Location: Southern Insect Management Research
2017 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
NI8 strain was evaluated under laboratory conditions for pathogenicity and infectivity against overwinter populations of tarnished plant bug (TPB). Thirty-two diapausing adult populations were collected from wild host plants at four different locations in Mississippi (Greenwood, Yazoo, Indianola, and Clarksdale), (Six populations per location), (6,480 diapausing adults). During October until mid December,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 days; mycelial growth appeared 2 to 4 days after inoculation. No significant differences in mortality (10 days after application) were observed 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 suggested that overwinter population might need higher concentrations of NI8 to be killed.
The median lethal concentration, sporulation and doses of the strain NI8 were estimated on Apis mellifera. Brood frames from the hives were evaluated, and those with more than 50% coverage of healthy brood were transferred to an incubator (33 degrees C; 65% relative humidity and photoperiod of 0 h:24 h (L:D). Thirty newly-emerged bees were transferred to each cage (600 workers:4 cages/concentration plus control) and maintained at 33 degrees C in an incubator for at least four days before being used for bioassays. Each cage was supplied with a 1 x 1 x 2 cm piece of Global Patties (purchased from Betterbee Inc., Greenwich, New York), and 20 mL each of sugar syrup (50%, V/V) and d-H2O in scintillation vials. A technique was developed to evaluate B. bassiana against TPB was used to bioassay the bees. Serial dilutions of four test concentrations of NI8 (3.9 x 104, 2.3 x 105, 4.2 x 106, and 1.5 x 107 spores/mL) were used to treat honeybee to evaluate mortality and infection. Differences in mortality and sporulation were found among concentrations. LC50s were compered with a laboratory colony of TPB. From the resulting data, no significant differences in mortality (10 days after application) were observed among TPB adults and honeybee workers. Both species were highly affected when exposed to the highest concentrations of NI8 with 99.0% and 98.2% mortality, respectively.
The second year of TPB collection from wild host plants at different locations in Mississippi to determine the natural incidence of Beauveria bassinna and parasitism was continued during 2016. Second, third, fourth, fifth instar nymphs and adults from each location were kept individually for 15 days on solid diet and checked daily for parasitism or microbial infection. No parasitism by Phasia spp. (Diptera: Tachinidae) was found during this year, and a range from 0 to 3% of parasitism by three unidentified braconid species (Hymenoptera: Braconidae) where observed in third, forth and fifth instar nymphs, and a range of 0 to 26% in adults. No differences in distribution of parasitism throughout the year were observed among 2015, where presence of parasitism of TPB was first observed in early April with continuing observations through early June. No parasitism was observed after that during 2016. Natural incidence of Beauveria bassiana, Metarhizium anisopliae and Aspergillus flavus continued being the main microbial in Mississippi. Results of these studies are a second year component of life table studies examining ecological targets for microbial control of TPB populations.
Several thousand adults and nymphs of TPB including populations of non-target arthropods were received and analyzed in the lab. Insects came from patches of wild host growing on field borders and ditches and crops sprayed with NI8 throughout the year (8.5 x 1012 spores/acre)(plots paired with untreated plots). Samples from 0-days, 5-days and 10-days following the application were bioassayed. Each insect was individually placed into diet cup and held for 15 days at room temperature. Insects were examined daily for mortality and sporulation. Detailed observations were also made on the effects of NI8 on TPB mortality by contact. Thirty 2-day old TPB from a laboratory colony were released in cages with sprayed branches or plants (5 or more plants or branch/cage) from the plots where the insects were collected (treated and untreated plots). Plants were cut 1-h after NI8 applications (planate, primrose, erigeron, ironweed, coreopsis, pigweed, marestail, grain sorghum, ragweed, goldenrod, corn, sorghum, and soybean. Insects were left for 24-h in the cages with the sprayed plants. Released insects were collected and individually placed into diet cup and observed daily for 10 days for mortality and infection. Data from 45 collections and 15 applications is being analyzed to determine the possible effect of NI8 on population of TPB density and its possible effect on other species.
Both adult and nymphs of TPB from samples collected across the Delta were subjected to stable carbon isotope (SCI) analysis. This analytical technique has the ability to differentiate between insects that developed on C4 hosts (corn and pigweed) and C4 hosts (most broad leaved plants, including soybean and cotton). Approximately 20 adults and up to 20 nymphs were removed from each of the collections. Samples from 2015 are complete, and samples taken in 2016 are currently being processed.
Accomplishments
1. Determined key factors that naturally regulate TPB population. ARS scientist in Stoneville, Mississippi, quantified the impact of biological control factors of TPB seasonal abundance and distribution. No parasitism by Phasia spp. (Diptera: Tachinidae) was found during 2016. Natural incidence of Beauveria bassiana, Metarhizium anisopliae and Aspergillus flavus continued being the main microbial in Mississippi. Using biological control agents is the major goal addressed in this investigation. It will implement a tarnished plant bug (TPB) management technology that will be environmentally safe and will contribute to improving profitability and sustainability of the U.S. cotton industry.
2. Determined the effect of NI8 on population of tarnished plant bug (TPB) density and its possible effect on non-target arthropods. ARS scientists in Stoneville, Mississippi quantified the impact of NI8 on feral populations of TPB and its possible impact on beneficial arthropods. Over 170 species of arthropods including TPB were collected from different locations across the Mississippi Delta. Preliminary results suggested that the control of TPB with NI8 will require significant ecological understanding of the interaction among the target host, fungal isolate, and the environment. NI8 will be suitable for control of TPB, not only because of its high pathogenicity against this insect, but also for its selectivity against some beneficial arthropods.
