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Title: Black Tea and Lignin as Ultraviolet Protectants for the Beet Armyworm Nucleopolyhedrovirus

item Ling, Kai-Shu

Submitted to: Journal of Entomological Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/27/2008
Publication Date: 1/1/2009
Citation: El Salamouny, S., Shapiro, M., Ling, K., Shepard, B.M. 2009. Black Tea and Lignin as Ultraviolet Protectants for the Beet Armyworm Nucleopolyhedrovirus. Journal of Entomological Science. 44(1):50-58

Interpretive Summary: The beet armyworm is a widely distributed insect pest that attacks a broad range of field and vegetable crops. Larvae will feed on the leaves, stems, buds, and sometimes the roots of host plants. Heavy infestations can lead to complete defoliation of a crop. This species is generally considered to be difficult to control in various crop situations. The discovery and use of a novel insect virus (a baculovirus) for biocontrol of beet armyworm showed great promise. However the activity of baculovirus agent against beet army worm in field conditions is greatly reduced upon exposure to sunlight (due to ultraviolet). In this study, we evaluated potentials of using two natural products (black tea and lignin) as UV blockers in a formulation to improve virus killing activity against beet armyworm larvae under laboratory setting. Results showed that a significant improvement in the biocontrol activity against beet armyworm was achieved when the baculovirus formulation was mixed with black tea or lignin extract even under extensive exposure to a UV source, up to five hours. The results showed that there is a great potential to use natural products, instead of synthetic chemicals, to serve as a UV protectant in the baculovirus formulation to improve biocontrol activity against beet armyworm. This finding could make it possible to use baculovirus to effectively control beet armyworm infestation on field and vegetable crop plants even during hot summer months.

Technical Abstract: One of major constraints to use baculoviruses for biocontrol of insect pests in field conditions is their sensitivity to breakdown by sunlight. In this study, we evaluated black tea and lignin (Reax 85A) as potential ultraviolet (UV) protectants for beet armyworm (BAW) Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae) multiple embedded nucleopolyhedrovirus (SeMNPV). The original activity remaining (OAR%) from SeMNPV upon exposure to various length of time (up to 5 h) to a source of UVA and UVB was evaluated in bioassays using third instar BAW under laboratory conditions. BAW mortality was measured after larvae fed on artificial diet treated with SeMNPV. Mortality of BAW due to SeMNPV, with no UV protectants added, was reduced to 23, 11.3 and 2.1% upon UV exposure for 15, 30 or 60 min, respectively. A modified DNA isolation technique was developed to measure levels of the full length viral genomic DNA of SeMNPV through electrophoresis on an agarose gel. Reduction in efficacy of SeMNPV when exposed to UV was corresponded to the degradation of full length viral genomic DNA. The efficacy of SeMNPV on BAW was lost in samples receiving more than two hours of UV and the full length genomic DNA was also degraded to levels that were not visible on agarose gel. However, both black tea and Reax 85A provided nearly 100% UV protection to SeMNPV as measured in bioassays even after five hours of UV irradiation. SeMNPV efficacy against BAW in samples containing black tea or Reax 85A resulted in no reduction of the full length viral genomic DNA. To investigate the mechanism of UV protection for SeMNPV from black tea and Reax 85A, absorption spectra of both protectants were measured with a spectrophotometer. High rate of absorption in the UV range, especially at the range of UVB (280-320nm), was detected for both materials. The absorption rate was higher with Reax 85A than with black tea. Whereas Reax 85A was good absorber for both UVB and UVA radiation, black tea was primarily an absorber of UVB. Therefore, both black tea and Reax 85A are potential natural UV protectants in the formulation of baculoviruses as biopesticides.