DOI: 10.5061/dryad.sj3tx963n
title: Data from: Differing thermal sensitivities in a host-parasitoid interaction: high, fluctuating developmental temperatures produce dead wasps and giant caterpillars

description: 1. Insect parasitoids, and the arthropod hosts they consume during
 development, are important ecological players in almost all environments
 across the globe. As ectothermic organisms, both parasitoid and host are
 strongly impacted by environmental temperature. If thermal tolerances
 differ between host insect and parasitoid, then the outcome of their
 interaction will be determined by the ambient temperature. As mean
 temperatures continue to rise and extreme temperatures become more
 frequent, we must determine the effect of high temperature stress on
 host-parasitoid systems to predict how they will fare in the face of
 climate change. 2. The majority of studies conducted on host-parasitoid
 systems focus on either performance under constant temperature, or a fixed
 metric of thermal tolerance (CTmax) for individual organisms. However,
 performance at constant temperatures is not predictive of performance
 under ecologically relevant, fluctuating temperatures, and measurements of
 thermal thresholds provide little information regarding the effects of
 temperature throughout development. We address this by testing the effects
 of increasing mean temperature in both constant and fluctuating (±10°C)
 environments throughout development on the performance of the parasitoid
 wasp Cotesia congregata and its lepidopteran larval host, Manduca sexta.
 3. The growth of M. sexta was influenced by mean temperature, diurnal
 fluctuations, and parasitization status. Caterpillar growth rate increased
 with increasing mean temperature, but decreased in response to diurnal
 fluctuations and parasitization by C. congregata wasps. 4. Wasp survival
 decreased with increasing mean temperature, and diurnal fluctuations
 decreased wasp survival, especially at higher mean temperatures. Diurnal
 fluctuations at our highest mean temperature treatment (30°C±10°C)
 resulted in complete wasp mortality, and parasitized hosts displayed
 abnormal physiology, wherein they failed to exhibit wasp emergence, did
 not enter the prepupal stage, continued to feed, and grew up to two-fold
 larger than a normal, unparasitized caterpillar. 5. Our results indicate
 hosts and parasitoids in this system have different thermal tolerances
 during development; the parasitoid wasp suffered complete mortality at a
 temperature regime that is mildly stressful for the unparasitized
 caterpillar host species. Our findings suggest C. congregata will suffer
 more severely under increasing temperatures than M. sexta, with cascading
 trophic and ecological effects.
description: Our experiment consisted of three
 mean temperatures (25°C, 28°C, 30°C), two diurnal fluctuation treatments
 (±0°C, ±10°C), and two parasitization treatments (parasitized or
 unparasitized controls). Sample sizes ranged from n = 24 to n = 47 (mean =
 35) for each treatment group (see Table S1). For logistical reasons, the
 28°C mean treatments were conducted in March—May 2017, the 25°C mean
 treatments were conducted in June—August 2017, and the 30°C mean
 treatments took place in January—March 2020. While our mean temperature
 treatments did not occur concurrently, analyses using data for the 25°C
 and 30°C constant temperature treatments from a previous study (Moore et
 al., 2019) did not alter the qualitative outcomes of our analyses and
 conclusions (see SOM for comparisons). Organisms were housed in climate
 control chambers (Percival Scientific 36VL) under 14L/10D hour light
 cycle. Fluctuating treatments ramped continuously between 2-hour soaks at
 the high and low temperatures. Humidity was not monitored, but an open
 container of water was placed in each chamber to prevent desiccation of
 organisms or artificial diet.  <i>Manduca sexta</i>
 eggs were collected from the UNC colony, maintained at 25°C for 3 days,
 and then placed on artificial diet. Eggs were placed into one of 3
 constant temperatures (25°C, 28°C, 30°C) and checked every 24 hours for
 hatching. Newly hatched 1<sup>st</sup> instars were
 transferred to new dishes with fresh diet, and either divided into
 fluctuation treatments (at 25°C and 28°C) or returned to the constant
 temperature (30°C). To avoid high hatching mortality at high and
 fluctuating temperatures, larvae at 30°C were kept at a constant
 temperature until the molt to the 3<sup>rd</sup> instar. At
 molt to 3<sup>rd</sup>, caterpillars entered the experiment,
 were given a unique ID number, and weighed. On day 0 of the
 3<sup>rd</sup> instar, caterpillars were divided into
 parasitized or unparasitized control treatments. After allowing the
 <i>M. sexta</i> to acclimate to room temperature, caterpillars
 were parasitized by exposing them to adult wasps. After successful
 oviposition was observed (oviposition lasting &gt;2-3 seconds),
 caterpillars were removed from the wasp enclosure. The number of
 ovipositions for each caterpillar was recorded. After molting to the
 3<sup>rd</sup> instar, <i>M. sexta</i> were housed
 individually in petri dishes. Containers were checked every 24 hours for
 molting, and food was provided <i>ad libitum</i>.
 <i>Manduca sexta</i> mass and development time were tracked at
 each instar until wandering (unparasitized controls), wasp emergence
 (parasitized), or until 3 weeks past the molt to the
 5<sup>th</sup> instar (parasitized without wasp
 emergence—WOWE; see below). At wandering, control caterpillars were
 weighed and euthanized. A small number of parasitized individuals
 displayed wandering behavior (see SOM); these were assumed to be the
 result of failed ovipositions and were excluded from analyses. At wasp
 emergence, parasitized caterpillars and wasp larvae were transferred to a
 clean petri dish and left undisturbed for 48 hours. At this time the total
 number of emerged wasp larvae was recorded, as well as the number of
 larvae that succeeded or failed to form cocoons. Caterpillar mass was also
 recorded at this time. Cocoons were transferred to a small plastic cup and
 returned to the climate chamber until adult eclosion. The hosts were
 frozen for later dissection to determine total parasitoid load. Cocoons
 were monitored daily until eclosion. Twenty-four hours after eclosion,
 wasps were frozen and the number of eclosed adults was counted
 Some hosts (specifically in
 the 30°C±10°C treatment) failed to exhibit wasp emergence. These hosts
 without wasp emergence (WOWE) were fed as usual, weighed weekly, and
 monitored daily for signs of wandering, illness (discoloration, flaccid
 cuticle), or death. At the 3<sup>rd</sup> week after the molt
 to 5<sup>th</sup> instar, WOWE hosts were weighed a final
 time, culled, and a subset was frozen for future dissection. A small
 subset of individuals (n = 8) exhibited wandering behavior, but none
 successfully pupated. Total parasitoid load was
 determined by dissection in hosts with wasp emergence. Dissecting scissors
 were used to cut the dorsal cuticle longitudinally along the body. The
 cuticle was pinned to the side and the gut removed. Wasp larvae were
 removed from host hemocoel and tissues, counted and recorded. The number
 of unemerged wasp larvae was added to the number that emerged to compute
 total parasitoid load. Individuals with total load &gt; 300 were
 excluded from analyses (n = 1).  
 The data has been processed to convert dates to Julian day, dead
 individuals have been removed, erroneous values have been removed, and
 various metrics of development time and survival have been
 calculated.
description: This data does contain missing values (coded as NA). Some missing
 values are context dependent (unparasitized caterpillars will have NA in
 parasitoid load columns). ReadMe files are available for data and are
 upoloaded here.