DOI: 10.5061/dryad.5qfttdz2c
title: Data from: Insect oviposition preference between Epichloë-symbiotic and -free grasses does not necessarily reflect larval performance

description: Variation in plant communities is likely to modulate the feeding and
 oviposition behavior of herbivorous insects, and plant associated microbes
 are largely ignored in this context. Here we take into account that
 insects feeding on grasses commonly encounter systemic and vertically
 transmitted (via seeds) fungal Epichloë endophytes, which are regarded as
 defensive grass mutualists. Defensive mutualism is primarily attributable
 to alkaloids of fungal origin. To study the effects of Epichloë on insect
 behavior and performance, we selected wild tall fescue (Festuca
 arundinacea) and red fescue (Festuca rubra) as grass-endophyte models. The
 plants used either harbored the systemic endophyte (E+) or were
 endophyte-free (E-). As a model herbivore, we selected the Coenonympha
 hero butterfly feeding on grasses as larvae. We examined both oviposition
 and feeding preferences of the herbivore as well as larval performance in
 relation to the presence of Epichloë endophytes in the plants. Our
 findings did not clearly support the female’s oviposition preference to
 reflect the performance of her offspring. First, the preference responses
 depended greatly on the grass-endophyte symbiotum. In F. arundinacea, C.
 hero females preferred E+ individuals in oviposition choice tests, whereas
 in F. rubra, the endophytes may decrease exploitation, as both C. hero
 adults and larvae preferred E- grasses. Second, the endophytes had no
 effect on larval performance. Overall, F. arundinacea was an inferior host
 for C. hero larvae. However, the attraction of C. hero females to E+ may
 not be maladaptive if these plants constitute a favorable oviposition
 substrate for reasons other than the plants’ nutritional quality. For
 example, rougher surface of E+ plant may physically facilitate the
 attachment of eggs, or the plants afford greater protection from natural
 enemies. Our results highlight the importance to consider the preference
 of herbivorous insects in studies involving the endophyte-symbiotic
 grasses as host plants.
description: We
 collected seeds from four E+ and four E- free-pollinated mother plants of
 red fescue (Festuca rubra) and tall fescue (Festuca arundinacea). As
 fescues were both wind- and cross-pollinated, we assumed that the
 offspring of an individual mother plant were half-siblings. Thus, this
 data set is based on four half-sibling groups in both E+ and E- plants of
 both species. The minimum of three pots (8 cm x 8 cm in size; each with
 more than five individuals) of each half-sibling group (50 pots in total,
 later referred to as “plants”) were grown in greenhouse conditions (stable
 ~15 °C; ambient light;
 potting soil: Biolan for saplings; fertilizer: 1 dl of Biopon
 Rose every other week according to instructions) at Ruissalo
 Botanical Garden for two months before they were transferred to growth
 chambers [16 h: ~22 °C,
 light; 8 h: ~16 °C, dark] at the University of Tartu,
 Estonia. All plants were cut to a height of 5 cm 2 weeks before the first
 experiments to induce tillering so as to obtain more plant
 material. The adult
 female insects used were caught from the wild in Estonia in the beginning
 of June 2016. When they were not used in the experiments, the
 wild-captured females were kept individually in small jars in a
 refrigerator. Food (sugar solution) for them was always present on tissue
 in the jars. The larvae in the feeding experiments were first-generation,
 laboratory-born offspring of the wild females used in the oviposition
 experiments. The eggs were kept in small jars and the newly-hatched larvae
 were not fed before the experiments so as to avoid biasing their
 preference for the food given beforehand. Oviposition-choice
 test To examine the
 oviposition preference of the <i>C. hero</i> females relative
 to the presence of endophytes, we conducted trials that introduced the
 butterflies individually to terrarium boxes (35 cm x 25 cm x 20cm) that
 gave them the choice between E+ and E- <i>F. arundinacea</i>
 or <i>F. rubra </i>plants. The pots with plants were placed
 under the terraria, and the above-ground parts of the potted E+ and E-
 plants were inserted in opposite corners of the terrarium through holes
 made in the bottom of the box. Both plants inside the same terrarium were
 approximately equal in biomass and similar in appearance. We investigated
 all possible combinations of E+ and E- half-sibling plant groups. During
 the experiment, some of the plant individuals were used twice with
 different counterparts making all the plant combinations unique. The
 positions of the E- and the E+ plants were alternated in the terraria, and
 an adjustable table lamp was put above each to provide the females with
 light and warmth (about 27 °C inside the terraria). The light was on daily
 from approximately 8 a.m. to 8 p.m. One female at a time was kept in a
 terrarium with the E- and E+ plants until it had laid several (&gt; 5)
 eggs on the plants. A different female was used in each trial. After the
 end of the experiment, we recorded the number of eggs attached to each
 plant. We examined the behavior of at least five females from the four
 insect populations on both plant species. Oviposition-rate
 test To determine
 the attractiveness of the E- and E+ plants as oviposition substrates, we
 conducted trials to measure the oviposition rate of the <i>C.
 hero</i> females exposed to a single plant, either E- or E+, for a
 fixed amount of time (single-substrate design). We assumed that the
 oviposition rate indirectly reflects the host’s quality, because the
 female should save her eggs if there is no preferred plant available. In
 contrast, the oviposition rate should be high if an ideal plant is
 present. The number of eggs laid in a fixed period provided an
 approximation of both the plant’s suitability for oviposition and the
 preference of the female. The experiment
 was conducted in growth chambers [17 h: ~27 °C, light; 7 h: ~20 °C,
 dark]. The adult females were placed in transparent plastic
 boxes (1.5 liters) into which the shoots of  potted E+ or E- plants of
 <i>F. arundinacea</i> or <i>F. rubra</i> had been
 inserted through a hole in the bottom. Small holes in the lids let excess
 humidity evaporate from the box. After 21 hours, the females were removed
 from the experimental arena, and the eggs they had laid were counted. Each
 female was used in this experiment up to four times if her condition
 allowed it. Each was exposed to all four plant types (two species with
 both E+ and E- individuals), and the first and second plants were of the
 same species before the plant species was switched. The starting plant
 type was randomly chosen for each female to take into account the possible
 effect of previous experience on oviposition decisions. Food-plant preference
 test To examine
 larval food preference, we conducted trials that enabled the mobile,
 newly-hatched <i>C. hero</i> larvae to choose between E- and
 E+ plants. The leaves of living, potted E+ and E- plants were inserted
 from opposite directions between the lid of a Petri dish, and a single
 larva was placed in the center of the Petri dish . After 18 h, the
 experiment was terminated, and the leaves were examined for signs of
 larval consumption (missing leaf parts). Larval-growth and survival
 test To compare the quality
 of the E- and E+ plants for larvae, we conducted a no-choice rearing
 experiment that mimicked the situation in which the larvae have no
 possibility of switching to another plant after hatching. We measured the
 growth and survival of the larvae that were feeding on either the E- or E+
 plants of <i>F. rubra</i> or <i>F.
 arundinacea</i> in a growth chamber. The leaves of a potted, living
 plant were placed so as to grow through the mesh tubes (12 cm x 10 cm) in
 which the larvae were reared. The amount of plant material enclosed in the
 tubes was more than sufficient to support all the larvae. These mesh tubes
 were closable at each end and had a wooden ring in the middle that kept
 the tube from collapsing. Each mesh tube contained five newly-hatched and
 active larvae from the same population. After two weeks, the living larvae
 were weighed using a precision balance, and the weight was used as an
 index of individual performance. Any larvae missing from the mesh tubes
 were counted as having died.
description: There were four plant types <em>F. rubra</em> E+,
 <em>F. rubra</em> E-, <em>F. arundinacea</em> E+
 and <em>F. arundinacea</em> E-. E+ stands for
 endophyte-symbiotic and E- is endophyte-free. Numbers
 like 2_7 or 38_10 are just plant codes. Plants with same plant code are at
 least half siblings. "d" in mass means dead
 (not weighted).