed to understand which classes may pose the greatest risks. The toxicity of imidacloprid mixed with seven different pesticide classes on honey bees through direct sprays and residues was determined by ARS scientists at Stoneville, Mississippi. Results demonstrated that residue levels of seven pesticides in pollens/hive may not adversely affect honey bees, but long term exclusive ingestion of the maximal residue levels of some insecticides may induce substantial bee mortality. Rotating pesticide chemistries and proper selection of pesticide mixtures can alleviate toxicity risks to honey bees.
2. Sweet potato variety evaluations. Many small-scale sweet potato producers in the Mississippi Delta have limited information regarding varieties that are compatible in the environmental conditions of the Mississippi Delta. Sweet potato varieties compatible to the climate and growing conditions of the Mississippi Delta were evaluated by ARS scientists at Stoneville, Mississippi. Varieties that produced the highest yields, best quality potatoes, and showed reduced insect damage were recorded. Results were presented at the National Sweet Potato Meeting and National Sweet Potato Collaborator’s Meeting. This information is being used by sweet potato growers in the Mississippi Delta and other areas of the Southern U.S. to choose varieties that will enhance their profit margin.
3. Native bees in agricultural production fields. Currently, there is little or no information regarding native bee communities in agricultural environments across the Mississippi Delta. Through a variety of sampling techniques, baseline information regarding the species richness and abundance of native bees inhabiting agricultural commodities in the Mississippi Delta was collected by ARS scientists at Stoneville, Mississippi. Sampling techniques included: modified pan traps, malaise traps, colored vane traps, monitoring pheromone bycatch, and directed netting. This baseline information will be used to evaluate impacts of various agricultural practices on populations of these insects.
Review Publications
Yao, J., Zhu, Y., Nanyan, L., Buschman, L.L., Zhu, K. 2017. Comparisons of transcriptional profiles of gut genes between cry1Ab-resistant and susceptible strains of Ostrinia nubilalis revealed genes possibly related to the adaptation of resistant larvae to transgenic cry1Ab corn. International Journal of Molecular Sciences. 18:301. doi:10.3390/ijms18020301.
Blackman, B.D., Allen, K.C., Jones, W.A., Little, N., Grodowitz, M.J., Luttrell, R.G. 2017. First report of soybean pest, Euschistus quadrator (Hempitera: pentatomidae) in Mississippi. Florida Entomologist. 100(1):192-194. doi:10.1653/024.100.0132.
Caprio, M.A., Edwards, K.T., Musser, F.R., Allen, K.C., Fleming, D.E. 2016. Impact of insect management on population dynamics and insecticide resistance of tarnished plant bug (Lygus lineolaris). Journal of Economic Entomology. 109(6):2517-2524.
Clay, N.A., Little, N., Riggins, J.J. 2016. Inoculation of ophiostomatoid fungi in Loblolly pine trees increases the presence of subterranean termites in fungal lesions. Arthropod-Plant Interactions. 16(3):260-264. doi:10.1111/afe.12053.
Zhu, Y., Yao, J., Adamczyk Jr, J.J., Luttrell, R.G. 2017. Feeding toxicity and impact of imidacloprid formulation and mixtures with six representative pesticides at residue concentrations on honey bee (Apis mellifera). PLoS One. 12(6):e0178421. doi:10.1371/journal.pone.0178421.
Zhu, Y., Yao, J., Adamczyk Jr, J.J., Luttrell, R.G. 2017. Synergistic toxicity and physiological impact of imidacloprid alone and binary mixtures with seven representative pesticides on honey bee (Apis mellifera). PLoS One. 12(5):e0176837. doi:10.1371/journal.pone.0176837.
Zhu, Y., Yao, J., Luttrell, R.G. 2016. Identification of genes potentially responsible for extra-oral digestion and overcoming plant defense from salivary glands of the tarnished plant bug (Lygus lineolaris) using cDNA sequencing. Journal of Insect Science. 16(1):60;1-11.
