Showing papers on "Infestation published in 1998"

Differential induction of apoplastic peroxidase and chitinase activities in susceptible and resistant wheat cultivars by Russian wheat aphid infestation

Abstract: The intercellular peroxidase and chitinase activities of three wheat cultivars [Triticum aestivum L. cvs `Tugela DN', `Molopo DN' (Gariep) and `Betta DN'] containing the Dn-1 gene for resistance to the Russian wheat aphid (RWA) Diuraphis noxia (Mordvilko) and the corresponding near-isogenic susceptible cultivars (`Tugela', `Molopo' and `Betta') were studied under conditions of infestation and non-infestation. The aim was to gain information on the mechanism of resistance. The resistance response was induced by RWA infestation. Infestation rapidly induced the activities of both enzymes selectively in resistant wheat to levels of magnitudes higher than those in susceptible wheat. The genetic background in which the Dn-1 resistance gene is bred played a role and the level of activity corresponded to the level of resistance. Immunologic studies confirmed that the induction of enzyme activities was due to the induction of higher protein levels. These results indicate that peroxidase and chitinase may have a role in insect resistance.

Density-dependent factors regulating feeding success of Ixodes scapularis larvae (Acari : Ixodidae)

Abstract: We studied the effects of different parasite and host densities on the feeding success of larval Ixodes scapularis ticks upon white-footed mice Peromyscus leucopus Mice were infested daily with 10, 25, 50, or 100 larvae and kept individually or in groups of 2 and 3 to simulate co-nesting in the field Engorgement weight and molting success of replete larvae did not change during more than 3 wk of continuous infestation, but overall larval feeding success decreased from 24% to 12% with increased infestation density Grooming was observed in response to unattached, crawling larvae, and grooming of unfed ticks increased with infestation density Nearly all larvae completed engorgement once attached, although a few were groomed accidentally along with unattached ticks Co-nesting mice fed 2-3 times fewer ticks than did solitary mice because of increased frequency of self-grooming in the presence of nest-mates, but differences between groups of 2 or 3 mice were not significant Thus, increased mouse density may reduce the density of the tick population at first, but further increase in the number of co-nesting mice does not affect the feeding success of larval I scapularis and increased mouse density will increase tick density

Survival and Extinction of Xanthomonas campestris pv. campestris in Soil

Abstract: Carry-over of inoculum of X.c. pv. campestris in the soil from one cropping season to the next was studied in field experiments over three years. These studies were supported by laboratory and greenhouse experiments on quantitative assessment of bacteria by bioassay using the Most Probable Number technique, and on recovery rates of bacteria from the soil. The mean recovery rate from artificially infested soil was 58%. Extinction of X.c. pv. campestris in soil infested with infected plant debris proceeded exponentially and extinction rates depended on temperature, as did the decomposition of plant debris. In replicated field plots, over three years, infection foci of black rot disease were established. At harvest time, all plants were chopped and resulting plant debris was rotovated into the soil. The resulting soil infestation was sampled and showed clear infestation foci reflecting the original infection foci of the crop. These infestation foci decreased with time and disappeared after the winter. Follow-up crops remained virtually uninfected. The results show that in The Netherlands good crop and soil management impedes survival of inoculum from one year to the next, so that cabbage can be grown continuously. Polyetic carry-over of inoculum by debris in the soil can be avoided in The Netherlands.

Changes in Neotyphodium coenophialum infestation levels in tall fescue pastures due to different grazing pressures

Abstract: Infection of tall fescue (Festuca arundinacea Schreb.) with the mutualistic fungal endophyte Neotyphodium coenophialum (Morgan-Jones & Gams) Glenn, Bacon & Hanlin results in numerous biochemical and physiological changes that increase host persistence. This study was conducted to determine effects of steer (Bos taurus L.) grazing on changes in endophyte infestation levels of tall fescue pastures. Eighteen 1.2-ha pastures were seeded in 1992 in 20-cm drill rows involving combinations of high, medium, or low grazing pressure and 'Ky 31' tall fescue infested with N. coenophialum at four levels ranging from endophyte-free (E - ) to 80% infestation (E + ). Pastures were grazed for about 10 mo. each year from fall 1993 until summer 1996, although animals on some of the high grazing pressure pastures occasionally had to be removed because of insufficient forage. Endophyte levels were monitored yearly with protein-A sandwich enzyme-linked immunosorbent assay (PAS-ELISA). Stand density of tall fescue remained satisfactory throughout the study. After 2 yr, endophyte infestation levels in low grazing pressure pastures were at the same level as at the beginning of the study, and E + levels remained constant in all pastures that started at high E + , regardless of grazing pressure. However, in high and medium grazing pressure pastures, E + levels increased by 20 to 30%. Based on these data, we conclude that moderate and high grazing pressures influence endophyte infestation level of pastures and must be taken into account when designing pasture management systems.

Midwest farmers' perceptions of crop pest infestation

Abstract: Region, soil type, and tillage are important factors in severity of crop pest infestation. This study was conducted to determine the relative importance of these factors on severity of crop pest infestation as perceived by farmers. Correlations between pests were also studied. In a 1992 survey, farmers in 12 U.S. Corn Belt states were asked to rate the severity of crop pest infestation in their fields. The categories of pests included perennial and annual weeds in row crops, insects and diseases of corn (Zea mays L.) and sorghum [Sorghum bicolor (L.) Moench], and insects and diseases of soybean [Glycine max (L.) Merr.]. Means ranked from highest to lowest in the following order: annual weeds, perennial weeds, corn and sorghum insects, corn and sorghum diseases, soybean diseases, and soybean insects. Correlation coefficients ranged between 0.47 to 0.69 among corn and sorghum diseases, among soybean insects, and among soybean diseases, and between 0.04 and 0.41 among perennial weeds. Correlation coeffidents among annual weeds and among corn and/or sorghum insects spanned both of these ranges. Effects of either region and/or tillage were very highly significant (0.001), while soil type was not as significant an effect. In farmers' perceptions, weeds were the most serious pests and soybean pests the least serious pests; there was less relationship among perennial weeds than among pests in any other category; the drier western region was generally less severely infested; higher amount of conventional tillage practices produced less infestation; and differences in soil type were due to more severe infestation in loams, followed by infestation in clays, and then infestation in sands.

Genetic diversity and origin of siam weed (Chromolaena odorata) in Australia

Abstract: Asynchronous flowering was noted in a recently discovered infestation of siam weed in north Queensland. This may indicate some genetic diversity in the infestation, increasing concerns about the origin of the infestation. Internal transcribed spacer 1 (ITS1) sequence data were obtained for siam weed individuals from north Queensland, Indonesia, Thailand, South Africa, Ivory Coast, Brazil, Colombia, and the U.S. The ITS1 region is 258 base pairs long, and the populations that flower at different times in north Queensland differ by four base substitutions. The genotype common in north Queensland is also reported throughout the native and introduced ranges. The other genotype is reported only in north Queensland and southern Brazil. These data, in conjunction with prior investigations into possible origins, indicate that Brazil is the most likely source of the infestation in Australia. Nomenclature: Siam weed, Chromolaena odorata (L.) King & Robinson. #3 EUPOD. Additional Index Words: Genetics, weed control, invasion, biotype, DNA sequence, ITS 1, EUPOD. Abbreviations: ITS1, internal transcribed spacer 1; CTAB, hexadecyltrimethyl-ammonium bro- mide; DNA, deoxyribonucleic acid; EDTA, ethylene-diaminetetraacetic acid; Tris-HCI, tris(hydroxymethyl)aminomethane; PVP40, polyvinyl pyrrolidone mol. wt. 40,000; Mes, 2-(N-mor- pholino)ethanesulfonic acid; PCR, polymerase chain reaction; dNTP, deoxy-nucleotide triphos- phate; U/>Ll, units per microliter; TAE, Tris-Acetate EDTA.

Changes in photosynthetic and transpiration rates of cotton leaves infested with the cotton aphid, Aphis gossypii: Unrestricted infestation

Abstract: Summary The influence of aphid, Aphis gossypii, feeding on photosynthesis and transpiration in cotton plants was investigated under greenhouse conditions. Four population densities of 0, 5, 10, and 25 aphids were used to infest individual cotton leaves. Gas exchange rates were determined for single attached cotton leaves after 9, 18, and 27 days of aphid infestation. Aphid feeding changed photosynthetic rates and transpiration rates. These changes were proportional to the number of aphids and the length of infestation period. Photosynthetic rates were significantly reduced in infested leaves with 25 aphids over 18 days, whereas significant reduction in photosynthetic rates was recorded within 27 days in infested leaves with 5, 10, and 25 aphids in comparison to their respective control. Initial population of 10 aphids increased significantly the transpiration rate of infested leaves over 9 and 27 days. Leaves of plants with 25 aphids had significantly greater transpiration rate than the control at all times.

Allocation of herbivory-induced hydroxamic acids in the wild wheat Triticum uniaristatum

Abstract: We characterized the induction of hydroxamic acids (Hx) by aphid infestation in the wild wheat Triticum uniaristatum by addressing the following questions: i) Do different leaves have similar responses to aphid damage?, ii) Is the Hx induction localized or systemic?, iii) How long does the induction last?, and iv) Is the degree of damage related to the magnitude of induced Hx? Based on earlier results on this wheat/aphid system (lack of costs of Hx induction) we expected to find the plant exhibiting cost-saving patterns of response to herbivory. Aphid infestation in the primary leaf led to induced levels of Hx, but no differences in Hx levels were found after infestation of the secondary leaf. Induction of Hx was restricted to the infested leaf (primary leaf). Induced Hx levels exhibited by the primary leaf at the end of aphid infestation were not observed 2 days later. Finally, different aphid densities (between 10 and 40 aphids per leaf) did not produce significant differences in Hx levels in infested primary leaves. Characteristics of Hx induction by aphid infestation in T. uniaristatum partially support the expected cost-saving patterns in the allocation of induced defenses.

Seasonal variation of ticks on cattle in Burkina Faso.

Abstract: Cattle of the Sahel Zebu peuhl breed from traditionally managed livestock herds in a representative area of north soudanese savana (with 400-900 mm of rainfall/year from May to September) located in the central land of Burkina Faso, were monitored over 12 months for tick and blood parasite. Two species of ticks were found: Amblyomma variegatum and Hyalomma marginatum rufipes. H. m. rufipes was found on cattle all year round with a highest infestation rate in June characterized by means of 10 +/- 4.72 male and 3 +/- 2.43 female ticks per animal. A variegatum appeared on cattle at the beginning of the rainy season in May and quickly reached its highest infestation rate in June with means of 36 +/- 3.67 male and 16 +/- 1.54 female ticks per animal. Thereafter, the infestation rate progressively decreased to reach almost zero in October at the end of the rainy season. There were three preferred body sites for attachment: the axilla area, the area of the scrotum or the udder and the teats depending on the sex of the animal, and the anal area. No blood parasites were found in blood smears. However, a higher prevalence rate of dermatophilosis was noticed on highly infested animals during the rainy season as well as wounds on teats leading to decreased milk production and feeding of calves. Effort should be done to fight against ticks of Amblyomma genus at the period of the year where they are most numerous. Manual removal of ticks could be practiced, making certain to completely detach all mouthparts of the ticks. Complete removal of ticks will avoid wounds and secondary bacterial infections as well as myiasis. During the period of highest prevalence, the rainy season, acaricides could be applied on animal either by dipping the animals or spraying on the predilection sites of the ticks which are the axilla, the scrotum or the udder and the teats, depending on the gender of the animal, and around the anus.

Prediction models of Nantucket pine tip moth, Rhyacionia frustrana (Comstock) (Lep., Tortricidae) infestation using soil and tree factors

Abstract: Prediction models for estimating infestations by Nantucket pine tip moth (NPTM), Rhyacionia frustrana (Comstock) in young loblolly pine plantations in East Texas were developed using multivariate regression analysis based on selected soil and tree factors. Results of regression models show that foliage nutrients, tree water potential and tree height play important roles in NPTM infestation. Overall, these factors predict whole tree infestation better than top two whorls infestation. The importance and correlation of the factors differed for the prediction model of top two whorl and whole tree infestations.

Characteristics of endemic-level mountain pine beetle populations in south-central Wyoming

Abstract: This study was conducted to evaluate the dynamics of endemic populations of mountain pine beetle (Dendroctonus ponderosae Hopkins). In addition, we extended the geographical range of an existing data base recorded in Utah with similar data from Wyoming. This work was accomplished in lodgepole pine (Pinus contorta Dougl. Var. latifolia Engelm.) stands on the Medicine Bow National Forest in south-central Wyoming. Thirty-eight variable-radius paired plots (BAF 10) were measured during the summer of 1987. Host-tree condition and mountain pine beetle infestation characteristics were determined from currently and previously infested trees. Presence and severity of Armillaria root disease and stem pathogens was determined. Tree condition and infestation patterns were similar at this site to those found in earlier studies. Trees selected by endemic mountain pine beetle populations were infested with Comandra blister rust (Cronartium Comandra PK) and root disease (Armillaria spp.). Host-tree condition and mountain pine beetle infestation patterns recorded in this study parallel those identified earlier in Utah and will help land managers identify trees to cut to reduce stand hazard to mountain pine beetle infestation.

Assessment of the risk of infestation of pastures by Ixodes ricinus due to their phyto-ecological characteristics.

Abstract: This study aims to assess the relationships between the phyto-ecological characteristics of grazing pastures and their risk of being infested by the hard tick Ixodes ricinus. To that purpose, 128 pastures belonging to 20 dairy farms were observed from April to July 1994. The farms were located in western France. Assessment of the tick population was made by four monthly, blanket-dragging sessions. The average infestation rate was 40.2%. Six types of pastures were identified according to their basic phyto-ecological characteristics using a factorial analysis of correspondences followed by a hierarchical ascending classification. These identified types were significantly related to the infestation rates, thereby making it possible to provide a predictive value in risk assessment. The infestation rates were high (96% on average) in two types of pastures characterized by their proximity to woods, and low (13%) in two other types characterized by seeded grass species located at some distance from woods, and intermediate (39% on average) in the last two types.

Insect Herbivory in a Eucalyptus maculata Forest on the South Coast of New South Wales

Abstract: In most years between 1977 and 1992, insect defoliation was negligible in a regrowth stand of E. maculata Hook. on the south coast of New South Wales. However, leaf consumption by winter–spring infestations of cup moth larvae accounted for c. 6%, 19% and 4% of the total leaf loss from the canopy in 1989–90, 1990–91 and 1991–92, respectively. During the most serious infestation of 1990, cup moth larvae produced 0.56 t ha–1 of frass, equivalent to the consumption of c. 0.8 t ha–1, or c. 0.5 m2 m–2 of eucalypt leaf (c. 12% of winter leaf area index). In early November 1990, shortly after the infestation, an assessment of insect defoliation in the crown of a dominant tree revealed that (i) 47% of the leaf population was damaged, (ii) a larger proportion of older than younger leaves was damaged, (iii) the proportion of damaged leaves increased down the tree-crown profile, and (iv) 13% of the potential leaf area was missing. In the absence of further insect attack, the process of canopy renewal (leaf production and leaf fall) reduced the proportion of damaged leaves to 23% by June 1991.

Interstadial and infestation level-dependent variation in the transmission efficiency of Borrelia burgdorferi from mice to Ixodes ricinus ticks.

Abstract: The efficiency with which the spirochaete Borrelia burgdorferi sensu stricto was transmitted from laboratory mice to larval and nymphal Ixodes ricinus ticks was assessed, using the polymerase chain reaction The transmission efficiency to nymphs was significantly greater than to larvae when both fed together on the same host Increased tick infestation levels of mice were correlated with significantly greater engorgement weights and higher B burgdorferi transmission coefficients from mice to nymphs These observations indicate that both the feeding success of ticks and the transmission coefficients from host to tick may be influenced by the tick infestation level of an infected host The infestation level and the relative numbers of each life stage of the tick are factors which should be considered in the design of transmission experiments

Impact of external factors on the population dynamics of beech scale (Cryptococcus fagisuga) (Hom., Pseudococcidae) in beech (Fagus sylvatica) stands during the latency stage.

Abstract: Within a natural occurrence of beech on weathered lime stone in the hilly region of southern Lower Saxony, the infestation dynamics of Cryptococcus fagisuga as dependent on the flushing status of its host, Fagus sylvatica, were investigated from 1988 to 1995 during the latency stage. Employing subpopulations on microstands with different water supply and under different silvicultural treatment but with equally good nutritional status, the infestation dynamics of the scale were compared by means of a differential analysis. Independent of the year of observation, the microstand, and the silvicultural treatment, beeches with a bhd 20 cm. In almost all cases the beeches of the higher diameter classes on the strongly thinned plots were attacked markedly stronger than the corresponding ones on the moderately thinned plots. Increasing infestation was promoted by a decreasing flushing status on dry stands and by an increasing flushing status on moister stands. With heavier thinning or stronger self-differentiation on the more humid stands, heavier infestation was promoted too by decreasing flushing status. The gradual transition was stopped when an equilibrium was reached comparable to the level of infestation of strongly thinned stands on dryer locations.

Nasal myiasis due to Oestrus ovis infestation in a dog.

Abstract: NASAL myiasis caused by the sheep bot fly, Oestrus ovis, is a common cause of disease in sheep in warm climates. In the Mediterranean, the disease occurs mainly in the spring and summer months when adult flies emerge, mate, and females deposit the first instar larvae on the nostrils of sheep. In the nasal cavity, larvae develop into the third instar which are recognised by the presence of two characteristic black oral hooks, two black posteri-

The influence of size and duration of aphid infestation on host plant quality, and its effect on sugar beet yellowing virus epidemiology

Abstract: This paper studies the influence of previous infestation on the host quality of sugar beet (Beta vulgaris L.) for aphids and the influence of previous infestation on sugar beet yellowing virus epidemiology. Sugar beet previously infested with Myzus persicae (Sulzer) or Aphis fabae Scopoli (Homoptera: Aphididae) had an improved host quality for subsequently infesting aphids of the same species. There was a significant negative relationship between the number of M. persicae infesting a plant and the proportion of those that died with a dark deposit in their stomachs, and a significant positive relationship between the number that settled on a plant and the number that infested it previously. Nymphs feeding on previously infested plants grew more rapidly than those on control plants. The beneficial effect of previous infestation persisted for at least 2 weeks and prolongation of the infestation beyond 2 weeks was of no further benefit to the aphids. Field grown sugar beet, previously colonised by M. persicae, was more susceptible to natural infestation by M. persicae up to 5 days after exposure. Previously infested plants were also more susceptible to infection with beet mild yellowing virus (BMYV) but not beet yellows virus (BYV), suggesting that the aphids on the previously infested sugar beet settled more readily and were more inclined to feed (and thus transmit BMYV) than aphids on the previously uninfested plants. The consequences for the control of sugar beet yellowing virus vectors are discussed.

Attractivity of cattle infested by Amblyomma variegatum (Acari: Ixodidae) for conspecific adult ticks from the field in Guadeloupe

Abstract: Four field experiments were conducted with creole cattle in Guadeloupe to study the attractivity for adult ticks of animals previously infested with males of Amblyomma variegatum producing aggregation attachment pheromones (AAPs). In each experiment, two groups of cattle were used; the first group was infested with adult A. variegatum and the second group was kept free of ticks and pheromones by acaricidal treatment and by washing the hair and skin of previously infested sites. Both groups were then exposed to natural infestation by ticks present in the environment or by ticks bred in the laboratory and released on the pasture. The number of additional ticks infesting animals were compared between the treated and control groups. There were no significant differences between both groups in the numbers of new male ticks infesting the animals during the first days following the beginning of the experiment. Thereafter, comparison of the slopes of infestation indicated that infested cattle were no more attractive for male ticks than uninfested hosts. Uninfested cattle were spontaneously and rapidly infested by male ticks. It is concluded that carbon dioxide or another host component was a major attractant for A. variegatum males. Female ticks attached on predilection sites exclusively in the presence of AAP-producing males, i.e. 5–10 days after the attachment of the first males. Based on these results we postulate that slow-release devices impregnated with pheromones have no additional attractive effect on A. variegatum males under Caribbean conditions. However, they may be useful in inducing the attachment of females, but only in the first days preceding the arrival of pioneer AAP-producing males. © Rapid Science Ltd. 1998

Comparison of effects of low and high tick infestations on acquired cattle tick resistance: Hyalomma marginatum marginatum.

Abstract: Three Holstein calves were infested with low numbers of ticks, two or three pairs of adults Hyalomma marginatum marginatum in cloth bag daily for 21 days. Infestation was carried out during tick proliferation periods. Two months later, cattle leads were challenged with 100 pairs of ticks. Another group of three Holstein calves were infested five times with 100 pairs of adult ticks of the same species. The five infestations were performed two weeks from the previous infestation. Three tick characteristics were recorded for each experiment: survival to detachment, females weight at detachment and egg mass weight. Light continuous infestations did not cause a significant change in this parameter, but every parameter declined gradually in the heavy infestations. Female and egg mass weight reached a significant difference from the first infestation by the fourth infestation. The circulating antibodies anti-salivary glands of Hyalomma m. marginatum showed that light infestation may induce like immuno-suppression. However, there is an inverse relationship between these antibodies and manifestation of resistance when calves were heavily infested. This is discussed in relation to a fraction of produced antibodies against protective antigens, and participation of another effector mechanism.