Water Deficit Stress - Host Plant Nutrient Accumulations and Associations with Phytophagous Arthropods - Abiotic Stress: Plant Responses and Applications in Agriculture - page 390

neonate lepidopteran performance (Mattson, 1980; English-Loeb et al., 1997; Showler, 2001,
2012; Showler & Moran, 2003; Moran & Showler, 2005; Chen et al., 2008). In terms of water def‐
icit stress, the mealybug Phenacoccus herreni Cox & Williams develops and reproduces better on
drought stressed than on well watered cassava, Manihot esculenta Crantz, in response to great‐
er concentrations and more nutritious combinations of free amino acids (Calatayud et al.,
2002). The eldana borer, Eldana saccharina Walker, a stalkborer of sugarcane in Africa, prefers
water deficit stressed host plants (Moyal, 1995), and the European corn borer, Ostrinia nubilalis
(Hübner), inflicts up to twice the injury to water deficit stressed corn than to corn under con‐
ventional irrigation (Godfrey et al., 1991). Correlations were reported between elevated free
amino acid concentrations in phloem sap of water deficit stressed wheat, Triticum aestivum L.,
and barley, Hordeum vulgare L., and population increases by the bird oat-cherry aphid (Wei‐
bull, 1987) and the cabbage aphid on Brassica spp. (Cole, 1997). Similarly, bark beetle out‐
breaks during times of drought are associated with greater concentrations of amino acids (and
soluble sugars) in host plant phloem that likely contribute toward improved scolytid perform‐
ance (Mattson & Haack, 1987).
In addition to elevated levels of free essential amino acids, free proline, a nonessential amino
acid that accumulates in most water deficit-afflicted plants, is a feeding stimulant for many
phytophagous arthropods (Mattson & Haack, 1987; Städler, 1984). Dadd (1985) reported that
a number of amino acids, particularly glycine, alanine, serine, methionine, histidine, proline,
and γ-aminobutyric acid, were phagostimulants to a number of insect species. Amino acids
that elicited the greatest response as feeding stimulants to southwestern corn borer larvae
were determined to be arginine, histidine, lysine, methionine, phenylanaline, valine (essen‐
tials), alanine, glycine, and serine (nonessentials) (Hedin et al., 1990), but not proline.
Water deficit stress has also been associated with increased concentrations of carbohydrates
(which have important roles in osmotic adjustment) in many plants (Schubert et al., 1995;
Kameli & Lösel, 1996; Massacci et al., 1996; Mohammadkhani & Heidari, 2008). Corn plants
with elevated soluble carbohydrate concentrations were preferred by the European corn
borer for oviposition (Derridj & Fiala, 1983; Derridj et al., 1986), and styloconic sensilla of
larvae and adults of three noctuid species were highly responsive to sugars, especially su‐
crose and fructose (Blaney & Simmonds, 1988). These two sugars are known to be important
feeding stimulants for both life stages (Frings & Frings, 1956; Blom, 1978), and fructose, glu‐
cose, maltose, and sucrose have been identified as phagostimulants for other insects (Ber‐
nays, 1985). Electrophysiological recordings revealed that the maxillary sensilla styloconica
of fifth instar African armyworm, Spodoptera exempta (Walker), and the lepidopteran stalk‐
borers E . saccharina , Maruca testulalis (Geyer), and Chilo partellus (Swinhoe), were stimulated
by 13 different carbohydrates (Otter, 1992). In an experiment involving fall armyworm larv‐
al feeding, sucrose elicited ≥5-fold more feeding response than fructose or glucose (Hedin et
al., 1990). Carbohydrates are well known as sources of energy for arthropods, and they are
therefore highly important as nutrients (Nation, 2002). Studies on larval rice stem borers, for
instance, showed that fructose, glucose, and sucrose are highly nutritious as compared with
other carbohydrates based on their growth and development (Ishii et al., 1959; Ishii, 1971).
Also, eastern spruce budworm, Choristoneura fumiferana Clemens, outbreaks often follow