Weeks Of Infestation Research Articles

Infestations of Aulacaspis yasumatsui Reduce Asexual Propagation and Transplantation Success of Cycas revoluta Plants

Cycad transplantation and asexual propagation by stem cuttings are highly successful horticultural procedures because the manoxylic stems contain copious nonstructural carbohydrates. The success of these horticultural procedures may be impaired by antecedent abiotic or biotic stress that decreases stem nonstructural carbohydrate content. The armored scale Aulacaspis yasumatsui Takagi has emerged as a global threat to cycad conservation, and the direct influence of A. yasumatsui herbivory on cycad transplantation or asexual propagation outcomes has not been adequately determined. Cycas revoluta Thunb. plants were infested with A. yasumatsui for 0, 20, or 40 weeks to determine the influence of infestation duration on transplantation or asexual propagation success. Following 20 weeks of infestation in one study, 100% of the undisturbed replications but only 60% of the transplanted replications survived. Following 40 weeks, 80% of the undisturbed replications but only 40% of the transplanted replications survived. Following 20 weeks of infestation in a second study, 100% of the intact replications but only 43% of the cuttings survived. Following 40 weeks, 86% of the intact replications and none of the cuttings survived. Leaf number and root, stem, and leaf dry weights followed similar trends, with declines in these metrics occurring with longer infestation durations. These outcomes indicated that adding the stress of asexual propagation or transplantation to C. revoluta plants that were damaged by A. yasumatsui herbivory decreased subsequent plant health and increased mortality.

Aphis spiraecola and Aphis (Toxoptera) citricidus differently manipulate plant metabolism to gain fitness in terms of population abundance or dispersal

AbstractThe response of plant cultivars to infestation by single aphid species has been widely reported, whereas the response of plants to multiple aphid species, and the mechanisms by which various aphids benefit from the induced changes, has been largely ignored. Here we analyzed the symptoms and physiological responses of sweet orange, Citrus sinensis (L.) Osbeck (Rutaceae), as affected by Aphis spiraecola Patch and Aphis (Toxoptera) citricidus (Kirkaldy) (Hemiptera: Aphididae). We further compared the feeding behavior, population abundance, and proportion of winged morph of the two aphid species when separately feeding on sweet orange. Results showed that feeding by A. spiraecola, but not A. citricidus, caused leaf curling, reduced shoot length, shoot fresh weight, and chlorophyll concentration. In addition, A. spiraecola feeding increased the concentration of essential amino acids in leaves when compared with A. citricidus and uninfested control plants. Electrical penetration graph‐studies showed that A. citricidus gained faster access and acceptance of phloem, and spent more time ingesting phloem sap, than A. spiraecola. Furthermore, after 2 weeks of infestation, A. spiraecola produced more winged morphs, whereas A. citricidus achieved higher population abundance. Thus, our results indicate that the two citrus aphids utilize divergent strategies to manipulate host metabolism, and gain fitness benefits in population abundance or winged form production. The results could improve our understanding of varied adaptive strategies of co‐existing insects and extend our knowledge of aphid‐plant interactions.

Volatile\xa0Organic Compounds as Insect Repellents and Plant Elicitors: an Integrated Pest Management (IPM) Strategy for Glasshouse Whitefly (Trialeurodes vaporariorum)

The glasshouse whitefly (Trialeurodes vaporariorum Westwood) is a polyphagous arthropod pest that is of particular detriment to glasshouse grown tomato (Solanum lycopersicum) across temperate regions of the world. Control of whiteflies with synthetic pesticides has resulted in the evolution of resistant genotypes and a reduction in natural enemies, thus highlighting the need for environmentally sound control strategies. Volatile organic compounds (VOCs) offer an environmentally benign alternative to synthetic chemical sprays and this study explored the use of VOCs as insect repellents and plant defence elicitors to control whiteflies on tomato in a commercial glasshouse setting. Limonene in the form of a volatile dispenser system was found to successfully repel whitefly from the target crop and increased fruit yield by 32% during a heavy whitefly infestation. Analysis of tomato herbivore induced plant volatiles (HIPVs) led us to select methyl salicylate (MeSA) as the plant elicitor and application of MeSA to un-infested tomato plants was found to successfully reduce whitefly population development and increase yield by 11%, although this difference was marginally statistically significant. Combination of these two methods was also effective but whitefly abundance in combined plots was similar to the standalone limonene treatment across the course of the experiment. All of the VOC based control methods we used had a negative impact on whitefly performance, with more pronounced effects during the first few weeks of infestation. In subsequent laboratory experiments, we found elevated peroxidase (POD) activity and a significant increase in TPX1 and PR1 transcripts in MeSA treated plants. This led us to deduce that MeSA immediately induced plant defences, rather than priming them. We did however see evidence for residual priming, as plants treated with MeSA and infested with whiteflies produced significantly higher levels of POD activity than whitefly infestation alone. Despite the fact that our treatments failed to synergise, our methods can be optimised further, and the effectiveness of the standalone treatments is promising for future studies. In particular, our repellent limonene dispensers were extremely effective at deterring whiteflies and offer a low economic cost and easy to implement whitefly control option. The methods we have used here could be incorporated into current integrated pest management (IPM) systems, a sustainable approach to pest control which will be central to our efforts to manage whitefly populations under glass in the future.

Artificial micro RNA (amiRNA)-mediated resistance against whitefly (Bemisia tabaci) targeting three genes

Whitefly (Bemicia tabaci) is an insect pest that causes severe losses in economically important crops by sucking the plant sap and transmitting plant viruses. We used the promising new approach of plant-mediated artificial miRNA (amiRNA) expression against three essential genes of whitefly. The Arabidopsis thaliana miR159 precursor was modified and engineered to express artificial miRNAs (amiRNAs) targeting three vital genes of whitefly, sex lethal (Sxl) protein, acetylcholinesterase (AChE) and orcokinin (Orc). The amiRNAWF construct was transformed into the Nicotiana tabacum plants. Whiteflies were infested in separate cages on both control and transgenic plants. After four weeks of infestation, the nymphs were counted and real time quantitative PCR (RT-qPCR) was performed to assess the relative expression of whitefly genes. The transgenic N. tabacum plants showed resistance against whitefly and the number of whiteflies in the next generation were substantially reduced on transgenic plants compared to control plants. Abnormal egg hatching and poor development was observed and only a small number of whitefly nymphs matured to adults. RT-qPCR results indicated that the expression of target genes (Sxl, AChE and Orc) in the nymphs was considerably down-regulated in whiteflies reared on transgenic plants. The amiRNA mediated resistance against whitefly in transgenic plants may pave the way for engineering resistance against whitefly in cotton plants.

Field Population Sex Ratio of the Date Palm Mite, Oligonychus afrasiaticus (McGregor)

The effect of some abiotic and biotic factors on the population sex ratio of the date palm mite (DPM), Oligonychus afrasiaticus, were evaluated on four date palm cultivars in two regions (Riyadh and Qateef) of Saudi Arabia. The week of infestation, fruit stage, and their interactions, as well as the cultivar, significantly affected the DPM sex ratio. The DPM infestation, in the first week, started with a high female proportion (from 0.78 to 1) in both regions of the ‘kimri' fruit stage, and remained female-biased till the fifth week of infestation (from 1.5:1 to 4:1) with a growing DPM population density in both regions. The DPM sex ratio declined to equality (1:1) during the sixth week of infestation, the onset of the ‘khilal’ fruit stage, and further declined to a male-biased sex ratio (4:1) on the Selj, Hamra and Shaishie cultivars, with a declining DPM population density in the last week of infestation. The date fruit stage affected the sex ratio of DPMs negatively in Riyadh and positively in Qateef. The interaction between the week and fruit stage had a significant positive effect on the DPM sex ratio in Riyadh, and a negative effect in Qateef. This study of the DPM sex ratio could be a step in establishing a female-based sampling programme during the early weeks of infestation.

Single- versus Multiple-Pest Infestation Affects Differently the Biochemistry of Tomato (Solanum lycopersicum ‘Ailsa Craig’)

Tomato is susceptible to pest infestations by both spider mites and aphids. The effects of each individual pest on plants are known, whereas multiple-pest infestations have received little interest. We studied the effects of single- versus multiple-pest infestation by Tetranychus urticae and Myzus persicae on tomato biochemistry (Solanum lycopersicum) by combining a metabolomic approach and analyses of carotenoids using UHPLC-ToF-MS and volatiles using GC-MS. Plants responded differently to aphids and mites after 3 weeks of infestation, and a multiple infestation induced a specific metabolite composition in plants. In addition, we showed that volatiles emissions differed between the adaxial and abaxial leaf epidermes and identified compounds emitted particularly in response to a multiple infestation (cyclohexadecane, dodecane, aromadendrene, and β-elemene). Finally, the carotenoid concentrations in leaves and stems were more affected by multiple than single infestations. Our study highlights and discusses the interplay of biotic stressors within the terpenoid metabolism.

Susceptibility of Three Groundnut Products to Infestation by Tribolium castaneum

The susceptibility of groundnut products to Tribolium castaneum was evaluated at ambient temperature of 28+ 2℃ and 78+2% relative humidity in the laboratory for 5 weeks. 50g of each sample was infested with 5 newly emerged. T. castaneum. The highest mortality of 46.6% was recorded in burger sample 40% was recorded in groundnut cake while the lowest mortality of 6.6% of T. castaneum was recorded in cookies after two weeks of infestation. The percentage of moisture, ash, fibre, fat, carbohydrate and protein increased in both groundnut cake and burger while it decreased in cookies sample after five weeks of infestation. The result of mortality obtained in burger and groundnut cake samples significantly differs from the result obtained in cookies sample. These shows that cookies is the most susceptible of the three groundnut products to infestation by T. castaneum, followed by groundnut cake, while burger being the least susceptible.

Cell Wall Property Changes of White Rot Larch during Decay Process

Larch flakes infested with white rot fungus were examined following several infestation durations with respect to the mass loss, tensile strength, hardness, porosity, and change in cell wall components. Nano-indentation, X-ray diffraction (XRD), nitrogen adsorption, and Fourier transform infrared (FTIR) spectroscopy testing methods were employed to investigate the property changes during the decay process. The testing results showed that the mass loss was greater and the longitudinal tensile strength decreased following the first three-week infestation. Nano-indentation measurements revealed that the average MOE of infested larch flakes decreased from 24.0 to 17.1 GPa and the average hardness declined from 528.47 to 427.87 MPa following 12 weeks of infestation. After the first three weeks, the relative crystallinity, surface area, and micropore area of the infested samples increased. These parameters decreased after three weeks had elapsed. Changes in the absorption peaks observed in FTIR explained that the first three-week infestation had a strong effect on the mass loss and strength changes. This suggests that white rot fungus intensely attacked the lignin component of the biomass during the first three weeks of infestation.

Participation of amino acid decarboxylases in biochemical interactions between triticale (Triticosecale; Poaceae) and bird cherry-oat aphid (Rhopalosiphum padi; Aphididae)

The roles of ornithine decarboxylase, lysine decarboxylase and tyrosine decarboxylase in biochemical interactions of two cultivars of winter triticale (Triticosecale), Tornado and Witon, and bird cherry-oat aphid (Rhopalosiphum padi L.) were determined. Results showed the resistant Witon had higher lysine decarboxylase activity than the susceptible Tornado. There was a significant negative correlation between the density of R. padi populations and lysine decarboxylase activity. Such correlations did not occur for the other decarboxylases. Aphid feeding induced a decrease of lysine decarboxylase activity within both cultivars after one week of infestation and increased its activity after two weeks in the moderately resistant Witon. Ornithine decarboxylase activity was induced in tissues of the susceptible Tornado and inhibited in Witon after two weeks of infestation. Aphid infestations did not change tyrosine decarboxylase activity in Witon, whereas in Tornado it decreased in activity after one day of aphid feeding and then increased after two weeks. It was concluded that of the three enzymes studied, lysine decarboxylase was the most important in the response of winter triticale to infestation by R. padi.

Preliminary studies on the damage symptoms and the spatial distribution of an emerging insect pest, Mecocorynus sp. (Coleoptera: Anthribidae) on cashew in Ghana

Cashew (Anacardium occidentale Linn.) has become a very important non-traditional tree crop in Ghana. The crop is, however, infested by numerous insect pests at different stages of its growth. Knowledge of the insect complexity associated with the tree is essential for developing pest control strategies for the crop. Following a reported outbreak of an unknown pest by officials of Ministry of Food and Agriculture (MOFA) and farmers in March 2009 in some cashew plantations in the Brong-Ahafo Region, an investigation was initiated to collect and identify the insect species involved and assess the extent of the damage caused by the insect. The cashew bark borer, Mecocorynus sp. (Coleoptera: Anthribidae) was identified and found to be responsible for the damage and could kill the attacked trees within weeks after infestation. Observations at Jaman south and Jaman north of death of mature trees within few weeks of infestation were indications of emergence of new pest of cashew in Ghana. Studies on the distribution and damage characteristics of the pest was conducted from April 2009 to December 2010 in 41 major cashew growing areas within five districts of the Brong-Ahafo Region. In the Jaman South District, symptoms of infestation of the insect were found on 14.2% of the tree population and the death rate of tree population was 2.2%.The incidence of the pest in the Jaman north was also high, with death rate of 2.8% and infestation rate of 13.6%. In the Tain district death rate was 0.6%; infestation was observed only at Banda-Biema, Nsawkaw, Mendji, Donkokrom and Brodi. This paper reports the status of a new emerging pest of cashew in Ghana, which needs an urgent attention. Key words: Damage symptoms, spatial distribution, Mecocorynus sp., cashew, Ghana.

Distribution and damage characteristics of an emerging insect pest of cashew, Plocaederus ferrugineus L. (Coleoptera: Cerambycidae) In Nigeria: A preliminary report

Among the numerous insect pests infesting cashew in Nigeria, the cashew trunk and root borer, Plocaederus ferrugineus L. (Coleoptera: Cerambycidae) is fast becoming the most dreaded because its infestation results in the sudden death of the tree within weeks. Observations at Ochaja in 1999/2000 and at Ibadan in 2005 of “sudden death” of mature cashew trees within few weeks of infestation were indications of emergence of new pest of cashew in Nigeria, which needs urgent investigation. Frass and gum exudates were collected from the trunk base of dead plants before they were cut down and exhumed carefully from the soil. Soil samples were collected from beneath the excavated roots. The bored holes on the trunk and roots were excised to expose their frass and gum contents. Both the frass and gum exudates collected from the base of the cashew trunk and those from excised trunk and roots together with the soil samples from beneath the excavated roots were thinly spread out in the laboratory to search for the various life stages of the beetles. Brief description of the beetle’s life stages and parts of the infested/dead stands were made. The rate of infestation of cashew trees at Ibadan was 18.13%, resulting in a death rate of 1.88% of trees, while the infestation rate at Ochaja was 13.3% with a death rate of 6.38%. The eggs were conspicuously absent at the time of this assessment as they had all emerged and developed into larvae, pupae and adults. The control of the pest at advanced stage of the larval development was very difficult; hence control measures were recommended to be initiated at early stage of infestation. Strict cultural practices gave desired results.

Xylem – as well as phloem – sustains severe damage due to feeding by the Russian wheat aphid

Investigation of comparative effects of feeding damage by the Russian wheat aphid (RWA, biotype SA1, Diuraphis noxia Mordvilko) on leaf blades of susceptible and resistant wheat cultivars ( Triticum aestivum L. var Betta and Betta- Dn1 respectively) were carried out to establish the level of ultrastructural damage caused by this aphid and the possible limitation of damage induced which could be ascribed to the resistance gene Dn1 over the susceptible cultivar. Ultrastructurally, Betta- Dn1 sustained less damage to the vascular tissue as well as to the mesophyll during the experimental period. Both inter- and intracellular probes resulted in considerable saliva deposition as the aphids probed for suitable feeding sites. Salivary tracks were observed between and within mesophyll, bundle sheath cells as well as the vascular tissue, including the xylem. Disruption of organelles and cytoplasm resulted from cell probing and sheath deposition. Cell and organelle damage was more evident in the non-resistant Betta cultivar. The aphids probed for and fed from thin-walled sieve tubes preferentially. Few thick-walled sieve tubes showed evidence of either aphid probing or feeding-related damage. Saliva was deposited when the aphids probed inter- and intracellularly for feeding sites. The aphids appeared preferentially to probe for and feed from thin-walled sieve tubes, as few thick-walled sieve tubes showed evidence of damage. Vessels, apparently probed for water, contained watery saliva that encased the secondary walls and sealed pit membranes between probed vessels and xylem parenchyma. The xylem probed by the RWA was rendered non-functional, probably contributing to symptoms of leaf roll, chlorosis and necrosis, which were observed within two weeks of infestation in the susceptible Betta cultivar. This damage was limited in the resistant Betta- Dn1 cultivar during the same time frame.

Effects of aphid herbivory on biomass and leaf-level physiology of Solanum dulcamara under elevated temperature and CO 2

Forecasted increases in atmospheric CO 2 and global mean temperature are likely to influence insect–plant interactions. Plant traits important to insect herbivores, such as nitrogen content, may be directly affected by elevated CO 2 and temperature, while insect herbivores are likely to be directly affected only by temperature. This study investigates changes in the effects of herbivory by the aphid Macrosiphum euphorbiae (Homoptera: Aphididae) on the C 3 perennial Solanum dulcamara under two conditions of atmospheric CO 2 concentration (350/750 ppm) and three temperature treatments (20/15, 23/18, 26/21 °C; day/night temperatures). Plants were grown in glass-topped chambers and initially infested with three apterous, adult aphids. Aphid population size, leaf photosynthetic capacity, carbon to nitrogen (C:N) ratio, specific leaf area, plant height, and total plant biomass were measured after 3 weeks of infestation. Aphid herbivory reduced photosynthetic capacity under all conditions, and resulted in smaller leaf C:N ratios. Aphid populations did not change significantly under elevated CO 2, but tended to increase slightly. Average aphid weight decreased at high temperatures. Plant height and biomass were not significantly affected by the CO 2 treatment, but growth rates before infestation were enhanced by elevated CO 2. These results indicate that the combined effects of both elevated CO 2 and temperature may exacerbate aphid damage to certain plants, particularly to plants which respond weakly to increases in atmospheric CO 2. Modifications of plant physiology under altered CO 2 and temperature do not impair, and may slightly enhance aphid population growth.

Gene Expression of Heme Oxygenase-1: Relationship to Fibrogenic and Apoptotic Factors in Murine Schistosomiasis

Schistosomiasis is characterized by a unique form of periportal fibrosis and not cirrhosis. Heme oxygenase (HO-1) is a stress inducible molecule that could modulate the fibrogenic process in the murine model of schistosoma mansoni. In this study, the extent of heme oxygenase-1 gene expression was evaluated by RT-PCR in liver tissues of thirty mice infested with schistosoma mansoni after the 2nd, 4th, 6th, 8th and 10th weeks of infestation. Furthermore, the gene expression of some fibrogenic and antifibrogenic factors [pro α2 (I) collagen, laminin β1, transforming growth factor β (TGF-β), platelet derived growth factor (PDGF) and hepatocyte growth factor (HGF)], apoptotic factors (Fas L) and the transcriptional factor nuclear factor-κB (NF-κB) were also evaluated in liver tissues of the same animals by RT-PCR techniques. The PCR bands densities were semi-quantitated using Biometra gel documentation system. The present study showed that the gene expression of HO-1 coincided with the expression of NF-κB. Both were induced from the 2nd week post infestation and their PCR band density remained high till the 8th week with a slight decline at the 10th week. The gene expression of HO-1 paralleled the levels of HO activity. On the other hand, increase in gene expression of HGF and Fas L was detected only in the 2nd and the 4th weeks post infestation. This may suggest a down regulation of Fas L and HGF by the sustained increase in gene expression of HO-1 and/or NF-κB. Meanwhile, there is increase in the gene expression of the profibrogenic cytokines PDGF and TGF-β, starting in the 4th week (PDGF) and 6th week (TGF-β). They were however expressed at low levels at the 2nd and 4th weeks, respectively. Thus a direct effect of HO-1 on the expression of these cytokines cannot be sharply delineated. However, the expression of these cytokines preceded and then paralleled pro α2 (1) collagen gene expression, indicating their role in the fibrogenic process. Laminin gene expression increased from the 6th week and remained highly expressed till the 10th weeks. Thus the similar patterns of gene expression of HO-1 and NF-κB at the selected stages in murine schistosomiasis and the accompanying down regulation of the Fas L suggest that, as a stress inducible protein, HO-1 might be part of the protective mechanisms elicited by the acute phase response in Schistosoma mansoni infection possibly by protecting the cells against the consequences of oxidative stress (i.e. apoptotic and necrotic pathways). HO-1 gene expression may play a role in the modulation of the immunopathology of schistosomiasis and hence, indirectly influence fibrogenesis and prevent cirrhosis.

Linognathus vituli (Anoplura: Linognathidae): population growth, dispersal and development of humoral immune responses in naı̈ve calves following induced infestations

Growth of Linognathus vituli populations following establishment at a point source was followed for 16 weeks on eight louse-naı̈ve Holstein calves. Dispersal of lice from the point of infestation (withers) was monitored by examination of known louse predilection sights. Mean louse indices increased during the initial weeks reaching maximum mean values at 8 weeks post-infestation (p.i.). Subsequently, mean indices decreased, reaching a plateau that persisted through weeks 14 and 15 p.i. There was little movement away from the withers until 5 weeks p.i. Subsequently, numbers of lice on the withers declined, while increasing at sites on the head. A few lice were noted on the dewlap and topline sites. Host antibody responses to crude nymph antigens, measured by enzyme-linked immunosorbent assay (ELISA), were generally evident within 2–4 weeks of infestation. Examination of individual host data showed louse populations could be categorized relative to the mean population size for the group. Two animals were considered ‘chronic’, having louse populations that persisted throughout the study and whose louse indices were >150% of the group mean. Two animals were classified as ‘resistant’ having lice present for only a portion of the study and whose louse indices <40% of the group mean. The remaining animals had louse indices between 62 and 137% of the group mean. Antibody profiles of the individuals were not as clearly categorized, although the ‘resistant’ animals were only positive for short periods of time, roughly corresponding to the time when lice were observed.

Host plant-mediated interactions between Tetranychus urticae and Eotetranychus carpini borealis (Acari: Tetranychidae).

Competitive interactions between Tetranychus urticae and Eotetranychus carpini borealis were investigated under laboratory and greenhouse conditions. When placed first to colonize red raspberry leaves, T. urticae caused extinction of E. carpini borealis populations. E. carpini borealis had detrimental effects on T. urticae but did not cause T. urticae population extinction. The area used by E. carpini borealis for egg deposition decreased with an increase in the number of T. urticae eggs. Red raspberry showed an induced response to T. urticae and E. carpini borealis feeding after two weeks of infestation. Population growth of each species was reduced on plants that were previously infested by conspecifics but inducible response by one species had no effects on the other species.

Location of genes controlling resistance to greenbug (Schizaphis graminum Rond.) in Hordeum chilense

AbstractWheat/Hordeum chilense disomic addition lines have been used to locate genes influencing resistance against greenbug (Schizaphis graminum Rond.) in specific chromosomes of H. chilense. H. chilense is a source of antixenosis, antibiosis and host tolerance to the greenbug, being resistant also to the Russian wheat aphid, the two key pests in wheat. For measuring antixenosis, the numbers of aphids per plant were recorded in a host free choice test; antibiotic resistance was determined by measuring the developmental time, the fecundity and the intrinsic rate of population increase of aphids reared on the different hosts, and host tolerance to aphids was evaluated by the leaf damage and the number of expanded leaves on the hosts after 3 weeks of infestation. The greenbugs belonged to a clone of biotype C.Plant genes with positive effects for antixenosis were located on chromosome 1Hch. Genes with positive effects for antibiosis were located on three different chromosomes and those that prolonged aphid developmental time were located on chromosomes 5Hch and 7Hch while those that reduced the total fecundity were on 4Hch. Chromosome 7Hch accounted for host tolerance to greenbug.

Ethylene production as an indicator of germination and vigor loss in stored rice seed infested by Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae)

Germination and vigor of stored “Taichung Native 1” (TN1) rice seed was significantly reduced by Rhyzopertha dominica (F.) infestation. Seed germination decreased by about 34, 51 and 66% with 6, 7 and 8 weeks of infestation, respectively. Ethylene produced by growing seedlings, the shoot length, and dry weights of seedlings grown from infested seeds decreased significantly with an increase in the duration of infestation. Ethylene produced by 4-day-old rice seedlings was highly correlated with shoot growth ( r = 0.99) and to a lesser extent with the dry weight of seedlings when 17-days old ( r = 0.72). The study revealed that ethylene produced during early shoot growth can be used for comparing insect infestation in rice seed stored under otherwise identical conditions.

Scanning electron microscopy of sarcoptic mange lesions in swine

Scanning electron microscopy revealed that lesions of sarcoptic mange in swine, pass through 3 different stages. During the first 3 weeks of infestation, adult female mites tunnel into the epidermis. During the following 3 or 4 weeks, the surface openings of these tunnels become covered with keratinized epidermal crust which increases in thickness. After 7 weeks of infestation, the crust falls off, the tunnel openings become apparent again and most of the mites vacate these tunnels.

Feeding Influence of Three Pecan Aphid Species on Carbon Exchange and Phloem Integrity of Seedling Pecan Foliage

Abstract Feeding injury by pecan aphids on fully expanded pecan [Carya illinoensis (Wangenh) K. Koch] seedling foliage reduced net CO2 exchange within 2 weeks of infestation and was dependent upon aphid density and species. Increasing aphid population levels resulted in increasing reductions in net photosynthesis. Carbon exchange rates after a buildup and subsequent rapid decline of either Monellia caryella (Fitch) or Monelliopsis pecanis (Bissell) populations resulted in a 50% reduction in net photosynthesis and 25% reduction in dark respiration. This effect can persist at least 12 weeks after the cessation of aphid infestation. Such leaves exhibit aphid-induced clogging of the phloem with callose and other substances. Such clogging may be associated with the commonly observed aphid population decline in pecan orchards. Observations indicate that the influence of aphid feeding on leaf photosynthetic physiology may impair pecan productivity.