Effect of Ecdysteroid UDP-Glucosyltransferase Gene Deletion on Efficacy of a Baculovirus Against Heliothis virescens and Trichoplusia ni (Lepidoptera: Noctuidae)

Abstract

Laboratory, greenhouse, and field studies were conducted to characterize the biological activity of a genetically altered form of Autographa californica (Speyer) nucleopolyhedrosis virus (AcNPV). The altered baculovirus (vEGTDEL) had a deletion in the ecdysteroid UDP-glucosyltransferase gene. Results from bioassays conducted with neonate and 3rd-instar tobacco budworm, Heliothis virescens (F.), as well as with 3rd-instar cabbage looper, Trichoplusia ni (Hübner), showed vEGTDEL caused larval death slightly, but significantly, quicker than AcNPV. Based on supposition (LT50 values were not calculated), it appeared that larval mortality occurred 0.5-1.0 d faster following exposure to vEGTDEL versus AcNPV. Greenhouse studies conducted against H. virescens on cotton showed that hastened virulence exhibited by vEGTDEL led to improved plant protection versus AcNPV. For example, following 5 weekly sessions of foliar application and H. virescens artificial infestation, cotton treated with wettable powder formulations of vEGTDEL or AcNPV at 2.5 x 10(12) OB/ha averaged 25.7 and 61.8% damaged flower buds, respectively. Although vEGTDEL tended to provide more consistent control of T. ni than AcNPV in greenhouse and field trials conducted on leafy vegetables, differences in efficacy between the 2 baculoviruses were marginal and usually not statistically significant. Generally, results from these studies suggest that genetic modification of NPVs to hasten their lethal effect may be a promising strategy for improving the insecticidal properties of the insect-specific pathogens.

Sequence comparison between three geographically distinct Spodoptera frugiperda multiple nucleopolyhedrovirus isolates: Detecting positively selected genes

“…The continued growth of the infected insect is reflected in an increased production of viral OBs. Deletion of egt from the viral genome has been shown to increase the speed of kill of the virus with a corresponding reduction in crop damage (Chen et al, 2000;Ó Reilly, 1995;Slavicek et al, 1999;Treacy et al, 1997). Harrison et al (2008) suggested that the deletion of most of the egt ORF in SfMNPV-3AP2 provided a potential explanation for its rapid speed of kill in bioassays.…”

Structural and ultrastructural alterations of Malpighian tubules of Anticarsia gemmatalis (Hübner) (Lepidoptera: Noctuidae) larvae infected with different Anticarsia gemmatalis multiple nucleopolyhedrovirus (AgMNPV) recombinant viruses

“…It has been previously shown that inactivation of the egt gene of baculoviruses usually leads to an enhancement of the killing efficacy of the virus (O'Reilly and Miller, 1991;Treacy et al, 1997;Slavicek et al, 1999;Chen et al, 2000;Pinedo et al, 2003). However, some egt mutant baculoviruses presented no such behavior when compared to the wild-type virus (Bianchi et al, 2000;Popham et al, 1997).…”

Comparative Insecticidal Properties of Two Nucleopolyhedrovirus Vectors Encoding a Similar Toxin Gene Chimer

“…Feral and genetically altered nucleopolyhedroviruses evaluated in studies described herein were as follows: (1) the V8 strain (Popham et al 1998) of AcNPV and an isolate of HzNPV, and (2) AcNPV and HzNPV, each with approximately a 1-kb internal deletion in the ecdysteroid UDP-glucosyltransferase gene (EGT) and an insertion of a 0.8-kb fragment encoding AaIT. The strain of HzNPV used in this study was isolated from H. zea larvae belonging to a laboratory colony maintained at the Cyanamid Agricultural Research Center in Princeton, NJ; EGT-deleted forms of AcNPV and HzNPV were constructed as described by OÕReilly andMiller (1990), OÕReilly et al (1991) and Treacy et al (1997a). Using a direct ligation technique, the following cassette was inserted into genomes of both of the aforementioned EGT-deleted viruses: AaIT under transcriptional control of the early viral promoter, DA26, and fused with the tobacco hornworm, Manduca sexta (L.), adipokinetic hormone signal peptide sequence to facilitate secretion of expressed toxin from infected host cells.…”