Bracoviruses recruit host integrases for their integration into caterpillar’s genome

Some DNA viruses infect host animals usually by integrating their DNAs into the host genome. However, the mechanisms for integration remain largely unknown. Here, we find that Cotesia vestalis bracovirus (CvBV), a polydnavirus of the parasitic wasp C. vestalis (Haliday), integrates its DNA circles into host Plutella xylostella (L.) genome by two distinct strategies, conservatively and randomly, through high-throughput sequencing analysis. We confirmed that the conservatively integrating circles contain an essential “8+5” nucleotides motif which is required for integration. Then we find CvBV circles are integrated into the caterpillar’s genome in three temporal patterns, the early, mid and late stage-integration. We further identify that three CvBV-encoded integrases are responsible for some, but not all of the virus circle integrations, indeed they mainly participate in the processes of early stage-integration. Strikingly, we find two P. xylostella integrases (PxIN1 and PxIN2) are highly induced upon wasp parasitism, and PxIN1 is crucial for integration of some other early-integrated CvBV circles, such as CvBV_04, CvBV_12 and CvBV_24, while PxIN2 is important for integration of a late-integrated CvBV circle, CvBV_21. Our data uncover a novel mechanism in which CvBV integrates into the infected host genome, not only by utilizing its own integrases, but also by recruiting host enzymes. These findings will strongly deepen our understanding of how bracoviruses regulate and integrate into their hosts.

The Use of Synthetic Herbivory-Induced Plant Volatiles That Attract Specialist Parasitoid Wasps, Cotesia vestalis, for Controlling the Incidence of Diamondback Moth Larvae in Open Agricultural Fields

We evaluated the effectiveness of using a blend of volatiles that attract Cotesia vestalis, a specialist parasitoid wasp of diamondback moth (DBM) larvae, to control DBM larvae on cabbage plants under open field conditions. We set three dispensers of the synthetic C. vestalis attractant together with one sugary-food feeder in a cabbage plot (10 m × 1 m; the treated plot) on one side of a pesticide-free open agricultural field (approximately 20 m × 20 m) from June to September in 2010 and July to August in 2011. On the other side of the field, we created a control cabbage plot of the same size in which neither dispensers nor a feeder was set. The incidences of DBM larvae and C. vestalis cocoons in the control and treated plots were compared. In 2010, the incidence of DBM larvae in the treated plot was significantly lower than that in the control plot. Poisson regression analyses in 2010 showed that the rate of increase in the number of C. vestalis cocoons along with an increase in the number of DBM larvae in the treated plot was significantly higher than that in the control plot. In 2011, the incidence in both the treated and control plots remained low (five larvae per plant or less) with no significant difference between the plots. Poisson regression analyses in 2011 showed that the number of C. vestalis cocoons in the treated plot was significantly higher than that in the control plot, irrespective of the number of DBM larvae. This 2-year field study suggested that the dispensers recruited native C. vestalis from the surrounding environment to the treated plot, and the dispensers controlled the number of DBM larvae in 2010 when the density of DBM larvae exceeded the economic injury levels for the cabbage crop. We also compared the incidences of other arthropods in the control and treated plots. The incidences of Pieris rapae larvae and Plusiinae spp. were not affected by the treatments. The number of aphids in the treated and control plots was inconsistent between the 2 years. Based on these 2-year results, the possible use of C. vestalis attractants in open agricultural fields is discussed.

Comparative Transcriptome Analysis Reveals Sex-Based Differences during the Development of the Adult Parasitic Wasp Cotesia vestalis (Hymenoptera: Braconidae)

The endoparasitic wasp Cotesia vestalis is an important biological agent for controlling the population of Plutella xylostella, a major pest of cruciferous crops worldwide. Though the genome of C. vestalis has recently been reported, molecular mechanisms associated with sexual development have not been comprehensively studied. Here, we combined PacBio Iso-Seq and Illumina RNA-Seq to perform genome-wide profiling of pharate adult and adult development of male and female C. vestalis. Taking advantage of Iso-Seq full-length reads, we identified 14,466 novel transcripts as well as 8770 lncRNAs, with many lncRNAs showing a sex- and stage-specific expression pattern. The differentially expressed gene (DEG) analyses showed 2125 stage-specific and 326 sex-specific expressed genes. We also found that 4819 genes showed 11,856 alternative splicing events through combining the Iso-Seq and RNA-Seq data. The results of comparative analyses showed that most genes were alternatively spliced across developmental stages, and alternative splicing (AS) events were more prevalent in females than in males. Furthermore, we identified six sex-determining genes in this parasitic wasp and verified their sex-specific alternative splicing profiles. Specifically, the characterization of feminizer and doublesex splicing between male and female implies a conserved regulation mechanism of sexual development in parasitic wasps.

Symbiotic bracovirus of a parasite manipulates host lipid metabolism via tachykinin signaling

Parasites alter host energy homeostasis for their own development, but the mechanisms underlying this phenomenon remain largely unknown. Here, we show that Cotesia vestalis, an endoparasitic wasp of Plutella xylostella larvae, stimulates a reduction of host lipid levels. This process requires excess secretion of P. xylostella tachykinin (PxTK) peptides from enteroendocrine cells (EEs) in the midgut of the parasitized host larvae. We found that parasitization upregulates PxTK signaling to suppress lipogenesis in midgut enterocytes (ECs) in a non-cell-autonomous manner, and the reduced host lipid level benefits the development of wasp offspring and their subsequent parasitic ability. We further found that a C. vestalis bracovirus (CvBV) gene, CvBV 9–2, is responsible for PxTK induction, which in turn reduces the systemic lipid level of the host. Taken together, these findings illustrate a novel mechanism for parasite manipulation of host energy homeostasis by a symbiotic bracovirus gene to promote the development and increase the parasitic efficiency of an agriculturally important wasp species.