The quote from Sunmark Credit Union is the following:
"Mosquitoes can smell which blood type you are. They're twice as likely to bite someone who is Type O as opposed to Type A."
Pfizer summarizes the current understanding well in their article titled Why Are Some People Tastier to Mosquitoes Than Others? (check out the article here)
"The question of whether mosquitos prefer a certain blood type is controversial. One theory suggests that blood type may also help determine mosquito preference. If that’s the case, what blood type do mosquitos like? A 2019 study found that the major mosquito vector of dengue virus preferred people with type O blood to those with other blood types.2 However, separate research notes that experimental and laboratory data evaluating whether blood type makes one person more (or less) attractive to mosquitoes has fueled a lot of speculation, but the science is contradictory. Instead, the researchers report that the likelihood of being a “mosquito magnet” has more to do with skin odors and microbiota than blood type.7"
The article that they reference as the "2019 study" is an scientific journal titled Blood Feeding Preference of Female Aedes aegypti Mosquitoes for Human Blood Group Types and Its Impact on Their Fecundity: Implications for Vector Control authored by Manushika Prasadini, Dilakshini Dayananda, Sachini Fernando, Iresha Harischandra, and Nissanka De Silva1. their conclusion, quite succinctly says:
"The highest preference blood type of dengue vector mosquito Ae. aegypti is O according to the current analysis." See the article here
The source claiming mosquito preferences come from skin odors and microbiota is a scientific journal titled Differential mosquito attraction to humans is associated with skin-derived carboxylic acid levels by Maria Elena De Obaldia, Takeshi Morita, Laura C. Dedmon, Emely V. Zeledon, Justin R. Cross, and Leslie B. Vosshall. In their conclusion, they say this:
"Therefore, there may be more than one way for a person to be highly attractive to mosquitoes. We did not identify any compounds that were reproducibly enriched on the skin of the least attractive humans, consistent with the idea that these individuals lack mosquito attractants, rather than emitting a shared set of repellent compounds..."
In reference to what Sunmark claims, there exists credible evidence that blood type determines how frequently someone would be targeted by a mosquito. However, the latter article credited mosquito behavior to be a much more complicated phenomenon and is quoted saying:
"A common explanation offered by non-experts is that differences in ABO blood type 'explain' attractiveness to mosquitoes, but experimental data that address this belief are contradictory..."
So, to conclude and give this claim a rating, I would say the claim is Exaggerated/Misleading
While there exists evidence that blood type may be tied to the preference of mosquitos, there exists as much if not more evidence that goes against this notion / finds differing results.
