Aedes aegypti are vectors for common arthropod-borne-diseases (arboviruses) such as Zika, yellow fever, dengue, and chikungunya, which are of significant public health concern. The management of vectors is critical to mitigating the incidence, reemergence, and expansion of these diseases. Vector control has been complicated by the emergence of insecticide resistance within vectors, which threatens the effectiveness of control efforts. Furthermore, vector management is also complicated by the interaction between insecticide susceptibility and abiotic factors, such as temperature. While it is well-documented that environmental factors affect insecticide susceptibility, it is poorly understood how insecticide resistant vectors with different genetic backgrounds respond to insecticides at different temperatures. This study aims to establish the relationship between deltamethrin susceptibility at varying temperatures across Ae. aegypti lines that differ in their susceptibility due to knockdown resistance (kdr) mechanism. This was done through exposures using the “WHO tube test method” using simulated climate environments (22°C, 27 °C, and 32 °C) on mosquitoes of varying resistance at 1016 and homozygous resistance at 1534. This experiment is still ongoing. This study found that IICC was the most resistant genotype, VVCC the least resistant, and VICC and intermediate. There was found to be no statistically significant relationship between temperature and insecticide susceptibility across kdr genotypes.

Vector-borne diseases, such as Zika, chikungunya, dengue, and yellow fever, cause a significant portion of the global infectious disease problem, thereby representing an enormous public health threat worldwide. The threat has become more concerning as Aedes aegypti, who serve as primary vectors for these infectious diseases, continue to thrive in highly populated, urban environments. To solve this problem, insecticides have commonly been used, but this has brought forward additional issues. The overreliance on insecticides has resulted in insecticide resistant individuals emerging within once susceptible populations. Insecticide resistance in Ae. aegypti is a worldwide problem because it compromises the ability to control Ae. aegypti populations, thus increasing the spread of vector-borne diseases. With pyrethroids being commonly used worldwide, the mechanisms behind the knock-down resistance (kdr) are essential to investigate. Investigating the fitness of kdr resistant Ae. aegypti is essential in order to better understand their ability to reproduce and survive in a natural environment. Kdr resistant mutations are known to come with fitness costs: a highly energetic cost or a significant disadvantage that diminishes an aspect of the individual’s fitness. Although it is known that resistance comes with a cost, many research gaps remain. Still, it is unknown whether resistant genotypes differ in larval development times, immature survival, and adult qualities (body weight and wing length). As such, this study observed the impact of the larval development of Ae. aegypti genotypes with varying resistance at loci 1016 and 1534 of the voltage gated sodium channels. The 1016 kdr mutation results in a valine to isoleucine amino acid substitution at position 1016 (V1016I), and the 1534 kdr mutation results in a phenylalanine to cysteine amino acid substitution at position 1534 (F1534C). All strains included in this study were homozygous resistant for the 1534 mutation, while genotype varied at the 1016 locus. Mosquito strains were named after their genotype and are VVCC, VICC, and IICC. Mosquito larvae of each genotype were placed at three temperatures (22℃, 27℃, 32℃) and time to pupation, emergence, immature mortality, sex ratio, dry weight, and wing length was measured. In congruence with previous data, larval pupation and emergence occurred at a faster rate in hotter temperatures (32℃) than in colder temperatures (22℃) for all genotypes. Furthermore, the observed data shows that male mosquitos generally emerged before female mosquitos, regardless of temperature or strain. Interestingly, there were no significant differences between different genotypes in any of the fitness parameters, although the times to pupation suggest a potential trend of increased developmental time with increased resistivity. Ultimately, this data brings important implications to come up with better solutions in vector control programs in order to decrease the likelihood of adult mosquitoes becoming infected and delivering more infective bites. The study also brings light into on where future studies should take place, such as immature competition experiments, and reproductive fitness parameters in order to provide a more complete picture of the life history traits of Ae. aegypti with kdr mutations.

Mosquitoes are estimated to kill roughly 700,000 people each year through the transmission of vector-borne diseases. Vector control via insecticides is a widely used method in order to combat the spread of mosquito populations; however, this comes at a cost. Resistance to insecticides has the potential to increase vector-borne disease rates. Aedes aegypti is an invasive mosquito species in Arizona and is a known potential vector for a variety of infectious diseases including dengue, chikungunya, Zika, and yellow fever. In contrast to many other mosquito species Ae. aegypti mosquito eggs can undergo quiescence, an active state of dormancy, over long periods of time. Variation in quiescent periods correlates to climatic rainfall alterations and can ultimately influence hatching and mating between multiple generations. I have studied the effect of quiescence on larvicide (i.e., temephos) susceptibility using mosquito eggs collected from a susceptible lab strain and stored under optimal temperature and humidity conditions. After undergoing various quiescent periods (3, 7, 14, 28, 84, and 182 days), the experimental eggs as well as 7-day quiescent control eggs were hatched and reared to 3rd instar larvae. Temephos susceptibility was tested using the WHO bioassay procedure at lethal concentration (LC) 20, LC50, LC80, diagnostic dose (twice LC99), plus an untreated control. Each concentration dose was replicated four times with 20 larvae each. The 3-day experimental group was excluded from analysis because the mortality was significantly lower than the 7-day for both the experimental and control groups. The 3 day experimental eggs displayed decreased mortality which did not align with the hypothesis, as the quiescence period elongates under optimal conditions, susceptibility to insecticides decreases, and this could have likely resulted from unintentional selection for increased fitness and faster developing eggs because the larvae that developed to 3rd instar first were those used for larvicide testing. ANOVA testing demonstrates variability in the LC80 experimental group which suggests the need for further investigation into high dose temephos concentrations. For the experimental LC20 linear regression, there were significant differences in mortality. The results indicate mortality gradually decreases when the quiescence period elongates, therefore there are significant differences in insecticide susceptibility when quiescence is 182 days (or longer), compared to when quiescence is 7 days. Further investigation into field mosquito’s genetic diversity, insecticide resistance profile, and environmental conditions should be considered.