Browsing by Author "Shrestha, Govinda"

Now showing 1 - 6 of 6

Entomopathogens in conjunction with imidacloprid could be used to manage wireworms (Coleoptera: Elateridae) on spring wheat
(2018-02) Antwi, Frank B.; Shrestha, Govinda; Reddy, Gadi V. P.; Jaronski, Stefan T.
We examined the effect of biopesticides used alone, mixed with other biopesticides, or in conjunction with an imidacloprid against wireworms (Coleoptera: Elateridae) in spring wheat Triticum aestivum Linnaeus (Poaceae) (variety: Duclair). The study was conducted at Ledger and Valier, Montana, United States of America in 2015 and 2016. Ten biopesticides (spinosad, azadirachtin, pyrethrin, Beauveria bassiana (Balsamo-Crivelli) Vuillemin (Fungi: Clavicipitaceae) GHA (Mycotrol), B. bassiana ANT-03 (BioCeres), Chromobacterium subtsugae Martin et al. (Bacteria: Neisseriaceae), Burkholderia Yabuuchi et al. (Burkholderiaceae) species, Metarhizium brunneum Petch (Fungi: Clavicipitaceae) ESC1 (MbESC1), and M. brunneum F52 (MetF52) as microsclerotial and corn grit-based granules) were tested in addition to thimet and imidacloprid. Treatment efficacy was based on plant stand protection, wireworm populations, and yield. In 2015, there was considerable variation between sites in treatment efficacy. Mycotrol, BioCeres, MetF52+spinosad, and MetF52+imidacloprid applications protected seedlings from wireworm damage better than the control at Ledger, while only MetF52 at Valier. Wireworm populations were significantly higher with Mycotrol, spinosad, MetF52+spinosad, MbESC1 (25 g/L), and MetF52 treatments, compared with control, at 14 and 28 days post application at Ledger, but without effect at Valier, 2015. We found significantly higher yield in plots treated with imidacloprid+MetF52 and Mycotrol+azadirachtin (Xpulse) compared with control at Ledger. In 2016, no significant treatment effects were observed at either site. In summary, this study provides insight on what treatments should be explored in more detail despite variable results.
Evaluation of toxicity of biorational insecticides against larvae of the alfalfa weevil
(2016-05) Reddy, Gadi V. P.; Antwi, Frank B.; Shrestha, Govinda; Kuriwada, Takashi
The alfalfa weevil, Hypera postica (Coleoptera: Curculionidae), is a major pest of alfalfa Medicago sativa L. (Fabaceae). While H. postica usually causes the most damage before the first cutting, in summer of 2015 damaging levels of the pest persisted in Montana well after the first harvest of alfalfa. Although conventional insecticides can control H. postica, these chemicals have adverse effects on non-target organisms including pollinators and natural enemy insects. In this context, use of biorational insecticides would be the best alternative options, as they are known to pose less risk to non-target organisms. We therefore examined the six commercially available biorational insecticides against H. postica under the laboratory condition: Mycotrol ^Â® ESO (Beauveria bassiana GHA), Aza-Direct ^Â® (Azadirachtin), Met52 ^Â® EC (Metarhizium brunneum F52), Xpectro OD ^Â® (Beauveria bassiana GHA+pyrethrins), Xpulse OD ^Â® (Beauveria bassiana GHA+Azadirachtin) and Entrust WP ^Â® (spinosad 80%). Concentrations of 0.1, 0.5, 1.0, and 2.0 times the lowest labelled rates were tested for all products. However, in the case of Entrust WP, additional concentrations of 0.001 and 0.01 times the lowest label rate were also assessed. Mortality rates were determined at 1 to 9days post treatment. Based on lethal concentrations and relative potencies, this study clearly showed that Entrust was the most effective, causing 100% mortality within 3days after the treatment among all the tested materials. With regard to other biorational, Xpectro was the second most effective insecticide followed by Xpulse, Aza-Direct, Met52, and Mycotrol. Our results strongly suggested that these biorational insecticides could potentially be applied for H. postica control.
Field efficacy of Bacillus thuringiensis galleriae strain SDS-502 for the management of alfalfa weevil and its impact on Bathyplectes spp. parasitization rate
(2018-03) Shrestha, Govinda; Reddy, Gadi V. P.; Jaronski, Stefan T.
Alfalfa weevil, Hypera postica Gyllenhal, is an important pest in forage alfalfa worldwide, and especially so on the Northern Plains of North America. Neither the weevil-specific fungus, Erynia phytonomi, nor the weevil's parasitoids are able to routinely suppress outbreaks as they do in the eastern U.S. A new Bacillus thuringiensis var. galleriae, having a Cry8Da coleopteran-active toxin, has been recently commercialized. We examined the efficacy of this B. thuringiensis product against the H. postica in replicated field trials in north central Montana. Because it has been suggested that efficiency of the parasitoids, Bathyplectes curculionis and Oomyzus incertus, was inversely proportional to host numbers (i.e., parasitoid efficiency increased when host population is low), we also sought to determine if a partial reduction of larval H. postica populations with a B. thuringiensis would yield to greater parasitoid efficiency, manifested as higher percent parasitism among the surviving larvae. The B. thuringiensis gave 27-40% reduction in weevil numbers at the low label rate, 55-59% for the high label rate. Mean parasitism at the two research locations varied from 5-26% and 17-36% respectively, but application of the B. thuringiensis had no significant effect on parasitism levels, i.e. parasitism was not greater in treated than in carrier control plots.
Field efficacy of insect pathogen, botanical and jasmonic acid for the management of wheat midge Sitodiplosis mosellana the impact on adult parasitoid ... populations in spring wheat
(2017-10) Shrestha, Govinda; Reddy, Gadi V. P.
The wheat midge, Sitodiplosis mosellana, is a serious pest of wheat worldwide. In North America, management of S. mosellana in spring wheat relies on the timely application of pesticides, based on midge adults levels caught in pheromone traps or seen via field scouting during wheat heading. In this context, biopesticides can be an effective alternative to pesticides for controlling S. mosellana within an integrated pest management program. A field study using insect pathogenic fungus Beauveria bassiana GHA, nematode Steinernema feltiae with Barricade polymer gel 1 %, pyrethrin, combined formulations of B. bassiana GHA and pyrethrin, Jasmonic acid (JA) and chlorpyrifos (chemical check) was performed to determine to which extent they affect midge larval populations, kernel damage levels, grain yield and quality, and the impacts on adult parasitoid Macroglenes penetrans populations. The results indicated that biopesticides JA and S. feltiae were the most effective in reducing larval populations and kernel damage levels, and produced a higher spring wheat yield when compared to the water control at both study locations (East Valier and North Valier, Montana, USA). Increased test weight in wheat had been recorded with two previous biopesticides at East Valier but not for North Valier, when compared over water control. These results were comparable in efficacy to the chlorpyrifos. The present study also suggested that B. bassiana and pyrethrin may work synergistically, as exemplified by lower total larval populations and kernel damage levels when applied together. This study did not demonstrate the effect of any treatments on M. penetrans populations.
Potential biopesticides for crucifer flea beetle, Phyllotreta cruciferae (Coleoptera: Chrysomelidae) management under dryland canola production in Montana
(2018-04) Shabeg, Briar Singh; Antwi, Frank; Shrestha, Govinda; Sharma, Anamika; Reddy, Gadi V. P.
The crucifer flea beetle, Phyllotreta cruciferae (Goeze), is an economically important and dominant pest of canola (Brassica napus L) in the Northern Great Plains of the USA. The current flea beetle management strategy is based on using synthetic chemical treated seeds and if necessary, foliar spray of chemicals at canola seedlings in early spring for targeting adult population. However, there is an increasing demand for development of alternative management strategies for P. cruciferae pertaining to concerns over the development of resistance to synthetic insecticides and non-target effects on pollinators and other beneficial insects. Replicated field trials were conducted to test the efficacy of several commercially available biopesticides including Entrust® (spinosad), entomopathogenic nematode Steinernema feltiae + Barricade® (polymer gel 1%), Aza-Direct® (azadirachtin), Pyganic 1.4® EC (pyrethrin), Grandevo® SC (Chromobacterium subtsugae), Venerate® XC (Heat killed Burkholderia sp. strain A396 as seed treatment and foliar application) and Gaucho® (imidacloprid) (chemical check) for the P. cruciferae management at two locations (Conrad and Sweetgrass) of Montana in 2016. Biopesticide products were evaluated based on canola leaf area injury ratings and seed yield levels. Although, there was no clear trend of canola yield increase, selected biopesticide treatments were effective in maintaining low leaf area injury ratings as compared to untreated control. Entrust was able to maintain low leaf area injury ratings (8.5–14.5%) when compared to untreated control (16.0–21.4%) at both the locations. Entomopathogenic nematodes, Steinernema feltiae + Barricade® and Venerate® applied as foliar treatments maintained significantly lower feeding injury pressure at Sweetgrass (11.8%) and Conrad (13.4%) locations respectively, when compared to the untreated control. Our study results suggest that these biopesticide treatment results were comparable in efficacy to the chemical seed treatment Gaucho®. Other two biopesticide products- Aza-Direct® and Pyganic 1.4® EC treatments did not provide effective control of P. cruciferae at both the locations.
Role of the aphid species and their feeding locations in parasitization behavior of Aphelinus abdominalis, a parasitoid of the lettuce aphid Nasonovia ribisnigri
(2017-08) Shrestha, Govinda; Skovgård, Henrik; Reddy, Gadi V. P.; Steenberg, Tove; Enkegaard, Annie
Aphid species feeding on lettuce occupy distinct feeding sites: the lettuce aphid Nasonovia ribisnigri prefers to feed on heart leaves, whereas the potato aphid Macrosiphum euphorbiae feeds only on outer leaves. The aphid parasitoid Aphelinus abdominalis, known to be able to regulate M. euphorbiae on many crops, has recently been indicated as a promising biocontrol candidate also for use against N. ribisnigri, a major pest of lettuce. This study therefore examined A. abdominalis parasitization preference between N. ribisnigri and M. euphorbiae and its ability to parasitize aphids feeding on different parts of lettuce plants. In addition, life history traits of A. abdominalis on these aphid species were investigated. In nochoice laboratory experiments on leaf discs and 24 h exposure, A. abdominalis successfully parasitized 54% and 60% of the offered N. ribisnigri and M. euphorbiae, respectively, with no significant difference. In the corresponding choice experiment, however, A. abdominalis had a tendency for a significantly higher preference for M. euphorbiae (38%) compared to N. ribisnigri (30%). Growth chamber experiments on whole plants demonstrated that A. abdominalis was able to parasitize aphids, regardless of their feeding locations on lettuce plants. However, aphid feeding behavior had a significant effect on the parasitization rate. A. abdominalis parasitized significantly higher percentages of M. euphorbiae or N. ribisnigri when aphids were exposed separately to parasitoids on whole lettuce plants as compared with N. ribisnigri exposed only on heart leaf. A significant preference of A. abdominalis for M. euphorbiae compared to N. ribisnigri was also observed in the growth chamber choice experiment. A high percentage of adult emergence (> 84%) and female-biased sex ratio (> 83%) were found irrespective of the aphid species.