The majority of plant viruses are transmitted by insect vectors between hosts, and transovarial transmission of viruses from vector parents to offspring has great significance to their epidemiology. Begomoviruses are transmitted by the whitefly Bemisia tabaci in a circulative manner and are maintained through a plantinsect-plant cycle. Other routes of begomovirus transmission are not clearly known. Here, we report that transovarial transmission from female whiteflies to offspring often happens for one begomovirus, Tomato yellow leaf curl virus (TYLCV), and may have contributed significantly to its global spread. We found that TYLCV entry of the reproductive organ of its vector mainly depended on the developmental stage of the whitefly ovary, and the transovarial transmission of TYLCV to offspring increased with whitefly adult age. The specific interaction between virus coat protein (CP) and whitefly vitellogenin (Vg) was vital for virus entry into whitefly ovary. When knocking down the expression of Vg, the entry of TYLCV into ovary was inhibited and the transovarial transmission efficiency decreased. In contrast, another begomovirus, Papaya leaf curl China virus (PaLCuCNV), CP did not interact with whitefly Vg, and PaLCuCNV could not be transovarially transmitted by whiteflies. We further showed that TYLCV could be maintained for at least two generations in the absence of virusinfected plants, and the adult progenies were able to infect healthy plants in both the laboratory and field. This study reports the transovarial transmission mechanism of begomoviruses, and it may help to explain the evolution and global spread of some begomoviruses.begomovirus | transovarial transmission | vector development | vitellogenin | whitefly

The cryptic species Middle East-Asia Minor 1 (MEAM1), formerly referred to as 'B biotype', of the whitefly Bemisia tabaci complex entered China in the mid 1990s, and the Mediterranean (MED) cryptic species, formerly referred to as 'Q biotype', of the same whitefly complex entered China around 2003. Field surveys in China after 2003 indicate that in many regions MED has been replacing the earlier invader MEAM1. The factors underlying this displacement are unclear. We conducted laboratory experiments and field sampling to examine the effects of insecticide application on the competitive interactions between MEAM1 and MED. In the laboratory, on cotton, a plant showing similar levels of suitability to both whitefly species, MEAM1 displaced MED in five generations when initial populations of the two species were equal and no insecticide was applied. In contrast, MED displaced MEAM1 in seven and two generations, respectively, when 12.5 and 50.0 mg l⁻¹ imidacloprid was applied to the plants via soil drench. Field sampling indicated that in a single season MED displaced MEAM1 on crops heavily sprayed with neonicotinoid insecticides but the relative abundance of the two species changed little on crops without insecticide spray. We also examined the effects of host plants on the competitive interactions between the two species in the laboratory. When cohorts with equal abundance of MEAM1 and MED were set up on different host plants, MEAM1 displaced MED on cabbage and tomato in five and seven generations, respectively, but MED displaced MEAM1 on pepper in two generations. As field populations of MED have lower susceptibility than those of MEAM1 to nearly all commonly used insecticides including imidacloprid, insecticide application seems to have played a major role in shifting the species competitive interaction effects in favour of MED in the field across China. Host plants may also shape competition between the two species depending on the relative levels of plant suitability.

Whereas most of the arthropod-borne animal viruses replicate in their vectors, this is less common for plant viruses. So far, only some plant RNA viruses have been demonstrated to replicate in insect vectors and plant hosts. How plant viruses evolved to replicate in the animal kingdom remains largely unknown. Geminiviruses comprise a large family of plant-infecting, single-stranded DNA viruses that cause serious crop losses worldwide. Here, we report evidence and insight into the replication of the geminivirus tomato yellow leaf curl virus (TYLCV) in the whitefly (Bemisia tabaci) vector and that replication is mainly in the salivary glands. We found that TYLCV induces DNA synthesis machinery, proliferating cell nuclear antigen (PCNA) and DNA polymerase δ (Polδ), to establish a replication-competent environment in whiteflies. TYLCV replication-associated protein (Rep) interacts with whitefly PCNA, which recruits DNA Polδ for virus replication. In contrast, another geminivirus, papaya leaf curl China virus (PaLCuCNV), does not replicate in the whitefly vector. PaLCuCNV does not induce DNA-synthesis machinery, and the Rep does not interact with whitefly PCNA. Our findings reveal important mechanisms by which a plant DNA virus replicates across the kingdom barrier in an insect and may help to explain the global spread of this devastating pathogen.

Biological control (biocontrol) is a safe, sustainable approach that takes advantage of natural enemies such as predators, parasitic insects or pathogens to manage pests in agroecosystems. Parasitoid wasps, a very large evolutionary group of hymenopteran insects, are well-known biological control agents for arthropod pests in agricultural and forest ecosystems. Here, we summarize the recent progress on the application of parasitoid wasps in biocontrol in China for the last five years. These include species diversity of parasitoid wasps, identification of dominant parasitoid wasps associated with insect pests and biocontrol practices (three types of biological control, i.e., classical, augmentative and conservation biological control) in several Chinese agroecosystems. We then treat different mass-rearing and release technologies and the commercialization of several parasitoid wasp species. We also summarize other work that may have a potential use in biocontrol, including the effect of plant volatiles on parasitoids and recent advance in the molecular mechanisms underlying the host regulation by parasitoid wasps. Future research area and applied perspectives are also discussed, noting that advances in biocontrol technologies in Chinese agriculture informs research at the global level.