DOI: 10.5061/dryad.nzs7h44z7
title: Data for: Mesocosm studies suggest climate change may release Aedes aegypti (Diptera:Culicidae) larvae from cold-inhibition and enable year-round development in a desert city

description: Global warming trends, human-assisted transport, and urbanization have
 allowed poleward expansion of many tropical vector species, but the
 specific mechanisms responsible for thermal mediation of range changes and
 ecological success of invaders remain poorly understood.  Aedes
 aegypti (Diptera: Culicidae) is a tropical mosquito currently expanding
 into many higher-latitude regions including the urban desert region of
 Maricopa County, Arizona. Here, adult populations virtually disappear in
 winter and spring, and then increase exponentially through summer and
 fall, indicating that winter conditions remain a barrier to development of
 A. aegypti. To determine whether cold limits the winter development of A.
 aegypti larvae in Maricopa County, we surveyed for larval abundance, and
 tested their capacity to develop in ambient and warmed conditions. Aedes
 aegypti larvae were not observed in artificial aquatic habitats in winter
 and spring but were abundant in summer and fall, suggesting winter
 suppression of adults, larvae or both. Water temperatures in winter months
 fluctuated strongly; larvae were usually cold-paralyzed at night but
 active during the day. Despite daytime temperatures that allowed activity,
 larvae reared under ambient winter conditions were unable to develop to
 adulthood, perhaps due to repetitive cold damage. However, warming average
 temperature by 1.7°C allowed many larvae to successfully develop to
 adults. Because daytime highs in winter will often allow adult flight, it
 is possible that relatively minor additional winter warming may allow A.
 aegypti populations to develop and reproduce year-round in Maricopa
 County.
description: From September of 2017, till August of 2019, water temperatures
 and <em>A. aegypti</em> larval presence was recorded in nine
 19 liter buckets placed in the backyard of Jon Harrison’s home in Tempe,
 Arizona (33.339, -111.924), as it was known to experience high abundances
 of <em>A. aegypti. </em>Buckets were 5 – 10 m apart, and so
 should not be considered ecologically independent.<em>
 </em>Onset HOBO Pendant® UA-002-08 data loggers (Bourne,
 Massachusetts) were used to record temperature levels, and larval presence
 was observed every 1-10 days depending on season (frequently in the
 summer, less so in winter). If mosquito larvae were observed, they were
 collected from the bucket with a net and their species identity confirmed
 with a dissection scope. The data set labeled Figure 2 data provides the
 water temperatures in one representative bucket from 2017-2019 as shown in
 Fig. 2 of the manuscript. <strong>Larval rearing
 for mesocosm experiments</strong> The parents of
 larvae used in the mesocosm overwintering experiments were reared from
 Maricopa County, AZ, origin eggs collected by Maricopa County Vector
 Control from September to November of 2019. These eggs were placed in a
 500 ml beaker, submerged, and hatched in a solution of 0.25 g/L baker’s
 yeast (Byttebier et al. 2014). As the 1<sup>st</sup> instar
 larvae emerged, they were fed TetraMin fish flakes every 1-2 days, making
 sure that an excess amount of food was visible in the container. The
 rearing density for the larvae was maintained at fewer than 500 animals
 per liter of water. As pupae began to appear, the beaker of larvae was
 placed in a 95-liter polymer-screened cage to contain the expected adults.
 Cotton balls saturated with 10% sucrose solution were made available for
 the adults as they began to emerge; these were taken away two days prior
 to blood feeding. One week after emerging, the adults were blood-fed using
 mice (IACUC protocol: 18-1662R). After a three-day gestation period, the
 females were supplied with moist seed-germinating paper to encourage
 oviposition. Once the females had finished ovipositing, the eggs were kept
 moist for an additional 48 hours before being dried, and placed in open
 zip lock sandwich bags which were stored at 100% humidity and 24°C. High
 humidity in the egg storage containers was achieved by storing damp paper
 towels along with the opened egg bags within a larger 3.8L bag. These eggs
 were kept for less than one month before the hatching procedure was
 repeated to produce the larvae for the experiment. In the lab, across all
 life stages, the mosquitoes were exposed to a 12:12 L/D photoperiod at
 24°C. After hatching, the 2<sup>nd</sup>
 instar larvae were moved to their outdoor experimental mesocosms. The
 larvae were randomly distributed with 20 larvae supplied per each of three
 ambient mesocosms (Amb1, Amb2, Amb3) and six to warmed mesocosms (W1 –
 W6), which were warmed by varying amounts (W1 = least warmed, W6 = most
 warmed). The goal was to achieve a range of warming from very small
 warming (1-2°C in the least-warmed mesocosm (W1), to near-summer
 conditions in the most-warmed mesocosm (W6). Each mesocosm was a 150 ml
 clear plastic container, filled with 125 mL dechlorinated tap water.
 TetraMin fish flakes were supplied to each mesocosm, with more added every
 three days or when food was completely consumed. Although the mesocosms
 were open, we observed no mosquitoes flying in the field, and none were
 captured in local water buckets, and all A.a. in the mesocosms were of
 uniform stage, so we believe that this experiment was not affected by
 oviposition from wild mosquitoes.
 <strong>Manipulation of thermal conditions for larval
 outdoor rearing</strong> All mesocosms were
 placed on a table one meter above the ground and protected from rain,
 wind, and sunlight by a roof. The mesocosms were placed within individual
 lidless pine boxes (10x10x14 cm, 0.95 cm thick walls), and so were exposed
 to normal fluctuations in air temperature.  Each warmed mesocosm was
 placed on 40mm<sup>2</sup> thermoelectric plates with
 40mm<sup>2</sup> aluminum heatsinks attached using thermally
 conductive adhesive on each side. The warming orientation of the
 thermoelectric plate was positioned upwards, towards the mesocosms, to
 ensure adequate energy transfer from the heating units to the water. Each
 thermoelectric device was powered by two KORAD KD3005D 30V, 5A power
 supplies (Shenzhen, China). The thermoelectric plates were wired in
 parallel. Variable warming was produced by changing the supplied voltage.
 Temperatures were measured in the cups using HOBO Pendant® UA-002-08 data
 loggers submerged in the center of each cup. We did not measure
 temperature gradients within the mesocosms, but believe that they are
 likely to be small except possibly in the mesocosms that were
 maximally-warmed, as the mesocosms were small and mostly not strongly
 warmed above air temperature. Temperatures were logged each hour in each
 warmed mesocosm, and in one ambient treatment mesocosm. The data file
 labeled Figure 3 data provides the wate temperatures at hourly intervals
 during the experiment for one mesocosm at ambient temperature, mesocosm W1
 (the least warmed mesocosm) and mesocosm W6 (the most warmed mesocosm) as
 shown in Fig. 3 of the manuscript.
description: # Data for Mesocosm studies suggest climate change may release Aedes
 aegypti (Diptera:Culicidae) larvae from cold-inhibition and enable
 year-round development in a desert city
 [https://doi.org/10.5061/dryad.nzs7h44z7](https://doi.org/10.5061/dryad.nzs7h44z7) Most of the data for this study are provided as supplementary files in the submitted manuscript. Here we provide representative thermal data. One file (Figure 2 data) contains the temperature data for the bucket kept under ambient conditions as shown in Figure 2, which also shows when Aedes aegypti larvae were found in the bucket. From to October 18 -November 29 2017, water temperatures were recorded every 6 minutes. Thereafter, water temperatures were recorded hourly until August 2, 2019. Another file (Figure 3 data) contains water temperatures for three of the mesocosms used in this study, as shown in the manuscript figure 3. This experiment ran from Jan 31, 2020 - March 1, 2020. One column sW1 was and ## Description of the data and file structure Figure 2 data has two columns, column A gives the date and column B the temperature of the ambient bucket in degrees Centigrade. Figure 3 data has four columns; column A gives the hours since the start of the experiment. Column B shows temperatures for an unheated mesocosm kept at ambient conditions. Column C shows temperatures for W6, the most warmed mesocosm (mean temperature 12C higher than the ambient mesocosm, to represent near-summer conditions). Column D shows temperatures for the least-warmed mesocosm (W1, mean temperature 1.8C higher than the ambient mesocosm). All temperatures are in degrees Centigrade.