By Carolyn Bernhardt

What if the most powerful allies in biological pest control aren’t just the insects released into the field but the viruses quietly living inside them? A team of entomologists from Israel’s Agricultural Research Organization (ARO) and the University of Haifa asked this bold question and found fascinating results.

In a field dominated by studies about bacterial symbionts, the researchers at ARO are breaking new ground by shifting their focus to viruses. Specifically, those that reside within the cells of beneficial insects, such as Anagyrus vladimiri, a wasp widely used to control mealybug pests across the globe. In their recent study, published in June in the Annals of the Entomological Society of America, Yehuda Izraeli, Ph.D., Einat Zchori-Fein, Ph.D., and their team recently discovered a double-stranded RNA virus, Anagyrus vladimiri Reovirus (AnvRV), in the ovaries of female wasps.

The virus didn’t appear to harm its host, prompting a deeper inquiry. The team at ARO explored whether AnvRV influences reproductive behaviors or helps wasps suppress the immune systems of their prey, the pesky mealybug. The experts set out to isolate the AnvRV’s effects, work that could have important implications for improving biological control strategies and expanding our understanding of symbiotic viruses in insects. Though technically difficult and often overlooked, this line of research could redefine how we think about viruses, not just as pathogens but as potential partners in sustainable agriculture.

To isolate the effects of the virus, the team established two genetically similar wasp lines: a naturally virus-negative field line (Field-RV−) and a derived virus-infected line (Field-RV+). The virus was introduced into the Field-RV− line through a series of complex crossings with a third, donor wasp line originating from a commercial insect-rearing facility. All wasps were raised under controlled lab conditions on citrus mealybugs. Researchers compared virus-positive and virus-negative wasps on development time, lifespan, reproduction, and offspring sex ratio. They also studied behavioral and immune-related traits such as superparasitism and the host’s encapsulation response. Statistical analyses, including t-tests and survival models, helped determine whether differences between the groups could be attributed to the presence of AnvRV.

To explore how the virus spreads, they tested both vertical transmission (parent to offspring) and horizontal transmission (between individuals via hosts or mating) routes. The team used reverse transcription PCR to detect the virus in individual wasps and crossed and monitored various combinations of virus-positive and virus-negative wasps for transmission.

The study revealed that Anagyrus vladimiri wasps infected with the newly discovered virus AnvRV experience a surprising benefit: Their eggs are significantly more likely to hatch inside their mealybug hosts. This advantage appears to stem from the virus’s ability to suppress the host insect’s immune response, reducing the likelihood of egg encapsulation—a defense mechanism that usually kills wasp eggs. Although this did not lead to an increase in total offspring under lab conditions, the consistent boost to egg survival suggests the virus may improve the wasp’s parasitism success, especially in competitive environments where superparasitism allows the virus to spread horizontally between developing larvae.

These findings carry important implications for biological control. AnvRV is already widespread in lab-reared wasp colonies and has been detected in wild populations across several continents, indicating it may be a naturally occurring and stable component of A. vladimiri ecology. The ability to selectively infect virus-free wasps with AnvRV creates new opportunities for researchers and insect-rearing facilities to explore how inherited viruses can enhance the performance of beneficial insects. If further studies show the virus also improves parasitism success in field settings, it could offer a low-risk, naturally integrated way to strengthen sustainable pest management efforts.

Yehuda Izraeli, Ph.D. (center), led a team of entomologists from Israel’s Agricultural Research Organization (ARO) and the University of Haifa in a recent study that found that a small parasitoid wasp, Anagyrus vladimiri, gets a boost in parasitizing mealybugs from a symbiotic virus that it carries. Much remains unknown about how the virus helps the wasp suppress its hosts’ immune response, but the discovery raises new questions about the role of viruses in parasitoid-host interactions and how they might be used to improve biological control efforts. (Photo courtesy of Yehuda Izraeli, Ph.D.)

According to Zchori-Fein, few researchers study insect-associated viruses because of the technical and biological challenges that make this work uniquely difficult. Unlike bacteria, which can be easily identified and manipulated using well-established molecular tools and antibiotics, viruses often can’t be classified with standard genetic methods. Scientists don’t yet know exactly how those organisms are related to each other, and there’s no simple way to eliminate them from hosts to study their effects. “Viruses are classified into two large groups, RNA and DNA viruses,” she says. “And DNA viruses are usually larger and easier to work with in the lab. And this specific virus is an RNA virus, which is even less known in the literature.” Despite these challenges, she says, Izraeli successfully transferred a virus from one wasp to another, allowing the team to compare wasp lines with and without the virus while keeping the same genetic background.

The researchers note that if they can verify that the virus does indeed benefit the parasitoid wasp, it’s important to explore whether the virus or other non-pathogenic viruses can be transmitted to other beneficial insects, too. However, the mechanism by which the virus helps the wasp overcome the mealybug’s immune system is still completely unknown. It’s also unclear whether the virus is transmitted directly into the host or only through the wasp’s egg, leaving the exact mode of action and transmission unresolved. “So this research is ongoing,” says Izraeli. “We actually have another paper, hopefully upcoming soon, which elaborates a bit more about the origins of the virus and perhaps something about the mechanism through which it works.”

To investigate the relationship between Anagyrus vladimiri and its newly discovered virus, AnvRV, the researchers surveyed viral databases for relatives of AnvRV across the Chalcidoidea superfamily. They found very few close matches, suggesting a highly specific and potentially unique symbiosis between the virus and its wasp host. This finding, which will be published in a forthcoming paper, provides further support for the notion that there is no concern that the virus could “get out of control” and infect other organisms.

The experts say that while viruses like baculoviruses are already used as biological control agents, the virus they’re studying is fundamentally different. It’s not a standalone biocontrol agent, but rather a symbiotic part of the wasp itself. Similar to polydnaviruses found in other parasitoid wasps, this virus is highly specific, non-pathogenic, and not easily spread or acquired—it functions as an integral part of the wasp’s biology rather than something applied independently in the field.

However, limitations remain. The virus’s benefits were observed in a single mealybug host species, leaving its ecological role in other hosts—including the wasp’s primary natural host—uncertain. Moreover, while the virus improved egg survival, it did not lead to higher overall wasp fitness under lab conditions, and its effects on later developmental stages remain unclear. Field data were limited to a small sample, and the scientists did not perform experiments to assess ecological relevance. Some transmission pathways also remain unexplored, and small sample sizes in certain tests may have limited statistical power. Still, the study offers an important foundation for future work on symbiotic viruses in insect biocontrol systems.

Up next, the team is pursuing two major research projects. One focuses on investigating how the virus spreads between levels in the food web, including whether other parasitoids or hyperparasitoids can acquire it through shared mealybug hosts. The second project, in collaboration with the University of Arizona, aims to uncover the mechanism by which the virus influences the wasp’s immunity. This research employs “omic” techniques and microscopy, but progress is challenging due to the limited understanding of the mealybug immune system. The team was surprised to find that, outside of a few model species like Drosophila, insect metabolic immune responses to parasitoids remain largely unexplored.

While this study sheds light on a single RNA virus in one parasitoid wasp species, it hints at a much broader, underexplored world. RNA viruses are everywhere—insects, mites, and beyond—yet their roles in host biology and ecological interactions remain largely overlooked. “At the beginning, symbiotic bacteria were called ‘guest microorganisms’—present, but assumed to do nothing,” says Zchori-Fein. Now, she says, experts know better. And she suspects the same shift is coming for viruses. She and Izraeli see untapped potential in studying these viral passengers, even if the work is difficult. “The reason it is not being studied,” Zchori-Fein says, “is because it’s hard. And, you know, that’s not a good reason not to do research.”

Carolyn Bernhardt, M.A., is a freelance science writer and editor based in Portland, Oregon. Email: [email protected].