Pestology Blog

Oral Toxicity of an Artificial Sweetener Sucralose on the German Cockroach (Blattodea: Ectobiidae) and its Impact on Water Balance and Gut Microbiome

The German cockroach is a classic structural pest that has been well studied by urban entomologists for decades. As is the case with most heavily researched organisms, the likelihood of discovering something completely isn’t very high simply due to the extensive amount of research that’s already been conducted. Which is precisely what makes the publication featured in this blog post so exciting!  

Researchers are in a never-ending battle to find the next silver bullet in the battle against the German cockroach. One notable challenge with managing this species is that infestations are typically found in sensitive environments such as food preparation sites such as kitchens where treatment options may be limited because of the sensitive nature of these areas. To investigate new control solutions for these environments, scientists have been exploring the use of artificial sweeteners for their insecticidal potential against a range of urban pests. That’s right, the same artificial sweeteners such as sorbitol, xylitol, saccharin, aspartame, and sucralose that come in the blue, pink, or yellow packets used to sweeten your morning coffee or tea.  

Before we jump to any conclusions about the general safety of artificial sweeteners to humans, it's important to note that just because something is toxic to one organism doesn’t necessarily mean it’s toxic to ALL organisms. Take dark chocolate for example. Most people can eat dark chocolate without much issue, but the cocoa in this sweet treat can be highly toxic to dogs and could result in an emergency trip to the vet if your four-legged friend gets their paws on even a small piece. What makes artificial sweeteners an ideal candidate for insecticidal studies is that these substances have an inherently low mammalian toxicity but can cause some serious issues for many insects when consumed. Past studies testing the potential toxicity of many artificial sweeteners on a range of pests have had mixed results ranging from changes in motor function, decreased response to the opposite sex, reduced feeding, dehydration, and reduced survival. And, until recently, there was limited testing of artificial sweeteners on cockroaches.

 

 

Xin Su and colleagues set out to address this gap in knowledge by investigating the oral toxicity of sucralose on the German cockroach. To do so, they ran three different experiments. In all experiments they compared feeding results using two different groups of cockroaches. One group (the susceptible strain) was susceptible to insecticides while the second group (the resistant strain) was known to be insecticide resistant.  

In their first experiment, the researchers wanted to assess the oral toxicity of sucralose, so they fed both susceptible and resistant strains of German cockroach on sucralose at three separate concentrations: 5%, 10%, and 20%. What they found was that more German cockroaches died on average (ranging from 62.5% to 92.5%) at the 20% concentration. In the second experiment Su and colleagues measured the impact of water loss on both cockroach strains when fed the 20% sucralose solution. All strains lost 23.0-30.29% body water by day 6 of the experiment. And, not surprisingly, the more dehydrated cockroaches were more prone to mortality than nondehydrated German cockroaches. In the last experiment, they looked at gut bacterial composition after both strains were fed 20% sucralose and what they found was that the diversity of gut bacteria was significantly reduced after 3 days.  

The conclusion from their study was that German cockroaches fed a 20% sucralose solution had a higher mortality rate than lower concentrations, they were more dehydrated, and they had a decreased diversity of gut bacteria. Overall, these results are promising. Given the impacts that sucralose has on dehydration and gut microbiome, and its palatability to German cockroaches, researchers could start looking at this artificial sweetener as an additive to enhance the toxicity of existing baits or possibly even as a standalone active ingredient. However, it is important to note that this was a laboratory study where the cockroaches were not given a choice between the sucralose and other food sources. So, there’s still more work to do to confirm that hungry German cockroaches would prefer sucralose to competing alternatives. Nevertheless, this study does show promise and I expect we’ll be seeing more follow up studies on this in the near future!  

Article by Mike Bentley, PhD, BCE

References

Shao-Hung Lee, Dong-Hwan Choe, Michael K Rust, Chow-Yang Lee, Oral toxicity of an artificial sweetener sucralose on the German cockroach (Blattodea: Ectobiidae) and its impact on water balance and gut microbiome, Journal of Economic Entomology, Volume 117, Issue 1, February 2024, Pages 268–279, https://doi.org/10.1093/jee/toad206

Histamine Excretion in Common Indoor and Hematophagous Arthropods

Histamine is involved in allergic reactions. It’s a biogenic amine and for our purposes the important thing to know is that it modulates the immune response in mammals, like us. Histamine is in many things including foods we eat, and when it comes into contact with certain receptors, it can cause allergic reactions.  

So what does that have to do with bed bugs? Bed bugs excrete histamine in their feces and it serves them as part of their aggregation pheromone as a “stop here” sign for fellow bed bugs. We call that an arrestant. What we didn’t know is if other household pests or blood feeding insects also produce histamine or if just closely related insects to bed bugs produce histamine. The researchers wanted to know if histamine production was related to blood feeding, hematophagy.

 

 

In this study, they looked at 22 species of arthropods to determine presence and production of histamine in excreta. These species were grouped into three categories, common indoor pests, which included several cockroaches, termite, flies, beetles, moths, and mites. Then blood feeding species which was mosquito, flea, and tick, and finally specifically blood feeding hemipterans like bat bugs, kissing bugs, and of course our star, the bed bug. Also a non-blood feeding hemipteran, the stink bug, was tested.   

They reared all the species in laboratory conditions according to individual best practices. They fed the blood feeding species on either lab alternatives or animal blood, don’t worry they didn’t sacrifice themselves. After rearing up enough adults or nymphs, they went to determine histamine presence. They took swabs and sampled the substrate in the rearing containers of the pests.  After swabbing, they tested the samples using gas chromatography and mass spectrometry commonly referred to as GCMS which is used to determine the chemical makeup of a sample. Its quite a process that is beyond the basics of what I remember from organic chemistry but the important part is what they found.  

If histamine was detected at all, they continued further testing with that species. Histamine was only found in 5 of the 22 species which were the bed bug, tropical bed bug, bat bug, and two kissing bugs. Two species, not two individual bugs that were kissing. These are all blood feeding hemipterans. No other blood feeders were found to have histamines.  

Further testing consisted of starving the arthropods then separating them into individual tubes and feeding them afresh. They were able to then weigh them to see how much blood was being consumed. They sampled the tubes again to collect the insect feces and then prepped the samples for analysis. The analysis showed them how much histamine was being produced per bug per day. They saw that there was a strong positive linear correlation between amount of blood consumed and amount of histamines excreted. Blood alone was not cause for histamines since other blood feeding insects didn’t have any. Hemipterans in general didn’t have it because the stink bug which is a non blood feeding hemipteran, didn’t produce any.  

They hypothesized that histamine was introduced to the bugs by blood but that hemipterans didn’t have a certain enzyme to break it down so they ended up excreting it, making bed bugs as major indoors pests compared to the other bugs tested, are the main arthropod source for histamines in a household. Bed bugs proportionately produce more histamines than other hematophagous hemipterans, making them the top concern for household histamines. Household hematophagous hemipteran histamines, try to say that five times fast.   

Article by Ellie Lane

References

Simona Principato, Alvaro Romero, Chow-Yang Lee, Kathleen Campbell, Dong-Hwan Choe, Coby Schal, Zachary DeVries, Histamine excretion in common indoor and hematophagous arthropods, Journal of Medical Entomology, Volume 60, Issue 6, November 2023, Pages 1269–1277, https://doi.org/10.1093/jme/tjad103

mRNA Vaccination of Rabbits Alters the Fecundity, but Not the Attachment, of Adult Ixodes scapularis

Ixodes scapularis, or more commonly known as the deer tick, can act as a vector for several different diseases. However, it is probably most known as the main vector for Lyme Disease, which is currently the most common vector-borne disease in the United States.~ Deer ticks obtain and spread diseases by feeding on the blood of several different vertebrates across the course of their lifetimes, including mammals, birds, and reptiles.  Their feeding habits, along with the dramatic expansion of their distribution across the eastern half of North America in the past 50 years, make deer ticks a top concern as a public health pest.* 

 

When these ticks feed, they release a series of molecules in their salivary glands that assist them in feeding. These molecules are proteins that are known as tick salivary proteins, and assist the tick in feeding by hindering the immune system of the host. However, some of these tick salivary proteins instead do the opposite in some vertebrate hosts, and create an immune response in the host called Acquired Tick Resistance. Ticks that feed on a host with Acquired Tick Resistance have diminished feeding and often detach from their hosts earlier than expected, which can have a huge effect on their ability to survive and reproduce. The hosts also often experience more redness and skin irritation at the bite site when they have Acquired Tick Resistance. A recent study revealed that a lipid nanoparticle which codes for 19 of these tick salivary proteins is responsible for inducing this Acquired Tick Resistance.  

 

Previous work had examined the potential of a vaccine created from this lipid nanoparticle in guinea pigs. While the study appeared promising in the terms of the potential of the vaccine, guinea pigs are unfortunately a poor model for understanding how the vaccine may impact the deer tick’s full life cycle.^ This study took the same lipid nanoparticle that coded for these 19 tick salivary proteins, and created an mRNA vaccine for rabbits. One group of rabbits received three doses of the vaccine, given at four week intervals. Another group of rabbits received a control version of the mRNA vaccine. After two weeks, the rabbits were checked for antibodies. This was to ensure that the vaccine worked as it should, and induced the correct immune response that would lead to Acquired Tick Resistance.  

A week following the antibody check, the rabbits were then exposed to 50 adult deer ticks. The researchers did so in perhaps my favorite line ever from a science article “all the rabbits wore Elizabethan collars and the ear that received the tick was isolated with an adapted sock, which prevented the ticks from moving to another location.” Fashion aside, the rabbits were monitored daily for any signs of host rejection by the tick and time of tick detachment. Once detached, the ticks were weighed as a measure of how well they were able to feed on a host. Female deer ticks were further monitored for their egg masses, where the researchers examined the size of the egg mass as well as how many of those eggs ended up hatching. 

Overall, researchers found there was no difference in the ways that ticks fed based on whether a rabbit was vaccinated. Both time of attachment and tick weight did not differ between the vaccinated rabbits and the control rabbits. Similarly, there wasn’t a difference in the number of eggs laid when comparing ticks that fed on vaccinated rabbits versus the control rabbits. However, there was a significant difference in the percent of eggs that hatched from the vaccinated rabbits versus the control rabbits. These results suggest that the vaccine for the tick salivary proteins in rabbits can significantly impair how well deer ticks are able to reproduce.  

While this is just one experiment, with one species, it is important to note that every new methodology for management of a pest starts somewhere. This study is extremely promising for its potential for reducing tick populations by simply giving a host a vaccine over the course of a few short weeks. In addition, Acquired Tick Resistance has been documented in several animals including guinea pigs, dogs and cattle. Eventually, it could be just as easy as having your livestock or pet vaccinated by your veterinarian to help reduce tick populations in your area.  

Article by Laura Rosenwald, BCE

References

Matias J, Cui Y, Lynn GE, DePonte K, Mesquita E, Muramatsu H, Alameh MG, Dwivedi G, Tam YK, Pardi N, Weissman D, Fikrig E. mRNA vaccination of rabbits alters the fecundity, but not the attachment, of adult Ixodes scapularis. Sci Rep. 2024 Jan 4;14(1):496. doi: 10.1038/s41598-023-50389-6. PMID: 38177212; PMCID: PMC10766947.

1. List

~ Centers for Disease Control and Prevention, National Center for Emerging and Zoonotic Infectious Diseases (NCEZID), Division of Vector-Borne Diseases (DVBD) (https://www.cdc.gov/lyme/index.html)  

* Lars Eisen, Rebecca J. Eisen. Changes in the geographic distribution of the blacklegged tick, Ixodes scapularis, in the United States, Ticks and Tick-borne Diseases,. Volume 14. Issue 6. 2023. https://doi.org/10.1016/j.ttbdis.2023.102233 

^ Andaleeb Sajid et al. mRNA vaccination induces tick resistance and prevents transmission of the Lyme disease agent. Sci. Transl