Water Deficit Stress - Host Plant Nutrient Accumulations and Associations with Phytophagous Arthropods - Abiotic Stress: Plant Responses and Applications in Agriculture - page 391

droughts (Mattson & Haack, 1987) because water deficit stressed trees accumulate sugar and
sugar alcohols (Price, 2002).
3. Water is a nutrient, too
Water deficit affects both the availability of water, which is a nutrient itself, to herbivores as
well as the nutritional quality of dietary biochemical components that accumulate as osmo‐
protectants or for other purposes. When herbivorous arthropods are unable to have access
to sufficient amounts of wager, their populations can decline. For example, aphid popula‐
tions are reduced under conditions of continued and severe host plant water deficit (Show‐
ler, 2012). Black bean aphid, Aphis fabae Scopali, survivorship was diminished on
continuously drought stressed sugar beet, Beta vulgaris L., leaves (Kennedy & Booth, 1959),
and reproduction and survival were negatively affected for the mustard aphid, Lipaphis ery‐
simi (Kalt.) on radish, Raphanus sativus L. (Sidhu & Kaur, 1976); the spotted alfalfa aphid,
Therioaphis maculata (Buckton), on alfalfa, Medicago sativa L. (McMurtry, 1962); the greenbug
on sorghum, Sorghum bicolor (L.) Moench (Michels & Undersander, 1986); the potato aphid,
Macrosiphum euphorbiae (Thomas), on potato, Solanum tuberosum L. (Nguyen et al., 2007); the
bird oat-cherry aphid, Rhopalosiphum padi (L.), on tall fescue (Bultman & Bell, 2003); and the
eastern spruce gall adelgid, Adelges abietis (L.), on Norway spruce, Picea abies (L.) Karst.
(Bjőrkman, 2000). The most likely cause of the host plants' unsuitability for aphids under
such conditions is low turgor which reduces the ability of aphids to feed (Levitt, 1951; Wear‐
ing & Van Emden, 1967). Turgor facilitates aphid ingestion by forcing fluids out of the plant
and through the aphids' stylet lumens (Kennedy & Mittler, 1953; Maltais, 1962; Auclair,
1963: Magyarosy & Mittler, 1987; Douglas & Van Emden, 2007); turgor loss reduces or cur‐
tails feeding by aphids despite their cybarial pump. This has been reported to occur for the
black bean aphid on different plant hosts (Kennedy et al., 1958); the cotton aphid, Aphis gos‐
sypii Glover on cotton, Gossypium hirsutum L. (Komazaki, 1982); the greenbug on wheat
(Sumner et al., 1983); and the pea aphid, Acyrthosiphon pisum Harris, on alfalfa (Girousse &
Bournoville, 1994). Also, greater concentrations of host plant osmolytes and other biochemi‐
cals associated with drought stress increase sap viscosity which resists flow through the
stylets (Douglas & Van Emden, 2007), impeding ingestion despite the enriched nutritional
quality of the sap (Kennedy et al., 1958).
The greater nutritional quality of water deficit stressed plants can be offset by the condition
that causes it: insufficient water. When provided with dried, ground material from water-
deficit stressed tomato plants, Lycopersicon esculentum Mill., incorporated into a nonnutritive
diet, beet armyworm, Spodoptera exigua (Hübner), larval growth decreased (English-Loeb et
al., 1997). Cecropia moth, Hyalophora cecropia L., larvae reared on water deficit stressed wild
cherry, Prunus serotina Ehrh., leaves grew more slowly than those fed on well-watered
plants, but they, and beet armyworm larvae on water deficit stressed cotton leaves, con‐
sumed greater quantities of leaf tissue in order to gain access to more water, and possibly in
order to supplement body water with water derived from respiration (Scriber, 1977; Showler
& Moran, 2003). Under field conditions, fall armyworm; soybean looper, Pseudoplusia inclu‐