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Mosquitos, German Cockroaches, and Mediterranean Flour Moths

Fairfax, VA – October 1, 2024

In the October 2024 episode of NPMA BugBytes, we cover new research on links between tires and mosquito populations, the efficacy of consumer control products against German cockroaches, and the impacts of pheromones on flight behavior of the Mediterranean flour moth. We're joined by special guest Bill Cowley of Cowley's Pest Services!

Featured Article Summaries

Mosquitos in Discarded Tires

Discarded Vehicle Tires and Their Association with Mosquito Vector Abundance across Socioenvironmental Gradients in New Orleans, LA  

A critical step in managing adult mosquito populations is known as source reduction where the goal is to reduce or eliminate standing water conditions that mosquitoes need to lay their eggs. Some mosquito species prefer temporary water holding containers such as tree holes, plant pots, and even discarded tires to serve as these larval development sites. These mosquito species are often referred to as “container” mosquitoes and include species such as Aedes albopictus (Skuse) and Ae. aegypti (L.), both vectors of dengue, chikungunya, and Zika viruses. 

Combatting and removing illegally discarded tires is an important challenge for the city of New Orleans in the fight against dangerous mosquitos. Recent surveys showed that tire dumping in public rights of way has more than doubling from 2010 to 2018. And, more tires mean more mosquito development sites. In fact, a previous discarded tire survey logged over 1,000 used tires throughout the city, with more than half of those tires occupied by mosquito larvae. Eliminating these tires to reduce mosquito development sites is critical to managing the mosquito problem, but this has proved to be a challenge for several reasons including a lack of awareness concerning the link between tires and mosquitoes among residents, and locating discarded tires for removal.  

To help the City of New Orleans tackle this issue, researchers surveyed tire piles and adult mosquitoes across 12 sampling sites in the city between May and October of 2020. Their goal was to better understand where and why tires were likely to be found in the city, as well as what mosquito species were more likely to be found in these areas with discarded tires. They hypothesized that tire distribution across the city would be linked to median income and vacancy of residences. In other words, they suspected that tires were more likely to be found in lower income neighborhoods with more abandoned homes that would serve as dumping grounds. To address these questions, researchers looked at many factors including median income, population density, tire counts, and heat severity.  

They also predicted that mosquito species distribution would differ in areas with a high tire density. To investigate this theory, they needed to look at data that could give them more information on a smaller scale. Variables such as rainfall and temperature were generally good factors used to predict mosquito distribution, but in this case both factors were likely to be relatively uniform across the city and therefore may not offer much help when trying to understand differences between neighborhoods. However, vegetation cover and urbanization across the city were more likely to differ from one neighborhood to the next. Another variable they wanted to consider was the condition known as the urban heat island effect where areas with more concrete and pavement absorb solar heat during the day and release it at night. This urban heat island effect combined with differences in vegetation could be creating microclimates that could influence mosquito species distribution across the city. For mosquito abundance and distribution, they focused on three species: Culex quinquefasciatus (Say) which is a vector for West Nile virus (WNV) and St. Louis encephalitis virus (SLE), as well as Ae. albopictus and Ae. aegypti.  

When researchers compared the mosquito collection data with urban heat island estimates and the various social factors, the data showed that tire abundance was in fact higher in low-income neighborhoods with lower population density. For mosquito species distribution, they found that Ae. albopictus were found in higher numbers in areas with higher tire abundance and a lower heat severity rating. For the other two species, Ae. aegypti were more abundant in areas of high heat and Cx. quinquefasciatus were more abundant in areas of low heat.  

To sum all of this up, their data showed that low-income areas with more abandoned homes in New Orleans were more likely to have discarded tires. And these areas with high tire density and low heat severity were also more likely to have higher populations of Ae. Albopictus, a medically important species. These findings give the City of New Orleans direction on where to prioritize source reduction efforts in the city, as well as offering more information to educate low-income communities on the risk posed by discarded tires as a potential exposure pathway for their communities.   

Article by: Mike Bentley, PhD, BCE

References

Rebeca de Jesús Crespo, Alexandros Pavlakis, Jennifer Breaux, Claudia Riegel, Discarded vehicle tires and their association with mosquito vector abundance across socioenvironmental gradients in New Orleans, LA, Journal of Medical Entomology, Volume 61, Issue 5, September 2024, Pages 1240–1250, https://doi.org/10.1093/jme/tjae092

German Cockroaches and Consumer Insecticides

Common Consumer Residual Insecticides Lack Efficacy Against Insecticide-Susceptible and Resistant Populations of The German Cockroach (Blattodea: Ectobiidae)    

German cockroaches are one of the most common pests especially in places like affordable multifamily housing. They are not just unwanted house guests, but also a public health concern with their ability to mechanically vector pathogens and their allergens that have been shown to exacerbate asthma. And beyond the physical, the psychological impact of a cockroach infestation can be a difficult burden on folks as well.  

When housing management companies are not reliable and do not hire professional pest control services, individuals may turn to whatever products they can find at a store for direct spraying or residual use. Even those who do not face barriers to access professional pest control may opt to use store bought products as it may seem easier to try to do it themselves.  

Use of pesticides by residents has been studied and shown to be quite high.  in this experiment they studied consumer available products including direct sprays, limited exposure sprays (the kind you spray on a surface like countertops or painted drywall or tile), and continuous exposure. In all of these, the researchers were looking to find success as defined by 90% mortality (as stipulated by the EPA for a product to be able to claim it is successful) 

The researchers tested the products on a lab reared susceptible population, and three field collected populations from the past few years. The products used included Spectracide bug stop, Raid ant and roach killer, Ortho home defense, and Hotshot roach ant and spider killer.  

They found that direct exposure was the most effective route for each of the tested products. But even so, a total of 4 of 16 product-population combos failed to achieve the needed 90%.  This included the resistant field collected strains with Ortho home defense and the most recently field collected population with Hotshot.

 

Percent mortality at 24 hr following limited exposure (30 min) to consumer-grade cockroach spray products (Hot Shot Roach, Ant and Spider Killer (A), Ortho Home Defense (B), Raid Ant and Roach Killer (C), and Spectracide Bug Stop (D)) compared across 4 German cockroach populations on 4 common household surfaces (Kruskal–Wallis test; P < 0.05). Error bars represent standard error. Different letters denote within-surface significant differences between populations for each surface (Dunn’s test).

 

Limited exposure was much less effective. They tested these population/product combos on different common household surfaces. The graphic here shows it pretty dramatically that across the board, painted drywall resulted in less than 20% mortality in all cases. the susceptible population had 100% mortality on ceramic tile and stainless steel across all products. The other field collected populations had less than 20% mortality across the board for all products and surfaces. 

The limited exposure studies are critical, because that is the best chance to hit the majority of the roaches, ones you do not see and at any time of the day. The mortality was shockingly low on painted drywall showing that is not a good surface to use the product on.  

The EPA regulations only stipulate that products must be tested on a population of German and American cockroaches but says nothing about them being recently field collected. This study proves that field collected strains from years ago and more recently are resistant against these products. The researchers make the argument that it is critical for products labeled for use on cockroaches to be tested using populations with known pyrethroid resistance.  

The researchers recommend people to choose a gel bait or better yet, seek professional pest control. The potentially high cost for professional services can be a barrier to those in low-income housing. There will always be people who for whatever reason try to do pest control themselves. Products on the market should be effective to field populations according to packaging claims. With this study, this is not true across the board. 

Article by: Ellie Sanders, BCE-Intern

References

Johnalyn M Gordon, Marla J Eva, Sudip Gaire, Arthur G Appel, Zachary C DeVries, Common consumer residual insecticides lack efficacy against insecticide-susceptible and resistant populations of the German cockroach (Blattodea: Ectobiidae), Journal of Economic Entomology, 2024;, toae158, https://doi.org/10.1093/jee/toae158   

 

 

Mediterranean Flour Moth Flight Activity

Flight Capacity and Behavior of Ephestia kuehniella (Lepidoptera: Pyralidae) in Response to Kairomonal and Pheromonal Stimuli 

Stored product pests are one of the biggest heavy-hitter pest groups when it comes to economic loss caused by pests. In post-harvest losses alone, stored product pests are estimated to damage up to 9% of the grain produced in developed counties, and up to 20% of the grain produced in developing countries.* Despite the huge amount of economic loss they cause in the world, we understand very little about the flight behavior of these pests, which could provide more context for appropriate treatment. 

Enter, Ephestia kuehniella, or more commonly known as the Mediterranean Flour moth. Previous studies had focused on the flight initiation, or what prompts stored product pests to begin flying, but there was little data on the flight capacity and actual behavior of the pests once they were in flight. This is important data to know, as it provides context on how far Mediterranean Flour Moths and other stored product pests may be willing to fly for food and mating pheromones.  

To test this, the researchers essentially built a scientific version of tying a fly to a string. Except, the fly was a moth, and the string was an extremely sensitive flight mill with sensors that measured how many times the flight mill rotated. Moths in the flight mills were additionally exposed to three treatments: unbaited control, a sex pheromone cue, known as (Z,E)-9,12-tetradecadienyl acetate (ZETA), and a food cue, made of a mixture of various wheat and brewer’s yeast.  They left the moths for 24 hours and then analyzed the data.

 

Figure 1c. (Abshire et al. 2024)

 

The total distance flown by these moths in the flight mills over 24 hours ranged between 24.7 to 34.3 kilometers, or 15.3 to 21.3 miles. This is an astonishing distance to potentially fly for such a tiny moth, and highlights how easily a Mediterranean Flour moth could travel from one building to another.  

While the treatments had no effect on the distance flown, they did have an effect on the distance per flight bout. Moths exposed to pheromones were traveled a further distance on average in their flight bouts compared to those exposed to the control and food. In fact, moths exposed to a food stimulus had the shortest flight bouts.  

Similarly, the number of flight bouts was also impacted by the treatment, where the moths exposed to pheromones were 1.6 times more likely to initiate a flight bout compared to food cues. This is thought to be because the exposure to ZETA may initiate a more localized searching behavior, which would mean that it would encourage a higher number of flights at a longer distance to find that special someone.  

The researchers also found that flight velocity was lower in moths that were exposed to food or pheromones. This could illustrate the same point of the localized searching behavior, as moths who feel that they are close to a source may feel the need to slow down in order to search.  

In addition to the flight mill tests, the researchers additionally tested for flight initiation by placing moths in a cage, and then pumping in either the food cues, the pheromone cues, or a control. Interestingly, moths that were exposed to food cues were the most likely to initiate flight in the cage assay when compared to the other treatments. Therefore, this study also calls attention to the importance of studying all aspects of a behavior, as clearly food still can be a driving factor for moth flight initiation.  

These results emphasize the power of pheromones, and that pheromone-based and behaviorally targeted management strategies may be the best option when it comes to management of Mediterranean flour moths. However, it also emphasizes that these flight behaviors are not black and white, as clearly some moths are more driven by food than finding a mate. Overall, this study lays important groundwork and provides more behavioral context on how to improve pheromone traps for not only Mediterranean Flour Moths, but potentially stored product pests in general.  

Article by: Laura Rosenwald, BCE

References

*Phillips TW, Throne JE. Biorational approaches to managing stored-product insects. Annu Rev Entomol. 2010;55:375-97. doi: 10.1146/annurev.ento.54.110807.090451. PMID: 19737083. 

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Have questions or feedback for the BugBytes team? Email us at training@pestworld.org, we'd love to hear from you!