The lab has been a very busy place for the last couple of months! Since May, Davi (lab technician), Zach (UF IFAS Intern), and I have been busy preparing for and executing field trials in collaboration with mosquito control programs throughout the state of Florida. In May, we completed 4 field trials in Indian River County and in June were able to complete 5 more in Walton County. Thank you to Indian River Mosquito Control and both North and South Walton Mosquito Control for all of your work in helping us make those trials happen.
My primary focus (at least currently) is on insecticide resistance, particularly in mosquitoes. The bulk of our resistance work has focused on Aedes aegypti and Aedes albopictus, but we have recently been working with other species such as Culex quinquefasciatus and Aedes japonicus. There are multiple methods for evaluating the insecticide susceptibility status of an insect and one of those methods is field trials. For my research, we have been using the CDC bottle bioassay and field trials to assess insecticide susceptibility status.
The CDC bottle bioassay is a lab-based assay where we treat a glass bottle with pure active ingredient and evaluate mortality over time. These assays can be great indicators of resistance developing within a population. However, there are a lot of factors that can influence the success of an insecticide in the field (weather conditions, vegetation, chemical product, etc.).
Since the results in the bottle do not necessarily match the mortality you might see in a field application of an insecticide, we do field trials to assess the efficacy of a formulated product. In Florida, public health mosquito control is done by mosquito control programs located throughout the state. When adulticiding, one of two chemical types is used: a pyrethroid or organophosphate. For our field trials, we wanted to assess the efficacy of both of these chemical types.
Pictured on the left is a representation of how our field site is set up for trials. Cages are place 100, 200, and 300 ft from the line of spray. Also at each of these locations is a spinner that collects droplets from the spray truck on glass slides. Control cages are placed upwind of the line of spray to ensure that the mortality observed during the trial is due to the insecticide spray and not something pre-existing in the environment.
Prior to the trial, mosquitoes are aspirated into the field cages and those cages are hung on stakes at each of the field locations. The spinners are mounted on top of the stakes and turned on immediately prior to the trial.
Once the cages are up and the spinners are on, we wait for the appropriate wind speeds (2-10 mph). It is important to wait until there is sufficient wind so that 1) the insecticide will actually be carried across the field site and 2) we are using the product according to label specifications.
After the cages have been treated, they are transferred to clean holding cages. To do this, we first knock down any surviving mosquitoes with CO2. Once they have been knocked down, the field cage is cut open and mosquitoes are transferred to a clean holding cup for the remainder of the trial. The mosquitoes quickly recover from their CO2 knockdown and mortality readings can be taken for the next 24 hours.
From these trials, we will learn more about the efficacy of each mosquito control program’s product in the field, and how that relates to the results we get in the laboratory.
As a side note (and kind of a funny one), doing field work at night in Florida is really fun. During these trials, we try to avoid using insect repellent so it doesn’t confound our results in some way. As a result, we may become prey to hungry mosquitoes. In Indian River, the Psorophora population was out in force. Take a look at the mosquito control director’s leg covered in mosquitoes!
Next week, we will head out to Pasco County for one more round of field trials before the end of the summer. Thank you to Indian River Mosquito Control, South and North Walton Mosquito Control, Dr. Connelly, Daviela, and Zach for helping make these trials go off so smoothly! It truly was a team effort and I think the trials went as well as they could.