Bionomics of Adult Anopheles pseudopunctipennis females (Diptera: Culicidae) in the Historically Malaria- Endemic Focus of Batopilas, Chihuahua, Northwest Mexico
This study characterizes the seasonal abundance, nocturnal host-seeking activity, and parity-derived survival of *Anopheles pseudopunctipennis* in Batopilas, Mexico, revealing significant seasonal fluctuations in population density and biting times alongside a consistently high proportion of older females, thereby providing essential baseline data for malaria surveillance in northern Mexico.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer
In the rugged canyons of northern Mexico, where the Sierra Madre mountains drop into deep, warm valleys, a persistent public health challenge lingers: malaria. While the disease has been largely controlled in many parts of the world, pockets of transmission remain, often driven by specific types of mosquitoes that thrive in these unique environments. One such mosquito, Anopheles pseudopunctipennis, is a known carrier of the parasite that causes malaria in mountainous regions across the Americas. To stop the disease, health officials need to understand the daily lives of these insects: when they are most active, how long they live, and what weather conditions bring them out to bite humans. This knowledge is the foundation of effective surveillance, allowing communities to time their protection measures when the risk is highest. Without these details, efforts to control the disease can miss their mark, leaving people vulnerable during the hours when the mosquitoes are most hungry.
In a specific canyon community called San José de Valenzuela, researchers set out to map the behavior of this mosquito over the course of a full year. They focused on the adult females, the ones that bite and potentially transmit disease, by standing outside homes and catching them as they landed on their legs. This method, known as a human landing catch, allowed them to count exactly how many mosquitoes were seeking a blood meal each night and to record the precise time they arrived. The team worked from August 2024 through July 2025, gathering data during five consecutive nights every month, with extra effort put into two specific periods to get a deeper look at the mosquitoes' biology. They wanted to see if the mosquitoes followed a predictable schedule, how many of them had already laid eggs at least once (a sign of age), and whether the local weather dictated their numbers.
The results revealed a mosquito population that is far more flexible and seasonal than a simple, fixed pattern would suggest. The number of mosquitoes biting people changed dramatically throughout the year. The highest density occurred in November 2024, when researchers counted an average of 51.2 female mosquitoes per person per night. In contrast, the numbers dropped to their lowest in January and February 2025, with averages of just 3.6 and 2.4 mosquitoes per person per night, respectively. This peak in November came after the main rainy season, suggesting that the wet weather created breeding grounds that took time to mature into adult mosquitoes, though the researchers could not pinpoint a single weather factor as the sole cause after accounting for other variables.
Perhaps the most striking finding was how the timing of the bites shifted with the seasons. The mosquitoes did not stick to one time of night. In November, when the population was at its peak, nearly all the biting happened before midnight, with almost half of all captures occurring in the very first hour after sunset. However, as the year moved into the warmer months of 2025, the schedule flipped. By June and July, the vast majority of mosquitoes waited until after midnight to bite, with the highest activity occurring around 2:00 AM. This means that a control strategy based on the assumption that mosquitoes only bite early in the evening would fail completely during the summer months, leaving people exposed when they are likely asleep or less vigilant.
Beyond when they bite, the researchers also looked at how old the mosquitoes were. They examined the ovaries of the captured insects to determine if they had laid eggs before, which indicates they have survived at least one full reproductive cycle. In both the 2024 and 2025 intensive sampling periods, about 69% of the mosquitoes were found to be older, having already reproduced. This high proportion of older females is significant because it means the population contains many individuals that have lived long enough to potentially transmit malaria if they were infected. The researchers estimated that the daily survival rate of these mosquitoes was very high, likely between 88% and 91% per day, depending on how long their reproductive cycle took. This high survival rate ensures that a large number of mosquitoes live long enough to become dangerous vectors.
Despite the clear seasonal swings in numbers and biting times, the researchers could not find a strict, repeating rhythm in the mosquitoes' reproductive cycle from their daily data. They had hoped to identify a precise number of days between egg-laying events, but the natural fluctuations in the population made this impossible to calculate directly. Instead, they used a range of likely scenarios to estimate survival, finding that the mosquitoes were consistently long-lived regardless of the exact timing of their reproduction. The study also noted that while the mosquitoes were active in a wide range of temperatures and humidity levels, the most intense biting activity in the summer coincided with cooler, more humid conditions that naturally occurred later in the night.
This detailed look at the mosquito's life in the Batopilas canyon provides a crucial baseline for understanding malaria risk in this region. The findings show that the threat is not constant; it ebbs and flows with the seasons, and the time of day when people are most at risk changes throughout the year. The presence of many older mosquitoes suggests a steady potential for transmission, while the shifting biting schedule warns against relying on a single time window for protection. For the health officials and residents of this remote area, the message is clear: vigilance must be adaptable, covering both the early evening and the late night, and must be heightened during the specific months when the mosquito population swells.
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