Pestology Blog

Endosymbiont Diversity Across Native and Invasive Brown Widow Spider Populations 

Invasive species are those that are not native to a particular area and have the potential to have severe economic and environmental impacts. The Brown Widow spider, Latrodectus geometricus, is arguably one of the most successful invasive spider species in the world. The Brown Widow is thought to have originated in Africa, but the species has since seen a drastic spread across the world. This cousin of the Black Widows can now be found in North and South America, the Middle East, Australia, and Asia. In fact, in some areas, Brown Widows are outcompeting Black Widows for the same kinds of habitats. Understanding the mechanisms of invasion can be extremely useful for management strategies, particularly with a medically relevant pest, like the Brown Widow.  

There are several factors that can dictate the success of an invasive species. Some factors of success are related to the species itself- for the Brown Widow, part of the success is due to this species having a very high reproductive potential. This species has been known to lay approximately 120-150 eggs per egg sac and can lay up to 20 egg sacs in a lifetime!  Other factors of success are related to the new environment, such as the ability to find prey and shelter. However, one of the factors that we often don’t consider on a species’ path to invasion is the tiny hitchhikers, like endosymbionts, that may accompany these invaders on their journeys. 

Endosymbionts are bacteria and viruses that live inside the cells of their arthropod hosts. Endosymbionts can play a wide variety of roles in arthropods, ranging from the good, the bad, and the neutral. As such, the presence of these endosymbionts can either be beneficial or can be detrimental to an invasive species trying to make it in a new environment. But, before we can determine the role of these endosymbionts in this invasive spider, we first need to document the diversity and how prevalent they are in Brown Widow populations around the world.  

My collaborators collected Brown Widows from populations found around the world, representing two areas where Brown Widows are invasive, with six locations in Israel and four locations in the United States, and an area where Brown Widows are considered to be native, with seven locations in South Africa. We then analyzed the microbiome, or bacterial diversity, to see how the infections differed across the world.  

We found that Brown Widows generally harbor two main endosymbionts: Wolbachia and Rhabdochlamydia. Wolbachia is a familiar face to the arthropod endosymbiont world, as it is well-known for its ability to reproductively manipulate its hosts to ensure that the bacteria lives on in the next generation. However, more work is needed to determine if it is performing that same role in Brown Widows. The other symbiont, Rhabdochlamydia, was detected in every single population of Brown Widows that were sampled, but further work is needed to determine what this endosymbiont is doing in these spiders. In addition, both Wolbachia and Rhabdochlamydia were found in the eggs of the Brown Widows that were collected, which is an indication that these bacteria are passed on through the mother spider. Maternal inheritance of a bacteria is often an indicator that these bacteria may be performing some kind of reproductive manipulation, like cytoplasmic incompatibility or feminization, in Brown Widows.  

Across the board, Brown Widows have mostly kept their symbionts as they have spread across the world. However, when we look a little deeper, we can see some interesting patterns emerge. For example, Wolbachia was not found in populations that were more recently established- such as Southern Israel and Los Angeles, California. Also interestingly, the populations from Israel featured a higher proportion of Rhabdochlamydia compared to other populations.   This suggests that loss and gain of these endosymbionts through a population can be common in the invasion process based on who gets there first and establishes, but it could also be an indicator that the new environment hit these Brown Widows a little fast and hard before their population took off in those areas. 

While this is just one species in a small snapshot look, it helps us understand how these species (and their hitchhikers) are affected by drastic changes in the environment, like the invasion process.  This can not only help us understand how these kinds of pests spread, but also provide context on how to manage them. Species that are well-adapted to environmental change are likely to be those pests that feel like they’re one step ahead of the game in terms of your management strategy. By having one more piece of knowledge to help us potentially stop invasive species in their tracks, we can have one less pest to worry about.  

If you’d like to learn more about the common widows found in North America, please check out the latest library update from NPMA, which can be found here.  

Article by: Laura Rosenwald, BCE

References

Sadir, Melissa, Marske, Katherine A. 2021. Urban Environments Aid Invasion of Brown Widows (Theridiidae: Latrodectus geometricus) in North America, Constraining Regions of Overlap and Mitigating Potential Impact on Native Widows. Frontiers in Ecology and Evolution. Volume 9. https://doi.org/10.3389/fevo.2021.757902 

Effect of Entomopathogenic Fungi on Behavior and Physiology of Solenopsis invicta (Hymenoptera, Formicidae)

If you’re a fan of HBO’s popular series, “The Last of Us,” (or you’ve played the video game the show is based on), then you’re already familiar with the concept behind the paper I’m covering in this episode. But, in case you aren’t up to speed on the show, here’s a very brief cliff notes version. Basically, a brain fungus called Cordyceps that is known to infect arthropods makes the terrifying leap to infect humans and turn them into zombies. While there isn’t any truth to the idea that Cordyceps can infect people in the way portrayed on the show, there are in fact hundreds of fungi that are known for turning arthropods into real-life zombies! And, just like the show, these fungi manipulate insect host behavior turning infected individuals into mindless food bags that are being eaten alive from the inside out by the predatory fungus.

Some zombifungi make adult insects wander to a high point on a wall or a tree branch, where they die frozen in place so the fungal spores can rain down and disperse more widely. Another fungus that infects houseflies causes the female carcass to give off an odor that attracts males to mate with the carcass and become covered with spores. And the list of crazy zombie side effects goes on!

Because these fungi self-replicate and the end result of infection is death, researchers have explored the use of certain entomopathogenic fungi as biological control agents against invasive insects for years. One widely used and well-studied species of fungi is Metarhizium anisopliae (MA). MA is known for being target specific and easy to mass-produce making it an ideal candidate for the development of mycoinsecticides that can be used to control invasive pests.

The red imported fire ant, Solenopsis invicta Buren, is one of the most notorious and ecologically damaging invasive ants on the plant. Efforts to stop the spread of this species around the world have fallen short thanks to human mediated transport and this ant’s ability to quickly dominate non-native habitats. While there are bait and liquid insecticide options for the RIFA, any chance to add another control tool to the arsenal is always a positive. Previous research showed that the fungus, MA, exhibited some toxicity to RIFA, demonstrating that it could be a viable option to explore further. Which brings us to the research by Hassan et al. (2024).

Remember, the way these fungi work is they change the host’s behavior. The hope is the change is impactful enough to reduce the target pest’s survival. To test the viability of MA as a possible mycoinsecticides against the RIFA, Hassan and colleagues directly applied MA spores at different concentrations to RIFA workers and measured their foraging behavior and movement patterns for up to36 hours after exposure. They even measured biochemical changes and antifungal activity to determine what internal changes could be occurring and how effective the ants were at fighting off the infection

What they found was that fungal infection impacted everything they measured. For foraging behavior, infected ants spent significantly less time in or near the feeding area compared to uninfected ants. For locomotion, infected ants traveled shorter distances and made fewer turns when traveling. Infected ants also measured significantly lower enzymatic activity of enzymes related to detoxification after fungal stress. Lastly, researchers found that antifungal activity did increase post exposure, but that survival of ants exposed decreased.

Overall, the results from this study were consistent with previous studies evaluating MA and should encourage further research into the use of MA to control RIFA. However, there are some important caveats to point out with this study that could impact the application of MA in the field. 

First, this study was conducted in a very controlled laboratory setting, and MA was physically applied to workers at varying concentrations. These exposure settings and rates are likely not ecologically relevant and would differ dramatically from how ants may be exposed in the field. So, more work needs to be done to determine if MA is a viable candidate. Secondly, and most importantly, is the fact that ants are NOTORIOUSLY difficult to control with entomopathogenic fungi for a number of reasons. Ants are packed with some highly sophisticated and impressive antifungal weapons at the individual and colony-wide levels that have evolved over millions of years to combat these natural pathogens. So, finding something that’s going to punch through these defenses is tough. Having said that, if MA does show through further research to be a viable option, it could prove to be an important support tool in helping to control one of the most damaging invasive ants on the planet.  

Article by: Mike Bentley, BCE, PhD

References

Ali Hassan, Lidong Kang, Kaixiong Zhang, Lei Wang, Xianjiao Qin, Guobin Fang, Yongyue Lu, Qiuying Huang, Effect of entomopathogenic fungi on behavior and physiology of Solenopsis invicta (Hymenoptera, Formicidae), Journal of Economic Entomology, 2024;, toae068, https://doi.org/10.1093/jee/toae068

ArTreeficial: An AI-tree Controlling Spotted Lanternfly Populations Using Computer Vision and Dynamic Response 

The spotted lanternfly (SLF), Lycorma delicatula, has been a hot topic over the past few years. For those unfamiliar, this is an invasive species that has spread from its initial introduction around 2014 in PA to much of the eastern US. The spotted lanternfly is native to southwest China. This plant hopper is large, clumsy, and does not bite or sting. They use their piercing mouthparts to feed on the phloem of many plants including their favorite tree, the tree of heaven. This is an introduced tree from their native range that has been spreading rapidly and taking over resources and space from native plants. It came over in the early 1800s and escaped cultivation. The lanternflies feeding causes significant damage to the plants they feed on from the removal of phloem, and sooty mold that can grow from the honeydew that they excrete. There are concerns for grapevines, both wine and juice types. But in the context of urban and structural, they are a pest for their damage to trees and the sticky honeydew that grows sooty mold where it falls. Hundreds of lanternflies can be found on a single tree, excreting a rain of honeydew covering cars, people, and structures under them.  

Current methods of controlling SLF numbers have not been widely successful due to the their high fecundity where a small base can grow into a large population quickly. There are some insecticidal products that show potential effectiveness but are non-specific and require repeated applications. The other option of using sticky trap bands around trees can get non-target animals stuck or get filled up with lanternflies. Even the public campaigns for folks to stomp on sight are only so effective.  

To combat this problem, Selina took her knowledge of AI technology and combined it with as she states, “inspiration from chess and dance dance revolution” to create ArTreeFicial. This ai “tree” provides a low labor, cost efficient, and environmentally friendly solution. The tree uses tree of heaven based incense which has been shown as an attractant to SLFs. The incense is blended tree of heaven that has been strained. This is placed onto an outdoor umbrella which provides shade and protection from weather. The trunk of the umbrella/tree is wrapped in electricity conducting nets and cameras are set up to watch the trunk. Spotted lanternflies crawl up trees and are poor fliers so a band of netting around the trunk is an effective shape to catch most of them.

A computer model called YOLO identifies the SLF and selectively shocks that area of the trunk, killing the bug. The section of netting is two layered so when detected, the inner layer is activated and the bug on it completes the circuit, only killing it and nothing else. There is no live electricity running constantly. This is a similar to the electric fly swatters you may be familiar with. To round out this well designed product, there’s even a collection bin at the base to keep the dead ones.

The initial building cost of the tree is 150-200$ and Zhang predicts this could be lowered by mass manufacturing. This is a very accessible price which I could envision would lead to ease of use. Imagine a pest control company renting this out during the season to clients. Such a product could be widespread and profitable.  

The article discusses that this type of device model could be used for other pests in the future with the attract and kill concept using computer vision for pest ID. The particular design works quite well considering the behavior of the SLFs. For occasional invaders or other structural pests, such devices would require some redesign, but it brings some hope for mechanical control options in pest control.

Article by: Ellie Lane

References

S. Zhang, "ArTreeficial: an AI-tree controlling spotted lanternfly populations using computer vision and dynamic response," 2023 IEEE International Conference on Advances in Data-Driven Analytics And Intelligent Systems (ADACIS), Marrakesh, Morocco, 2023, pp. 1-6, doi: 10.1109/ADACIS59737.2023.10424285.
keywords: {YOLO;Computer vision;Technological innovation;Sociology;Pesticides;Solar panels;Statistics;Spotted lanternfly;Lycorma delicatula;computer vision;agricultural application of computer vision;yolo;ailanthus altissima},

https://www.smithsonianmag.com/innovation/this-high-schooler-invented-an-ai-powered-trap-that-zaps-invasive-lanternflies-180983918/