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Wolbachia Mosquitoes in Hawaii: Unsettled Science (Part 1)
Public outcry seems to have fallen on deaf ears as the State of Hawaii moves forward with its plan to release biopesticide laboratory-reared Wolbachia bacteria-inoculated mosquitoes on Maui and Kauai, with future expansion of the project to additional islands. Serious concerns have been raised about the potential for unexpected evolutionary events and horizontal spread of disease. Questions regarding invasive species control, environmental impact, public health, and conflicts of interest have not been adequately addressed. While this plan is being presented as a conservation project, scientific research raises the alarm about the very real risks to Maui’s endangered native birds, including the possibility of increased pathogen infection in mosquitoes. There are many unknowns here, and this shortsighted project is moving forward with little consideration for input from unbiased scientific experts or from the people of these islands.
I’ve been reaching out to knowledgeable professionals who can help me navigate the science as I continue to research the scope and details of this plan. Following is an overview of my initial findings, focused on the topics of increased pathogen infection, horizontal spread, and unexpected evolutionary events – three areas that merit in-depth review and discourse.
First, let’s look at some specifics of the plan. The state is notifying the public that the strategy being implemented has decades of research behind it and is therefore safe. The reality is that the Sterile Insect Technique (SIT) that these decades of research are based on uses irradiation-induced sterility. This is not the technique planned for use in this project. The Incompatible Insect Technique (IIT), based on Wolbachia-induced cytoplasmic incompatibility (a kind of male sterility), planned for use here in the islands is something entirely different. It is also a relatively new approach, and certainly has not been studied in Hawaii’s unique ecosystems.
The HDLNR Application to the HDOA Advisory Committee on Plants and Animals (6/9/22)1 explains the science behind the planned IIT method:
“As outlined in the suggested conditions for importation, these mosquitoes will either contain the same wild type bacterium (Wolbachia spp.) which is already endemic in Culex quinquefasciatus mosquitoes in Hawaii, or will be inoculated with an incompatible bacterium (Wolbachia spp.) that is not native to the wild mosquito’s current internal fauna. The presence of this different strain of bacteria within the male mosquito’s reproductive system will render the imported male mosquitoes unable to successfully mate with wild females found within Hawaii, a process called cytoplasmic incompatibility.”
The document goes on to explain the different Wolbachia bacterium strains involved in this project:
“Within Culex quinquefasciatus, the strain of incompatible bacterium will be Wolbachia wAlbA, Wolbachia wAlbB, or Wolbachia wPip4. These Wolbachia bacterium are not present within the corresponding species of Hawaii’s established mosquito population. The presence of this bacterium will make these males sexually incompatible with the wild, established female mosquitoes. Once imported, the sexually incompatible males will be released according to EPA and HDOA label directions to suppress the population of the established mosquito populations. Based on the prior use of this technology in California, Florida, and Kentucky, there are no data to suggest releases of these male mosquitoes to have a negative impact on agriculture, the environment, or public health and safety. Existing wild-type bacteria strain that may be imported is wPipV, which is already found on all of the main Hawaiian islands.”
The combination of bacterial strains brings potentially serious complications to this proposal. More on that later.
I reached out to Dr. Anon (name changed by request for anonymity), Professor of Disease Epidemiology at a prestigious university in the United States. Anon has worked with modified mosquitoes, both as a lab tool and to combat disease, for over 20 years. He describes the Wolbachia-based IIT method as another type of SIT, with both focused on reductions in pathogen transmission resulting from reductions in the size of the mosquito population. Anon states that the Incompatible Insect Technique is “an implementation of the Sterile Insect Technique which has been performed by various methods for over 70 years.” However, this is somewhat misleading as it is the irradiation-induced sterility method (SIT) that has decades of study behind it. What we are dealing with here (IIT) is instead a new form of biopesticide created in a lab using modification via inoculation.
Anon gives an overview of how Wolbachia techniques are used:
“There are two very different ways Wolbachia is being used to control mosquitoes. It is easy to confuse the two, and the media often conflates them, but they are very different and have drastically different risk profiles.” In the first method, “Wolbachia spreads through populations of insects by maternal inheritance – the mother is infected, and all the offspring are infected, and so forth. It has been found that when mosquitoes are infected with non-native Wolbachia strains, the mosquitoes often become unable to transmit viruses. Wolbachia infected female mosquitoes have been released into wild populations where the Wolbachia spreads until the entire population is infected and thus cannot transmit viruses anymore.”
Dr. Anon doesn’t like this first strategy because, he says, “we find that this virus blocking phenomenon (at least in the lab) is not universal.” He points out boldly that this is not what’s happening in Hawaii:
“In Hawaii, only Wolbachia-infected male mosquitoes are being released. Male mosquitoes do not bite and do not transmit pathogens. The Wolbachia in the males makes them infertile when they mate with the wild female mosquitoes. Since mosquitoes usually only mate once, these wild female mosquitoes are thus sterilized and do not reproduce. Over time (if it works) the mosquito population is eliminated.”
Dr. Anon maintains that SIT strategies are safe as they have almost a century of research behind them. Again, this does not take into account the clear difference between traditional SIT (irradiation-induced, and sometimes chemically-induced, sterility) and the novel IIT biopesticide. Anon also notes that it’s an open question as to whether or not the IIT technique will be effective.
Beyond the question of effectiveness, there is also the issue of disease transmissibility. Anon promotes IIT as a safe strategy in that it differs from other SIT approaches where Wolbachia invades the population by maternal inheritance. His concern with maternal inheritance centers on the risk of the mosquitoes still being capable of transmitting viruses. This is where things get tricky. Safety assurances for the IIT technique do not take into account the possibility of accidental release of misidentified females or the unanticipated evolutionary events resulting from their breeding.
Even if the exclusive release of males could be guaranteed, there is also the issue of increased pathogen infection in the mosquitoes due to horizontal spread of bacteria and viruses between the introduced and the existing mosquitoes. Further, if existing “wild” female mosquitoes become infected with the introduced bacteria strain via horizontal spread (the spread of an infectious agent from one group or individual to another, usually through contact with contaminated material such as saliva), those wild females now become introduced-strain-infected. This would essentially cause the same concerns as those due to accidental release of misidentified lab-reared females. These infected females can produce viable offspring. They can breed with the lab-reared introduced males. The capacity of those offspring to spread disease is unknown. It cannot be emphasized enough that this specific population control technique (biopesticide lab-reared Wolbachia-bacteria-infected mosquito release) has NEVER been done in the state of Hawaii.
End of Part 1
Stay tuned for Part 2 where tropical disease expert Dr. Lorrin Pang (speaking as a private citizen) explains the problem in more detail. Incompatible bacterial strains, behavior-altering parasites, and the tale of the suicidal grasshoppers…What could go wrong?
1. HDLNR Application to the HDOA Advisory Committee on Plants and Animals (6/9/22) https://hdoa.hawaii.