Location: Southern Insect Management Research
2018 Annual Report
Objectives
Objective 1: Determine key factors that naturally regulate tarnished plant bug (TPB) population increases and develop new tools for managing tarnished plant bug, including bio-control strategies.
Sub-objective 1.A. Quantify the impact of biological control on TPB seasonal abundance and distribution.
Sub-objective 1.B. Identify and develop new biological control options (including entomopathogens, entomophagous insects, host manipulation and behavioral modification) as possible regulators of TPB population growth.
Sub-objective 1.C. Identify sampling methods for TPB that are cost and time effective for landscape level monitoring, evaluate their use as tools in TPB population management, and link information about seasonal habitat changes to population dynamics.
Objective 2: Develop novel alternative ways to deploy tarnished plant bug control agents, and evaluate effectiveness of these deployment methods in large-scale field experiments.
Sub-objective 2. A. Determine if sprays of the NI8 strain of Beauverua (B.) bassiana applied alone and in combination with novaluron will suppress TPB populations colonizing adjacent cotton.
Sub-objective 2. B. Measure impacts of NI8 and new biological control agent identified in Sub-objective 1B on TPB populations infesting wild hosts and crops in the Mississippi Delta.
Approach
The key factors that naturally regulate tarnished plant bug (TPB) population will be determined by collecting feral population from wild host plants, and when available, in cultivated crops at different locations within the Mississippi Delta. TPB nymphs and adults will be collected at each location. Collected insects will be used for microbial and parasitoids identification, molecular identification studies, life table construction, and stable carbon isotope study. Potential entomopathogenic fungi will be bioassayed in replicated laboratory tests and compered with NI8. The most effective fungus will be tested in large-scale field experiments.
Progress Report
Two isolates of Beauveria bassiana, the commercial strain GHA and the Mississippi Delta native NI8 strain, and two emulsifiers, tween-80 and a starch-based sprayable bioplastic, were evaluated in the field for pathogenicity and infectivity against the tarnished plant bug, (TPB), Lygus (L.) lineolaris. The effect on fruit damage based on the within-season cotton plant mapping also was evaluated. Plots sprayed with Beauveria (B.) bassiana showed at least a 2-fold decrease in TBP adults 3-d after treatment compared to control plots. Little or no differences were found in TPB nymph populations between treated and untreated plots, suggesting that B. bassiana will not affect early stages of TPB. Within-season plant mapping provided clear evidence of the damage caused by TPB to cotton. The highest percentage retention of all first position fruit were observed in plots treated with NI8+tween-80 (93.41±1.51[SE]) followed by NI8+bioplastic (90.25±1.52[SE]). Both were significantly different when compared with formulations including GHA. Overall, these results indicate that B. bassiana applications resulted in >50% decreased survival of TPB regardless of the isolate by direct spray or by contact. However, the superior performance of the Delta native strain NI8 was observed in all treatments applications and times of evaluation.
The virulence of Beauveria bassiana strain NI8 was assessed on tarnished plant (TPB) bugs and on beneficial arthropods including honeybees, green lacewings, three lady beetle species, jumping spiders, and crab spiders. Insects were treated with four concentrations of NI8 (7 x 104, 105, 106 and 107 spores/mL) directly via topical spray. LD50 and LS50 were estimated for all species except for the jumping and crab spiders. From the resulting data, no significant differences in mortality were observed among TPB, honeybees and green lacewings. All three species were highly affected when exposed to the highest concentrations of B. bassiana with 99.0%, 98.2%, and 90.0% mortality, respectively. Between 35 and 45% of the tested populations of orius bugs, convergent lady beetle, crab spiders, and pink lady beetle were infected at 7 x 107 spores/mL; whereas only 22% and 27%, respectively of the jumping spiders and Asian lady beetle were killed at 10 days with the same concentration. No significant differences were found between the LD50s measured for TPB and green lacewings. The LD50 for honeybees was 652-fold greater than the LD50 for TPB.s. Results indicate that green lacewings will be highly affected by the NI8 strain of B. bassiana when applied for control of TPB. In contrast, B. bassiana appeared to have limited effects on the other beneficial arthropods assayed at the test concentrations targeted for TPB control.
A Mississippi Delta native strain (NI8 ARSEF8889) of Beauveria bassiana (Balsamo) Vuillemin (Sordariomycetes: Hypocrales), isolated from Lygus lineolaris (Palisot de Beauvois), was bioassayed on green lacewings, Chrysoperla (C.) rufilabris Burmeister (Neuroptera: Chrysopidae) at four spray concentrations (7.02 x 104, 105, 106 and 107 spores/mL) to evaluate effects on the insect predator’s reproductive rates and adult life expectancy. The application method simulated atomized spray and concentrations tested were similar to those used to measure impacts of the fungus on L. lineolaris. Significant effects of B. bassiana on adults of C. rufilabris were found and the severity of impact depended on the concentrations tested. Beauveria bassiana impacted all demographic measurements of C. rufilabris reproduction and survival. Intrinsic and finite rate of increase and gross and net reproductive rates of adults treated with the highest concentrations tested were significantly decreased while doubling time increased for adults treated with the lowest test concentrations. Based on these observations, C. rufilabris will be affected by sprays of B. bassiana targeted at L. lineolaris if they are present at the time and location of treatment. The measured LD50 of 2.11 viable spores per mm2, compares to a LD50 of 2.71 spores per mm2 for L. lineolaris (Portilla, 2014). Higher concentrations were needed for sporulation (LS50 of 13.60 viable spores per mm2) of the entomopathogenic fungus on C. rufilabris.
A second year of tarnished plant bug collections from wild host plants at different locations in Mississippi was conducted to determine pathogenicity and infectivity against overwintering populations. Thirty-two diapausing adult populations were collected from Greenwood, Yazoo, Indianola, and Clarksdale (Six populations per location) (6,480 diapausing adults) during the end of September until mid-December 2017. Insects were treated every week with four concentrations of NI8 (3.9 x 104, 2.3 x 105, 4.2 x 106, and 1.5 x 107 spores/mL) directly via topical spray. Lethal concentration, sporulation response, and resistance ratios were estimated. Results were compered among feral populations and a laboratory colony. The pathogenicity test of feral populations showed similar behavior when compared with the laboratory colony. Mortality of the diapausing treated adults was recorded from 3 to 5 d; mycelial growth appeared 2 to 4 days after inoculation. As was observed in 2016, no significant differences in mortality (10 days after application) were obtained among feral populations. However, higher mortality and infection on the laboratory colony of TPB was observed, which was significantly different among the feral populations. These results suggest that overwintering populations of TPB may need higher concentrations of NI8 to be killed.
Accomplishments
1. Determine key factors that naturally regulate tarnished plant bug populations. Microbial control agents and parasitoids have been codified and identified from field samples in the Mississippi Delta by ARS scientist at Stoneville, Mississippi. Spore powder of new microbial agents have been produced and used in bioassays to evaluate the pathogenicity on tarnished plant bugs adults and nymphs. Using biological control agents is the major goal addressed in this investigation. It will implement a tarnished plant bug management technology that will be environmentally safe and will contribute to improving profitability and sustainability of the U.S. cotton industry.
2. Determine the effect of the NI8 strain of Beauveria bassiana on populations of tarnished plant bugs and its possible effect on non-target arthropods. The impact of NI8 on feral populations of tarnished plant bugs and beneficial arthropods was quantified by ARS scientist at Stoneville, Mississippi. Seven species of beneficial arthropods including honeybees, green lacewings, three lady beetle species, jumping spiders, and crab spiders were evaluated to quantify the impact of NI8 on lab and field populations. Results suggested that control of tarnished plant bugs with NI8 will required significant ecological understanding of the interaction among the target host, fungal isolate, and the environment. NI8 will be suitable for control of tarnished plant bugs not only because of its high pathogenicity against this insect, but also, for its selectivity against some beneficial arthropods.
3. Field experiments were established to determine mortalities and estimate lethal doses of potential microbials of feral tarnished plant bug populations on southern crops and non-crop hosts. ARS scientist at Stoneville, Mississippi, evaluated field pathogenicity and infectivity of B. bassiana NI8 against the tarnished plant bug. The effect on fruit damage based on the within-season cotton plant mapping was evaluated depending on tarnished plant bug populations. Results indicated that B. bassiana applications resulted in decreased survival of tarnished plant bugs by >50% regardless of the isolates by direct spray or by contact. It was clear the superior performance of the Delta native strain NI8 observed in all treatments applications and times of evaluation.
Review Publications
Portilla, M., Luttrell, R.G., Snodgrass, G.L., Zhu, Y., Riddick, E.W. 2017. Lethality of the entomogenous fungus Beauveria bassiana strain NI8 on Lygus lineolaris (Hemiptera: Miridae) and its possible impact on beneficial arthropods. Journal of Entomological Science. 52(4):352-369. https://doi.org/10.18474/JES17-15.1.
Parys, K.A., Luttrell, R.G., Snodgrass, G.L., Portilla, M., Copes, J. 2017. Longitudinal measurements of tarnished plant bug (Hemiptera: Miridae) susceptibility to insecticides in Arkansas, Louisiana and Mississippi: Associations with insecticide use and insect control recommendations. Insects. 8(4),109. https://doi.org/10.3390/insects8040109.
Portilla, M., Snodgrass, G.L., Luttrell, R.G. 2017. Lethal and sub-lethal effect of Beauveria bassiana strain NI8 on Chrysoperla rufilabris (Neuroptera:Chrysopidae). Florida Entomologist. 100(3):627-633. https://doi.org/10.1653/024.100.0321.
Parys, K.A., Luttrell, R.G., Snodgrass, G.L., Portilla, M. 2018. Patterns of tarnished plant bug (Heteroptera: Miridae) resistance to pyrethroid insecticides in the lower Mississippi Delta for 2008-2015: Linkage to pyrethroid use and cotton insect management. Journal of Insect Science. 18(2):29. https://doi.org/10.1093/jisesa/iey015.
