A Comparison of Oak Leaf and Fescue Hay Infusion-Baited Gravid Trap Collections-An Analysis Steeped in the Context of La Crosse Virus Vector Surveillance Effectiveness

Neuroinvasive La Crosse virus disease remains the primary cause of pediatric arboviral encephalitis in the USA. In spite of the persistent public health burden, there are limited entomologic surveillance options that target both native and invasive La Crosse virus (LACV) vectors. In this study we used Reiter/Cummings tacklebox gravid traps to compare white oak (Quercus alba) and hay (predominately Festuca arundinacea) infusions within a LACV-endemic area of western North Carolina. Paired gravid traps (approximately 1,728 total trap-hours for each infusion) yielded 485 mosquitoes, with 3 species (Aedes japonicus [n = 265], Ae. triseriatus [n = 156], and Culex restuans [n = 45]) accounting for 96.1% of the total collection. The hay-infusion traps collected 2.5 times more Ae. triseriatus and 1.3 times more Ae. japonicus than the oak-infusion traps. The sum differences in overall collections for these 2 species by infusion type were statistically significant (χ2 = 9.61, df = 1, P = 0.0019). Poisson ratio tests to compare capture rates suggest that hay infusions were more effective for capturing Ae. triseriatus, but that hay and white oak leaf infusions had equivocal capture rates for Ae. japonicus (an invasive LACV accessory vector) and Cx. restuans (an enzootic West Nile virus vector). These results are discussed in the context of operational considerations for LACV vector surveillance.

Aedes albopictus (Diptera: Culicidae) Has Not Become the Dominant Species in Artificial Container Habitats in a Temperate Forest More Than a Decade After Establishment

Aedes albopictus (Skuse) (Diptera: Culicidae) is one of the most invasive species globally, and has led to rapid declines and local extirpations of resident mosquitoes where it becomes established. A potential mechanism behind these displacements is the superior competitive ability of Ae. albopictus in larval habitats. Research on the context-dependent nature of competitive displacement predicts that Ae. albopictus will not replace native Aedes triseriatus (Say) (Diptera: Culicidae) in treeholes but could do so in artificial container habitats. Aedes albopictus remains rare in temperate treeholes but less is known about how Ae. albopictus fares in artificial containers in forests. Tyson Research Center (TRC) is a field station composed of mostly oak-hickory forest located outside Saint Louis, MO. The container community has been studied regularly at TRC since 2007 with permanently established artificial containers on the property since 2013. Aedes albopictus was detected each year when these communities were sampled; however, its abundance remains low and it fails to numerically dominate other species in these communities. We present data that show Ae. albopictus numbers have not increased in the last decade. We compare egg counts from 2007 to 2016 and combine larval sample data from 2012 to 2017.We present average larval densities and prevalence of Ae. albopictus and two competitors, Ae. triseriatus and Aedes japonicus (Theobald) (Diptera: Culicidae), as well as monthly averages by year. These data highlight a circumstance in which Ae. albopictus fails to dominate the Aedes community despite it doing so in more human-impacted habitats. We present hypotheses for these patterns based upon abiotic and biotic environmental conditions.

Population Growth Rates of Aedes atropalpus (Diptera: Culicidae) Are Depressed at Lower Temperatures Where Aedes japonicus japonicus (Diptera: Culicidae) Are Naturally Abundant in Rock Pools

Recent studies report extensive reductions in the abundance of the North American rock pool mosquito, Aedes atropalpus (Diptera: Culicidae), following the invasion of Ae. japonicus japonicus in the United States. Although developmental temperature is recognized as an important component of the invasion biology of Ae. j. japonicus, its impacts on the population growth and fitness of Ae. atropalpus remain largely undefined. In this study we reared Ae. atropalpus larvae at three temperature ranges reflecting ecologically important temperatures in natural rock pools: a low temperature range (mean: 19°C) where Ae. j. japonicus is common and Ae. atropalpus is often rare, a middle temperature range (mean: 25°C) where both species are naturally found in similar relative abundances, and a higher temperature range (mean: 31°C) where Ae. atropalpus is the dominant species. We measured survival, development time, wing length, and fecundity to calculate a finite population growth rate at each temperature. Our results indicate that Ae. atropalpus population growth suffers in colder rock pools, which informs the perceived displacement of the species in temperate habitats. The population growth rate was highest in the middle temperature range, but not significantly higher than in the highest temperature range used in this study. The developmental success of Ae. atropalpus at the intermediate temperature range suggests that competition with Ae. j. japonicus in rock pools within that range may significantly impact natural Ae. atropalpus populations.

Aedes japonicus and West Nile Virus in New York

Identifying the array of vectors that play a role in perpetuating West Nile virus (WNV) infection in endemic foci will help in controlling the disease. Aedes japonicus has the potential to be a vector in the wild of at least 3 kinds of encephalitis, including WNV. Aedes japonicus is a nonnative species in the USA that is temperature tolerant and a potential human biter. Detection of WNV in mosquito pools of this field-collected invasive species, combined with their ability to feed on humans, make this mosquito species a possible public health concern. In this study, we collected mosquito abundance data and tested them for WNV-positive mosquito samples from 3 counties in New York State. We found a significant association between the season and land demography and the likelihood of the virus in Ae. japonicus.

Phenology of Rock Pool Mosquitoes in the Southern Appalachian Mountains: Surveys Reveal Apparent Winter Hatching of Aedes japonicus and the Potential For Asymmetrical Stage-Specific Interactions

The North American rock pool mosquito, Aedes atropalpus, has reportedly decreased in abundance following the introduction of Ae. japonicus japonicus to the USA, but the specific mechanisms responsible for the reduction remain unclear. Thus, there is a need for field studies to improve our knowledge of natural rock pool systems where both species co-occur. We sampled rock pool invertebrates over a 12-month period along the Chattooga River at a high-elevation site (728 m) near Cashiers, NC, and at a lower-elevation site (361 m) near Clayton, GA. We identified 12 orders of macroinvertebrates representing at least 19 families and 5 mosquito species. Aedes j. japonicus was present year-round at both sites. We observed overwintering Ae. j. japonicus larvae in pools with water temperatures as cold as 3°C and detected apparent winter egg hatching in water below 10°C. Aedes atropalpus was rarely encountered at the high-elevation site but was highly abundant in the summer months at the low-elevation site. Late-stage Ae. j. japonicus larvae inhabited pools in March 2019 when Ae. atropalpus first appeared in the same pools, creating the potential for asymmetrical stage-specific interactions. Our observations provide evidence of overwintering and early hatching of Ae. j. japonicus in the southeastern climate. Further study of the importance of stage-dependent competition and winter egg hatching of diapausing Ae. j. japonicus eggs is warranted.

Know Your Enemy: Effects of a Predator on Native and Invasive Container Mosquitoes

We tested the effect of the native container-dwelling predator Toxorhynchites rutilus on the codominant container-dwelling mosquitoes: native Aedes triseriatus and invasive Aedes japonicus. We established two predator treatments (predator, no predator) by removing T. rutilus from all containers, and stocking T. rutilus larvae (1/3.5 liters) in the predator treatment. Removal and stocking was repeated every 3 d and established significantly different predator abundances in both large and small containers. Repeated-measures analysis of variance (ANOVA) on standard samples showed larvae+pupae/liter of A. japonicus was greater without versus with predation, and this difference increased across samples. In contrast, repeated-measures ANOVA showed larvae+pupae/liter of A. triseriatus was statistically indistinguishable for predation treatments and was greater in small versus large containers. Thus, predation reduced invasive A. japonicus while having no detectable effect on A. triseriatus larvae and pupae. A final destructive census of pupae showed that predation reduced pupae/liter of both species, but this effect was greater and more consistent across container sizes for A. japonicus. Predator effects on abundances were not products of the nonlethal effect of predator avoidance by ovipositing females, as T. rutilus presence did not lead to reduced egg inputs by either Aedes, nor by Aedes spp. as a group. Effects of predation thus are best explained by differential success of developing larvae due to the greater lethal effect of T. rutilus on A. japonicus than on A. triseriatus. Thus, this system is consistent with the hypothesis that native predators can limit success and potential impacts of invasive mosquitoes.

A Statewide Survey of Container Aedes Mosquitoes (Diptera: Culicidae) in North Carolina, 2016: A Multiagency Surveillance Response to Zika Using Ovitraps

Native and invasive container-inhabiting Aedes mosquitoes (Diptera: Culicidae) play important roles in the transmission of endemic and traveler-introduced arboviruses in the United States. In response to the emergence of Zika virus into the Americas, we surveyed the distribution of container Aedes spp. of public health importance within North Carolina during 2016 using ovitraps. A seasonal survey was conducted in 18 counties from the mountains to the coast to identify species incriminated in the transmission of chikungunya, dengue, La Crosse, yellow fever, and Zika viruses. Multiple local, state, and federal agencies participated in the study and submitted more than 3,600 ovistrips. Aedes albopictus (Skuse) (81.4%, n = 54,458) was the most common and widespread species found in this survey, followed by Aedes triseriatus (Say) (10.7%, n = 7,169) and Aedes japonicus (Theobald) (7.9%, n = 5,262). We did not find Aedes aegypti and rarely found Aedes hendersoni (Cockerell). We assessed broad-scale climatic and other factors and determined that longitude, elevation, rainfall, and temperature had significant effects on explaining the variation in presence, abundance, and phenology of container Aedes in North Carolina. However, much of the variation in these outcomes was not explained at this coarse scale and may benefit from finer-scale analyses. These efforts represent the largest ovitrap survey ever conducted in the state.