Water Deficit Stress - Host Plant Nutrient Accumulations and Associations with Phytophagous Arthropods - Abiotic Stress: Plant Responses and Applications in Agriculture - page 389

biomass in water deficit stressed plants, in combination with the increased quantities of nu‐
tritional metabolites (White, 1984; Dubey, 1999; Ramanulu et al., 1999; Garg et al., 2001), may
contribute toward the increased nutritional value of plants per unit of surface area con‐
sumed by arthropods. It is likely that arthropods can perceive cues about host plant suitabil‐
ity from emission of plant volatile compounds, or semiochemicals.
Chemical cues from plants play a major, perhaps decisive, role in host plant selection and
utilization by herbivorous arthropods (Schur & Holdaway, 1970; Fenemore, 1980; Waladde,
1983; Burton & Schuster, 1981; Ramaswamy, 1988; Salama et al., 1984; Udayagiri & Mason,
1995). Water deficit stress in plants alters plant metabolism which can affect quantities and
combinations of volatile compounds (Apelbaum & Yang, 1981; Hansen & Hitz, 1982; Zhang
& Kirkham, 1990). Apple trees, Malus domestica Borkh., for instance, emit 29 volatile com‐
pounds, some of them in elevated amounts during water deficit stress (Ebel et al., 1995).
Many phytophagous arthropods appear to respond to certain blends of volatiles (Miller &
Strickler, 1984) that signal the host plant's nutritional value (Mattson & Haack, 1987; Ber‐
nays & Chapman, 1994; Showler, 2012). Increased production of volatiles ( e.g. , ethylene, ace‐
taldehyde, and ethanol) resulting from plant stress (Kimmerer & Kozlowski, 1982) can be
attractive to some herbivorous arthropods and repellent to others (Chrominsky et al., 1982;
Dunn et al., 1986; Haack & Slansky, 1987; Bernays & Chapman, 1994). Ethylene, for example,
attracts the boll weevil, Anthonomus grandis grandis Boheman (Hedin et al., 1976), and, in
many host plants it can increase susceptibility to the Egyptian cotton leafworm, Spodoptera
littoralis Boisd. (Stotz et al., 2000), but ethylene deters the fall armyworm from corn (Harfou‐
che et al., 2006) and the olive moth, Prays oleae Bern, from olive trees (Ramos et al., 2008).
Forest outbreaks of many species of scolytid bark beetles (Hodger & Lorio, 1975; Wright et
al., 1979; Vité et al., 1986; Ormeño et al., 2007; Branco et al., 2010) and the western spruce
budworm, Choristoneura occidentalis Freeman, are related to amounts and kinds of host plant
volatiles emitted during conditions of drought (Cates & Redak, 1988).
Once the phytophagous arthropod has found or selected the host plant, contact chemorecep‐
tors on many are important in the acceptance or rejection of a host plant based on the presence
or absence of stimulant ( e.g. , sugars, amino acids, vitamins) or deterrent chemicals, and mois‐
ture (Dethier, 1980; Schoonhoven, 1981; Städler, 1984; Otter, 1992; Krokos et al., 2002). Free
amino acids, for example, elicit electrophysiological responses from the sensillae of lepidopter‐
an larvae (Städler, 1984; Blaney & Simmonds, 1988). Many free essential amino acids (essential
for insect growth and development) accumulate in plant tissues during water deficit stress in
crop plants that range from cotton to sugarcane, Saccharum species, to pine trees, Pinus species
(Mattson & Haack, 1987; Showler, 2012). Amino acids were even found to be more important
determinants of corn susceptibility to neonate fall armyworms than toxins or other biochemi‐
cal factors (Hedin et al., 1990). Resistance against the sugarcane aphid, Melanaphis sacchari
(Zehnter), and the yellow sugarcane aphid, Sipha flava (Forbes), involved absence of some free
essential amino acids in resistant sugarcane varieties (Akbar et al., 2010). Free amino acids are
more available for use by herbivorous arthropods because insects absorb nitrogen through the
gut mostly as free amino acids or small peptides (Brodbeck & Strong, 1987). Hence, enhanced
foliar nutritional value as a result of water deficit is known to be an important determinant of