Pestology Blog

Blacklegged Ticks, Ixodes scapularis, Reduce Predation Risk by Eavesdropping on Communication Signals of Formica oreas, Thatching Ants

When we think about ticks, we mostly concentrate on their ability to vector disease. This is especially true of Ixodes scapularius, or the black legged tick or the deer tick, which is responsible for transmitting up to sixteen different diseases. Ixodes scapularis is most notorious for its ability to spread Borrelia burgdoferi, which is the bacterium that causes Lyme Disease. However, what we often don’t consider is the way that ticks interact with their fellow arthropods. Ticks, particularly the nymphs, are common prey of other arthropod predators such as spiders and ants. This type of biological control could be the key to unlocking new means of tick management, as previous studies have documented that the presence of ants can negatively affect tick abundance. However, it was not clear on how ticks could identify that ants were present in an area.  

 

So how do ticks “crack the code” when it comes to avoiding potential predators? This study sought to understand some of the mechanisms concerning predator avoidance behavior in ticks, specifically looking at how Ixodes scapularis responded to the semiochemicals, or the communication signals that Formica oreas, or thatching ants, produced.

To test tick avoidance of ant semiochemicals, the ticks were offered a choice test between two chambers that were lined with filter paper. One chamber featured 20 ants that were permitted to walk around the chamber for 16 hours, while the other was the control chamber that only featured filter paper without any arthropod exposure. The ticks were allowed 20 hours to “respond” to the choice test being offered to them, and their final location was noted. Most ticks who responded to the choice test exhibited avoidance behavior of filter paper that had been previously touched by Formica oreas workers. 

 

The researchers then looked at which chemicals may be causing the avoidance behavior by dissecting the poison gland and the Dufor’s gland of the Formica oreas workers. Both glands are found in the abdomen of the ant and are important for secretion of semiochemicals, meaning that they’re essential organs for ant communication. As previous studies had shown, the semiochemicals produced from the poison gland and the Dufor’s gland were different, with the poison gland producing formic acid and the Dufor’s gland producing hydrocarbons. Ticks were offered choice tests of semiochemicals isolated from the poison gland alone, the Dufor’s gland alone, and both glands combined. Ticks did not exhibit any avoidance behaviors with the semiochemicals derived from the poison gland alone, or the Dufor’s gland alone, but did show avoidance behavior to the chemicals when they were combined. The researchers duplicated this experiment using synthetic compounds derived from the poison gland (which was formic acid), and the Dufor’s gland (which was hydrocarbons). Once again, the formic acid and the hydrocarbons by themselves did not elicit a response from the ticks, but the formic acid and the hydrocarbons combined lead to the ticks avoiding that filter paper.  

 

Lastly, the researchers also examined what kind of response the ants would have to these derived semiochemicals. Ants were presented with two options: a piece of filter paper that had been soaked in the synthesized semiochemicals, or a piece of filter paper that had been soaked in dichloromethane as a control. In the choice test with Formica oreas workers, the workers were more likely to interact with the filter paper with the synthesized semiochemicals, which showed that the ants responded to the synthesized semiochemicals in the same way that they would respond to the naturally produced semiochemicals. In particular, these synthesized chemicals elicited an alarm-recruitment response, which called more ants to the area with the filter paper with the synthesized semiochemicals. Makes sense that ticks want to avoid an area with more ants potentially coming to it! 

This study documented that ticks have a clear avoidance response to ant semiochemicals. By paying attention to and spying on ant semiochemicals like formic acid and ant hydrocarbons, the ticks can potentially avoid predation by ants, and like James Bond, live to Die Another Day. Additionally, formic acid and hydrocarbons are extremely common communication signals to many ant species, which suggests that Ixodes scapularis may be spying on not just this species of ant, but many different species. Interestingly, these two species rarely interact with each other, as Formica oreas is generally restricted to the northwestern parts of North America, while Ixodes scapularis is mostly restricted to the eastern part of North America. However, given the adverse reaction the ticks had to this particular species, it suggests that tick avoidance is likely tuned to many ant species. 

This study presents potential for a new generation of tick repellents, that could easily be synthesized from ant semiochemicals. Low concentrations of formic acid are approved for use in cosmetics, meaning that we could see clothing-based and topical tick repellents made from synthesized ant semiochemcials eventually down the line. Overall, what I think this study proves is that we need to dedicate a little more attention to the antics of ants and ticks to determine new repellent strategies for tick management. 

Article by Laura Rosenwald, BCE

References: 

Burtis, J.C., Pflueger, C.  2017. Interactions between soil-dwelling arthropod predators and Ixodes scapularis under laboratory and field conditions. Ecosphere, Vol. 8, Issue 8. E01914. https://doi.org/10.1002/ecs2.1914 

Zingg, S., Dolle, P., Voordouw, M.J. et al. 2018. The negative effect of wood ant presence on tick abundance. Parasites Vectors 11, 164. https://doi.org/10.1186/s13071-018-2712-0 

Gooding Claire E., Pinard Charlotte, Gries Regine, Devireddy Anand and Gries Gerhard 2024 Blacklegged ticks, Ixodes scapularis, reduce predation risk by eavesdropping on communication signals of Formica oreas thatching antsR. Soc. Open Sci.11231355231355

Overcoming Insecticide Resistance in Anopheles Mosquitoes by Using Faster-Acting Solid Forms of Deltamethrin

 

Mosquitoes may seem like small, unassuming insects. But, in reality these tiny blood suckers spread a number of dangerous diseases including malaria and dengue, making them one of the deadliest animals on the planet. From 2010-2019, over half a million people died each year from malaria alone. That doesn’t include the death toll of any other diseases from the unfortunately long list of potentially life-threatening illnesses mosquitoes can vector.

Given their public health impacts, managing mosquito populations is critical. Particularly those species that spread malaria. But mosquitoes are quick to develop resistance to many of the insecticides commonly used for control. This is particularly true when it comes to pyrethroids. However, one group of researchers may have found an interesting way to “breathe new life” so to speak back into a commonly used active ingredient that malaria-transmitting mosquitoes are known to have some resistance too.

 

 

Deltamethrin is widely used pyrethroid to control many dangerous mosquito species including Anopheles quadrimaculatus¸ a common malaria-vector in the US. Due to the long-time use of deltamethrin, resistance among many mosquito species is well documented. Trying to develop new active ingredients to overcome the resistance issue can be incredibly expensive and time consuming. So, rather than try to “reinvent the chemistry wheel,” researchers may investigate ways to enhance the effectiveness of an existing active ingredient. Which is exactly what Jessica Carson and her colleagues were able to do.

In a previous study published in 2020, Bart Kahr and colleagues determined that heating deltamethrin in an oven changed its crystalline structure enough to increase the knockdown time and potency of the insecticide by a factor of up to 12 compared to using the original unheated form. An important note here was that the researchers used susceptible mosquitoes in this study, meaning the mosquitoes exposed to the heated deltamethrin were already known to be sensitive to the insecticide.

In a continuation of this work, Kahr teamed up with Jessica Carson and the other authors of the most recent 2023 study that is the focus of this summary to determine how heating Deltamethrin would impact the effectiveness of the insecticide when exposed to DELTAMETHIRN RESISTANT mosquitoes. In this study they used a commercially available, powdered formulation of deltamethrin. And, because entomologists are wild and crazy folks, they decided to literally throw the stuff in the microwave to see if that achieved the same result as heating the powder to a prescribed temperature in an oven. Turns out, the microwave worked just as well! The researchers ultimately exposed the heated deltamethrin to five different strains of resistant Anopheles mosquitoes and found that the heated insecticide killed the resistant mosquitoes.

On the one hand, these results are incredibly exciting because this could pave the way for an easy-to-use technique to enhance the effectiveness of deltamethrin (and maybe even other insecticides) to resistant mosquitoes. Or even other resistant pest groups!

Butthere are a handful of important caveats and disclaimers here to run through. Some by the authors, and some by me personally. First, the researchers used a controlled laboratory environment to microwave their insecticide. This wasn’t your microwave in the breakroom that your colleague just used to heat up their burrito. They had a dedicated machine used for this purpose alone. Second, they followed a handful of other safety protocols when conducting this study so…basically, don’t go thinking you can just start zapping your products in the microwave to fix your next tough-to-control pest issue.

Another consideration here is that many current commercially uses for deltamethrin to control mosquitoes, such as cotton bed nets impregnated with the AI, may not lend well to heat treatments. Though, the researchers did suggest some methods of application that could work around these considerations that seem to be promising for the near future. At any rate, this is an exciting discovery and will seemingly lead to new important developments in the fight against insecticide-resistant mosquitoes and perhaps other pests as well.

Article by Mike Bentley, PhD, BCE

References

Carson, J., Erriah, B., Herodotou, S. et al. Overcoming insecticide resistance in Anopheles mosquitoes by using faster-acting solid forms of deltamethrin. Malar J 22, 129 (2023). https://doi.org/10.1186/s12936-023-04554-x 

The Emergence and Sustainability of Urban Entomology

This review article goes through the history of urban entomology publications and brings us to the current state of today. The term urban entomology was first used in 1884 in a note by AH waters. Skip to almost a century later, and the book “Urban Entomology” was published in 1975 by W. Ebeling. This began the common usage of the term in subsequent studies and publications.  

 

Urban entomology developed as a response to urbanization, it is a field of study that came about relatively recently and has expanded along with humans spread across the world. Although the term urban entomology wasn’t more official until the 1970s, we have some very notable books published before that including Mallis’s handbook of pest control in 1945 and then the scientific guide to pest control operations in 1962.  

The paper moves on to talk about some factors contributing to the importance of urban entomology starting with urbanization. We mentioned that the field has grown along with humanity. We've shifted to mostly rural living to increasing urban living. The shift has created huge opportunities for pests to thrive including the emergence of new pests and their natural habitats were built over. An interesting point they mention is that with urbanization, there is an increase in disgust with insects indoors and what may have been ignored in rural areas is considered more of a pest, and calls for control measures in more urban areas.  

Invasive pests have been a huge factor with new pests emerging in areas they never would have got to without the global nature of the world today. More trade created more pests and required futher study and exchange of information in the field of urban entomology. Similarly, resurgance of known pests especially with insecticide resistance, demands further research and expansion of the field. A classic example of this is bed bugs.  

With this understanding established, we move into the discussion of the “who” of urban entomology. The structural pest control and professional pest management industry began in the US in the 1930s and has grown over the last hundred years to surpass 11 billion in 2022. That’s a huge number and proves how widespread the pest management industry really is. With FIFRA, federal insecticide fungicide and rodenticide act, in 1947 and amendment in 1972, this brought us to the requirements of licensing, training, and reeducation that are what we all know today. With these requirements, land grant universities increased their cooperative extension services  and created endowed positions in the universities to create space for urban entomologists in higher education. Nowadays, these positions and ccooperative extension programs have been reduced as retireees are not replaced.  

There are organizations and societies that have held educational conferences including and elevating urban entomology as a field, with the Entomological Society of America, National Conference on Urban Entomology, and Pi Chi Omega, creating space for urban entomologists to share information and innovate in the field.

 With the decline in the number of urban entomologists in academia and the obstacles the modern pest management professional faces, I want to make sure that I'm not painting the state of today as being one of doom and gloom. There has been amazing progress in scientific advancements in the field. NPMA and the Pest Management Foundation are dedicated to supporting the next generation of urban entomologists through scholarships, research funding, and showcasing research at our events. To learn more about the Pest Management Foundation, visit our site, https://www.npmapestworld.org/foundation/.

Article by Ellie Lane

References

Rust MK, Lee CY, Bennett GW, Robinson WH. The Emergence and Sustainability of Urban Entomology. Annu Rev Entomol. 2024 Jan 25;69:59-79. doi: 10.1146/annurev-ento-012423-110612. Epub 2023 Aug 10. PMID: 37562050.