Water Deficit Stress - Host Plant Nutrient Accumulations and Associations with Phytophagous Arthropods - Abiotic Stress: Plant Responses and Applications in Agriculture - page 397

In addition to water deficit stress associations with Mexican rice borer preferences for physi‐
cal ( i.e. , dry, curled leaf tissue) and nutritional factors ( i.e. , amino acids and possibly sugar
accumulations), water availability has a strong influence on abundances of a voracious pred‐
ator, the red imported fire ant, Solenopsis invicta Buren, which has already been shown to be
an efficient predator of the stalk boring moth, D. saccharalis , in Louisiana (Showler, 2012;
Showler & Reagan, 2012). Originally from wet habitats of South America, the red imported
fire ant entered the United States in 1929 and it spread throughout much of the wet southern
states (Lofgren, 1986). To provide another example of the predator's effectiveness against in‐
sect pests, red imported fire ant foraging activity accounts for 58% of boll weevil mortality
along the relatively wet coastal cotton-growing region of Texas (Sturm & Sterling, 1990), and
red imported fire ant predation on immature boll weevils averaged 84% compared with
0.14% and 6.9% mortality caused by parasitism and desiccation, respectively (Fillman &
Sterling, 1983). In the drier subtropics of south Texas, however, even in cotton with rank
weed growth commonly associated with thriving red imported fire ant populations in wet‐
ter regions (Showler et al., 1989; Showler & Reagan, 1991), few or no red imported fire ants
were found and boll weevil infestations were not affected by predation (Showler & Green‐
berg, 2003). While sugarcane in relatively dry regions, such as south Texas, is not protected
by red imported fire ants, it is possible that the predator's greater abundance in the more
moist sugarcane growing conditions of Louisiana will suppress Mexican rice borer popula‐
tions (Showler & Reagan, 2012) despite its cryptic larval behavior.
6. Conclusion
Water deficit might initially appear to affect herbivorous arthropod populations because of
a single factor, but the associations of the Mexican rice borer with water indicate a more
complex relationship that can involve physical, biochemical, and ecological factors. Levels of
Mexican rice borer infestation are likely influenced by low water availability in at least three
ways, only one of which is directly related to the nutritional status of the crop. Drought
changes many environmental conditions relative to arthropods, such as soil condition, leaf
size and color, lignification of plant cell walls, secondary protective compounds, and natural
enemy activity, but accumulations of nutrients, particularly free amino acids and carbohy‐
drates, unlike the other drought-related conditions, directly result from water deficit stress
to the plant. This plant stress response to water deficit influences levels of pest infestations
by causing the plant emit volatile semiochemicals and by enhancing the nutritional quality
of the plant. Water deficit can also make it difficult for some plant sucking insects ( e.g. ,
aphids) to attain water and nutrients, and soft-bodied lepidopteran larvae living on surfaces
of water deficit stressed plants ingest insufficient amounts of water to sustain themselves
against desiccation despite compensating by consuming greater quantities of plant tissue.
While non-nutritional factors are often important under conditions of water deficit, the nu‐
tritional status of the plant to herbivorous arthropods is directly modulated by water deficit
stress, and host plant nutritional quality is arguably the most fundamental component of
plant-herbivore interactions.