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Native bees are important pollinators in neotropical forests. Tetragonisca angustula (Latreille) (Apidae: Meliponini) is a stingless bee widely distributed from the south of Mexico to Argentina. We characterized the patterns of preference of T. angustula for pollen in relation to the richness and abundance of plant species in the Tucumano-Boliviano Forest. During two field campaigns in different seasons (winter and spring), six colonies of T. angustula were studied. Pollen from flowers of plant species in the study area (pollen offer) and pot-pollen in each hive (pollen demand) were collected and their plant family of origin identified. Pollen from Asteraceae was more abundant in the winter than in the spring. Pollen of Solanaceae in the winter and Bignoniaceae in the spring were the most selected by the worker bees. Pollen from plants outside the sampling area was also found in the pots; it was mainly from Asteraceae. Tetragonisca angustula workers showed a polylectic foraging behavior, being able to use in a dynamic way the resources that are present in their environment at different times of the year; occasionally, it selected less abundant specific resources likely based on their nutritional value. More studies are needed to evaluate aspects of pollen quality consumed by this bee.

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Host plant recognition are highly dependent on chemosensory perception, which involves chemosensory proteins (CSPs) that bind key chemical compounds the host plants. In this work, we hypothesize that two closely related aphid taxa, which differ in diet breadth, also differ in their CSPs. We detected a non-synonymous difference (lysine for asparagine) between M. persicae sensu stricto (Mpp) and the subspecies M. p. nicotianae (Mpn) in the sequence of a CSP (CSP5). We modeled in silico the binding capacity of both CSP5s variants with 163 different potential ligands from their host plants (120 unique from tobacco, 29 unique from peach, and 14 common ligands). After docking analysis with all ligands, we selected the three best ligands for each variant to perform molecular dynamics (tobacco: 2-cyclopentene-1,4-dione, salicylaldehyde, and benzoic acid; peach: phenol, valeric acid, and benzonitrile). The binding energy of the MpnCSP5 model to the studied ligands was, in all cases, lower than with the MppCSP5 model. The ligands from the host plants showed more stable binding with MpnCSP5 than with MppCSP5. This result suggests that the set of CSPs studied among M. persicae s. str. and M. p. nicotianae are very similar, but focusing on the CSP5 protein, we found a single key mutation that increases affinities for host compounds for M. p. nicotianae, which might have contributed to the specialization to tobacco. This study provides new insights into an evolutionary trend toward specificity in a binding protein.

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Control of the Chagas disease vector, Triatoma infestans (Klug) (Hemiptera: Reduviidae) with synthetic pesticides in Bolivia has become increasingly inefficient due to the development of resistance in the insects. In the Chaco region of Bolivia, guaraní populations have approached the problem by fumigating their houses with the smoke of native plants. Through interviews and field work with local guides, the main plant used by the guaraníes was collected and later identified as Capsicum baccatumL. var. baccatum (Solanaceae). In choice bioassays, filter papers exposed to the smoke of the plant repelled nymphs of T. infestans. Activity remained significant after storing the exposed filter papers for 9 days. Chemical analysis of smoke and literature data suggested that capsaicinoids present in the smoke were responsible for the repellent effect. The data presented provide a rationale for the use of C. baccatumvar. baccatumto control the Chagas vector bythe guaraní populations.

El control del vector de la enfermedad de Chagas, Triatoma infestans (Klug) (Hemiptera: Reduviidae) con plaguicidas sintéticos en Bolivia se ha vuelto cada vez más ineficiente debido al desarrollo de resistencias en los insectos. En la región del Chaco de Bolivia, las poblaciones guaraníes han abordado el problema fumigando sus casas con el humo de las plantas nativas. A través de entrevistas y trabajo de campo con guías locales, se recogió la principal planta utilizada por los guaraníes y posteriormente se identificó como Capsicum baccatumL. var. baccatum (Solanaceae). En bioensayos selectos, los papeles de filtro expuestos al humo de la planta repelieron a las ninfas de T. infestans. La actividad siguió siendo significativa después de almacenar los papeles de filtro expuestos durante 9 días. El análisis químico del humo y los datos de la literatura sugieren que los capsaicinoides presentes en el humo eran responsables del efecto repelente. Los datos presentados proporcionan una justificación para el uso de C. baccatum var. baccatum para el control del vector Chagas por las poblaciones guaraníes.

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INTRODUCTION: Chagas disease currently affects some 6 million people around the world. At the chronic stage, cardiomyopathy occurs in about 20-30% of infested people. Most prevalence studies have focused on young to adult people due to the drastic consequences of acquiring the pathogen and the possibility to cure the disease at this age; the prevalence of this disease, the effect of patients' sex and the consequences to senescent people have been largely neglected. This study looks to characterize the seroprevalence of Chagas disease and its relation with occurrence of electrocardiographic anomalies associated with sex and age, and to compare rural and urban populations in Bolivia. METHODOLOGY: Seroprevalence of Chagas disease was determined in blood samples and electrocardiograms were performed on seropositive individuals. RESULTS: The rural population showed higher seroprevalence than the urban population (92% and 40%, respectively). The proportion of Chagasic cardiac anomalies in seropositive persons was highest in patients of the 50-59 age group (36%) as compared with the 40-49 (8%) and the ≥60 (17%) age groups. CONCLUSIONS: Higher seroprevalence in rural population was attributable to a higher probability to encounter the vector in rural areas. Increased exposure to infection and to development of the disease symptoms together with increased lethality of the disease as patients age explains the age-related Chagasic electrocardiographic anomalies. Since rural and urban populations showed different reactions under Chagas disease and the rural population was mainly of guaraní stock, the genetic and environmental determinants of the results should be further explored.

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INTRODUCCIÓN: Las desigualdades socioeconómicas y territoriales se relacionan con la salud de la población santiaguina; sin embargo, los mecanismos causales que generan las inequidades en salud no están del todo claros. En este trabajo, se cuantifica el estrés de individuos viviendo en diferentes comunas, y se lo discute como causa y consecuencia de procesos vinculados con inequidades en salud. EL OBJETIVO era relacionar el Índice de Calidad de Vida Urbana (ICVU) de la comuna de residencia de individuos en Santiago de Chile con las concentraciones de cortisol en pelo (CCP), un biomarcador de los niveles de estrés fisiológico crónico. MATERIALES Y MÉTODOS: Se exploró la relación entre CCP y la edad, el sexo y el ICVU de la comuna de residencia en 80 estudiantes de educación superior en Santiago de Chile. RESULTADOS: No se encontraron correlaciones significativas entre CCP y la edad o el sexo de los participantes. Se encontró una correlación significativa entre CCP y los valores del ICVU de la comuna de residencia, además de encontrar diferencias significativas entre CCP y los distintos rangos de ICVU (Superior, Promedio e Inferior).DISCUSIÓN: Los resultados sugieren considerar las diferencias individuales de CCP como resultado de desigualdades socio-territoriales y también como posible causa de inequidades en salud. Se recomienda incluir el rol del estrés en las políticas públicas de salud, ampliando las redes de apoyo y prevención de estrés en los sectores con bajo ICVU.

INTRODUCTION: Socioeconomic and urban inequalities are associated with health in Santiago; nonetheless, the causal mechanisms underlying health inequalities are not entirely clear. This article quantifies the stress of individuals living in different municipalities and discusses its role as cause and consequence in the generation of health inequalities. THE OBJECTIVE of this study was to determine the relationship between the Urban Quality of Life Index (UQoLI) of individuals' municipality of residence in Santiago, Chile with their hair cortisol concentrations (HCC), a biomarker of chronic physiological stress.MATERIALS AND METHODS: The relationship of HCC with age, sex and UQoLI was explored in a sample of 80 university students in Santiago, Chile. RESULTS: No significant correlations were found between HCC and age and sex. A significant correlation was found between HCC and UQoLI, and significant differences were found be-tween HCC at different levels of UQoLI (High, Average, and Low).DISCUSSION: Results suggest that HCC differences could be considered a result of urban in-equalities, as well as a possible cause of health inequalities. The role of stress should be inclu-ded in public health policies, to expand support networks and prevent stress, especially among people living in areas with low urban quality of life.

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Triatoma infestans (Klug) es el vector principal de la enfermedad de Chagas en Bolivia y los países vecinos. El objetivo de este estudio fue determinar la composición química del AE del laurel chileno, Laurelia sempervirens (Ruiz & Pav.) Tul. (Monimiaceae) y evaluar su efecto repelente en ninfas del quinto estadio de T. infestans. La AE de L. sempervirens se obtuvo por hidrodestilación y se analizó por cromatografía de gases acoplada a espectrometría de masas (CG-EM). Sus componentes principales fueron cis-isosafrol (89.8%), ß-terpineno (3.9%), trans-ocimeno (2.7%) y metileugenol (2.2%). La repelencia se evaluó en un círculo de papel de filtro dividido en dos zonas iguales que se impregnaron con sustancias de prueba [AE o N,N-dietil-3-metilbenzamida (DEET) como control positivo] y acetona como control en blanco, respectivamente. Se analizaron varias concentraciones de sustancias de prueba entre 4.125 y 132 µg/cm2. El AE de L. sempervirens produjo una repelencia significativa a concentraciones iguales o superiores a 66.0 µg/cm2, mientras que DEET repelió a partir de 16.5 µg/cm2. Futuros trabajos serán orientados al estudio de las propiedades repelentes de cis-isosafrol solo y mezclado con ß-terpineno, trans-ocimeno y metileugenol en T. infestans.

Triatoma infestans (Klug) is the principal vector of Chagas disease in Bolivia and neighboring countries. The objective of this study was to determine the chemical composition of the EO of the Chilean laurel, Laurelia sempervirens (Ruiz & Pav.) Tul. (Monimiaceae) and to evaluate its repellent effect on fifth-instar nymphs of T. infestans. The EO from L. sempervirens was obtained by hydrodistillation and analyzed by gas chromatography coupled to mass spectrometry (GC-MS). Their main components were cis-isosafrole (89.8%), ß-terpinene (3.9%), trans-ocimene (2.7%) and methyleugenol (2.2%). Repellency was evaluated on a circle of filter paper divided into two equal zones which were impregnated with test substances [EO or N,N-diethyl-3-methylbenzamide (DEET) as positive control] and acetone as blank control, respectively. Several concentrations of test substances between 4.125 and 132 µg/cm2 were tested. The EO from L. sempervirens produced significant repellency at concentrations equal or above 66.0 µg/cm2, while DEET repelled starting at 16.5 µg/cm2. Future works will be oriented to the study of repellent properties of cis-isosafrole alone and mixed with ß-terpinene, trans-ocimene and methyleugenol on T. infestans.

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Two unusual caprolactam alkaloids, 3-(dimethylamino)hexahydro-2H-azepin-2-one and 3-(methylamino)-hexahydro-2H-azepin-2-one, were isolated from the aerial parts of Astragalus cryptanthus Wedd.; their structures were unambiguously determined based on data from extensive 1D and 2D NMR, GC-MS and FT-IR spectroscopic analyses. This is the first report of this alkaloid type in the genus Astragalus.

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The chemical composition of the essential oil of Kurzamra pulchella (Lamiaceae) was determined. Twelve compounds were identified, with isomenthone (60.6%) and pulegone (37.1%) predominating. Chemotaxonomical considerations were discussed.

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Treehoppers (Membracidae) exhibit different levels of sociality, from solitary to presocial. Although they are one of the best biological systems to study the evolution of maternal care in insects, information on the biology of species in this group is scarce. This work describes the biology and ecology of Alchisme grossa (Fairmaire) (Hemiptera: Membracidae) in a rain cloud forest of Bolivia. This subsocial membracid utilizes two host-plant species, Brugmansia suaveolens (Humb. & Bonpl. ex Wild) Bercht. & J.Presl and Solanum ursinum (Rusby) (both Solanaceae), the first one being used during the whole year and the second one almost exclusively during the wet season. The development of A. grossa from egg to adult occurred on the plant where eggs were laid. Maternal care was observed during the complete nymphal development, and involved behavioral traits such as food facilitation and antidepredatory defense. Life cycle was longer on B. suaveolens during the dry season and shorter on S. ursinum during the wet season. Mortality was similar on both host plants during the wet season but was lower on B. suaveolens during the dry season. The presence of a secondary female companion to the egg-guarding female individual and occasional iteropary is also reported.

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The floral volatile chemicals of four Heliotropium (Boraginaceae) species endemic to Chile are described and their relationship with an Heliotropium phylogeny assessed. Twenty-two compounds were identified; the most prominent family of compounds in H. floridum, H. myosotifolium and H. stenophyllum were benzenoids, and in H. pycnophyllum prominence of benzenoids was shared with two monoterpenes, (E)-Ocymene and 1,8-cineol. The similarity between chemical mixtures of the species significantly decreased with increasing phylogenetic distance between them. Neighbor-joining analysis produced a tree topology with one clade comprised by H. myosotifolium and H. stenophyllum and an unresolved relationship between this clade and H. floridum and H. pycnophyllum; this topology bears a close relationship with molecular phylogeny proposed for the group. These preliminary results presented suggest that the genus Heliotropium complies with the condition of phylogenetically-related floral scent interspecific variation, a key condition in studies of plant-pollinator coevolution mediated by them.

Se describieron los volátiles florales de cuatro especies de Heliotropium (Boraginaceae) y se evaluó su relación con una filogenia del género. Se identificaron 22 compuestos; los bencenoides fueron los más abundantes en H. floridum, H. myosotifolium and H. stenophyllum, acompañados de dos monoterpenos, el (E)-Ocimeno y el 1,8-cineol, en H. pycnophyllum. La similitud entre los componentes de cada especie aumentó con la distancia filogenética entre ellas. El análisis “neighbor-joining” produjo un árbol con un clado que contenía a H. myosotifolium y H. stenophyllum y una relación no resuelta entre ese clado y H. floridum y H. pycnophyllum; esta topología guarda similitud con la hipótesis filogenética molecular propuesta para el grupo. Estos resultados preliminares sugieren que el género Heliotropium cumple con la condición de mostrar variación interespecífica en sus volátiles florales, condición básica para estudios de coevolución planta-polinizador mediada por ellos.

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A screening was undertaken of the native flora of Chile excluding Pteridophyta, Cactaceae and Poaceae the study included 396 species. Alkaloids were found in 189 species, the highest concentration being 3 mg/g dry tissue. A table was produced listing all species collected and specifying the subset containing alkaloids, the species with a particularly high alkaloid content and also the endemic species within this latter set. Alkaloid concentration as well as presence or absence data in different vegetational subregions correlated with mean collection latitude, under the limitations imposed by the relationship between alkaloid concentration and species lineage. In practical terms, the results indicate that in studies aimed at identifying alkaloids in the native flora of Chile, plant collections should take into consideration the promising species listed in the table and take place at the lowest possible latitude if the chance of finding alkaloids and the yield of isolated alkaloids are to be maximized.

Se muestreó un conjunto de 396 especies de la flora nativa de Chile (excluyendo Pteridophyta, Cactaceae y Poaceae), encontrándose alcaloides en 189 de ellas (concentración máxima: 3 mg/g de tejido seco). Se generó una tabla que contiene todas las especies analizadas y especifica aquellas que contienen alcaloides, aquellas que los contienen en altas concentraciones y, entre estas últimas, aquellas que son endémicas. La concentración de alcaloides y también los datos de presencia/ausencia correlacionaron con la latitud media de colecta, bajo las limitaciones impuestas por la relación entre concentración de alcaloides y linaje de la especie. En términos prácticos, los resultados señalan que en estudios que apunten a la identificación de alcaloides en la flora nativa de Chile la colecta de plantas debería tomar en consideración las especies promisoras incluídas en la tabla y ser realizada a la latitud más baja posible dentro del rango de distribución de la especie, maximizando así la probabilidad de encontrar alcaloides en altas concentraciones.

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Since the preferential body temperature should positively correlate with physiological performance, behavioural fever should enhance an organism's immune response under an immune challenge. Here we have studied the preferential body temperature (T(p)) and its consequences on immune response performance after an immune challenge in larvae of Tenebrio molitor. We evaluated T(p) and immune responses of larvae following a challenge with various concentrations of lipopolysaccharide (LPS), and we studied the correlation between T(p) and two immune traits, namely antibacterial and phenoloxidase (PO) activities. Larvae that were immune challenged with higher LPS concentrations (C(50) and C(100)) preferred in average, warmer temperatures than did larvae challenged with lower concentrations (C(0) and C(25)). T(p) of C(25)-C(100) (challenged)-mealworms was 2.3°C higher than of C(0) (control) larvae. At lower LPS concentration immune challenge (C(0) and C(25)) antibacterial activity correlated positively with T(p), but at C(50) and C(100) correlation was lose. PO activity was higher at higher LPS concentration, but its magnitude of response did not correlate with T(p) Our data suggest that behavioural fever may have a positive effect on host performance by enhancing antibacterial response under a low pathogen load situation.

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In spite of the high degree of endemism of the native vascular flora of Chile (ca. 52 percent) and predictions based on the frequency of occurrence of alkaloids in the world flora (they have been found in 40.4 percent of the families, 13.1 percent of the genera and 2.7 percent of the species), alkaloids have been isolated from only 12.5 percent of families, 3.9 percent of genera and 1.7 percent of species of the native flora of Chile. The slope of the linear correlation between these two sets of figures suggests that the alkaloid potential of the native Chilean flora has been exploited to the extent of only 29 percent. Currently known alkaloid-containing species from the native flora of Chile are listed in this review together with pertinent references. The distribution of alkaloids was compared between the native flora of Chile and the world flora; this led to the identification of several families with good potential as sources of alkaloids.

A pesar del alto grado de endemismo de la flora vascular nativa de Chile (ca. 52 por ciento) y predicciones basadas en la frecuencia con que se encuentran alcaloides en la flora del mundo (en 40.4 por ciento de las familias, 13.1 por ciento de los géneros y 2.7 por ciento de las especies), se han aislado alcaloides solo desde 12,5 por ciento de las familias, 3,9 por ciento de los géneros y 1,7 por ciento de las especies de la flora nativa de Chile. La pendiente de la correlación entre estos dos conjuntos de datos sugiere que el potencial de la flora nativa de Chile como productora de alcaloides ha sido explotado solo en un 29 por ciento. En esta revisión se entrega una lista de las especies de la flora nativa de Chile que contienen alcaloides y las referencias pertinentes. La distribución de alcaloides fue comparada entre la flora nativa de Chile y la flora del mundo, lográndose identificar varias familias con un buen potencial como fuentes de alcaloides.

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The analysis by gas chromatography coupled with mass spectrometry (GC-MS) of the alkaloidal extract of Browningia candelaris (Cactaceae) showed the presence of N-acetyl-3,4-dimethoxyphenylethylamine; N,N-dimethyl-3,4-dimethoxyphenylethylamine; N,N-dimethyl-4-methoxyphenylethylamine; and 4-methoxyamphetamine. The presence of these psychoactive compounds is discussed in terms of their possible ritual use in Andean cultures of Northern Chile.

El análisis por medio de cromatografía de gases acoplada a espectrometría de masas (CG-EM) del extracto alcaloidal de Browningia candelaris (Cactaceae) mostró la presencia de N-acetil-3,4-dimetoxifeniletilamina; N,N-dimetil-3,4-dimetoxifeniletilamina; N,N-dimetil-4-metoxifeniletilamina y 4-metoxianfetamina. La presencia de estos compuestos psicoactivos se discute en términos de su posible utilización en ceremonias mágico-religiosas por culturas andinas del norte de Chile.

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A new withanolid amine was isolated from Dunalia spinosa (Solanaceae). Its relative stereochemistry was determined using FT-IR, 1H and 13C NMR spectroscopies and high resolution mass spectrometry. Nicotine was also isolated; chemotaxonomic and archaeological implications are discussed.

Un nuevo amino-witanólido fue aislado de Dunalia spinosa (Solanaceae). Su estereoquímica relativa fue determinada usando espectroscopías FT-IR y RMN de 1H y 13C, y espectrometría de masas de alta resolución. También fue aislada nicotina; se discuten las implicancias quimotaxonómicas y arqueológicas.

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Although the study of thermoregulation in insects has shown that infected animals tend to prefer higher temperatures than healthy individuals, the immune response and energetic consequences of this preference remain unknown. We examined the effect of environmental temperature and the energetic costs associated to the activation of the immune response of Tenebrio molitor larvae following a lipopolysaccharide (LPS) challenge. We measured the effect of temperature on immune parameters including phenoloxidase (PO) activity and antibacterial responses. Further as proximal and distal costs of the immune response we determined the standard metabolic rate (SMR) and the loss of body mass (m(b)), respectively. Immune response was stronger at 30°C than was at 10 or 20°C. While SMR at 10 and 20°C did not differ between immune treatments, at 30°C SMR of LPS-treated larvae was almost 25-60% higher than SMR of PBS-treated and naïve larvae. In addition, the loss in m(b) was 1.9 and 4.2 times higher in LPS-treated larvae than in PBS-treated and naïve controls. The immune responses exhibited a positive correlation with temperature and both, SMR and m(b) change, were sensitive to environmental temperature. These data suggest a significant effect of environmental temperature on the immune response and on the energetic costs of immunity.

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'Superclones' are predominant and time-persistent genotypes, exhibiting constant fitness across different environments. However, causes of this ecological success are still unknown. Therefore, we studied the physiological mechanisms that could explain this success, evaluating the effects of wheat chemical defences on detoxification enzymes [cytochrome P450 monooxygenases (P450), glutathione S-transferases (GST), esterases (EST)], standard metabolic rate (SMR), and fitness-related traits [adult body mass and intrinsic rate of increase (r(m))] of two 'superclones' (Sa1 and Sa2) of the grain aphid, Sitobion avenae. Additionally, we compared 'superclones' with a less-frequent genotype (Sa46). Genotypes were reared on three wheat cultivars with different levels of hydroxamic acids (Hx; wheat chemical defences). Detoxification enzymes and SMR did not differ between wheat hosts. However, GST and EST were different between 'superclones' and Sa46, while Sa1 showed a higher SMR than Sa2 or Sa46 (p=0.03). Differences between genotypes were found for r(m), which was higher for Sa1 than for Sa2 or Sa46. For all cases, genotype-host interactions were non-significant, except for aphid body mass. In conclusion, 'superclones' exhibit a broad host range, flat energetic costs for non-induced detoxification enzymes, and low variation in their reproductive performance on different defended hosts. However, physiological specialization of 'superclones' that could explain their ecological success was not evident in this study.

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Host-plants can mediate the interactions between herbivores and their mutualists and also between parasitic plants and their mutualists. The present study reveals how a hemiparasitic plant parasitizing three host species gives rise to three distinct hemiparasite-host neighborhoods which differ in terms of volatile composition and pollinator attractiveness. The study was performed in a population of the mistletoe Tristerix verticillatus infecting three different species of hosts occurring in sympatry within a small area, thus exposing all individuals studied to similar abiotic conditions and pollinator diversity; we assessed the effect of hosts on the hemiparasites' visual and olfactory cues for pollinator attraction. During the study period, the hemiparasite individuals were flowering but the hosts were past their flowering stage. We collected volatile organic compounds from the hemiparasite and its hosts, measured floral display characteristics and monitored bird and insect visitors to inflorescences of T. verticillatus. We showed that: (1) floral patches did not differ in terms of floral display potentially involved in the attraction of pollinators, (2) hosts and hemiparasites on each host were discriminated as distinct chemical populations in terms of their volatile chemical profiles, (3) insect visitation rates differed between hemiparasites parasitizing different hosts, and (4) volatile compounds from the host and the hemiparasite influenced the visitation of hemiparasite flowers by insects. The study showed that a species regarded as "ornithophilic" by its floral morphology was actually mostly visited by insects that interacted with its sexual organs during their visits and carried its pollen, and that host-specific plant-volatile profiles within the T. verticillatus population were associated with differential attractiveness to pollinating insects.

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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.

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Many cereals accumulate hydroxamic acids derived from 2-hydroxy-2H-1,4-benzoxazin-3(4H)-one. These benzoxazinoid hydroxamic acids are involved in defense of maize against various lepidopteran pests, most notably the European corn borer, in defense of cereals against various aphid species, and in allelopathy affecting the growth of weeds associated with rye and wheat crops. The role of benzoxazinoid hydroxamic acids in defense against fungal infection is less clear and seems to depend on the nature of the interactions at the plant-fungus interface. Efficient use of benzoxazinoid hydroxamic acids as resistance factors has been limited by the inability to selectively increase their levels at the plant growth stage and the plant tissues where they are mostly needed for a given pest. Although the biosynthesis of benzoxazinoid hydroxamic acids has been elucidated, the genes and mechanisms controlling their differential expression in different plant tissues and along plant ontogeny remain to be unraveled.

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