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J Exp Biol

Title:		"Energetic costs of detoxification systems in herbivores feeding on chemically defended host plants: a correlational study in the grain aphid, Sitobion avenae"
Author(s):		Castaneda LE; Figueroa CC; Fuentes-Contreras E; Niemeyer HM; Nespolo RF;
Address:		"Instituto de Ecologia y Evolucion, Facultad de Ciencias, Universidad Austral de Chile, Casilla 567, Valdivia, Chile. lecastane@gmail.com"
Journal Title:		J Exp Biol
Year:		2009
Volume:		212
Issue:		Pt 8
Page Number:		1185 - 1190
DOI:		10.1242/jeb.020990
ISSN/ISBN:		0022-0949 (Print) 0022-0949 (Linking)
Abstract:		"Herbivorous insects have developed mechanisms to cope with plant barriers, including enzymatic systems to detoxify plant allelochemicals. Detoxification systems may be induced when insects are feeding on plants with increasing levels of allelochemicals. Increases in enzymatic activity have been related to energetic costs, and therefore less energy may be allocated to fitness-related traits. In this study, we explored the induction and energetic costs of detoxifying hydroxamic acids (Hx; a wheat allelochemical) in the grain aphid, Sitobion avenae. Aphids were reared on three wheat cultivars with different levels of Hx (0.26+/-0.08, 2.09+/-0.6 and 5.91+/-1.18 mmol kg(-1) fresh mass). We performed a nested ANOVA to test the effect of Hx (main factor) and intrahost variation (nested factor) on body mass, standard metabolic rate (SMR) and the enzymatic activity of cytochrome P450s monooxygenases (P450s), glutathione S-transferases (GSTs) and esterases (ESTs). We found non-significant effects of Hx levels (P>0.5 for all tests), but there was significant intrahost variation (P<0.05 for all tests). In addition, we found a negative correlation between SMR and ESTs (P=0.003) and no correlation between SMR and GSTs or P450s (P=n.s after a Bonferroni correction). Multiple regression between SMR (dependent variable) and enzymatic activities (predictor variables) was significant (P=0.007), but detoxification enzymes only explained about 5% of the variation of SMR. Finally, we found a non-significant path coefficient between ;metabolism' and ;detoxifying capacity' (P>0.05). These results suggest that increased enzymatic activities do not entail increased metabolic rate. Therefore, low energetic costs in aphids would facilitate the use of different hosts and promote a wider ecological niche"
Keywords:		Animals Aphids/*metabolism Cytochrome P-450 Enzyme System/metabolism *Energy Metabolism Esterases/metabolism Glutathione Transferase/metabolism Hydroxamic Acids/*metabolism Insect Proteins/metabolism Pheromones/*metabolism Regression Analysis Species Spec;
Notes:		"MedlineCastaneda, Luis E Figueroa, Christian C Fuentes-Contreras, Eduardo Niemeyer, Hermann M Nespolo, Roberto F eng Research Support, Non-U.S. Gov't England 2009/03/31 J Exp Biol. 2009 Apr; 212(Pt 8):1185-90. doi: 10.1242/jeb.020990"