A new look, and new interaction

As you may have noticed, we have completely overhauled our website. We hope that you will find it a more informative and streamlined experience. We have added many new features. One that we think will be popular is a new signup form for citizens wishing to be notified for certain things that have been scheduled for their area. Another new feature is this blog. Each month, look for a new column that will discuss a new topic, or perhaps revisit something with additional information. Topics will cover many wide-ranging subjects—some will feature the basics of mosquitoes and our methods to control them. There will also be blogs discussing current news stories relating to mosquitoes or mosquito-borne diseases.

We are both entomologists and will share the writing duties for these blogs. Our goal is to get a new one out each month (written alternately by each of us), but our hope is to get them out a little faster than that. We have a loose schedule for the topics that we will cover, but feel free to send us an email if you think you have something that you think would be of interest to others.

You’ve probably seen our trucks at night. Maybe you’ve even heard our plane flying overhead in the evening or our inspectors treating ditches during the day. But how are we determining where to make our treatments? Are we just randomly assigning areas for applications? What information are we basing our operational decisions on?

Tangipahoa Mosquito Abatement uses an Integrated Mosquito Management (IMM) strategy. This means we base our treatment plans on multiple components (you can read more about this approach here). One of these components is mosquito surveillance, which includes mosquito trapping and disease testing. This is an on-going process that tells us what species are present as well as population density. We also collect specific species to be tested for West Nile virus either in our lab or the Louisiana State University vet lab. So what exactly does “mosquito trapping” entail?

There are two main types of traps that we use in our operations. Though there are multiple types of traps available, these have historically worked well for us. Both types are set twice each week during our mosquito season (typically early March thorough mid-November but can vary).

How do you “catch” mosquitoes?

Gravid trap: 

• Battery-powered, portable
• Consists of a tube containing a fan that is placed over a bucket
• Bait is fish emulsion
• Attracts mosquitoes that mainly breed in septic ditches (largely Culex quinquefasciatus the Southern House mosquito) 

How it works:

The trap attracts female mosquitoes that have typically had a blood meal and are gravid (egg bearing). These mosquitoes are looking for a place to lay eggs and are attracted by the fish emulsion. As they fly over the bait, they are sucked into a net by the fan. The net is collected the following day and mosquitoes are identified and counted.

CDC light trap:

• Based on a CDC (Centers for Disease Control) designed CO2 (Carbon Dioxide) trap
• Battery-powered and portable
• Typically attracts more aggressive, nuisance mosquitoes

How it works:

A one-gallon cooler is filled with dry ice, and a battery-powered light and fan hang beneath the trap. As this dry ice sublimes, CO2 is released, which serves as an attractant for mosquitoes. As they approach, they are sucked into a net. The net is collected the following day and the mosquitoes are identified by species and counted.

What happens if we can’t wait an entire night for mosquito numbers, like in the event of a major storm?

…Live bait?

Yes, you read that correctly. When we need to know mosquito numbers quickly, our inspectors will use themselves as “bait.” 

How it works:

• Stand in a wooded area (agitate the surrounding vegetation first)

• Record number and species of adults landing in a given period of time (usually one minute)
• May also count mosquitoes approaching, but not landing
• Do this three times and take the average

So what do you do with the mosquitoes after you catch them?

Disease Testing

• Adult female mosquitoes from traps are pooled into samples of 5-100 and sent to the Louisiana Veterinary Medical Diagnostic Laboratory.
  • Tested for the presence of West Nile Virus, St. Louis Encephalitis (SLE), and Eastern Equine Encephalitis (EEE) antibodies
• Data collected from traps are also used to determine if an outbreak in specific mosquito species has occurred.
• In 2018, we implemented protocol for loop-mediated isothermal amplification (LAMP) testing in our laboratory. Learn more about this testing here
  • Allows us to test for West Nile virus in-house in addition to what we send to LSU
  • Gives greater insight into where treatment is needed
  • Allows us to be more proactive than reactive-we can treat an area BEFORE West Nile becomes a huge problem

These strategies are one part of a multi-faceted effort to control the mosquitoes in our area. Stay tuned for more pieces that make up our “mosquito control puzzle!”

Ground Adulticiding Operations

Ground adulticiding is the aspect of mosquito abatement that the general public is most aware of. This is the term we apply for the use of what are commonly called “spray trucks”. These are light pickup trucks with a spray rig in the truck bed.

The type of spray rig that we use starts with a commercial grade 18-horsepower gasoline engine and fuel tank. This engine serves one purpose—it powers the blower. This blower generates a powerful air blast which is channeled through a spray nozzle. The spray nozzle is where the flow of the chemical used meets the air blast, and shears the chemical into very small droplets which are then dispersed into a spray cloud.

This process is controlled by a computerized spray control system. Now this is where the magic happens! There is an onboard GPS system which determines the location and speed of the vehicle. Then a pump adjusts the flow of the chemical based upon the speed of the vehicle. This ensures that our applications are being made at a constant amount per acre treated. Therefore, whether the truck is travelling at 5mph or 20mph, the flow of the chemical is adjusted as necessary to produce the same application rate. Lastly, this controller records all of the information for download. We are able to review each mission and see where the truck was at any given point in time, how fast it was going, whether the sprayer was turned on, and the chemical flow rate. Also, our drivers have a toggle switch inside the cab which allows them to turn off the chemical pump to avoid spraying someone who might be standing in their front yard, or to accommodate someone who does not wish their yard to be sprayed at all.

There are times we receive phone calls from residents concerned that we have missed their street. This system allows us to review the mission and determine whether that happened or not. Most of the time, we are able to tell the caller exactly what time we passed in front of their home. There are occasions where we do miss a street, and we will tell them that as well. Either way, we can positively verify what happened. The same is true if a resident calls saying that we have sprayed an area that we have been requested not to. We can see whether the driver turned off the pump or not as instructed in the particular area. 

These spray rigs are highly calibrated. First, we calibrate the rate at which the volume of chemical is pumped (the flow rate). This is then input into the software to get the variable rate that we are looking for. Once the flow rate is correct, we then measure the size of the droplets being produced to ensure that they are in the proper range. These droplets are collected onto slides near the nozzle and measured using a compound microscope, which is connected to a computer that analyzes the droplets using specialized software.

As you can see, this is a very involved process. However, we take our job seriously, and work hard to ensure that our equipment is in good running condition, calibrated correctly, and controlled by a sophisticated flow control system that ensures our applications are done properly.

Another Puzzle Piece - Mosquito Pools and Disease Surveillance: So you’ve trapped some mosquitoes…now what?

A major component of mosquito control operations is disease monitoring. Which poses a very important question: What roles do our operations play in this monitoring? 

Mosquito Collection

Twice a week, CDC and gravid mosquito traps are placed throughout the district. These traps are set out overnight, collected the next day, and brought back to the lab to be sorted and counted.  Learn more about these traps from my previous blog piece here. The species that are at greater risk of transmitting West Nile virus (more on that later), are collected in “pools.” 

                   CDC trap                                                                                                                   Gravid trap

What exactly is a mosquito “pool”?

A mosquito pool is essentially a “sample” of mosquitoes that is collected in a small vial for testing. The vial is a 2mL microcentrifuge container that can test a range of 5-100 mosquitoes in each. We can send up to three vials per species per trap night, with a maximum of six vials for each site.  

2mL microcentrifuge vial

Mosquito Species testing and testing site

Certain species are a greater risk of transmitting West Nile virus than others, so those species are collected in these vials and either sent off to the LSU Diagnostic lab (most of our samples go here) or tested in our own lab. The typical species collected are: 

• Culex quinquefasciatus (southern house mosquito)

• Culex nigripalpus (Florida SLE mosquito)

• Aedes albopictus (Asian tiger mosquito)

• Culex salinarius 

What diseases are the samples tested for?

Mosquitoes transmit a multitude of viruses and parasites, but the main threat to the citizens in our district continues to be West Nile virus (more information here). All the samples sent to the LSU lab are tested for West Nile virus, and typically starting in May, they are additionally tested for St. Louis encephalitis and Eastern Equine encephalitis. For our in-house LAMP testing, we are currently only monitoring for West Nile virus. Although in the future, we may explore testing for other arboviruses.

What happens if you get a positive sample?

Results from every sample are recorded, regardless if they are a positive or a negative result to monitor historical data. This data is stored both in our own databases as well as shared databases with other mosquito districts. If we receive a positive sample or samples, we will then treat these locations more aggressively for a few weeks until we verify that no more positives are developing out of the area.  This more aggressive treatment includes having inspectors treat standing water, assigning our night trucks to do additional ground spraying, and/or flying aerial missions.

By monitoring disease activity, we are better able to see where our problem areas are, and more effectively treat those areas. If we can lower the populations of the mosquito vectors in an area, we can reduce the risk of an infected mosquito biting a citizen, and therefore reduce the risk of disease transmission. It is another piece of the Integrated Mosquito Management strategy puzzle!

Earlier blog entries have mentioned “LAMP” testing, but what exactly is that? So let’s shine a light on the subject! (You see what I did there?)

A major component of our operations is collecting mosquitoes (to read more about surveillance, click HERE). I have previously covered what happens to most collected mosquitoes (for a review, click HERE). Still, at TMAD, we like to go big or go home, which is why in 2018, our board of directors voted to invest in implementing our own in-house West Nile Virus testing.

We were the first mosquito control district in the state to incorporate this specific technology into our routine operations, and we are especially proud of this!

That’s nice and all, but what is it?

LAMP stands for “loop-mediated isothermal amplification.” It’s a mouthful, but the basic idea is simple: isolate and amplify genetic material to show the presence of the West Nile virus. By having this equipment and technology in our own lab, we eliminate turnaround time and can even test mosquito samples on the same day as collection. This is a big deal for public health! During peak West Nile virus season, we can essentially set out a trap, collect extra mosquitoes from that trap, and test them as soon as they are brought back to the lab. Then, instead of waiting a week or two weeks for results from the state lab, we can know the same day if we need to send out our trucks or our plane to a specific area. This allows us to be more “proactive” rather than “reactive.” 

The Process

LAMP testing is all about the genetic material within the cells or ribonucleic acids (RNA). Ribonucleic acids are present in living cells, and the general purpose is to carry instructions about making proteins to your cell’s DNA (deoxyribonucleic acid). Once mosquitoes are collected from a trap, this RNA must be extracted. This means that the rest of the cell needs to be essentially dissolved so that the RNA is easily isolated.

This is done by pulverizing the mosquitoes (making a mosquito milkshake!), separating the solids from the liquids by centrifuging, taking out some of the “slush” (i.e., homogenate), and then washing away the “unnecessary” parts of the cell to get the RNA by itself. 

This is the most labor-intensive part of the test and usually takes about 45 minutes to an hour, depending on how many samples are being extracted. Cells are stubborn little things!

After the extraction has taken place and the RNA is isolated, we must then amplify it to make it easily visible to the processing equipment. Finally, dyes and primers are added to enable the RNA to show up in the last step-the all-powerful Genie!

The Genie is the little machine that does all the final analysis and clearly reports positive and negative results. It usually takes about thirty minutes for this processing to complete.

How do you know the test was done correctly?

In every test run in our lab, we also run a positive and negative control. What does that mean? For every group of samples tested, we also run one sample that we know will be positive by adding specific reagents and one test with only water added instead of mosquito RNA to know it will be negative. If either shows anything other than the expected positive or negative result, we know that the test was possibly contaminated and will retest. This ensures that we are only working with the most accurate results better to serve the public health needs of our citizens. 

You should see four “peaks.” These represent a positive result for the presence of the West Nile virus. The dotted yellow line is a positive control, and though hard to see, a light green line flat on the X-axis represents negative control. This demonstrates that the test is not contaminated and the results are accurate.

How many samples can you run at once?

We can run up to 16 samples at once, including the positive and negative controls. We can do this twice a day if we need even more samples tested, for a total of 32 samples a day. We are exploring our options for increasing this number in the future.

Final thoughts

We strive to use science-based evidence to make our treatment decisions. LAMP testing is just one facet of the ongoing Integrated Mosquito Management strategy we use in our operations. Knowing where the West Nile virus is located quickly, we can better target our treatments and keep our citizens safer!

Have more questions or want to chat? Call our office, and we will be happy to help!