Conserved and specific genomic features of endogenous polydnaviruses revealed by whole genome sequencing of two ichneumonid wasps

Polydnaviruses (PDVs) are mutualistic endogenous viruses associated with some lineages of parasitoid wasps that allow successful development of the wasps within their hosts. PDVs include two taxa resulting from independent virus acquisitions in braconid (bracoviruses) and ichneumonid wasps (ichnoviruses). PDV genomes are fully incorporated into the wasp genomes and comprise (1) virulence genes located on proviral segments that are packaged into the viral particle, and (2) genes involved in the production of the viral particles, which are not encapsidated. Whereas the genomic organization of bracoviruses within the wasp genome is relatively well known, the architecture of endogenous ichnoviruses remains poorly understood. We sequenced the genome of two ichnovirus-carrying wasp species, Hyposoter didymator and Campoletis sonorensis. Complete assemblies with long scaffold sizes allowed identification of the integrated ichnovirus, highlighting an extreme dispersion within the wasp genomes of the viral loci, i.e. isolated proviral segments and clusters of replication genes. Comparing the two wasp species, proviral segments harbor distinct gene content and variable genomic environment, whereas viral machinery clusters show conserved gene content and order, and can be inserted in collinear wasp genomic regions. This distinct architecture is consistent with the biological properties of the two viral elements: proviral segments producing virulence proteins allowing parasitism success are fine-tuned to the host physiology, while an ancestral viral architecture was likely maintained for the genes involved in virus particle production. Finding a distinct genomic architecture of ichnoviruses and bracoviruses highlights different evolutionary trajectories leading to virus domestication in the two wasp lineages.

HELICOVERPA ARMIGERA-PEST ON TOBACCO PLANTS

Helicoverpa armigera Hubner is а migratory, cosmopolitan and polycyclic species. The pest is known as tobacco bollworm or budworm. The species is polyphagous and is an economically important agricultural pest. The studies were conducted on tobacco plants in the Experimental Field of the Scientific Tobacco Institute - Prilep during 2017/2018. Monitoring of population dynamics of H. armigera was performed during tobacco vegetation in a 10 -day period, using the method of examining 100 tobacco plants, with Zig-Zag review of pest scouting. The collected larvae were additionally fed and grown in a laboratory according to the standard laboratory methodology. Field and laboratory trials were carried out for control of H. armigera, with five insecticides/ active ingredients: Spinetoram (a.i. 250 g/kg)- 0.3 kg/ha, Indoxacarb (a.i. 150 g/L)- 0.3 L/ha, Metaflumizone (a.i 240 g/L)- 1 L/ha; Emamectin (a.i. 9.5 g/kg)- 2 kg/ha and Flubendiamide (a.i. 480g/L)- 250 g/ha. Larvae of tobacco budworm damage flowers, seed capsules and top tobacco leaves. The population dynamics of H. armigera showed that the species was present on tobacco from the beginning of July (when plants produce flowers) until the end of tobacco vegetation. The population was the most numerous in August and reached its highest level of density on 20th August in both years. In field trials, were determined five predatory species that fed with young larvae of H. armigеrа: Chrysopa formosa (Neuroptera, Chrysopidae), Chrysopa perla (Neuroptera, Chrysopidae), Chrysopa carnea (Neuroptera, Chrysopidae), Coccinella septempunctata (Coleoptera, Coccinellidae) and Adonia variegata (Coleoptera, Coccinellidae). In the beginning of October on tobacco plants we found parasitized larvae of H. armigera. In laboratory conditions parasitized larvae ate less and ceased developing at their 4th stage- L4. In each parasitized larva was developed one parasite species of Hyposoter didymator (Hymenoptera, Ichneumonidae). H. didymator is endoparasitoid wasp, and it lives on host tissues. According to field and laboratory trials during 2017/2018, all applied insecticides showed high efficacy in H. armigera control. The highest average mortality of 100% was caused by insecticides: Spinetoram, Indoxacarb and Emamectin. Flubendiamide had 97.5% efficiency in control of this pest, and the insecticide Metaflumizone 95.0%. This pest represents a significant challenge to tobacco filed and it produces high economic losses of tobacco seed each year. For the control of H. armigera, it is required constant monitoring of the lifecycle of the pest. One part of management strategy is to study parasitoids, predators and microorganisms and use them against H. armigera. Chemical control is still the most reliable and economic way of protecting tobacco crop from tobacco bollworm.