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.

Hello Darkness, My Old Friend: A Tutorial of Nanda-Hamner Protocols

Plants and animals use circadian and photoperiodic timekeeping mechanisms to respond to daily and seasonal changes in light:dark and appropriately coordinate their development. Although the mechanisms that may connect the circadian and photoperiodic clock are still unclear in many species, researchers have been using Nanda-Hamner protocols for decades to elucidate how seasonal time is measured and determine whether seasonal responses have a circadian basis in a given species. In this brief tutorial we describe how to design and interpret the results of Nanda-Hamner experiments, and provide suggestions on how to use both Nanda-Hamner protocols and modern molecular experiments to better understand the mechanisms of seasonal timekeeping.