Co-infection with iflaviruses influences the insecticidal properties of Spodoptera exigua multiple nucleopolyhedrovirus occlusion bodies: Implications for the production and biosecurity of baculovirus insecticides

Abstract

Biological insecticides based on Spodoptera exigua multiple nucleopolyhedrovirus (SeMNPV) can efficiently control S. exigua larvae on field and greenhouse crops in many parts of the world. Spanish wild populations and laboratory colonies of S. exigua are infected by two iflaviruses (SeIV-1 and SeIV-2). Here we evaluated the effect of iflavirus co-infection on the insecticidal characteristics of SeMNPV occlusion bodies (OBs). Overall, iflavirus co-inoculation consistently reduced median lethal concentrations (LC50) for SeMNPV OBs compared to larvae infected with SeMNPV alone. However, the speed of kill of SeMNPV was similar in the presence or absence of the iflaviruses. A reduction of the weight gain (27%) associated with iflavirus infection resulted in a 30% reduction in total OB production per larva. Adult survivors of SeMNPV OB inoculation were examined for covert infection. SeMNPV DNA was found to be present at a high prevalence in all SeIV-1 and SeIV-2 co-infection treatments. Interestingly, co-inoculation of SeMNPV with SeIV-2 alone or in mixtures with SeIV-1 resulted in a significant increase in the SeMNPV load of sublethally infected adults, suggesting a role for SeIV-2 in vertical transmission or reactivation of sublethal SeMNPV infections. In conclusion, iflaviruses are not desirable in insect colonies used for large scale baculovirus production, as they may result in diminished larval growth, reduced OB production and, depending on their host-range, potential risks to non-target Lepidoptera.

An iflavirus found in stink bugs (Hemiptera: Pentatomidae) of four different species

“…For example, the asymptomatic infection of Helicoverpa armigera with Helicoverpa armigera densovirus-1 (HaDNV-1) correlates with increased resistance to lethal infection of H. armigera larvae with its baculovirus, Helicoverpa armigera nucleopolyhedrovirus (HearNPV) and also to Bacillus thuringiensis (Bt) toxin. In contrast, co-infections of Spodoptera exigua larvae with both a baculovirus and an iflavirus reduced the dose of baculovirus occlusion bodies required to kill larvae relative to infections with baculovirus alone (Carballo et al, 2017). The presence of covert iflavirus infections of stink bugs may also have an impact on the deployment of pathogens for stink bug control.…”

Identification and RNAi Profile of a Novel Iflavirus Infecting Senegalese Aedes vexans arabiensis Mosquitoes

“…Further, virus interactions at the whole organism level may produce a different outcome as compared to the cellular level. In lepidopterans, co-infections of iflaviruses and the large dsDNA baculovirus (Baculoviridae) show either decreased [62] or enhanced [63] pathogenicity of the baculovirus, but in both studies, the environmental stability and infectivity of the iflavirus were increased. Whether ISVs, such as an iflavirus, interact with dual-host arboviruses in hematophagous insects is not clear due to the lack of available data.…”

Discovery and characterization of a novel picorna-like RNA virus in the cotton bollworm Helicoverpa armigera

“…Secondly, although nonpathogenic viruses may not directly impact host mortality, the interactions between them and other virus species residing in their host should be studied further as multiple-species interactions might occur, e.g. Iflavirus was shown to reduce baculovirus Spodoptera exigua multiple nucleopolyhedrovirus pathogenicity and affect occlusion bodies production (Carballo et al, 2017;Jakubowska et al, 2016); densovirus HaDV2 in H. armigera appears to offer its host some protection, increasing host resistance to the baculovirus HaNPV (Xu et al, 2014). As HaNV was found in seemingly healthy individuals of cotton bollworm (showing no pathology), HaNV appears not to be an overtly pathogenic virus and might have a mild or non-pathogenic effect on its host.…”