DOI: 10.5061/dryad.8kprr4xn4
title: Data from: Developmental timing of extreme temperature events (heat waves) disrupts host-parasitoid interactions

description: 1. When thermal tolerances differ between interacting species, extreme
 temperature events (heat waves) will alter the ecological outcomes. The
 parasitoid wasp Cotesia congregata suffers high mortality when reared
 throughout development at temperatures that are non-stressful for its
 host, Manduca sexta. However, the effects of short-term heat stress during
 parasitoid development are unknown in this host-parasitoid system. 2.
 Here, we investigate how duration of exposure, daily maximum temperature,
 and the developmental timing of heat waves impact the performance of C.
 congregata and its host¸ M. sexta. We find that the developmental timing
 of short-term heat waves strongly determines parasitoid and host outcomes.
 3. Heat waves during parasitoid embryonic development resulted in complete
 wasp mortality and the production of giant, long-lived hosts. Heat waves
 during the 1st-instar had little effect on wasp success, whereas heat
 waves during the parasitoid’s nutritionally and hormonally critical 2nd
 instar greatly reduced wasp emergence and eclosion. The temperature and
 duration of heatwaves experienced early in development determined what
 proportion of hosts had complete parasitoid mortality and abnormal
 phenotypes. 4. Our results suggest that the timing of extreme temperature
 events will be crucial to determining the ecological impacts on this
 host-parasitoid system. Discrepancies in thermal tolerance
 between interacting species and across development will have important
 ramifications on ecosystem responses to climate change.
description: The current study consisted of two
 experiments: one determining how parasitoid sensitivity to heat shock
 varies across ontogeny (developmental timing experiment), and the other
 investigating the effects of heat shock temperature and number of heat
 shock exposures on <i>C. congregata </i>survival and
 development early in parasitization (temperature/duration experiment). The
 rearing treatment was the same for both experiments (25°C±10°C), and has
 been determined to be non-stressful for both parasitoid and host (Moore et
 al., 2021). The temperature/duration experiment was conducted in
 January—April, 2018, and the developmental timing experiment took place in
 October—December, 2018. Organisms were housed in climate control chambers
 (Percival Scientific 36VL) under 14L/10D hour light cycle. An open
 container of water was placed in each chamber to prevent desiccation of
 organisms or artificial diet (Moore et al., 2020). Newly hatched
 caterpillars<i> </i>were reared on an artificial diet in
 communal petri dishes until the molt to the 3<sup>rd</sup>
 instar. On the day of the molt to 3<sup>rd</sup> instar (day
 0), caterpillars were assigned a unique ID, allocated to a heat shock
 treatment, weighed, parasitized, and housed individually in small petri
 dishes. Caterpillars were parasitized by exposing individual caterpillars
 to a colony of adult wasps, and observing until an oviposition event of 
 &gt;2-3 seconds occurred.    The
 development timing experiment consisted of three heat shock treatments and
 one control. The heat shock regime was the same for all treatments: three
 days at 31°C±11°C (daily maximum of 42°C). Recent work has shown that a
 single exposure to this heat wave regime does not reduce survival,
 development time or pupal mass of unparasitized <i>M.
 sexta</i> regardless of developmental stage (Kingsolver et al.,
 2021). The treatments differed in the developmental stage of the
 parasitoid larvae at which they experienced the heat shock temperatures
 (recall that caterpillars in all treatments were parasitized).
 <b>Early</b> Heat Shock started on day 0 of the
 3<sup>rd</sup> instar, the same day as oviposition; the
 <b>Middle </b>Heat Shock treatment started 5 days after
 oviposition (when the majority of <i>C. congregata</i> eggs
 have hatched); the <b>Late</b> Heat Shock started on day 1 of
 the host 5<sup>th</sup> instar (when the majority of
 <i>C. congregata</i> larvae have molted to the
 2<sup>nd</sup> instar), which ranged from 8-12 days after
 oviposition. Sample sizes for each treatment ranged from 30-60 parasitized
 <i>M. sexta </i>caterpillars (see SOM). Individuals in heat
 shock treatments were transferred to the heat shock chamber at least 2
 hours before the DMT, and were removed at 4-5pm on the last day of the
 heat shock treatment. Parasitized hosts in the control treatment remained
 in the rearing temperature throughout development. The
 temperature/duration experiment consisted of a 2x4 factorial design plus
 one control treatment for a total of 9 treatment combinations. All
 <i>M. sexta </i>caterpillars were parasitized for this
 experiment. Parasitized <i>M. sexta</i> were exposed to one of
 two fluctuating heat shock temperatures, one with a daily maximum
 temperature of 40°C (30°C±10°C) and the other with a DMT of 42°C
 (31°C±11°C). Both temperature treatments ramped continuously between
 2-hour periods at the high and low temperatures in a 24-hour cycle.
 Parasitized <i>M. sexta </i>were placed in a heat shock
 treatment on the same day as oviposition, at least 2 hours before the
 daily maximum temperature. Experimental insects remained in the heat shock
 treatments for 1, 2, 3, or 4 days (i.e. they experienced the DMT 1-4
 times). Caterpillars were removed from the heat shock treatment at 4 pm –
 5pm on the day of their last heat shock, and then returned to the
 25°C±10°C rearing treatment. Parasitized hosts in the control treatment
 remained in the rearing temperature throughout development.  
 The data has been cleaned to remove
 most erroneous values, though some data cleaning is also required in the R
 scripts provided. Dates have been converted to Julian day, and life
 history metrics have been calculated.