Energy relationships between larvae of Phaedon cochleariae (Coleoptera; Chrysomelidae) or Plutella maculipennis (Lepidoptera; Plutellidae) and radish or turnip plants

Calorific values per gram of freeze-dried leaves, roots, pupae and larval faeces were used to convert dry weights of plants and insects into measurements of energy content. The decreased yield, or loss of energy, of plants resulting from injuries to leaves caused by a single insect during its larval life differed considerably between each of the four possible combinations of insect and plant, being 0 to 22 times the energy content of the leaf tissue eaten by the larva and 0 to 76 times the energy content of the pupa.

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Zusammenfassung Der Kalorienwert je Gramm gefriergetrockneter Blätter und Wurzeln von Rettich-und Rübchen-Pflanzen wurde bestimmt. Er betrug mit Ausnahme für Rettich-Wurzeln (3.32 kcal/g) ungefähr 4 kcal/g. Die Kalorienwerte für gefriergetrocknete Puppen von Phaedon cochleariae bzw. Plutella maculipennis lag bei etwa 6 kcal/g.Der Energieverlust, der an den Pflanzen bis zur Ernte durch den Fraß eines einzelnen Insekts während seines Larvallebens verursacht wird, wurde für jede der möglichen Kombinationen von Pflanze und Schädling berechnet. Plutella verringert den Ertrag der Rübchen nicht, aber andererseits betrug der Verlust von Blatt-und Wurzelgewebe zwischen dem 12-und 22-fachen des Energiegehalts der durch das Insekt zerstörten Blattgewebe und das 45-bis 76-fache des Energiegehalts der Puppe.

     

Predation by Podisus maculiventris (Hemiptera: Pentatomidae) on Plutella xylostella (Lepidoptera: Plutellidae) larvae parasitized by Cotesia plutellae (Hymenoptera: Braconidae) and its impact on cabbage

Biological control offers potentially effective suppression of the diamondback moth (DBM), Plutella xylostella, a serious pest of Brassica crops. Little is known of whether multiple natural enemies have additive, antagonistic, or synergistic effects on DBM populations. No-choice and choice tests were conducted to assess predation by Podisus maculiventris on DBM larvae parasitized by Cotesia plutellae and unparasitized larvae. In no-choice tests, P. maculiventris preyed on greater numbers of parasitized than unparasitized larvae and greater numbers of young larvae than old larvae. In choice tests with early third instar DBM, there was no difference in predation between parasitized or unparasitized larvae. However, in choice tests with older prey, P. maculiventris preyed on more parasitized than unparasitized larvae. Two field studies were conducted to test if this predator and parasitoid have additive, antagonistic or synergistic effects on DBM populations and plant damage in cabbage (Brassica oleracea var. capitata). In 2002, DBM populations were significantly lower in the presence of C. plutellae but not in the presence of P. maculiventris. There was not a significant interaction between the natural enemies. Plant damage was reduced only with C. plutellae. In 2003, DBM populations were significantly lower in the presence of C. plutellae and P. maculiventris, although the combination of natural enemies did not lead to a non-additive interaction. Plant damage was unaffected by the presence of either natural enemy. Because of its greater predation on parasitized larvae, P. maculiventris could be an intraguild predator of C. plutellae. Yet, their overall combined effect in the field was additive rather than antagonistic.     

Agar and chemostimulant concentrations and their effect on intake of synthetic food by larvae of the mustard beetle, Phaedon cochleariae Fab.

Summary Mustard oil glucosides are necessary to maintain feeding on synthetic media by larvae of the mustard beetle, Phaedon cochleariae Fab. Suitable physical texture of the medium increases intake. Attention should be paid to these factors before developing and modifying the nutrient content of synthetic media.

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Zusammenfassung Bei der Herstellung einer synthetischen Nahrung zur Aufzucht von Larven des Meerrettichblattkäfers, Phaedon cochleariae Fab., ist zur Erreichung kontinuierlichen Fraßes die Beigabe des Senfölglukosides Sinigrin in optimalen Konzentrationen von 5000–10000 ppm notwendig.Der Zusatz des Senföls Allylisothiocyanat ergab in Kontrollversuchen keine Erhöhung der Fraßmenge, ebensowenig die Beimischung eines grünen Futterfarbstoffes. Die Anwendung von Farbreizen zur Einschränkung des Umherwanderns der Larven und der Variabilität der Resultate erwies sich als erfolglos. Von 3 auf 6% ansteigende Agarkonzentration verdreifachte die Nahrungsaufnahme der Larven.

     

Growth and food consumption during the larval stages of Paropsis atomaria (Coleoptera: Chrysomelidae)

The relative gross efficiency of food utilization by the larvae of Paropsis atomaria was estimated on eight occasions during their development on shoots of their preferred host plant, Eucalyptus blakelyi. The overall conversion ratio of 0.200 is compared with the ratios determined by other authors for a range of phytophagous insects. The ratios obtained for the separate growth stages of P. atomaria suggest that conversion efficiency declines temporarily following each ecdysis, and as the final-instar larva approaches maturity.

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Zusammenfassung Die Käferlarven wurden im Laboratorium auf abgeschnittenen Trieben der bevorzugten Wirtspflanze, Eucalyptus blakelyi Maiden, gezüchtet. Außer während des ersten Larvenstadiums und während der letzten Tage des vierten Larvenstadiums vergrößerte sich der Zuwachs der Larven mit der Zeit geometrisch.Der große Futterausnützungs-Quotient oder die Umsatzrate (Lebendgewichtzuwachs der Larven/Frischgewicht des aufgenommenen Futters) wurde während der 18 Tage des Larvenlebens 8mal gemessen. Die Umsatzrate sank vorübergehend nach jeder Häutung und auch in den letzten Tagen des vierten Larvenstadiums. Während dieser letzten Periode nahm das Wachstum der Larven verhältnismäßig schneller ab als die Nahrungsaufnahme; gleichzeitig erhöhte sich der Wassergehalt im Kot.Die Umsatzraten von P. atomaria (0.200) und der ebenfalls Eucalyptus-Blätter fressenden Sägewespe Perga affinis (0.242) liegen in der Mitte des Bereichs des Quotienten, der von anderen Autoren für pflanzenfressende Insektenarten ermittelt wurde.

     

Behavioural response to different wavelength bands and attraction to colour by larvae of the mustard beetle Phaedon cochleariae

Larvae of the mustard beetle Phaedon cochleariae Fab. show differential response to light of different wavelengths. With brightness of wavelength bands adjusted to correct for sensitivity of the receptors, greatest numbers of larvae go to yellow (570–600 nm) and yellow-green (520–570 nm) bands.

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Über morphologischer unterschiede innerhalb acyrthosiphon pisum und in der Übertragungsfähigkeit für das schwerechlorosevirus der ackerbohne

Zusammenfassung Larven des Meerrettichblattkäfers zeigen eine unterschiedliche Reaktion gegenüber Licht verschiedener Wellenlänge über den Bereich von 440 bis 680 nm. Die Zahl der Larven, die sich auf Leuchtschirme zu bewegen und diese erreichen, wurde als Reaktionsmass verwendet. Am meisten Tiere bewegten sich auf gelbgrünes Licht (520–570 nm) zu. Die Intensität der Wellenlängebereiche wurde nun der Empfindlichkeit der larvalen Rezeptoren angepasst, und es wurde zur Ausschaltung der Reaktion auf Helligkeit eine andere Lichtquelle verwendet. Damit konnte bestätigt werden, dass die Larven von Farben angezogen werden und nicht bloss auf Helligkeit reagieren.

     

Antixenosis in maize reduces feeding by western corn rootworm larvae (Coleoptera: Chrysomelidae)

SUM2162 is the first known example of a naturally occurring maize, Zea mays L., genotype with antixenosis (nonpreference) resistance to western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), larval feeding. Behavioral responses of neonate western corn rootworm larvae were evaluated in laboratory bioassays with seven maize genotypes selected for native resistance to rootworm feeding damage. Two susceptible maize genotypes and one transgenic (Bacillus thuringiensis) maize genotype were included as controls. In soil bioassays with cut roots, no larvae entered the roots of the resistant variety SUM2162, but at least 75% of the larvae entered the roots of every other maize type. Larvae made significantly fewer feeding holes in the roots of SUM2162 than in all the other maize genotypes, except the isoline control. In feeding bioassays, larval feeding varied significantly among maize genotypes, but there was no significant difference between the resistant varieties and the susceptible controls. There were no significant differences among any of the genotypes in host recognition (search) behavior of larvae after exposure to the roots. Little variation in feeding stimulant blends was observed among maize genotypes, indicating minimal contribution to the observed antixenosis.     

Identification of feeding stimulants in corn roots for western corn rootworm (Coleoptera: Chrysomelidae) larvae

Using a bioassay-driven approach, we have isolated and identified a blend of compounds from the roots of germinating corn, Zea mays L., that serve as feeding stimulants for neonate western corn rootworm larvae, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae). The active blend is a combination of simple sugars (30:4:4 mg/ml glucose:fructose:sucrose in the corn root) plus at least one of the free fatty acids in germinating corn roots (2:5 mg/ml oleic acid:linoleic acid in the corn root). When an extract of germinating corn was partitioned into an ethyl acetate fraction and an aqueous fraction, full feeding occurred only when the two fractions were recombined, indicating that the phagostimulant was comprised of both polar and nonpolar components. Gas chromatography-mass spectrometry analysis of root extracts from germinating corn seedlings revealed a blend of 20 compounds from a variety of chemical classes, including small sugars, diacids, amino acids, inorganic compounds, and free fatty acids. When the major components were tested in feeding bioassays, the sugars and lipids were shown to be essential for feeding by larvae, but the two classes of compounds were only effective when combined. The sugars alone elicited feeding by only 40% of larvae, but the percentage of larvae feeding was increased significantly with the addition of linoleic acid (91.7% larvae feeding) or oleic acid (85.8% larvae feeding). The amino acids alone were not essential elements for feeding by western corn rootworm larvae.     

Insecticide enhancement with feeding stimulants in corn for western corn rootworm larvae (Coleoptera: Chrysomelidae)

Amounts of the insecticide thiamethoxam required for 50% mortality of western corn rootworm larvae, Diabrotica virgifera virgifera LeConte, were reduced 100-fold when extracts of germinating corn, Zea mays L., were used to entice neonate larvae to feed on it. In behavioral bioassays, neonate rootworm larvae fed vigorously on filter paper disks treated with liquid pressed from corn roots. Moreover, disks treated with an acetone extract of corn (dried and rewetted with water) also elicited strong feeding from larvae. Larvae wandered away from filter paper disks treated with distilled water without feeding. Dilutions of thiamethoxam were tested in the bioassay alone or with corn extract and the efficacy of this insecticide was improved by the addition of the corn extract. For solutions containing 10 ppm thiamethoxam, 95% larval mortality occurred after 30 min of exposure when corn extract was present, but only 38% mortality occurred when the same concentration of insecticide alone (no feeding stimulants) was tested. Larval mortality after 24 h was significantly higher for corn extract-treated disks with 0.01, 0.1, 1, or 10 ppm insecticide than for the same concentrations without corn extract. Thiamethoxam did not deter larval feeding on corn extract, even at the highest concentration of thiamethoxam tested.     

Insecticidal effectiveness ofMammea Americana (Guttiferae) extracts on larvae ofDlabrotica Virgifera Virgifera (Coleoptera:Chrysomelidae) andTrichoplusia Ni (Lepidoptera:Noctuidae)

Seed and leaf extracts ofMammea americana (mamey apple) have a historical use as a biopesticide with the active components previously characterized. We reexamined the utility of this natural bioinsecticide in light of existing sources of material as a by-product of the fruit processing industry. Our results addDiabrotica virgifera virgifera andTrichoplusia ni to the list of insects which are susceptible to the insecticidal ingredients ofM. americana and confirms earlier reports of activity againstBlatella germanica, Periplaneta americana, andPlutella xylostella. We report LD5Os for crude hexane extracts ofM. americana leaves and seeds againstT. ni. These materials represent renewable sources of bioinsecticides for agriculture, and should regenerate interest in coumarin-type compounds for novel pesticidal action.     

Effects of feeding by larvae of Phaedon cochleariae (F.) and Plutella maculipennis (Curt.) on the yield of radish and turnip plants

Different numbers of larvae of the beetle Phaedon cochleariae (F.) and the moth Plutella maculipennis (Curt.) were fed on the leaves of turnip plants (variety Early Milan White) and radish (variety French Breakfast) growing in a constant-environment room. Turnips grew more slowly than radish, were less affected by insect feeding and were affected more by Phaedon than by Plutella. Phaedon larvae severed leaf veins and rasped the leaf surface, thus killing more leaf tissue by desiccation than they ate. They remained on and greatly damaged the older leaves and their feeding reduced yield. Plutella larvae fed on leaves of all ages, which they ate cleanly, leaving the veins. They pupated sooner than Phaedon and did less damage to older leaves, which grew larger and lived longer than corresponding leaves on intact plants. This compensatory growth by turnip prevented loss of yield and may have increased it, as indicated by dry weight of the roots. Both species of insect decreased the yield of radish similarly. Loss of yield of turnip caused by Phaedon or of radish caused by both species of insects was negatively and linearly proportional to the number of larvae that fed on the leaves.     

新烟碱类杀虫剂拌种对马铃薯甲虫幼虫食物利用和生长发育的影响

为研究马铃薯甲虫Leptinotarsa decemlineata（Say）幼虫取食新烟碱杀虫剂噻虫嗪和吡虫啉处理（有效成分18 g/100 kg种薯拌种）播种90 d后马铃薯叶片的消化吸收和生长发育情况,在室内采用重量法测定了幼虫取食量、体重增加量、食物利用率,近似消化率以及蛹重等营养指标。 结果表明：70%噻虫嗪种子处理可分散粉剂拌种后,马铃薯甲虫幼虫的取食量、体重增加量、食物利用率、食物转化率、近似消化率和相对生长率以及蛹重显著低于10%吡虫啉可湿性粉剂拌种和空白对照（P＜0.05）,发育历期显著长于10%吡虫啉可湿性粉剂拌种和空白对照（P＜0.05）;而10%吡虫啉可湿性粉剂拌种后,马铃薯甲虫幼虫的取食量和3～4龄期的体重增加量与空白对照差异显著（P＜0.05）,蛹重、1～2龄幼虫的体重增长量、食物利用率、食物转化率、近似消化率、相对生长率和生长发育历期与空白对照差异不显著（P＞0.05）。 说明70%噻虫嗪种子处理可分散粉剂拌种对马铃薯甲虫幼虫的取食有显著抑制作用,不能很好地满足其生长发育营养物质的需要,幼虫取食其叶片后,近似消化率和相对生长速率显著降低,生长发育历期显著延长。 这有利于减少当季世代数,降低危害。     

Yield response of pumpkin and winter squash to simulated cucumber beetle (Coleoptera: Chrysomelidae) feeding injury

Field studies were conducted to characterize the yield responses of pumpkin, Cucurbita pepo L., and wintersquash, Cucurbita maxima Duch., to simulated striped cucumber beetle, Acalymma vittatum (F.), feeding damage. Preliminary studies in pumpkin ('Spookie') were conducted in 1993, and more complete studies in 1994 and 1995 in pumpkin (Spookie), and in 1995 and 1996 in winter squash ('Waltham'). Plants were artificially injured 1 time at the cotyledon, 1st, 2nd, or 3rd true leaf stages by clipping specified percentages of leaf area from all leaves on the plant. Treatments consisted of a control treatment with no simulated injury and 4 levels of simulated injury. Pumpkin treatments were 10, 20, 40, and 80% leaf area removal in 1993 and 1994 and 20, 40, 60, and 80% in 1995. Winter squash treatments were 20, 40, 60, and 80% leaf area removal in 1995, and 10, 20, 40, and 80% in 1996. In 1993, 5 wk after planting, mean leaf, stem, and total dry weight were significantly lower on pumpkin plants subjected to > or = 20% simulated leaf injury regardless of the growth stage when the injury occurred. Injury at the 3rd leaf stage resulted in a significant reduction in the mean leaf and total dry weight of plant, across all levels of injury. At 2-3 wk before crop maturity, fruit weight and number of fruit per plant were significantly lower with 80% leaf area removal. In 1994 and 1995, and when pumpkins were grown to full maturity and apparently able to compensate for the simulated damage, neither number nor weight of marketable fruit per plant were affected significantly by simulated injury at any stage of development nor level of simulated injury. In contrast, > or = 20% and 80% leaf area removal to winter squash resulted in significant reductions in the weight of marketable fruit and/or number of marketable fruit, in 1995 and 1996, respectively. The results of this study indicate that pumpkins can tolerate relatively high levels of simulated defoliation, whereas winter squash is less tolerant. Variable results across years in winter squash may indicate an interaction between injury and plant stress caused by abiotic factors such as soil moisture availability.     

食物和温湿度对二点委夜蛾幼虫取食和为害玉米苗的影响

【目的】调查显示,二点委夜蛾Athetis lepigone在田间的虫口密度与玉米被害率之间无明显的相关性,田间虫口密度并不能准确预测玉米苗被害率。为了探索二点委夜蛾幼虫发生量与玉米苗被害程度之间的关系,解释田间调查遇到的幼虫即使有时大量发生玉米苗却受损轻微的现象,本研究室内检测了外部环境条件如温度和湿度对二点委夜蛾幼虫取食为害玉米的影响以及昆虫自身的相关取食习性。【方法】将3龄末、4龄初二点委夜蛾幼虫分别置于下述8种温湿度和食物组合条件下进行处理：低温低湿无食物(15℃, 30%RH, 饥饿)、低温干燥无食物(15℃, 0%RH, 饥饿)、低温低湿有食物［15℃, 30%RH, 饲喂人工饲料(AD)］、低温干燥有食物(15℃, 0%RH, AD)、高温高湿有食物(36℃, 90%RH, AD)、高温干燥有食物(36℃, 0%RH, AD)、高温高湿无食物(36℃, 90%RH, 饥饿)、高温干燥无食物(36℃, 0%RH, 饥饿);处理4 h后,评价其对盆栽玉米苗的为害程度,并测定幼虫在4个不同温度(15℃, 24℃, 28℃和33℃)下对玉米叶片的取食量。分别用8种食物(马齿苋、紫苏、甘薯、白菜、大豆、南瓜和玉米叶叶片以及麦秸)将初孵幼虫驯化饲喂至3龄后,检测经过驯化处理后的幼虫对初始驯化食物、麦秸和和玉米叶片的选择性。【结果】在干燥条件下,无论是否经过饥饿处理,幼虫对玉米苗的为害程度均较高,尤其是高温干燥处理后,对玉米苗的平均为害级别达3.1级;低温干燥处理组和高温干燥处理组为害级别在4级以上(含4级)的幼苗数分别占幼苗总数的50%和40%。在15-33℃,二点委夜蛾幼虫的取食量随温度的升高而逐渐增加,48 h校正取食量分别为12.8, 31.8, 38.0和60.0 mg。用甘薯、白菜、大豆和南瓜叶片驯化的幼虫对初始驯化食物的选择率显著高于对玉米和麦秸的选择率;初始取食紫苏叶片的幼虫对紫苏和麦秸的选择率显著高于对玉米的选择性,初始取食玉米叶片、麦秸的幼虫分别对玉米、麦秸的选择性更高。【结论】干燥是二点委夜蛾幼虫增加对玉米摄入量的一个主要因素;二点委夜蛾适应短时高、低温的能力较强,在一定的温度范围(15-33℃),短时间内的取食量随温度升高而增加。作为干燥的一个辅助因素,温度通过影响二点委夜蛾幼虫的取食量而决定其为害玉米苗的程度;二点委夜蛾倾向于选择初孵幼虫最先接触的食物;二点委夜蛾在玉米苗上的发生为害在很大程度上取决于其自身食性。     

Karyology and Cytotaxonomy of the Genus Chrysolina Motschulsky (Coleoptera, Chrysomelidae)

Eight species of Chrysolina have been chromosomally studied in male individuals from Central Europe, South France and the Urals, in Russia. Ch. rufa had 2n = 23, Ch. purpurascens crassimargo 2n = 24 and a meioformula of 11 + Xy_p, Ch. globosa and Ch. bigorrensis 12 + Xy_p, Ch. umbratilis 2n = 30 and 14 + XY_p, a new non-chiasmate sex-chromosome system with both male sex-chromosomes of large size, Ch. cf. subcostata 12 + XY_p with large sex-chromosomes also, Ch. interstincta 2n = 40 and 19 + Xy_p, and Ch. obscurella 2n = 47. The taxonomic implications of these findings are discussed in relation with the current subgeneric classification of Chrysolina and principally that of the subgenera Colaphoptera, Sphaerochrysolina, Pleurosticha, Chalcoidea and Threnosoma.     

Impact of Galerucella birmanica (Coleoptera: Chrysomelidae) on growth and seed production of Trapa natans

Success in biological weed control programs depends upon the ability of host-specific herbivores to suppress populations of their host plant. While pre-release predictions of field host range (i.e., specificity) appear widely accurate, predictions about which agent or agent combination may suppress plant populations have lately been compared to predictions in a lottery. The history of weed biocontrol does not offer immediately obvious approaches to improve the lottery model, however, pre-release assessments of the impact of different herbivore densities on the invasive plant may provide an opportunity to improve predictions of success. In this paper, we report on the impact of the leaf beetle Galerucella birmanica on growth and reproduction of water chestnut, Trapa natans, in the native range in China. At low herbivore densities (10–50 larvae/rosette), plants compensated for leaf herbivory by increasing leaf production at the expense of reproductive effort. Inoculating >50 first instar larvae per rosette greatly suppressed biomass production and plants were unable to grow when three or more G. birmanica pairs were released per seven rosettes. In the native range, similar densities are found in the field, resulting in complete defoliation of T. natans. Our study indicates that G. birmanica feeding has significant negative impacts on T. natans. This chrysomelid species appears to be a promising biological control agent and we would predict that the species will be able to attain sufficiently high populations to control its host plant—if approved for release in North America.     

The food plant preferences of Phratora vitellinae (Coleoptera: Chrysomelidae)

In the Upper Rhine (Petite Camargue, Saint Louis, France) study site, Ph. vitellinae are found mainly on Salix nigricans on which they are bivoltine. Some beetles are occasionally observed on S. purpurea, especially in Spring, but never on S. alba, S. caprea and S. cinerea. In other European localities, S. nigricans or S. hegetschweileri at higher elevations are frequently recorded as host-plants. However, some populations are also found on S. purpurea, P. tremula and P. trichocarpa x deltoïdes, usually when neither S. nigricans nor S. hegetschweileri are present.All the Salicaceae on which Ph. vitellinae was observed in the field have leaves rich in phenylglycosides and with glabrous lower surfaces, at least in Spring. Ph. vitellinae was never recorded on those Salix species with leaf undersurfaces densely covered with trichomes.At the time of emergence of the beetles from hibernation, S. nigricans leaves are more developed than those of S. purpurea and S. cinerea. Moreover, those S. nigricans trees with the longer shoots in Spring support the largest number of beetles at their emergence. The preference of Ph. vitellinae for S. nigricans might be reinforced by these plenological differences.In the Petite Camargue, the same S. nigricans trees support the largest populations of beetles from one generation to the next and from year to year. This suggests that S. nigricans does not respond to defoliation with induced resistance to the beetles.All shoots on the branch seem to be equally suitable and attractive for oviposition. The older leaves at the base of the shoot and the younger ones at the top are less favored by ovipositing females. Survival of the egg batches and the groups of freshly emerged larvae is lower on the distal shoots of the branch and on the younger leaves. This might be due to a higher degree of exposure to predators.     

Endophyte isolate and host grass effects on Chaetocnema pulicaria (Coleoptera: Chrysomelidae) feeding

Endophytic fungi belonging to the genus Neotyphodium, confer resistance to infected host grasses against insect pests. The effect of host species, and endophtye species and strain, on feeding and survival of the corn flea beetle, Chaetocnema pulicaria Melsheimer (Coleoptera: Chrysomelidae) was investigated. The grass-endophyte associations included natural and artificially derived associations producing varying arrays of common endophyte-related alkaloids or alkaloid groups, peramine, lolitrem B, ergovaline, and the lolines. Preference and nonpreference tests showed that C. pulicaria feeding and survival were reduced by infection of tall fescue with the wild-type strain of N. coenophialum, the likely mechanism being antixenosis rather than antibiosis. In the preference tests, endophyte and host species effects were observed. Of the 10 different Neotyphodium strains tested in artificially derived tall fescue associations, eight strongly deterred feeding by C. pulicaria, whereas the remaining two strains had little or no effect on feeding. Infection of tall fescue with another fungal symbiont, p-endophyte, had no effect. Perennial ryegrass, Lolium perenne L., infected with six strains of endophyte, was moderately resistant to C. pulicaria compared with endophyte-free grass, but four additional strains were relatively inactive. Six Neotyphodium-meadow fescue, Festuca pratensis Huds., associations, including the wild-type N. uncinatum-meadow fescue combination, were resistant, whereas three associations were not effective. Loline alkaloids seemed to play a role in antixenosis to C. pulicaria. Effects not attributable to the lolines or any other of the alkaloids examined also were observed. This phenomenon also has been reported in tests with other insects, and indicates the presence of additional insect-active factors.     

Role of egg density on establishment and plant-to-plant movement by western corn rootworm larvae (Coleoptera: Chrysomelidae)

The effect of egg density on establishment and dispersal of larvae of the western corn rootworm, Diabrotica virgifera virgifera LeConte, was evaluated in a 3-yr field study. Implications of these data for resistance management plans for Bt crops are discussed. Viable egg levels of 100, 200, 400, 800, and 1600 eggs per infested plant were evaluated in 2000, 2001, and 2002. A 3200 viable egg level was also tested in 2001 and 2002. All eggs were infested on one plant per subplot in a field that was planted to soybean, Glycine max (L.), in the previous year. For each subplot, the infested plant, three plants down the row, the closest plant in the adjacent row of the plot, and a control plant at least 1.5 m from any infested plant (six plants total) were sampled. In 2000, there were five sample dates between egg hatch and pupation, and in 2001 and 2002, there were six sample dates. On each sample date, four replications of each egg density were sampled for both larval recovery and plant damage. Initial establishment on a corn plant seemed to not be density-dependent because a similar percentage of larvae was recovered from all infestation rates. Plant damage and, secondarily, subsequent postestablishment larval movement were density-dependent. Very little damage and postestablishment movement occurred at lower infestation levels, but significant damage and movement occurred at higher infestation rates. Movement generally occurred at a similar time as significant plant damage and not at initial establishment, so timing of movement seemed to be motivated by available food resources rather than crowding. At the highest infestation level in 2001, significant movement three plants down the row and across the 0.76 m row was detected, perhaps impacting refuge strategies for transgenic corn.     

小菜蛾血淋巴对玫烟色棒束孢入侵的生理防御反应

为了探讨小菜蛾Plutella xylostella血淋巴对玫烟色棒束孢Isaria fumosorosea的防御机制, 利用吉姆萨染色法在光镜下观察了小菜蛾4龄幼虫血细胞感染不同致病力玫烟色棒束孢后的免疫反应。结果表明： 玫烟色棒束孢的入侵可导致小菜蛾血细胞数量发生改变, 表现为入侵初期血细胞总数增加, 不同类型血细胞比例改变等。体表接种后8-45 h, 高致病力菌株PFCF-001处理的幼虫血细胞总数在24 h出现最高值6 250个/mm³, 而低致病力菌株PFCF-D58处理在36 h达到最高值3 000个/mm³, 比高致病力菌株处理滞后12 h。不同菌株处理下虫体参与防御反应的主要血细胞类型为浆血细胞和粒血细胞。小菜蛾幼虫血细胞在感菌初期能够产生粘附、吞噬、包被及形成结节等一系列防卫反应, 但最终无法抵挡高致病力菌株PFCF-001的侵染。结果说明小菜蛾幼虫血淋巴对玫烟色棒束孢的防御反应只有短暂的抑制作用, 不能从根本上清除、 消灭玫烟色棒束孢。