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

Abstract

Laboratory, greenhouse and field studies were conducted to characterize the insecticidal properties of genetically altered forms of Autographa californica (Speyer) nucleopolyhedrovirus (AcNPV) and Helicoverpa zea (Boddie) NPV (HzNPV) against selected heliothine species. The altered viruses each contained a chimeric 0.8-kb fragment encoding the insect-specific, sodium channel neurotoxin from the Algerian scorpion Androctonus australis Hector (AaIT, hence recombinant viruses designated Ac-AaIT and Hz-AaIT). Based on LD50 values, results from diet-overlay bioassays showed Ac-AaIT and Hz-AaIT to be equally virulent against larval tobacco budworm, Heliothis virescens (F.), but Hz-AaIT averaged 1,335-fold greater bioactivity than Ac-AaIT against larval cotton bollworm, Helicoverpa zea (Boddie). Hz-AaIT killed larvae of both heliothine species at rates significantly faster than those imparted by HzNPV (viral LT50 values averaged 2.5 and 5.6 d, respectively). In greenhouse studies, foliar sprays of Ac-AaIT and Hz-AaIT were equally effective in controlling H. virescens on cotton; however, Hz-AaIT provided control of H. zea on cotton at a level superior to that of Ac-AaIT. For example, after three weekly sessions of foliar application and H. zea artificial infestation, cotton treated with Ac-AaIT or Hz-AaIT at 10 x 10(11) occulsion bodies (OB)/ha averaged 2.5 and 16.2 nondamaged flower buds per plant, respectively. Another greenhouse study conducted against heliothine species on cotton showed that the quicker killing speed exhibited by Hz-AaIT led to improved plant protection versus HzNPV. Finally, results from three field trials demonstrated that Hz-AaIT at 5-12 x 10(11) OB/ha provided control of the heliothine complex in cotton at levels slightly better than Bacillus thuringiensis, equal to the macrolide, spinosad, and only slightly less than that of selected pyrethroid and carbamate insecticides. Overall, results from these studies indicate that, because of host range differences between the two wild-type viruses, HzNPV is the better vectoring agent (versus AcNPV) for designing recombinant clones as insecticides targeted at the multi-species heliothine complex. Further, these studies suggest that if appropriately tailored for the pest complex, recombinant NPVs may be very effective, insect-specific approaches to managing pests in many cropping scenarios. Possible Hz-AaIT deployment strategies for control of heliothine species on conventional and transgenic cotton varieties are discussed.

Insecticidal activity of two proteases against Spodoptera frugiperda larvae infected with recombinant baculoviruses

“…The recombinant baculovirus expressing TxP-1 had a reduction of 30-40% in the time to induce insect death when compared to the wild type virus [60,13,61]. Similar results were found with the introduction of the scorpion toxin AaIT gene from Androctonus australis with lethal time reduced by 25-40% when compared to wild-type virus [11,12,62,8]. Other toxins from scorpions [63,64], spiders [65], sea anemones [65] and B. thuringiensis [34,35,37] were also expressed using recombinant baculoviruses, and most of them showed an improvement on the virus speed of kill.…”

Baculoviruses — re-emerging biopesticides

“…These facts are consistent with higher susceptibility of earlier instars of larvae to baculovirus infection. It should be pointed out that though AcMNPV, which infects many lepidopteran species, is by far the most frequently used baculovirus for genetic modifications, other baculoviruses, including HzSNPV, Helicoverpa armigera SNPV, RoMNPV, are also employed for this purpose (Li et al, 1999;Treacey et al, 2000;Sun et al, 2004b).…”

Comparative analysis of the genomes of Rachiplusia ou and Autographa californica multiple nucleopolyhedroviruses

“…Wild-type baculoviruses have been effective when deployed against agricultural and forestry pests (Cunningham, 1995;Moscardi, 1999). Genetic engineering of NPVs to shorten the survival time of infected hosts has improved the performance of NPV-based insecticides in the field (Treacy & All, 1996;Smith et al, 2000;Treacy et al, 2000). Further studies on the molecular mechanisms of baculovirus infection, replication and host specificity are essential for additional augmentation of insecticidal potential.…”