Response of last instar Heliothis zea larvae to carbohydrates: stimulation of biting, nutritional value

Several carbohydrates were tested for their ability to stimulate last instar Heliothis zea larvae to bite and, as a measure of nutritional value, for their ability to prolong the lives of H. zea larvae in the absence of a protein. Sucrose, fructose and glucose strongly stimulated biting. Maltose and sorbose were weakly stimulating, and mannitol, rhamnose, galactose, and lactose did not stimulate biting at the concentrations tested. Sucrose, fructose, mannitol, maltose, glucose, galactose, corn starch, and lactose all prolonged life, but larval longevity varied among these carbohydrates. Rhamnose did not prolong life, nor did sorbose, which was slightly toxic. When fructose, glucose, or mannitol replaced sucrose in a nutritionally complete defined diet containing protein, utilization efficiencies were minimally affected. When sorbose was substituted for sucrose, it did not cause mortality, but it did depress the efficiency of utilization significantly below that of a control diet that lacked any carbohydrate except cellulose powder.

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Résumé L'étude a porté sur l'apitude de plusieurs carbohydrates à stimuler les morsures des chenilles du dernier stade de H. zea et à prolonger leur vie, (mesure de la valeur nutritive), en absence de protéines. Sucrose, fructose et glucose stimulent fortement les morsures. Maltose et sorbose ont été faiblement stimulants, et rhamnose, galactose, lactose et mannitol n'ont pas stimulé aux concentrations examinées. Sucrose, fructose, mannitol, maltose, glucose, galactose, amidon de maïs et lactose ont tous prolongé la vie, mais d'une façon différente suivant les carbohydrates.La rhamnose n'a pas prolongé la vie, tout comme le sorbose, qui s'est révélé légèrement toxique. Quand le fructose, le glucose ou le mannitol ont remplacé le sucrose dans un régime complètement défini contenant des protéines, la perturbation de l'efficacité d'utilisation a été minimale, mais la substitution du sorbose par le sucrose, bien qu'elle n'ait pas provoqué de mortalité, a donné une efficacité d'utilisation significativement plus faible qu'un témoin négatif ayant perdu tous les carbohydrates, à l'exception de poudre de cellulose.

     

Effects of prococene II on the nutritional physiology of last instar Heliothis zea larvae

When precocene II was fed to last instar larvae of Heliothis zea, it caused significant reductions in the calculated rate of growth, rate of nutrient assimilation, and conversion of ingested and digested food to body mass. No change in the rate of food consumption occurred but respiration was significantly higher. Transport of the nutrient [1-¹⁴C] linoleic acid across midgut tissue was hindered when larvae were fed precocence II. There was also a precocene-induced change in the apical (luminal) morphology of midgut cells, including absence of the glycocalyx and loss of the microvillar absorptive surface. The influence of precocene II on the midgut physiology and metabolic processes in last instar larvae of H. zea may account for the observed reduced growth and delayed development. © 1992 wiley-Liss, Inc.     

Relationship of Heliothis zea predators, parasitoids and entomopathogens to canopy development in soybean as affected by Heterodera glycines and weeds

The influence of canopy development in soybean on the survival of corn earworm, Heliothis zea (Boddie) (Lepidoptera: Noctuidae), egg and larval stages and population dynamics of arthropod fauna were evaluated in field trials during 1986–88 in eastern North Carolina. Soybean canopy size decreased as soybean cyst nematode, Heterodera glycines Ichinohe (Nematoda: Heteroderidae), initial population densities increased. Plant species composition of the soybean canopy was affected by weed population densities. Mortality of H. zea larvae due to parasitism and infection with entomopathogens was greater in closed canopy and (or) weedy soybeans than in very open and (or) weed free soybeans. Predation and parasitism of corn earworm eggs were similar across nematode and weed density treatments. Natural enemy populations increased to highest levels during July in closed canopy and (or) weedy soybeans, coinciding with availability of largest prey population reservoirs. A delay in colonization of very open and (or) weed free soybeans by beneficial arthropods until mid to late August allowed greater H. zea larval survival than in closed canopy and (or) weedy soybeans. Arthropod species richness was generally greatest in closed canopy and (or) weedy soybeans during mid to late July, with differences becoming nonsignificant in August and early September. Mean and maximum ambient temperatures were higher and relative humidities lower in open canopy than in closed canopy plots. These conditions were less favorable for development of pathogens and natural enemies.     

Drought tolerance processes in soybeans

Fifteen soybean cultivars were evaluated in two water supply conditions, inducing or not a drought stress. Main canopy traits were measured several times during the reproductive period and, at maturity date, the yield components were estimated. Using principal components analysis, the main physiological functions involved in soybean drought tolerance are described: leaf cells enlargement and assimilates transport. These processes could be a good basis on which to define new selection criteria for soybean drought tolerance.     

Effect of soil pH and sewage sludge on VA mycorrhizal infection of soybeans

Summary Small plots were amended in 1976 or 1978 with four kinds of sewage sludge. The sludges represented samples considered to be relatively free of heavy metals as well as sludges highly contaminated with heavy metals. Sludges were added to a silt loam soil at rates of 224 or 448 Mgha⁻¹. The soils were maintained at a high or low pH regime. In 1984, soybeans (Glycine max L. Merril. var. ‘Clark’) were planted and grown to the R4 stage. After harvest, roots were removed from the soil, washed, and examined for VA mycorrhizal infection. It was found that the heavy metal content of the sludge alone was generally not related to determining the extent of mycorrhizal infection. A heat treated sludge, high in heavy metals, exhibited the highest degree of mycorrhizal infection when the soil was maintained at a pH of 6.2. With this treatment, 52% of the root segments examined were infected by mycorrhiza. When the same sludge was added to a soil with a slightly lower pH (5.7) none of the roots examined were infected by mycorrhiza. When soybean roots were examined from soils that received no sludge and were maintained at either a low (5.6) or high (6.2) pH, there was no significant difference in mycorrhizal infection between the pH regimes. These results therefore indicate that sewage sludge may inhibit mycorrhizal infection if the sludge contains a high concentration of heavy metals and the sludge is applied to the soil with a low pH. Scientific Article No. A-4093 and Contribution No 7078 of the Maryland Agric. Exp. Stn., Dept. of Agronomy, University of Maryland, College Park, MD 20742.     

Conditional lethality involving nuclear and cytoplasmic chlorophyll mutants in soybeans

Summary A conditionally lethal phenotype occurred when a nuclear chlorophyll mutant (y ₂₀-k ₂) was present with a cytoplasmic chlorophyll mutant (cyt-Y ₂) in soybean (Glycine max [L.] Merr.). Nuclear mutant y ₂₀-k ₂, Genetic Type Collection Number T253, has yellow foliage, tan-saddle-pattern seed and is viable. The y ₂₀-k ₂ mutant cannot be separated by classical genetic tests into two separate components, y ₂₀ (yellow foliage) and k ₂ (tan-saddle-pattern seed). Mutant cyt-Y ₂, T275, is inherited cytoplasmically, has yellow foliage, and is viable. The genotype cyt-Y ₂ y ₂₀-k ₂/ y ₂₀-k ₂ is a conditional lethal; the genotype is lethal under field conditions, but plants survive under greenhouse conditions. This interaction is unique to y ₂₀-k ₂. This conditionally lethal genotype may be useful in molecular studies on the interaction between nuclear and plastid genomes.This is a joint contribution of North Central Region, USDA ARS, and Journal Paper No. J-11429 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa, and the Agriculture Experiment Station, Univ. of Puerto Rico, Mayaguez Campus, Mayaguez, Puerto Rico 00708. Projects 2471 and 2475. The research was supported in part by the Iowa Soybean Promotion Board.     

Self-selection and utilization efficiency of Heliothis zea larvae feeding on seeds and the walls of snap bean pods

First instar Heliothis zea larvae tended to feed on the leaves of snap beans, but later instars preferred to burrow in the pods. Fifth instars offered only leaves grew poorly because they ate them in small quantities, presumably because of deterrency. The utilization efficiency and growth of fifth instars fed pulp was slightly but significantly inferior to that of seed-fed larvae but was greatly superior to that of leaf-fed larvae. Since the dry matter content of pulp is less than one-third that of seeds, larvae allowed to eat only pulp had abnormally large fresh weight intakes and devoted about three times as much time to feeding as did seed-fed larvae. Larvae offered a mix of seeds and pulp ate both and had a total fresh weight food intake somewhat greater than that of seed-fed larvae but much less than that of pulp-fed larvae. Eating both seeds and pulp offers no obvious nutritional advantage but presumably offers a significant ecological advantage. It is argued that the number of foraging trip a larva must make to discover pods is minimized by feeding on a mix, thus reducing exposure to mortality factors such as predation.     

Temporal oviposition patterns of Heliothis zea and Spodoptera ornithogalli

Egg production under laboratory conditions was examined over the lifespan of Heliothis zea (Boddie) and Spodoptera ornithogalli Guenée (Lepidoptera: Noctuidae). Although H. zea oviposits singly and S. ornithogalli oviposits in masses, temporal trends were similar. Egg numbers peaked shortly after mating and then rapidly declined. Egg weights also peaked shortly after mating, but decreased gradually over time. Temporal oviposition patterns were more erratic for unmated than mated females, suggesting the importance of mating in establishing the shape of the oviposition curve.

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Résumé La production d'ufs d'Heliothis zea (Boddie) et de Spodoptera ornithogalli Guenée (Lepidoptera: Noctuidae) durant toute la vie adulte a été examinée au laboratoire. Bien que H. zea dépose ses ufs isolément et que S. ornithogalli les dépose en groupes, les courbes temporelles d'oviposition chez des individus fécondés sont similaires. Le nomber d'ufs culmine peu après l'accouplement, puis décline rapidement. Le poids des ufs culmine aussi peu après l'accouplement, puis décroît graduellement. Des femelles fécondées produisent environ deux fois autant d'ufs que les femelles non fécondées, quoique la longévité ne diffère pas significativement entre les deux groupes. Des femelles non fécondées montrent des distributions temporelles plus irrégulières que des femelles fécondées, en ce qui concerne le nombre des ufs et leur poids. Ces irrégularités ont été attribuées à la tendance des femelles non fécondées à retenir leur ufs, ce qui suggère que l'accouplement exerce une influence sur la forme de la courbe temporelle d'oviposition. Des femelles d'H. zea contenant un, deux ou trois spermatophores n'ont pas produit des nombres d'ufs significativement différents.

     

Behavioral changes and growth inhibition in last instar larvae of Heliothis zea induced by oral and topical application of precocene II

In diet choice tests, newly-ecdysed fifth instar Heliothis zea larvae randomly chose diet containing 4 mM precocene II or diet without precocene II but initially preferred to feed on diet without precocene II. After two days, however, they were found more frequently on diet containing precocene II. Nevertheless, larval growth and development were inhibited when forced to eat diet containing precocene II. Removal of the maxillae, the site of the primary gustatory receptors, did not prevent the growth inhibition caused by larval consumption of diet with precocene II. Topical treatments with precocene II also caused larval growth inhibition, and daily treatments were more detrimental to the larvae than a large single dose. Addition of methylenedioxyprecocene (6,7-methylenedioxy-2,2-dimethylchromene) to the diet did not reverse the observed larval growth inhibition and this compound was itself significantly toxic. These results indicate that larval growth and development are disrupted after precocene II ingestion, but not because of preingestive discrimination by olfaction and gustation.     

Effect of vesicular-arbuscular mycorrhizae on the growth and yield of rice-stubble cultured soybeans

Summary Inoculation with vesicular-arbuscular (VA) mycorrhizal fungiGlomus fasciculatus, G. mosseae, G. etunicatus orAcaulospora scrobiculatus, increased plant dry weight and seed yields of pot-grown soybean plants in sterilized soil. Inoculation with a mixture ofG. fasciculatus, G. mosseae andG. etunicatus, orG. fasciculatus alone, increased seed yields and other agronomic traits of soybean plants grown in a no-tillage, rice-stubble field.     

Nutrient self-selection by Heliothis zea larvae: A time-lapse film study

When presented with two nutritionally incomplete diets, one lacking only the protein (casein) and the other lacking only the digestible carbohydrate (sucrose), last instar larvae of Heliothis zea (Boddie) (Lepidoptera: Noctuidae) switched between the diets frequently. The ratio (casein:sucrose) of time they spent on the two diets was about 83:17. As the stadium proceeded, the relative time they spent on the sucrose diet increased. Control larvae, offered two identical, nutritionally complete diets, seldom switched between them.

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Résumé Récemment nous avions montré que les chenilles du dernier stade d'H. zea (Boddie) (Lep.: Noctuidae) composaient elles-mêmes leurs repas à partir de 2 cubes d'aliments, l'un carencé en protéine (caséine), l'autre en carbohydrate assimilable (sucrose). Dans cette nouvelle étude, les témoins ont reçu deux cubes nutritivement complets et les lots expérimentaux (en auto-complexification) deux cubes nutritivement incomplets, l'un carencé en caséine, l'autre en sucrose. Les chenilles ont traversé 3 étapes pendant ce dernier stade; une phase initiale de perturbations durant laquelle elles ne mangeaient presque pas, mais changeaient souvent de cube, une phase d'installation pendant laquelle elles consommainet d'une façon plus ou moins continue; et une phase de prénymphose pendant laquelle elles vagabondaient. La phase perturbée était moins longue chez les témoins, mais les deux lots présentaient le même comportement pendant cette phase: changeant de cube jusqu' à neuf fois par heure. Dès que la prise d'aliment a commencé dans la phase installée, les témoins changeaient de cube au hasard, tandis que les chenilles en expérience en changeaient relativement plus, passant 17% de leur temps sur le sucrose et 83% sur la caséine. Les comportements étaient identiques chez les deux lots pendant la phase de prénymphose. L'autocomplexification correspond à un comportement particulier pendant le dernier stade: l'alimentation sur caséine domine tôt, elle tend ensuite à rester constante tandis que l'alimentation sur caséine est maximale vers la fin du stade. Notre hypothèse est que l'auto-complexification est gouvernée par des feedbacks physiologiques internes déterminant la prise d'aliments, et que la chenille peut apprendre à associer un goût à un contenu nutritif.

     

The effect of silicon on the manganese nutrition of soybeans (Glycine max (L.) Merrill)

Summary Silicon during the early vegetative stage did not affect the oven dry weight of any of the various tissues of the soybean plant. Silicon did, however, decrease the Mn concentration in the youngest fully mature leaf at intermediate levels of Mn. This effect did not occur at the lowest or highest Mn levels. Deficiency and toxicity symptoms were moderated to a slight degree by Si except at the highest level of Mn.     

The role of active Bradyrhizobium japonicum in iron stress response of soybeans

The objective of this study was to identify the sites of H-ion exudation and Fe(III) reduction along both inoculated and non-inoculated roots of A7 and T203 soybeans. A split-root system was used in which half the roots of each plant were inoculated and actively fixing nitrogen and the other half were not. Expectedly, the Fe-stress response was strong on both sides of the split-root system in the +N-Fe treatment of variety A7 (inactive nodules) but not of variety T203. The Fe-stress response of A7 was enhanced by the presence of active nodules. Variety T203 is Fe inefficient and normally fails to produce any Fe-stress response, but in the absence of nitrogen and iron (–N–Fe), inoculated roots responded to Fe stress with exudation of both H-ions and reductants. Intact split-root systems were embedded in agar to determine the location of H-ion exudation and Fe(III) reduction. On the inoculated side of the –N–Fe and –N+Fe treatments (active nodules) of both soybean varieties, H-ion production was associated mainly with the active nodules. However, quantities of H-ion release were much greater under Fe stress (–N–Fe) than with adequate Fe (–N+Fe). Reduction of Fe(III) to Fe(II) was found only on the nodulated side with T203, but on both sides with A7. In variety T203 the Fe reduction was associated with younger roots located just below the nodule clusters on the inoculated side of the –N treatments. Active nodules appear to play a key role in the Fe-deficiency stress response of T203 soybean.     

Effects of N-serve on soybeans and soil nitrogen transformations

Summary Plant dry weight, total N, and total Ca was increased at 0.1 and 1 ppm N-serve. At greater 10 ppm the plants showed visual symptoms of a stunted growth, stem elongation, flowers, and pods failed to form or were aborted, young leaves were curled, and roots were club shaped with many branches. These symptoms were increasingly evident with increasing N-serve application rates. The reason was attributed to an auxin effect. Dry wt and total N in the plant was less than the control at the higher N-serve applications. There was little effect on nitrogenase activity at less than 10 ppm N-serve. Nodulation tended to increase at 0.1 and 1 ppm N-serve.Nitrification was inhibited up to 104 days at 20 ppm N-serve. The soil pH of the high N-serve rates was decreased at 104 days probably due to nitrification. Generally there were little detectable differences among treatments in soil organic N. The average soil organic N from 0 to 104 days decreased by 0.01%. Average increase in total N within each pot at harvest was equivalent to about 138 kg N/ha.     

Factors affecting pathogenicity of NPV preparations to the corn earworm,Heliothis armigera

Pathogenicity ofHeliothis nuclear polyhedrosis virus (HSNPV) to the corn earworm,Heliothis armigera, was studied using 3 different inoculative methods. The LD50 values of 4^th-instar larvae inoculated with corn-fed, diet-fed and inoculum-imbiding method were 1.85×10⁶, 2.55×10⁵ and 1,22×10³ PIBs/larva, respectively. The inoculum-imbiding is more sensitive and convenient for inoculatingH. armigera with HSNPV. The HSNPV product, Elcar^®, was highly pathogenic toH. armigera, the LD50 values of 2^nd-, 3^rd- and 4^th-instar larvae being 27, 83 and 1,221 PIBs/larva, respectively, as measured by the inoculum-imbiding method. The mortality of 4^th-instar larvae caused by HSNPV was increased, but the incubation period was shortened with higher incubation temperatures. However, the high temperature at 35°C caused a lower mortality, and a prolongation of the median lethal time (LT50). Stability and persistence of HSNPV preparations were better in January–February and April–May than in June–July and October–November periods when sprayed on corn silks under field conditions. The HSNPV was inactivated by weak alkaline dew (pH 8.1) collected from soybean leaves, but it remained active on those from corn, tomato and asparagus with pH 7.2–7.3. The artificial heavy rainfall of 242 mm/h for 30 min did not wash off HSNPV preparations sprayed on the corn silks.     

Breeding soybeans for the tropics capable of nodulating effectively with indigenousRhizobium spp.

Summary Most soybean varieties fail to nodulate effectively in tropical soils unless inoculated with a competitive strain ofRhizobium japonicum. Developing countries in the tropics, with few exceptions, lack inoculant industries to produce and distribute viable inoculants to small farmers and extension programs to teach them to use inoculant. Several soybean genotypes have been identified that nodulate effectively with many strains of the cowpea inoculation group which is ubiquitous in tropical soils of Africa. Soybean genotypes that nodulate and grow well without inoculant application are called promiscuous. Methodologies for incorporation of the promiscuity character into high-yielding backgrounds are discussed.Supported in part by grant 05-0560 from United Nations Development Program to the International Institute of Tropical Agriculture.     

Development of resistant transgenic soybeans with inverted repeat-coat protein genes of soybean dwarf virus

In an attempt to generate soybean plants resistant to soybean dwarf virus (SbDV), we transformed a construct containing inverted repeat-SbDV coat protein (CP) genes spaced by β-glucuronidase (GUS) sequences into soybean somatic embryos via microprojectile bombardment. Three T₀ plants with an introduced CP gene were obtained, and one generated T₁ seeds. The presence of the transgene in T₁ plants was confirmed by PCR and Southern blot hybridization analysis, but expression of CP was not detected by northern blot hybridization analysis. Two months after inoculation of SbDV by aphid, T₂ plants contained little SbDV-specific RNA and remained symptomless. These plants contained SbDV-CP-specific siRNA. These results suggest that the T₂ plants achieved resistance to SbDV by an RNA-silencing-mediated process.     

Natural diets and self-selection: Heliothis zea larvae and maize

Although the first two instars tend to eat the silks, last instar larvae of the corn earworm, Heliothis zea (Boddie) (Lepidoptera: Noctuidae), prefer to feed on the kernels rather than on the other components of the maize ear. They feed preferentially on the germ of the kernel, but when offered whole kernels also eat some of the endosperm. Larvae that eat cut portions of the kernels that include all of the germ and some endosperm utilize their food for growth more efficiently than do larvae that eat portions of the kernel that include only endosperm. Adults that ate germ portions or endosperm portions of the kernel as larvae do not differ significantly in longevity, number of days on which they oviposit, number of eggs laid per day or the percentage of the eggs that hatched. We suggest that the larvae use self-selection to increase their intake of germ, thus increasing utilization efficiency and decreasing the amount of food that they must eat. When they feed on plants (other than maize) with small fruits, this probably increases their ability to compete for food when it is scarce and minimizes exposure to predation by decreasing the number of foraging trips and the distance that they must travel in search of food.

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Résumé Bien que les deux premiers stades larvaires d'H. zea (Lepid.: Noctuidae) tendent à consommer les soies, les trois derniers stades préfèrent les grains aux autres parties de l'épi de maïs. La chenille du dernier stade consomme de préférence le germe du grain, mais quand on lui offre l'ensemble du grain, elle consomme aussi une partie de l'albumen. Les chenilles qui coupent des morceaux du grain comprenant la totalité du germe et une fraction d'albumen ont une alimentation permettant une croissance plus efficace que les chenilles qui consomment des portions de grain ne contenant que de l'albumen. Ainsi, les chenilles qui mangent des fractions de germe ont besoin de consommer moins, pour atteindre le même poids que les chenilles qui consomment des morceaux d'albumen. Les longévités, les nombres de jours de ponte, les fécondités quotidiennes et les fertilités des oeufs sont les mêmes pour les papillons provenant des chenilles ayant consomme des morceaux de germe ou des morceaux d'albumien. L'albumen seul est un aliment suboptimal, et H. zea pourrait théoriquement améliorer ultérieurement son régime en mangeant plus de germes. Nous estimons que ceci ne serait pas rentable puisque la durée des stades devrait être prolongée et que la manutention et les rejets d'albumen devraient être accrus. H. zea se serait adapté à une solution de compromis pour l'optimalisation du régime alimentaire. Il réduit le temps de récolte et perd en efficacité en consommant de l'albumin suboptimal; mais il regagne autant que possible en efficacité en mangenat le germe de pratiquement tous les grains attaqués. Cette augmentation de l'efficacité diminue la quantité d'aliments qui doit être ingéré, et fournit un potentiel adaptatif quand les chenilles consomment des plantes (autres que le maïs) avec des petits fruits. L'exposition à la prédation est réduite, puisque la distance parcourue pour la recherche des fruits est diminuée.

     

The use of the two T-DNA binary system to derive marker-free transgenic soybeans

Summary A binary vector, pPTN133, was assembled that harbored two separate T-DNAs. T-DNA one contained a bar cassette, while T-DNA two carried a GUS cassette. The plasmid was mobilized into the Agrobacterium tumefaciens strain EHA101. Mature soybean cotyledonary node explants were inoculated and regenerated on medium amended with glufosinate. Transgenic soybeans were grown to maturity in the greenhouse. Fifteen primary transformants (T₀) representing 10 independent events were characterized. Seven of the 10 independent T₀ events co-expressed GUS. Progeny analysis was conducted by sowing the T₁ seeds and monitoring the expression of the GUS gene after 21 d. Individual T₁ plants were subsequently scored for herbicide tolerance by leaf painting a unifoliate leaf with a 100 mgl⁻¹ solution of glufosinate and scoring the leaf 5 d post application. Herbicide-sensitive and GUS-positive individuals were observed in four of the 10 independent events. Southern blot analysis confirmed the absence of the bar gene in the GUS positive/herbicide-sensitive individuals. These results demonstrate that simultaneous integration of two T-DNAs followed by their independent segregation in progeny is a viable means to obtain soybeans that lack a selectable marker.