DOI: 10.5061/dryad.fttdz0912
title: Indirect effect of earthworms on wheat-aphid interactions

description: The aboveground and belowground compartments of terrestrial ecosystems,
 which are generally separated in interaction studies, are nevertheless
 linked by their dependence on the same plant. Soil organisms can influence
 interactions between plants and above-ground herbivores by changes in
 plant growth and chemistry. In the present study, under controlled
 conditions the direct influence of earthworms and aphids on wheat traits
 (biomass; C and N content) was investigated. The effect of earthworms on
 aphid reproduction was also investigated, in order to demonstrate the
 indirect plant-trait-mediated effects. The results showed a significant
 effect of both above and below-ground organisms on plant traits. Indeed,
 wheat biomass and carbon and nitrogen contents were influenced by the
 presence of earthworms and aphids, suggesting that earthworms can promote
 aboveground and belowground plant growth by promoting resource
 acquisition. Interestingly, the nitrogen content was significantly higher
 in the presence of aphids or earthworms alone and it was even higher when
 the two organisms were present together. Moreover, the results showed a
 strong effect of earthworms on aphids, with a reproduction rate almost
 twice as high as in the absence of earthworms. These results could have
 implications for crop management, as they indicate that the presence of
 earthworms compensate the negative effect of aphids on plant biomass,
 probably by acting on nutrient uptake and plant defensive traits, despite
 a higher aphid reproduction rate in the presence of earthworms probably
 linked to nitrogen content. By addressing the effects of earthworms on
 both the pest performances and plant traits, this study highlights the
 need for further research on the indirect effects of below-ground
 compartments on pest performance. This study builds towards a better
 understanding of the interaction between soil, plant and herbivores and
 highlights the importance to study the pest management with a more
 holistic view of agroecosystems.
description: A factorial greenhouse experiment was performed using wheat under
 four conditions: absence/presence of earthworms, and absence/presence of
 aphids. A total of 60 pots (4x15 pots, height = 21.8 cm; diameter = 18.7
 cm) was filled with soil. The study soil was a Haplic Luvisol and was
 sampled in an agricultural field. After being air-dried, the soil was
 sieved at 4 mm. Gauze was attached at the bottom of each pot to prevent
 earthworms from escaping. On 3 March 2023, five untreated wheat seeds,
 <em>Triticum aestivum L</em>. (Fructidor variety) were
 planted. Plants were watered twice a week and kept in a greenhouse with
 ambient temperature (an average of 12 °C at night and 25 °C by day, for 61
 days), humidity, and light. Once the seeds had germinated and reached the
 early tillering stage, the plants were thinned to two plants per
 pot. On 4 April 2023, aphids and earthworms were
 inoculated. Fifteen pots were prepared for each treatment: 15 pots without
 earthworms nor aphids; 15 pots with aphids but without earthworms; 15 pots
 with earthworms but without aphids; 15 pots with both earthworms and
 aphids. Each pot was randomly distributed in the greenhouse. Replication
 statement is summarised in Table 1. Two or three <em>Lumbricus
 terrestris L</em>. (Lumbricidae) (corresponding to a biomass of
 10 g) were placed in each of the 15 aphid-free pots and the 15 pots with
 aphids. Similar earthworm densities have been reported for agroecosystems,
 though with considerable variation (Dulaurent et al. 2023). Earthworms
 were purchased at Decathlon® (Live fishing bait, Canadian worms). Six
 aphids of the species <em>Sitobion avenae Fabricius
 </em>(Aphididae), were placed on the plant leaves using a brush, in
 each of the 15 earthworms-free pots and the 15 pots with earthworms.
 Aphids reared on wheat were provided by Crisop society (Koppert
 Ervibank®). Nylon bags (100×50 cm) with 0.05×0.05 cm mesh (Kweekzak
 100×50 cm from Vermandel Entomologie Speciaalzaak) were used to contain
 the aphids in the pots. To homogenize the experiment, nylon bags were
 placed around all the pots, with and without aphids, and all the pots were
 regularly randomly moved around the greenhouse. At the
 end of the experiment (2 May 2023), all the wheat was harvested, and the
 roots separated from the shoots. All shoot samples were left for 48 hours
 at 8 °C to facilitate aphid counting to estimate a simplified reproduction
 rate (corresponding to the final number of aphids over the total number of
 days, 28 days). Shoots and roots were dried for 48 h at 50 °C directly
 after aphid counting; weighted to obtain dry biomass; and finally, ground
 to fine powder before further chemical analyses. Shoot and root C and N
 contents were quantified with a gas chromatography in an automatic
 elemental analyser (FlashSmartTM; Thermo Fisher Scientific) using
 approximately 0.0060 g of dried powder.
description: # Indirect effect of earthworms on wheat-aphid interactions | Column  |
 Description | | :-------------- |
 :------------------------------------------------------------------------------------ | | Nb\_Pot | Number of pot | | Mod | Treatments: V: Presence of earthworms; P: Presence of aphids; T: Control (wheat only) | | ID | Pot ID: Treatment + pot number | | Nb\_Ver\_i | Number of earthworms in pot at the beginning of experiment | | Nb\_Ver\_f | Number of earthworms in pot at the end of experiment | | Biom\_Ver\_i | Initial biomass of earthworms (g) | | Biom\_Ver\_f | Final biomass of earthworms (g) | | Galerie | Presence (O) absence (N) of earthworm gallery | | Biom\_Rac\_Fr | Fresh root biomass (g) | | Biom\_Rac\_Sec | Dry root biomass (g) | | Biom\_Feui\_Fr | Fresh shoot biomass (g) | | Biom\_Feui\_Sec | Dry shoot biomass (g) | | N\_Rac | Nitrogen root content (%) | | C\_Rac | Carbon root content (%) | | C\_N\_Rac | Root C/N ratio | | N\_Feui | Nitrogen shoot content (%) | | C\_Feui | Carbon shoot content (%) | | C\_N\_Feui | Shoot C/N ratio | | Nb\_puceron | Number of aphids at the end of the experiment (at the beginning, n = 6) | | If NA | Missing values correspond to missing measurements | | :---- | :------------------------------------------------ |