Effect of glyphosate on indole-3-acetic acid metabolism in tolerant and susceptible plants

A comparison study was conducted on the effect of glyphosate (N-[phosphonomethyl]glycine) on indole-3-[2-¹⁴C]acetic acid (IAA) metabolism, ethylene production, and growth of 7-day-old seedlings of different plants. The plants tested were American germander (Teucrium canadense L.), soybean (Glycine max L. Merr.), pea (Pisum sativum L. cv. Alaska and Little marvel), mungbean (Vigna radiata L.), and buckwheat (Fagopyrum esculentum Moench). A spray with 2 mM glyphosate affected IAA metabolism to a varied degree. The induced increase of IAA metabolism was greater in buckwheat, Alaska pea, and mungbean than soybean, Little marvel pea, and American germander. The increased IAA metabolism was correlated with the inhibition of growth and with the decrease of ethylene production. The natural rate of IAA metabolism was markedly different among the plant species and cultivars tested and appeared to be related to the sensitivity of the plants to glyphosate. American germander and Little marvel pea with high rates of IAA metabolism were more tolerant to glyphosate than buckwheat and Alaska pea, which had low rates of IAA metabolism. Plants with a high natural rate of IAA metabolism were probably less dependent on IAA and thus less susceptible to glyphosate.     

Effect of glyphosate on indole-3-acetic acid metabolism in tolerant and susceptible plants

A comparison study was conducted on the effect of glyphosate (N-[phosphonomethyl]glycine) on indole-3-[2-¹⁴C]acetic acid (IAA) metabolism, ethylene production, and growth of 7-day-old seedlings of different plants. The plants tested were American germander (Teucrium canadense L.), soybean (Glycine max L. Merr.), pea (Pisum sativum L. cv. Alaska and Little marvel), mungbean (Vigna radiata L.), and buckwheat (Fagopyrum esculentum Moench). A spray with 2 mM glyphosate affected IAA metabolism to a varied degree. The induced increase of IAA metabolism was greater in buckwheat, Alaska pea, and mungbean than soybean, Little marvel pea, and American germander. The increased IAA metabolism was correlated with the inhibition of growth and with the decrease of ethylene production.The natural rate of IAA metabolism was markedly different among the plant species and cultivars tested and appeared to be related to the sensitivity of the plants to glyphosate. American germander and Little marvel pea with high rates of IAA metabolism were more tolerant to glyphosate than buckwheat and Alaska pea, which had low rates of IAA metabolism. Plants with a high natural rate of IAA metabolism were probably less dependent on IAA and thus less susceptible to glyphosate.     

Production of reactive oxygen species and antioxidant enzymes of pea and soybean plants under hypoxia and high CO<Subscript>2</Subscript> concentration in medium

Generation of reactive oxygen species (ROS) and activities of antioxidant enzymes (catalase, peroxidase, ascorbate peroxidase) in pea (Pisum sativum L.) and soybean (Glycine max L.) under hypoxia (3–24 h) and high CO₂ concentration in medium were studied. In sensitive to hypoxia pea seedlings, hypoxia enhanced markedly production of superoxide anion-radical, hydroperoxides, and especially hydrogen peroxide. In more tolerant soybean plants, these changes were less pronounced. During first hours of hypoxia, activity of lipoxygenase in plant cells increased. This allows a suggestion that this enzyme is involved in the processes of hydroperoxide accumulation in plant tissues under oxygen deficit. In pea and soybean plants, a correlation between tolerance to hypoxia, the rate of ROS generation, and antioxidant enzyme activities was established. During the first hours of hypoxia, the catalase activity in soybean plants increased stronger than in sensitive to hypoxia pea plants. At longer exposure to hypoxia (24 h), peroxidases started to play the higher role in cell defense against hypoxia, but only in soybean plants. The medium with the higher CO₂ content induced higher changes in the processes of ROS accumulation and activities of lipoxygenase and antioxidant enzymes. This permits us to refer CO₂, accumulated as a product of respiration in the cells, to low-molecular signal molecules switching on plant adaptation to hypoxic stress.     

Interactions of alternate hosts, postemergence grass control, and rootworm-resistant transgenic corn on western corn rootworm (Coleoptera: Chrysomelidae) damage and adult emergence

Field studies were conducted in 2003 and 2004 to determine the effects of grassy weeds, postemergence grass control, transgenic rootworm-resistant corn, Zea mays L., expressing the Cry3Bb1 endotoxin and glyphosate herbicide tolerance (Bt corn), and the interactions of these factors on western corn rootworm, Diabrotica virgifera virgifera LeConte, damage and adult emergence. Three insect management tactics (Bt corn, its nontransgenic isoline, and isoline plus tefluthrin) were evaluated with two weed species (giant foxtail, Setaria faberi Herrm, and large crabgrass, Digitaria sanquinalis L. Scop), and four weed management regimes (weed free, no weed management, early [V3-4] weed management and late [V5-6] weed management) in a factorial arrangement of a randomized split split-plot design. In each case, the isoline was also tolerant to glyphosate. Root damage was significantly affected by insect management tactics in both years, but weed species and weed management did not significantly affect damage to Bt corn in either year. Adult emergence was significantly affected by insect management tactics in both years and by weed species in 2003, but weed management and the interaction of all three factors was not significant in either year. The sex ratio of female beetles produced on Bt corn without weeds was generally greater than when weeds were present and this difference was significant for several treatments each year. Average dry weight of male and female beetles emerging from Bt corn was greater than the weights of beetles emerging from isoline or isoline plus tefluthrin in 2003, but there was no difference for females in 2004 and males weighed significantly less than other treatments in 2004. The implications of these results in insect resistance management are discussed.     

Stimulation of glutathione synthesis in photorespiring plants by catalase inhibitors

The effect of various herbicides on glutathione levels in barley (Hordeum vulgare L.), tobacco (Nicotiana tabacum L.), soybean (Glycine max [L.] Merr.), and corn (Zea mays L.) was examined. Illumination of excised barley, tobacco, and soybean plants for 8 hours in solution containing 2 millimolar aminotriazole (a catalase inhibitor) resulted in an increase in leaf glutathione from 250 to 400 nanomoles per gram fresh weight to 600 to 1800 nanomoles per gram fresh weight, depending on the species tested. All of this increase could be accounted for as oxidized glutathione. Between 25 and 50% of this oxidized glutathione was reduced when plants were darkened for 16 hours, but there was no significant decline in total glutathione. Another catalase inhibitor, thiosemicarbazide, was as effective as aminotriazole in elevating glutathione in soybean but was less effective in barley and tobacco. Glyphosate, an inhibitor of aromatic amino acid biosynthesis, had no significant effect on glutathione levels in any of the plants examined. Whereas methyl viologen (paraquat), which is a sink for photosystem I electrons, caused oxidation of leaf glutathione in all of the plants but did not increase the total amount of glutathione present.     

Haloxyfop Inhibition of the Pyruvate and the alpha-Ketoglutarate Dehydrogenase Complexes of Corn (Zea mays L.) and Soybean (Glycine max [L.] Merr.)

The grass-specific herbicide haloxyfop, ((±)-2-[4-((3-chloro-5-(trifluoromethyl)-2-pyridinyl)oxy)-phenoxy] propionic acid) has been shown to inhibit lipid synthesis and respiration, to cause the accumulation of amino acids, and not to affect cellular sugar or ATP levels. Thus studies were carried out with enzyme activities from corn (Zea mays L.) (haloxyfop sensitive) and soybean (Glycine max [L.] Merr.) (haloxyfop tolerant) to locate the possible inhibition sites among the glycolytic and tricarboxylic acid (TCA) cycle enzymes. Following along the oxidative metabolism pathway of sugars, the pyruvate dehydrogenase complex (PDC) was the first enzyme among the glycolytic enzymes that demonstrated noticeable inhibition by 1 millimolar haloxyfop. Kinetic studies with corn and soybean PDC from both purified etioplasts and mitochondria gave K_i values of from 1 to 10 millimolar. Haloxyfop also inhibited the activity of the TCA cycle enzyme, the α-ketoglutarate dehydrogenase complex (α-KGDC) which carries out the same reaction as PDC except for the substitution of α-ketoglutarate for pyruvate as one of the substrates. The K_i values were somewhat lower in this case (near 1 millimolar). The relatively high K_i values for both enzyme complexes would indicate that these may not be the herbicidal sites of inhibition, but it is possible that the herbicide could be concentrated in compartments and/or the substrate concentrations may be well below optimal. Likewise little difference was seen in the haloxyfop inhibition of the enzyme activities from the sensitive species, corn, and from the tolerant species, soybean, so the selectivity of the herbicide is not evident from these results. The inhibition of the PDC and α-KGDC as the mode of action of haloxyfop is, however, consistent with the observed physiological effects of the herbicide, and these are the only enzymic activities so far found to be sensitive to haloxyfop.     

Diurnal changes in sucrose phosphate synthase activity in leaves

Studies were conducted to identify and compare diurnal changes in sucrose phosphate synthase (EC 2.4.1.14) activity in leaves of different species, and the effect of nitrogen nutrition on the rhythm in soybean [ Glycine max (L). Merr] leaves. In recently expanded corn ( Zea mays L.) leaves, a single peak of enzyme activity was observed at the beginning of the photoperiod. A similar pattern was observed in older corn leaves, but activities (leaf fresh weight basis) were lower. In recently expanded pea ( Pisum sativum L.) and soybean leaves, two peaks of sucrose phosphate synthase activity were observed over a 24-h light:dark period, one at the beginning and one at the end of the photoperiod. A similar pattern was observed in older soybean leaves, but activities were generally lower and the amplitude of the changes was reduced. In a separate experiment, soybean plants were grown in the greenhouse with either 2 or 10 m M nitrate. The high-N plants had higher rates of photosynthesis and translocation, and greater activities of sucrose phosphate synthase in leaf extracts, compared to low-N plants. Over both experiments with soybeans, changes in sucrose phosphate synthase activity during the photoperiod were closely aligned with changes in translocation rate.     

Influence of preceding crop on wireworm (Coleoptera: Elateridae) abundance in the coastal plain of North Carolina

Three studies were conducted to determine the effect of preceding crop on wireworm (Coleoptera: Elateridae) abundance in the coastal plain of North Carolina. In all three studies, samples of wireworm populations were taken from the soil by using oat, Avena sativa L., baits. Treatments were defined by the previous year's crop and were chosen to reflect common crop rotations in the region. Across all three studies, eight wireworm species were recovered from the baits: Conoderus amplicollis (Gyllenhal), Conoderus bellus (Say), Conoderus falli (Lane), Conoderus lividus (Degeer), Conoderus scissus (Schaeffer), Conoderus vespertinus (F.), Glyphonyx bimarginatus (Schaeffer), and Melanotus communis (Gyllenhal). The effect of corn, Zea mays L.; cotton, Gossypium hirsutum L.; fallow; soybean, Clycine max (L.) Merr.; sweet potato, Ipomoea batatas (L.) Lam.; and tobacco (Nicotiana spp.) was evaluated in a small-plot replicated study. M. communis was the most frequently collected species in the small-plot study and was found in significantly higher numbers following soybean and corn. The mean total number of wireworms per bait (all species) was highest following soybean. A second study conducted in late fall and early spring assessed the abundance of overwintering wireworm populations in commercial fields planted to corn, cotton, peanut (Arachis hypogaea L.), soybean, sweet potato, and tobacco in the most recent previous growing season. C. lividus was the most abundant species, and the mean total number of wireworms was highest following corn and soybean. A survey was conducted in commercial sweet potato in late spring and early summer in fields that had been planted to corn, cotton, cucurbit (Cucurbita pepo L.), peanut, soybean, sweet potato, or tobacco in the most recent previous growing season. C. vespertinus was the most abundant species, and the mean total number of wireworms per bait was highest following corn.     

Germination of grass species in soil affected by crude oil contamination

Many grass species exist in the oil exploration areas of North Dakota. The objective of this study was to evaluate seed germination of 65 grass species affected by crude oil. Germination of all species was reduced by crude oil, ranging from 4.3 to 100%. Twenty-eight species were tolerant, 29 moderately tolerant, 6 moderately sensitive, and 2 sensitive. Based on the tolerance levels, the following were used to further test the dose response to crude oil: strong creeping red fescue (Festuca rubra L. ssp. rubra), perennial ryegrass (Lolium perenne L.), orchardgrass (Dactylis glomerata L.), buffalograss [Buchloe dactyloides (Nutt.) Engelm.], little bluestem [Schizachyrium scoparium (Michx.) Nash], witchgrass (Panicum capillare L.), sand dropseed [Sporobolus cryptandrus (Torr.) Gray], Johnsongrass [Sorghum halepense (L.) Pers.], and smooth crabgrass [Digitaria ischaemum (Schreb.) Schreb. ex Muhl.]. The EC₅₀ of germination and biomass was effective in ranking the 9 species. Buffalograss, sand dropseed, and orchardgrass were ranked as the most tolerant species with EC₅₀ values of 0.1, > highest concentration tested, 0.05 m³ m^?3 (P < 0.05), respectively. Smooth crabgrass and little bluestem were ranked as most sensitive with EC₅₀ values of 0.03 and 0.04 m³ m^?3 (P < 0.05), respectively. Buffalograss showed the lowest germination (10.4%) and biomass reduction (25%) (P < 0.05).     

Estimation of cadmium availability using transformed roots

We have explored cultures of roots transformed by Agrobacterium rhizogenes to test the availability of cadmium in sewage sludges. The toxic effects of Cd and the kinetics of Cd accumulation were examined for three species of transformed roots, grown for 2 weeks in nutrient media, containing Cd as a salt. Roots of sugar beet (Beta vulgaris L.) were highly sensitive, while those of tobacco (Nicotiana tobaccum L.) and morning glory (Calystegia sepium R. Br) were more tolerant. Cd accumulation was higher in sugar beet and morning glory than in tobacco. We developed a non-sterile, 5-day procedure for testing the accumulation (an indication of availability) of Cd from sludge suspensions, using transformed roots of morning glory and tobacco. Cd accumulation varied with plant species and source of sludge. Ranking of Cd availability using this biological assay for Cd accumulation was confirmed by chemical tests with NH₄ acetate and EDTA. Results from transformed roots were also compared with those from normal, excised, tobacco roots and normal and transformed tobacco plantlets. No major alteration in Cd uptake was associated with genetic transformation. We thus demonstrated the feasibility of using transformed roots to estimate the availability of Cd in metal-contaminated materials like sewage sludges.     

Effects of supplemental UV-B radiation on primary photosynthetic carboxylating enzymes and soluble proteins in leaves of C3 and C4 crop plants

Effects of increased UV-B radiation on activities of primary photosynthetic carboxylating enzymes and on contents of soluble proteins were studied in soybean (Glycine max [L.] Merr. cv. Bragg), pea (Pisum sativum L. cv. Little Marvel), tomato (Lycopersicon esculentum L. cv. Rutgers), and sweet corn (Zea mays L. cv. Golden Cross Bantam). The purpose was to evaluate the responses of agronomic crops to increases in solar UV-B radiation. Plants were grown and exposed under greenhouse conditions for 6 h daily to supplemental UV-B radiation which was provided by Westinghouse FS-40 fluorescent sun lamps filtered with 0.127-mm film of cellulose acetate (UV-B treated) or Mylar S (Mylar control). Three UV-B levels were tested: 1.09 (treatment T₁), 1.36 (treatment T₂), and 1.83 (treatment T₃) UV-B_seu where 1 UV-B_seu equals 16.0 mW-m² weighted by EXP-[(λ-265)/21]². These UV-B levels corresponded to 6%,21%, and 36%, respectively, of decrease in stratospheric ozone content, based on the interpolations of UV-B irradiances at a solar elevation angle of 60°. Leaves of plants of soybean, pea, and tomato exposed to UV-B radiation were generally low in RuBP carboxylase activity. On a fresh weight basis, all three UV-B radiation levels significantly reduced the enzyme activity in soybean and pea, whereas tomato plants showed significant reduction in RuBP carboxylase activity only when exposed to 1.83 and 1.36 UV-B_seu. An apparent decrease in soluble proteins was observed in leaf extracts of soybean and pea plants exposed to 1.36 and 1.83 UV-B_seu whereas higher amounts of proteins were detected in leaves of tomato plants grown under UV-B radiation. Leaves of sweet corn plants grown under Mylar control were low in PEP carboxylase activity and proteins as compared with those of control plants receiving no supplemental UV and UV-B treatment. Activities of PEP carboxylase in crode extracts from leaves of sweet corn were significantly suppressed under 1.36 and 1.83 UV-B_seu as compared with the no UV control. Some stimulation of PEP carboxylase activity was observed in corn plants exposed to 1.09 UV-B_seu.     

Effects of crop rotation and fertilization on catalase activity in a soil of the southeastern United States

Summary Catalase activity of a loamy sand under a 3-year crop rotation in the southeastern U.S.A. was monitored. Corn (Zea mays L.), cotton (Gossypium hirsutum L.), and soybean [Glycine max (L.) Merr.] were the summer crops in the rotation. Winter wheat (Triticum aestivum L.) was planted after corn, and soybean was followed by a winter fallow period. Cotton was followed by a mixture of common vetch (Vicia sativa L.) and crimson clover (Trifolium incarnatum Gibelli & Belli) which was eventually plow-incorporated as a green manure. Highest mean catalase activities were recorded in soil under the wheat, soybean, and winter legume crops; lowest activities were found in soil bearing corn and cotton, and during the winter fallow period. The fertilization regime influenced soil catalase activity independently of the crop. Soil deficient in any of the major elements showed low enzyme activity. Highest activity was found in soil fertilized with P and K, and with N supplied by a winter legume crop. Addition of supplementary mineral nitrogen to this regime reduced catalase activity. Elimination of the winter legume crop from an otherwise complete fertilization regime resulted in a drastic reduction in enzyme activity. In soil receiving a complete fertilization regime there was a close correlation between soil catalase and xylanase activities. A similar correlation between these two enzymes was not found in soil receiving incomplete fertilization.     

N2 fixation by soybean-Bradyrhizobium combinations under acidity,low P and high Al stresses

Five strains of Bradyrhizobium japonicum (USDA 6, 110, 122, 138, and 143) were screened in cell culture for tolerance to acidity (pH 4.2, 4.4, and 4.6) and Al (0, 3, 4, 5, and 6 mg L^–1) under low P conditions. Each strain was later grown in association with seven soybean [Glycine max. (L) Merr.] cultivars which were also screened for tolerance to the same stresses in nutrient culture to determine which soybean-Bradyrhizobium combinations would establish the most effective symbiotic N₂ fixing relationships. Results indicated that strains USDA 110 and 6 were more tolerant than USDA 122, 138 and 143 with USDA 110 being the most tolerant. Acidity appeared to be the more severe stress; but even when strains showed tolerance to the stresses, cell numbers were significantly reduced. This suggests that colonization of soils and soybean roots can be adversely affected under similar conditions in the field which may result in reduced nodulation. The strains found to be more tolerant to the stresses were more effective N₂ fixers in symbiosis with all soybean cultivars, with USDA 110 being definitely superior. The association between the more tolerant strains and cultivars had the largest nitrogenase activity. Further studies on the inclusion of tolerant Bradyrhizobium strains in inoculum used on tolerant soybean cultivars in the field are warranted.     

A comparative analysis of fructose 2,6-bisphosphate levels and photosynthate partitioning in the leaves of some agronomically important crop species

Starch, sucrose, and fructose 2,6-bisphosphate (F2, 6BP) levels were measured in pea (Pisum sativum L.), maize (Zea mays L.), onion (Allium cepa L.) and soybean (Glycine max L.) leaves throughout a light/dark cycle. Leaf starch accumulated in pea, maize, and soybean but not in onion. Sucrose was a major leaf storage reserve in pea, maize, and onion but was only found at low levels in soybean. In all species examined, the most dramatic changes in F2,6BP concentration coincided with light/dark transitions. During the light period F2,6BP levels were about 0.1 nanomole/milligram chlorophyll in soybean source leaves and there was a small increase in effector concentration in the dark. Levels of F2,6BP were also low in pea and maize leaves during the light period but then increased 10- or 20-fold in the dark. Dark onion leaf F2,6BP levels were about 1.1 to 1.3 nanomole/milligram chlorophyll and these values decreased by 20 to 30% in the light. Thus, three different patterns were identified that describe diurnal F2,6BP levels in source leaves. These results support the suggestion that F2,6BP is involved in the regulation of sucrose biosynthesis. However, it was not possible to demonstrate that high levels of F2,6BP are essential for starch synthesis in the chloroplast.     

Atrazine metabolism and herbicidal selectivity

Metabolism of the herbicide 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) was investigated in resistant corn (Zea mays L.) and sorghum (Sorghum vulgare Pers.), intermediately susceptible pea (Pisum sativum L.), and highly susceptible wheat (Triticum vulgare Vill.) and soybean (Glycine max Merril.). This study revealed that 2 possible pathways for atrazine metabolism exist in higher plants. All species studied were able to metabolize atrazine initially by N-dealkylation of either of the 2 substituted alkylamine groups. Corn and wheat, which contain benzoxazinone, also metabolized atrazine initially by hydrolysis in the 2-position of the s-triazine ring to form hydroxyatrazine. Subsequent metabolism by both pathways resulted in the conversion of the parent atrazine to more polar compounds and eventually into methanol-insoluble plant residue. No evidence for s-triazine ring cleavage was obtained.

Both pathways for atrazine metabolism appear to detoxify atrazine. The hydroxylation pathway results in a direct conversion of a highly phytotoxic compound to a completely non-phytotoxic derivative. The dealkylation pathway leads to detoxication through one or more partially detoxified, stable intermediates. Therefore, the rate and pathways of atrazine metabolism are important in determining the tolerance of plants to the herbicide. Both quantitative and qualitative differences in atrazine metabolism were detected between resistant, intermediately susceptible, and susceptible species. The ability of plants to metabolize atrazine by N-dealkylation and the influence of this pathway in determining tolerance of plants to atrazine are discussed.

     

Enzymes of the glyoxylate cycle in rhizobia and nodules of legumes

The relatively high level of fatty acids in soybean nodules and rhizobia from soybean nodules suggested that the glyoxylate cycle might have a role in nodule metabolism. Several species of rhizobia in pure culture were found to have malate synthetase activity when grown on a number of different carbon sources. Significant isocitrate lyase activity was induced when oleate, which presumably may act as an acetyl CoA precursor, was utilized as the principle carbon source. Malate synthetase was active in extracts of rhizobia from nodules of bush bean (Phaseolus vulgaris L.), cowpea (Vigna sinensis L.), lupine (Lupinus angustifolius L.) and soybean (Glycine max L. Merr.). Activity of malate synthetase was, however, barely detectable in rhizobia from alfalfa (Medicago sativa L.), red clover (Trifolium pratense L.) and pea (Pisum sativum L.) nodules. Appreciable isocitrate lyase activity was not detected in rhizobia from nodules nor was it induced by depletion of endogenous substrates by incubation of excised bush bean nodules. Although rhizobia has the potential for the formation of the key enzymes of the glyoxylate cycle, the absence of isocitrate lyase activity in bacteria isolated from nodules indicated that the glyoxylate cycle does not operate in the symbiotic growth of rhizobia and that the observed high content of fatty acids in nodules and nodule bacteria probably is related to a structural role.     

Evaluation of Ostrinia nubilalis (Lepidoptera: Crambidae) neonate preferences for corn and weeds in corn

Choice tests were conducted to determine feeding preferences of European corn borer, Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae), neonates for 15 species of plants. Percentage of neonates accepting (found on) each leaf disc after 24 h was measured using choice tests. Initially, nine species of plants were evaluated. The following year, 10 plant species were evaluated during O. nubilalis first generation and 11 species during the second generation. Pennsylvania smartweed, Polygonum pennsylvanicum (L.), had the highest percentage of neonates accepting leaf discs in both years. Other plants with high acceptance rates included swamp smartweed, Polygonum amphibium L.; velvetleaf, Abutilon theophrasti Medicus; cocklebur, Xanthium strumarium L.; and yellow foxtail, Setaria glauca (L.). Corn, Zea mays L., consistently had low percentages of neonates accepting leaf discs along with common waterhemp, Amaranthus rudis Sauer. Implications these results may have on O. nubilalis host plant selection in central Iowa's corn dominated landscape are considered.     

Feeding preferences and related types of behaviour of Neomegalotomus parvus

Laboratory studies with Neomegalotomus parvus(Westwood) (Hemiptera: Alydidae) with one nymph per Petri dish in multiple-choice tests indicated that seeds of pigeon pea [Cajanus cajan(L.) Mills.], lablab (Dolichos lablabL.), and soybean [Glycine max(L.) Merrill] were visited before seeds of common bean (Phaseolus vulgarisL.) and rice (Oryza sativaL.). The percentage of individuals engaging in dabbing/antennation resulting in probing, and percentage probing resulting in feeding, were higher on common bean (97%) and pigeon pea (87%) seeds than on lablab (55%), soybean (50%), or rice (5%) seeds. No significant differences were found in preference (number of flanges) among pigeon pea, common bean, and lablab, and preference (insects on foods) varied throughout the assessment period (5 d). In tests using 10 nymphs per dish, pigeon pea was the preferred food (number of flanges and insects on plants) throughout the period (5 d). In no-choice tests, the average duration of a feeding session and the longest feeding session were greater on lablab and common bean than on pigeon pea, soybean, or rice seeds. The number of feeding sessions was greater on seeds of common bean, pigeon pea, and soybean than on those of lablab or rice. Laboratory tests with N. parvusadults indicated that pigeon pea seeds were located faster, followed by common bean, soybean, and rice. When pods were tested, dabbing/antennation time was shorter on pigeon pea than on soybean, and probing time was longer on soybean than on pigeon pea or common bean. On pigeon pea, 100% of the insects probed the host, while on common bean and soybean pods, and on rice panicles, these values dropped to 71.8%, 46.0%, and 10.5%, respectively. Adults showed similar feeding times on pigeon pea, common bean, and soybean pods, but did not feed on rice panicles. Electronmicroscopical analysis showed the presence of two apical lobes with 12 peg sensilla on the labial tip. Sensillum tips were stained with silver nitrate solution, indicating a permeability of the cuticle and, therefore, their function as taste receptors.