A comparison of the adaptations of strains of Lymantria dispar multiple nucleopolyhedrovirus to hosts from spatially isolated populations

The adaptation of pathogens to either their hosts or to environmental conditions is the focus of many current ecological studies. In this work we compared the ability of six spatially-distant Lymantria dispar (gypsy moth) multiple nucleopolyhedrovirus (LdMNPV) strains (three from eastern North America and three from central Asia) to induce acute infection in gypsy moth larvae. We also sequenced the complete genome of one Asian (LdMNPV-27/0) and one North American (LdMNPV-45/0) strain which were used for bioassay. We found that all of the North American virus strains, with the exception of one, demonstrated higher potency than the Asian virus strains, either in North American (Lymantria dispar) larvae or, in Asian (Lymantria dispar asiatica) larvae. Complete genome sequencing revealed two gene deletions in the LdMNPV-27/0 strain: the virus enhancin factor gene (vef-1) and the baculovirus repeated orf gene (bro-p). These deletions were not seen in the LdMNPV-45/0 strain nor in other American strains available in archiving systems. We also found deletions of the bro-e and bro-o genes in LdMNPV-45/0 strain but not in the LdMNPV-27/0 strain. The phylogenetic inference with an alignment of the 37 core gene nucleotide sequences revealed the close relationship of the LdMNPV-45/0 strain with other American strains accessed in GenBank (Ab-a624 and 5-6) while the LdMNPV-27/0 strain was clustered together with the LdMNPV-3054 strain (isolated in Spain) instead of predicted clustering with LdMNPV- 3029 (isolated in Asia). Our study demonstrated that first, different LdMNPV isolates from the same metapopulations of L. dispar exhibit little or no difference in the degree of virulence towards host larvae and second, that locality of host population is not an important driver of LdMNPV virulence. Virulence of LdMNPV is determined only by viral genetics. The genetic differences between North American and Central Asian virus strains are discussed.

Effect of bacterial infection on antioxidant activity and lipid peroxidation in the midgut of Galleria mellonella L. larvae (Lepidoptera, Pyralidae)

Bacillus thuringiensis is one of the most widely used sources of biorational pesticides, as well as a key source of genes for transgenic expression to provide pest resistance in plants. In this study the effect of Bacillus thuringiensis ssp. galleriae (Bt) infection on the activity of superoxide dismutase (SOD), glutathione S-transferase (GST), catalase (CAT), concentrations of oxidated and reduced thiols (RSSR/RSH) and malondialdehyde (MDA) was tested in the midgut of Galleria mellonella larvae. We found that Bt infection resulted in increased activities of SOD, GST, malondialdehyde and RSSR/RSH ratio the first day after inoculation. However, catalase activity decreased on the first and following days after bacterial infection by Bt. Our results confirm the hypothesis that Bt infection increases the level of oxidative stress in the larval midgut. In light of this study, it seems possible that oxidative damage contributes to cell death in the midgut during bacteriosis.

Application of the nitroblue tetrazolium-reduction method for studies on the production of reactive oxygen species in insect haemocytes

The in vitro generation of reactive oxygen species (ROS) in haemocytes of Galleria mellonella, Aporia crataegi, Dendrolimus sibiricus, Aglais urticae (Lepidoptera) and Gryllus bimaculatus (Orthoptera), was studied by the method of nitroblue tetrazolium (NBT) reduction. Formazan formation (product of NBT reduction) was observed in haemocytes of all the insects examined, except A. urticae. Lypopolysaccharide and zymosan reduced the number of NBT-positive cells after 1 h incubation and an increase was registered after 4 h incubation. The inhibitors of the respiratory chain enzyme (sodium azide) and melanogenesis (phenylthiourea) reduced formazan formation in nonactivated insect blood cells. No influence of sodium azide and phenylthiourea was found on the activated haemocytes. The results suggest that the generation of ROS in insect haemocytes occured as a result of processes such as respiration and melanization during phagocytosis and encapsulation.