Plant‐mediated effects of drought on aphid population structure and parasitoid attack

Abstract

The effects of predicted climate change on aphid-natural enemy interactions have principally considered the effects of elevated carbon dioxide concentration and air temperature. However, increased incidence of summer droughts are also predicted in Northern Europe, which could affect aphid-plant interactions and aphid antagonists. We investigated how simulated summer drought affected the bird cherry-oat aphid, Rhopalosiphum padi L., and its natural enemy the parasitoid wasp Aphidius ervi. Drought and, to a greater extent, aphids reduced barley (Hordeum vulgare) dry mass by 33% and 39%, respectively. Drought reduced leaf and root nitrogen concentrations by 13% and 28%, respectively, but foliar amino acid concentrations and composition remained similar. Aphid numbers were unaffected by drought, but population demography changed significantly; adults constituted 41% of the population on drought-treated plants, but only 26% on those receiving ambient irrigation. Nymphs constituted 56% and 69% of the population on these plants, respectively, suggesting altered aphid development rates on drought-stressed plants. Parasitism rates were significantly lower on drought-stressed plants (9 attacks h À1 compared with 35 attacks h À1 on ambient-irrigated plants), most likely because of lower incidence of nymphs and more adults, the latter being more difficult to parasitize. Any physiological changes in individual aphids did not affect parasitoid preferences, suggesting that attacks were postponed because of drought-induced changes in aphid demography. This study demonstrates the potential for sporadic climate change events, such as summer drought, to be disruptive to herbivore-antagonist interactions.

Influence of drought on plant performance through changes in belowground tritrophic interactions

“…Interactions between soil moisture, plants, herbivores and natural enemies are expected to depend on a number of factors, including (a) the range of soil moisture levels (Aslam, Johnson, & Karley, 2013; Mahmoud et al., 2016; Schmitz & Barton, 2014), (b) the timing of changes in soil moisture relative to the development of all three trophic levels (Rosenblatt & Schmitz, 2016; Schmitz & Barton, 2014; Wade, Karley, Johnson, Hartley, & Bell, 2017) (c) the plant genotype (Stam et al., 2014), (d) the severity of herbivore attack (Soler, Bezemer, van der Putten, Vet, & Harvey, 2005) and (e) the abundance and diversity of herbivore natural enemies (Erb & Lu, 2013; Thomson, Macfadyen, & Hoffmann, 2010). Our study was conducted at low soil moisture close to the plant's wilting point, relatively low WCR infestation levels and a relatively short period between the application of EPNs and plant performance measurements.…”

Effects of maternal diet on offspring fitness in the bird cherry‐oat aphid

“…The bird cherry-oat aphid, R. padi L. (Hemiptera: Aphididae), is an important pest of wheat, Triticum aestivum L., and other cereals, and is also a major vector of the barley yellow dwarf virus, which causes significant yield losses to wheat crops throughout the world (Kieckhefer & Kantack, 1988;Leather et al, 1989;Razmjou et al, 2012;Aslam et al, 2013). R. padi is a host-alternating oligophagous aphid species, feeding on rosaceous hosts in winter and graminaceous hosts in summer.…”

Prey-Mediated Effects of Drought on the Consumption Rates of Coccinellid Predators of Elatobium abietinum

“…Host-induced changes to insect herbivore quality, often through changes to plant secondary metabolites, have been shown to mediate the tritrophic interaction [24,25,26], with changes to consumption rates and functional responses also observed in response to host plant quality [27,28,29]. Furthermore, by altering insect herbivore performance and survival, drought stress can result in changes to prey population demography, which can, in turn, alter predation/parasitisation rates due to prey/host suitability [30,31]. …”