Location: Southern Insect Management Research2019 Annual Report
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.
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.
Laboratory assays were conducted to evaluate the effect of seven potential native entomopathogenic fungi (NI9, NI10, NI11, NI12, NI13, NI14, NI15) of Beauveria bassiana strains isolated from tarnished plant bug (TPB) samples collected in the Mississippi delta from 2015 and 2016. Each strain was screened based on virulence with 1 to 4 days mortality after exposure and 2 to 4 days sporulation after dead, which is the standard measurement for NI8 activity. The median lethal concentration, sporulation and doses of the seven native strains of B. bassiana including the Mississippi Delta native NI8 ARSEF8889 were estimated on lab colonies of mixed-sex 2 d old TPB adults (3 groups of 30 adults / strain). Serial dilutions of four test concentrations of NI8 and the 10 strains (n x 107, n x 106, n x 105, n x 104 spores/ mL) were prepared to treat TPB adults. All treatments were applied using a specially designed spray tower. After application, adults were released in an insect observation cage to let them dry and then transferred individually into solo cup with diet. Insects were held in an environmental room at 27ºC, 65%RH, and 12L: 12D photoperiod and examined daily for five day for mortality. Differences in mortality and sporulation were found among strains. Higher mortality and sporulation were observed in TPB treated with B. bassiana strains NI8 and NI15. Field experiments were carried out to evaluate mortality of TPB using the entomopathogenic fungus B. bassiana strain NI8 alone and in conjunction with the growth regulator novaluron. Both the fungus and growth regulator were evaluated for compatibility and compared to a conventional treatment. Twenty plots, sixteen rows wide and 400’ long (0.465 acres) were planted with BGII cotton. Each treatment (Untreated control, NI8, novaluron, NI8+novaluron, and conventional) was replicated four times. Treatments were randomized within each replication and a plot of 4 rows of corn were planted between cotton plots to avoid contamination among treatments. Concentration of B. bassiana was 6x1012 (spores / acre). All sprays included 1.5 ml of Tween-80 per gallon of spray. Insect assessment were made by employing four sets of ten sweeps per plot at 1 day before spray and 3, 7, and 14 days after treatment. The number of TPB adults and nymphs for each plot and rating were recorded. No broadcast applications of compounds for the control of TPB or any other insects were made during the duration of the test. No significant differences were found in lint yield between treatments. The conventional, Diamond, and NI8+Diamond treatments resulted in a higher lint yield than the control and B. bassiana alone. A second year of field study will be conducted in 2019. Tarnished plant densities will be assessed before and after the application of treatments. A third 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) (about 6,500 diapausing adults) during the end of September until mid-December 2018. 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 compared 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 and 2017, 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. Two strains of Beauveria bassiana were evaluated for potential control of redbanded stink bug. Four concentrations (7 x 104, 7 x 105, 7 x 106, 7 x 107) of both a Mississippi Delta native strain (NI8) and a commercially available formulation (GHA) were tested against field collected adult redbanded stink bugs in the laboratory and evaluated at four time points (3, 5, 10, and 15 days). Application methods simulated field sprays and were similar to those previously used to screen several other pests and beneficial insects. Both isolates of B. bassiana tested were pathenogenic to adult redbanded stink bugs. A significant overall difference between strains (regardless of the concentration) was observed at 3 days after treatment, while differences among concentrations were observed at 5, 10, and 15 days after treatment. The lethal concentration (LC50) and lethal sporulation (LS50) were not significantly different between strains at either 10 or 15 days after treatment. However, higher mortality was observed in cohorts sprayed with GHA at lower concentrations than those sprayed with NI8. Unlike other control options, B. bassiana has a short re-entry interval and no harvest interval, making it a potentially attractive and environmentally benign alternative to conventional synthetic insecticides for control of redbanded stink bugs in soybeans. Further testing on juvenile life stages and field testing is needed to evaluate potential for in field control. Microbial control agents have been codified and identified from field samples collected in Mississippi Delta during 2016-2018. Spore powder of new microbial agents have been produced and used in bioassays to evaluate the pathogenicity on tarnished plant bugs and other pestiferous insects of southern crops and potential impact on beneficial insect populations. Using biological control agents is the major goal addressed in this investigation. Result indicated that the Mississippi Delta native strain NI8 may be suitable for control of TPB, not only because of its high pathogenicity against targeted pest, but also for its selectivity against some beneficial arthropods. This further refines our knowledge in the development of field application strategies of B. bassiana for Lygus and other cotton pest managements.
1. Field efficacy of Beauveria bassiana for control of the tarnished plant bug. Microbial insecticides are an important component of many insect pest management programs. Field experiments to determine mortalities and estimate lethal doses of potential microbial insecticides including the native Delta strain NI8 and the commercial strain GHA on feral tarnished plant bug populations on cotton were completed and published. Results indicated that B. bassiana applications resulted in decreased survival of tarnished plant bugs by >50% regardless of the isolate by direct spray or contact. This is the first study conducted in a production cotton field to measure the effect of B. bassiana on TPB populations in cotton. This study will impact the development of non-chemical control methods used in cotton integrated pest management systems across the southern United States.
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