Effects of host plant drought stress on the performance of the bird cherry‐oat aphid, Rhopalosiphum padi (L.): a mechanistic analysis

Abstract

1. The growth (increase in height and leaf number) of four grass species was reduced by a À0.5 MPa drought stress, but the performance of an associated herbivore, Rhopalosiphum padi (L.), was not affected consistently. The intrinsic rate of increase of R. padi was reduced by drought stress on three grass species, including Dactylis glomerata (L.), but was unaffected on Arrhenatherum elatius (L.). Therefore, there is no general relationship in the effect of plant drought on an insect herbivore, even among closely related host plant species.2. Drought stress increased the quality of plant phloem sap, as indicated by increased sieve element osmotic pressure and essential amino acid concentrations. Thus, diet quality could not account for the reduced performance of R. padi under drought stress. The concentration of essential amino acids in the phloem of wellwatered A. elatius was, however, lower than that of well-watered D. glomerata, correlating with the decreased performance of aphids on well-watered A. elatius.3. There were no differences in aphid feeding duration between watering treatments or plant species but sap ingestion rates were reduced significantly under drought stress.4. Using the measure of dietary amino acid concentrations and the estimate of sap ingestion, the essential amino acid flux through aphids was calculated. Compared with the flux through aphids feeding on well-watered D. glomerata, there was a reduction in aphids feeding on drought-stressed D. glomerata and droughtstressed A. elatius due to lower sap ingestion rates. The flux through aphids on well-watered A. elatius was also reduced due to low phloem essential amino acid concentrations. Thus, the performance of an aphid is correlated with the availability and accessibility of essential amino acids.

A Diurnal Component to the Variation in Sieve Tube Amino Acid Content in Wheat

“…In this study, the average ST sap total amino acid concentration was 460 mM, with a range of 134 to 1,047 mM. These values tend to be higher than previously published figures, which ranged from just below 200 mM to over 400 mM in alfalfa (Girousse et al, 1996) and were 180 mM in barley seedlings (Ponder et al, 2000), 69 mM in Dactylis glomerata (Hale et al, 2003), 262 mM in wheat, and 125 mM in rice Chino, 1986, 1990). However, high values of up to 1,232 mM have been reported in maize (Zea mays; Faria et al, 2007).…”

“…For example, 15-to 60-nL samples were used for sugar beet (Beta vulgaris) analysis (Lohaus et al, 1994), 30-to 100-nL samples were collected by stylectomy for the Mexican sunflower (Tithonia diversifolia; Bernays and Klein, 2002), while only samples above 50 nL were used for a study of alfalfa (Medicago sativa; Girousse et al, 1996). A mean volume of 34 nL was reported in studies of oat (Avena sativa) and barley (Weibull et al, 1990), and 250 to 500 nL was used in a study of British grasses (Hale et al, 2003). Work on Arabidopsis employed sap volumes between 10 and 50 nL (Hunt et al, 2006).…”

“…Stylectomy was performed on feeding aphids using a high-frequency microcautery device (Unwin, 1978) as outlined by Ponder et al (2000) and Hale et al (2003). Stylectomy was always performed between 12 PM and 5.30 PM at 18°C to 20°C.…”

“…Limitations in the sensitivity of the HPLC technique, however, meant that analysis could only be performed where enough phloem sap was obtained. In the literature, volumes between 15 and 500 nL were used to determine directly the ST solute concentrations in various species using HPLC (Weibull et al, 1990;Lohaus et al, 1994;Girousse et al, 1996;Bernays and Klein, 2002;Hale et al, 2003), while lower collected volumes could not be analyzed directly. Since severed stylets exude at a range of rates, limitations of analytic techniques have previously restricted study to those stylets with a high exudation rate, thus producing larger sample volumes and leading to potentially unrepresentative data in the literature.…”

Stressing food plants by altering water availability affects grasshopper performance

“…Changes of precipitation regimes have been observed in the past years in climate studies (Beck et al 2001, Schonwiese et al 2003, Schmidli and Frei 2005 and have been predicted for the future by various models (Raisanen and Joelsson 2001, Christensen and Christensen 2003, Sanchez et al 2004, Semmler and Jacob 2004. In addition to direct effects on animal populations these environmental influences could as well affect the interaction of plants and their herbivores (Mattson and Haack 1987, Coviella and Trumble 1999, Hunter 2001, Bale et al 2002, Hale et al 2003, Villalpando et al 2009). …”