Densovirus Is a Mutualistic Symbiont of a Global Crop Pest (Helicoverpa armigera) and Protects against a Baculovirus and Bt Biopesticide

Abstract

Mutualistic associations between symbiotic bacteria and their hosts are common within insect systems. However, viruses are often considered as pathogens even though some have been reported to be beneficial to their hosts. Herein, we report a novel densovirus, Helicoverpa armigera densovirus-1 (HaDNV-1) that appears to be beneficial to its host. HaDNV-1 was found to be widespread in wild populations of H. armigera adults (>67% prevalence between 2008 and 2012). In wild larval populations, there was a clear negative interaction between HaDNV-1 and H. armigera nucleopolyhedrovirus (HaNPV), a baculovirus that is widely used as a biopesticide. Laboratory bioassays revealed that larvae hosting HaDNV-1 had significantly enhanced resistance to HaNPV (and lower viral loads), and that resistance to Bacillus thuringiensis (Bt) toxin was also higher at low doses. Laboratory assays indicated that the virus was mainly distributed in the fat body, and could be both horizontally- and vertically-transmitted, though the former occurred only at large challenge doses. Densovirus-positive individuals developed more quickly and had higher fecundity than uninfected insects. We found no evidence for a negative effect of HaDNV-1 infection on H. armigera fitness-related traits, strongly suggesting a mutualistic interaction between the cotton bollworm and its densovirus.

Characterization of a novel member of genus Iflavirus in Helicoverpa armigera

“…Filtered liquid containing an unpurified form of the iflavirus was prepared (Xu et al, 2014) . RNA was isolated and the concentration of the virus was quantified.…”

“…RNA was isolated and the concentration of the virus was quantified. A NONINF strain was established from a single breeding pair that was not infected with the iflavirus, according to the method described by Xu et al (2014). An infected line (INF strain) of H. armigera was established by orally infecting NONINF strain larvae with the filtered liquid.…”

“…Moreover, high-through-put analytical methods such as metagenomics and RNA sequencing provide sensitive and effective methods for the discovery of novel viruses and asymptomatic disease agents that may be useful as biological control products (Diatchenko et al, 1996;Ge et al, 2012;Marguerat and Bähler, 2009;Mokili et al, 2012;Radford et al, 2012;Roossinck et al, 2015), or conversely, may negatively or positively impact upon the biopesticide products being used. For example, the recent discovery of a novel densovirus (HaDV2) from healthy migratory cotton bollworms revealed that HaDV2 infection significantly increased host resistance to the host-specific baculovirus HaNPV and to the generalist biopesticide Bt toxin (Xu et al, 2014).The development of molecular tools and next generation sequencing technology paves the way for a greater understanding as to how we may manipulate the host-pathogen system, with the aim of reducing pest outbreaks and economic crop damage.…”

Diverse Array of New Viral Sequences Identified in Worldwide Populations of the Asian Citrus Psyllid (Diaphorina citri) Using Viral Metagenomics

“…All members of Ambidensovirus are pathogenic to their insect hosts, and members of this genus are known to infect insects belonging to at least five orders (Lepidoptera, Diptera, Orthoptera, Odonata, and Hemiptera) (83). A mutualistic association between a novel densovirus, Helicoverpa armigera densovirus-1 (HaDNV-1), and its host, Helicoverpa armigera, has recently been reported (84). However, a phylogenetic tree constructed based on NS2 amino acid sequences placed DcDNV closer to the viruses from the genus Iteradensovirus (Fig.…”

Move Over, Bacteria! Viruses Make Their Mark as Mutualistic Microbial Symbionts

“…As the bollworm is a serious crop pathogen, control measures are used in cotton fields, including the biopesticide Bacillus thuringiensis and biocontrol with a polyhedrosis virus. In field studies, the densovirus increased resistance to these agents (19), making it a bane for cotton farmers but a boon for the bollworm host. Another insect densovirus infects the rosy apple aphid.…”