Critical Photoperiod and Its Potential to Predict Mosquito Distributions and Control Medically Important Pests

Diapause, a period of arrested development that allows mosquitoes to survive inhospitable conditions, is triggered by short daylengths in temperate mosquitoes. Different populations of mosquitoes initiate diapause in response to a specific photoperiod, or daylength, resulting in population-specific differences in annual cycles of abundance. The photoperiod that causes approximately 50% of a population to initiate diapause is known as the critical photoperiod (CPP). The autumn daylength corresponding to the CPP in the field likely marks the day beyond which the photoperiods would trigger and maintain 50% or more diapause incidence in a population, although temperature, diet, and other factors can impact diapause initiation. In the Northern Hemisphere, northern populations of mosquitoes experience lower temperatures earlier in the year and must be triggered into diapause by longer daylengths than southern populations. CPP is genetically based, but also adapts over time responding to the population’s environment. Therefore, CPP has been shown to lengthen with increasing latitude and altitude. While the positive correlation between CPP and latitude/altitude has been established in a few mosquito species, including Aedes albopictus (Skuse, Diptera: Culicidae), Aedes triseriatus, Aedes sierrensis, and Wyeomyia smithii (Coquillett, Diptera: Culicidae), we do not know when most other species initiate their seasonal responses. As several of these species transmit important diseases, characterizing the CPP of arthropod vectors could improve existing control by ensuring that surveillance efforts align with the vector’s seasonally active period. Additionally, better understanding when mosquitoes and other vectors initiate diapause can reduce the frequency of chemical applications, thereby ameliorating the negative impacts to nontarget insects.

Evolutionary transition from blood feeding to obligate nonbiting in a mosquito

The spread of blood-borne pathogens by mosquitoes relies on their taking a blood meal; if there is no bite, there is no disease transmission. Although many species of mosquitoes never take a blood meal, identifying genes that distinguish blood feeding from obligate nonbiting is hampered by the fact that these different lifestyles occur in separate, genetically incompatible species. There is, however, one unique extant species with populations that share a common genetic background but blood feed in one region and are obligate nonbiters in the rest of their range: Wyeomyia smithii. Contemporary blood-feeding and obligate nonbiting populations represent end points of divergence between fully interfertile southern and northern populations. This divergence has undoubtedly resulted in genetic changes that are unrelated to blood feeding, and the challenge is to winnow out the unrelated genetic factors to identify those related specifically to the evolutionary transition from blood feeding to obligate nonbiting. Herein, we determine differential gene expression resulting from directional selection on blood feeding within a polymorphic population to isolate genetic differences between blood feeding and obligate nonbiting. We show that the evolution of nonbiting has resulted in a greatly reduced metabolic investment compared with biting populations, a greater reliance on opportunistic metabolic pathways, and greater reliance on visual rather than olfactory sensory input. W. smithii provides a unique starting point to determine if there are universal nonbiting genes in mosquitoes that could be manipulated as a means to control vector-borne disease.

Seasonal dynamics of three inquiline species in isolated island populations of Sarracenia purpurea L. in Lake Michigan

A seasonal survey of the abundances of three inquilines species in Sarracenia purpurea L. leaves was conducted by sampling 240 leaves from three pitcher plant populations on Beaver Island in Lake Michigan, United States. Leaf characteristics such as fluid pH, fluid volume, and keel length were quantified. The study focused primarily on the larvae of three dipteran inquiline species – the midge, Metriocnemus knabi Coquillet, the mosquito, Wyeomyia smithii (Coquillet), and the flesh fly, Fletcherimyia fletcheri Aldrich. Dipteran inquiline abundances varied with sampling season. Most pitchers contained one of the three studied inquilines species. Mosquito abundances were low relative to the other inquilines. In samples collected soon after new leaves open, a mixture of mosquito and midge larvae was characteristic. We related inquilines abundances to leaf parameters using generalized linear mixed models. The midge and mosquito responded differently to leaf parameters during different sampling seasons, where as the flesh fly showed no response. The most important leaf parameters were pH and percent of total leaf volume filled with fluid (relative volume). The midge and mosquito were more likely to be present in pitchers with low pH and higher fluid volume. Our results indicate that pitchers of isolated northern populations of S. purpurea are inhabited by a less diverse insect community than reported elsewhere. Our study also suggests that site isolation may play an important role in the seasonal variation of inquiline community structure.