Pestology Blog

Red Imported Fire Ants Cover the Insecticide-Treated Surfaces with Particles to Reduce Contact Toxicity

Solenopsis invicta Buren, the red imported fire ant (RIFA), is a destructive invasive ant species that has spread around the world. Due to the devastating effects this ant can have on nonnative environments, researchers are constantly searching for new clues on how to better control it. 

Two common methods of control for pest ants are insecticidal baits and contact insecticides. Since ant behavior can differ wildly between species, understanding how ants respond to different products can provide clues that researchers can use to improve the effectiveness and application methods of these products in the field. The authors of this research paper set out to do exactly that by evaluating the behavioral responses of RIFA workers to surfaces treated with various insecticides.  Specifically, they looked at beta-cypermethrin, thiamethoxam, fipronil, indoxacarb, chlorfenapyr, spinetoram, rotenone, avermectin, and chlorantraniliprole.

In previous studies, the authors observed RIFA workers covering wet, sticky, or repellent surfaces with soil particles to avoid direct contact with the treated surface. Their goal in this study was to evaluate if foraging RIFA workers would respond similarly when exposed to various insecticidal active ingredients. And, if workers did cover a treated surface with soil, would that be enough to reduce the effectiveness of the treatments. This isn’t all they looked at in this study, but I’ll only be focusing on these experiments in this review.

In a series of laboratory and field trials, the researchers observed RIFA workers foraging for food that was placed on a treated surface. During the experiments, they measured 1) the number of foragers that would travel on the treated surfaces and 2) how much sand (if any) was brought onto treated surfaces. What they found was that surfaces treated with beta-cypermethrin or rotenone significantly reduced the number of foraging ants. And, RIFA workers transported significantly more particles onto surfaces treated with fipronil (at 50, 500, and 5000 µg/mL), rotenone (5000 µg/mL), or avermectin (5000 µg/mL) when compared to controls. Lastly, they found that when surfaces treated with fipronil or rotenone were covered by particles, RIFA workers had a higher survival rate.  

There were a few key takeaways from this study for me. First, the RIFA has an interesting behavioral avoidance strategy that can reduce the efficacy of some contact insecticides, and that this particle-covering behavior appeared to be concentration-dependent. Meaning that the workers were only observed moving particles onto the treated surface when higher concentrations of active ingredients were used. This to me would suggest that even non-repellents such as fipronil may be detectable by RIFA workers and their efficacy could be impacted at higher rates. Further reinforcing the point that, when targeting ants, the product you apply and how you apply it truly matters in the success of your control program. Ants are notoriously difficult to manage, and don’t need our help making that task any harder than it already is. 

Lastly, we still have more to learn about the behavior of the pests we manage, even on an organism as well studied as the red imported fire ant.  

Article by Mike Bentley, PhD, BCE

References

Wen, C., Shen, L., Chen, J. et al. Red imported fire ants cover the insecticide-treated surfaces with particles to reduce contact toxicity. J Pest Sci 95, 1135–1150 (2022). https://doi.org/10.1007/s10340-021-01474-0

Image Credits

Red Imported Fire Ant – Solenopsis invicta, Givhans Ferry State Park, Ridgeville, South Carolina. Photo by Judy Gallagher, Flickr.com

Termite IPM in Historic Sites

Termites are wood destroying insects found across much of the world. It is no wonder that they can be of concern in historic sites around the world. This article looks at termite control in a few selected historic buildings including the Statue of Liberty in New York, The Christiansted National Historic site in St. Croix in the US Virgin Islands, and the Tzu–Su temple in Taiwan. Historic sites like these often use wood as the original key building material. Back then, treated wood like we have today wasn’t invented so these historic sites are left vulnerable to pests. Use of cedar wood which is repellent to most insects was as close as these historic sites could get to pretreatments. 

IPM uses threshholds of pests to determine when actions should be taken. These are easy to define for crops and agriculture, and less easy to determine for urban and structural pests since much of that is subjective. The presence of termite damage prompts immediate treatment without considering a particular economic injury threshold as you might for other commodity’s IPM. In historic buildings any damage is monumental and economic injury is immediate.  

Subterranean termite treatments can be preventative or remedial. In the case of historic buildings the ship has long since sailed on most preventative measures. In the process of restorations, treated materials can be used but that can only go so far. This leaves us with remedial.

There are a few different options for termite treatments, these include liquid termiticides in soil, in ground baiting stations, and above ground baiting stations. In each of the historic sites, the Statue of Liberty, Christiansted Historic site, and the Tzu Su temple, these options were explored. Liquid termiticides were less viable options in these historic sites as drilling into foundations was not feasible. The fragile nature of historic sites means that disruptions to the structure are to be avoided at all costs. Bait stations therefore became the main tool.  

In the late 90s, termites were found in each of the aforementioned historic sites. I won’t go through the details of the exact years and timing for each site but in each case, in ground and above ground monitoring stations were deployed to determine extent of infestation. You can access the full paper for more details if you are curious in the references section at the end of this article. They also used technology like acoustic emissions devices that monitors the sounds of termite activity.

They applied in ground bait stations and above ground bait stations around the sites discretely. In each case, the monitoring stations showed reduced numbers of termites over the course of months and years since bait installation. The Statue of liberty saw complete reduction in about a year after bait deployment, The most troublesome section of Christiansted took up to 39 months so around three years for complete elimination of termite activity, and the Tzu Su temple had elimination of formosan termites in some sections within 6 months and others closer to a year. 

The moral of the story here is that pest control in historic sites can be a tricky thing to handle and this paper gives a detailed overview of the success in some iconic sites where termite infestations were eliminated using only baits in a relatively short period of time.  

Article by Ellie Lane, BCE-Intern

References

Nan-Yao Su, Termite IPM in historic sites, Journal of Integrated Pest Management, Volume 15, Issue 1, 2024, 26, https://doi.org/10.1093/jipm/pmae013 

Evaluating the carnivorous efficacy of Utricularia aurea (Lamiales: Lentibulariaceae) on the larval stages of Anopheles stephensi, Culex quinquefasciatus, and Aedes aegypti (Diptera:Culicidae)

With the rising tide of insecticide resistance in mosquitoes, or more commonly known as the deadliest creature on Earth, desperation for new methods of mosquito management often leads to innovation. However, sometimes innovation comes in more… carnivorous ways than we originally set out with.

Enter Utricularia aurea, or more commonly known as bladderwort. This plant is an aquatic species that captures and feeds on everything from nematodes, snails, tiny crustaceans, fish, tadpoles, and mosquitoes. The suction trap of this plant is the fastest known of all the carnivorous plants and can reach its prey up from up to 0.01 inches away. Once captured, the prey dies from lack of oxygen, and then is digested by the plant for nutritional purposes.

Utricularia aurea is a species of bladderwort that is found in India, Japan, and Australia, where several mosquito species of concern are also found. The purpose of this study was to evaluate the effectiveness of U. aurea as a potential mosquito management strategy both in the lab and the field using three different species of mosquitoes: Aedes aeygpti, or the Yellow Fever Mosquito, Anopheles stephensi, one of the Malaria mosquitoes, and Culex quinquefasciatus, or the Southern House Mosquito.

The researchers collected wild shoots of U. aurea and brought them into the lab. They then exposed mosquito larvae from their three chosen species to the plants and monitored their survival. This study also looked at the application of this plant out in the field, by using a scenario that’s common to India, and common breeding grounds of mosquitoes. When concrete slab is laid in India, it is a common practice to inundate it with water to prevent the slab from drying too quickly. These areas are known to be filled with “curing water” and are well-known as mosquito breeding grounds. These sites provided perfect field controls for studying how bladderwort would perform in the field as a mosquito management tool. The researchers specifically looked at Aedes aegypti and Anopheles stephensi, as they were respectively the largest and the smallest of the mosquito larvae tested, and they happened to be found at the curing water locations. The researchers added in the bladderwort in this curing water scenario, and then measured the populations of mosquito larvae and pupae over the course of sixteen days.

The researchers were able to successfully demonstrate that bladderwort can eat all three species of mosquito larvae. Unsurprisingly, the larger instars of each species had the highest survival probability compared to their younger and smaller compatriots. However, after just twelve hours in the lab, the bladderwort predated 95% of the first, second and third instars of all three mosquito species.

Out in the field, the researchers were able to demonstrate similar success. In the “curing water” scenario, the researchers showed that adding bladderwort to these mesocosms reduced immature mosquito populations of both A. aegypti and A. stephensi by 76% and 71% respectively over the course of just sixteen days.

This study is extremely promising for several reasons. First, bladderwort is a common plant that is found all over the world, so different species could be used in different locations. Previous studies have also shown that in man-made water storage containers, bladderwort was able to selectively target mosquito species, and leave other nontarget organisms. And lastly, bladderwort is also documented as being highly resistant to insecticides, herbicides, and pesticides, so it could be used in conjunction with chemical treatments. However, further research is needed on the ecological side of things. Not only does this include evaluating bladderwort’s potential for invasive spread, but it should also include a comparison of when the plants and the mosquitoes are the most active.

Article by Laura Rosenwald, BCE

References

Mohanty AK, Govekar A, de Souza C, Mohapatra A, Janarthanam MK, Vukanti R, Montemarano JJ, Balabaskaran Nina P. Evaluating the carnivorous efficacy of Utricularia aurea (Lamiales: Lentibulariaceae) on the larval stages of Anopheles stephensi, Culex quinquefasciatus, and Aedes aegypti (Diptera: Culicidae). J Med Entomol. 2024 May 13;61(3):719-725. doi: 10.1093/jme/tjae038. PMID: 38521610