Water Deficit Stress - Host Plant Nutrient Accumulations and Associations with Phytophagous Arthropods - Abiotic Stress: Plant Responses and Applications in Agriculture - page 388

Although severe water deficit stress that causes plant mortality usually renders plants useless
to herbivores, chronic lower level or pulsed water deficit stress can enhance the nutritional val‐
ue of plants to arthropods, resulting in selection preference, heightened populations, intensi‐
fied injury to crops, and even outbreaks that affect production on area-wide scales.
Twospotted spider mite, Tetranychus urticae Koch, populations, for example, increase on
drought stressed soybeans, Glycine max (L.) Merrill (Klubertanz et al., 1990) and populations of
the Russian wheat aphid, Diuraphis noxia (Morvilko), increased in nonirrigated wheat, Triti‐
cum aestivum L., fields as compared with fields that received irrigation (Archer et al., 1995). The
cabbage aphid, Brevicoryne brassicae L., infested water deficit stressed rape, Brassica napus L.,
more heavily than nonstressed plants (Burgess et al., 1994; Popov et al., 2006), and greenbug,
Schizaphis graminum (Rondani), densities were higher and more injurious to wheat stressed by
drought (Dorschner et al., 1986). Water deficit stressed host plants are also known to favor the
xerophilic maize leaf weevil, Tanymecus dilaticollis Gyllenhall (Popov et al., 2006); scolytid bark
beetles infesting trees (Lorio et al., 1995); flea beetles on corn, Zea mays L. (Bailey, 2000); and the
fall armyworm, Spodoptera frugiperda (J. E. Smith), on tall fescue, Festuca arundinacea Schreb.
(Bultman & Bell, 2003). Under circumstances where water deficit is beneficial to arthropod
pests, population growth generally results in further damage to crops that have already been
injured or stunted by water deficit stress itself.
Water deficit stress in plants can affect the amounts and composition of volatile compounds,
and the concentrations of several kinds of nutrients beneficial to arthropod pests. Its associa‐
tions with free amino acids and carbohydrates are chiefly described in this chapter because
those two kinds of nutrients have been researched to an appreciable extent, permitting some
conclusions to be drawn about arthropod host plant selection and levels of infestation.
2. Water deficit, host plant nutrient accumulation, and associations with
phytophagous arthropods
Water deficit stress alters plant metabolism and biochemistry (Hsiao, 1973; Beck et al., 2007),
and consequent changes to plant physiological processes have been reported as being fac‐
tors affecting herbivorous arthropod host plant preferences, growth, and development
(Mattson & Haack, 1987; Showler, 2012). Although soil dries in association with drought,
evapotranspiration rates in affected plants are often maintained (Jordan & Ritchie, 1971) by
elevated accumulations of free amino acids, especially proline, and other organic solutes
(Janagouar et al., 1983). Osmotic stress in plants involves several interlinked molecular path‐
ways that transmit signals and produce stress-responsive metabolites (Ingram & Bartels,
1996; Zhu, 2002), and gene transcripts associated with signaling can be up- or down-regulat‐
ed minutes after stress induction (Seki et al., 2001; Showler et al., 2007). Water deficit
stressed plants often have diminished osmotic potential (Labanauskas et al., 1981; Golan-
Goldhirsch et al., 1989; Bussis & Heineke, 1998), heightened oxidative stress (Becana et al.,
1998; Knight & Knight, 2001), and accumulations of osmolytes such as antioxidants, amino
acids, carbohydrates, and inorganic ions, altering the attractiveness and nutritional value of
the plant (Jones, 1991; Showler & Castro, 2010a). Reduced leaf water content relative to dry