Pest Feeding Research Articles

Whitefly, Trialeurodes ricini (Genn) feeding stress induced defense responses in castor, Ricinus communis L. plants

Behavioral responses of whitefly, Trialeurodes ricini's parasitoid, Encarsia formosa to induced plant surface chemicals due to T. ricini infestation of castor, Ricinus communis (L.) plants were studied. The impact of whitefly infestation in the form of quantitative and qualitative changes in the leaf biochemical constituents was also analyzed. The results of Y-tube olfactometer assays performed to investigate the role of pest induced plant semiochemicals in locating host plants by E. formosa showed that whitefly induced plants were not attractive to conspecifics and that the crude surface extracts of infested plants were attractive to the parasitoid when tested against extracts of uninfested plants. Hexane extract of whiteflies was more attractive to E. formosa when tested against surface chemicals of infested plants. The total free amino acids, proteins and the secondary metabolites such as phenols enhanced in whitefly fed plants. On the other hand, total carbohydrate content was reduced in whitefly infested castor leaves over healthy ones. Enzyme analyses after whitefly infestation showed that pest feeding significantly increased the activities of foliar phenyl alanine ammonia lyase (PAL), poly phenol oxidase (PPO) and catalase (CAT). A decrease in superoxide dismutase (SOD) and peroxidase (POD) enzyme activities was evident in pest infested plants. The individual phenolic acids from pest fed plants were identified using high performance liquid chromatography (HPLC) and compared with normal, intact plants. Hence it is concluded that pest infested plants exhibited defense strategies which may be exploited as a tool in the Integrated Pest Management for crop protection.

A new colour vision system to quantify automatically foliar discolouration caused by insect pests feeding on leaf cells

Leaf colour and leaf area are key parameters for many plant studies, including plant protection. The quantification of foliar bleached area is often used to evaluate the strength of plant attack by pests or diseases, to compare the efficiency of different treatments, the resistance of some populations, and to set up some control methods. The quantification of such area by human vision often lacks accuracy and reliability. Image analysis systems could bring a more accurate and objective measure, and could be automated to treat a great number of samples. Such an automated tool has been developed in order to measure quantitatively foliar bleaching due to the sycamore lace bug, Corythucha ciliata (SAY) on Plane tree. This tool was built up with a colour image capture bench and a fast automated segmentation process based on an original chlorophyll histogram unsupervised classification. Dedicated software was developed and integrated in an operational image processing platform capable of routine use by non-specialists in image analysis. The accuracy of the tool was determined by comparison to human expert segmentation. A very low error rate was observed in the absence of artefacts, but artefacts such as powdery mildew symptoms were not well distinguished and lead to weaker performance. Comparing its reliability and robustness to classical visual estimation and classification method, the tool performance was similar to the most experienced rater. The advantage of such a system is the possibility to treat automatically a large number of pictures and produce accurate, reliable, repeatable and non-subjective quantitative measurements.

The whitefly‐associated facultative symbiont Hamiltonella defensa suppresses induced plant defences in tomato

Summary Maternally inherited bacterial symbionts are present in many, if not most, insect species. While there is rapidly accumulating evidence that facultative, heritable symbionts often protect insect hosts from natural enemies, there have been few clear examples where facultative symbionts mediate herbivore–plant interactions. The phloem‐feeding whitefly, Bemisia tabaci, is a major agricultural pest that frequently harbours facultative symbionts, including Hamiltonella defensa. While H. defensa and other facultative symbionts have been shown to improve whitefly performance on particular food plants, no direct and specific roles for symbiont‐mediated interactions with food plants have been identified. Here, we conducted a series of assays to determine whether infection with H. defensa improved whitefly performance on tomato (Solanum lycopersicum) and whether this benefit was associated with symbiont effects on induced plant defences. Finally, we tested whether impacts on induced defences involved in the modulation of a salivary factor. The downregulation of plant defences was associated with increased whitefly fecundity and survival. Feeding by H. defensa‐infected whiteflies suppressed JA and JA‐related anti‐herbivore‐induced defences in tomato relative to uninfected controls. That saliva‐only treatments of damaged tomato leaves from H. defensa‐infected whiteflies suppressed induced plant defences compared to saliva from uninfected controls, suggesting that elicitors in saliva were responsible. Characterization of the putative salivary factor(s) revealed they are likely small (< 3‐kDa) and nonproteinaceous. Interestingly, suppression of defences was not observed in SA‐deficient NahG plants, indicating that suppression of JA‐regulated defences depends on the SA signalling pathway. This finding reveals an intriguing example of the crosstalk between SA and JA signalling pathways and suggests that infection with facultative symbionts can result in the manipulation of induced plant defences to the benefit of the insect host and heritable symbiont. Our results show that the bacterial symbiont H. defensa mediates whitefly–plant interactions by suppressing induced plant defences in tomato. This finding is among the first showing a direct role for facultative symbionts in mediating plant–herbivore interactions and demonstrates a novel tactic for insect herbivores to circumvent plant defences. Symbiont‐mediated suppression of plant defences may enhance the deleterious effects of insect pests feeding on important crops.

First Report of 'Candidatus Phytoplasma asteris' Associated with "Witches'-Brooms" on Jointleaf Rush (Juncus articulatus) in Poland.

Juncus articulatus L. (Juncaceae) is a species of rush occurring in Eurasia, Canada, and the United States. In 2013, symptoms of "witches'-brooms," similar to those associated with phytoplasma infection in other plants, were observed on jointleaf rush plants in Lower Silesia (southwest Poland), with some pests feeding on them. Livia junci (Liviinae, Hemiptera) is a small plant-feeding sap-sucking insect that affects monocotyledonous plants. To confirm the presence of phytoplasma in 15 examined plants, total DNA was extracted from 100 mg of inflorescence and leaf samples collected in July 2013 in Bogatynia, Poland, from six symptomatic and six asymptomatic plants using a DNeasy Plant Mini Kit (Qiagen, Syngen Biotech, Wrocław, Poland) according to the manufacturer's protocol. Additionally, three leaf samples from asymptomatic rush plants, collected from a location where the disease was not observed (Wrocław, Poland), as well as water blank samples were included as negative controls. Moreover, thirty-two insects were collected from symptomatic plants and preserved in ethanol (75%). DNA from L. junci specimens (the imago and the last larva stage) was extracted using DNeasy Blood and Tissue Kit (Qiagen, Syngen Biotech). Extracted nucleic acids were used as templates for PCR employing a) phytoplasma universal rRNA primer pairs P1/P7 followed by R16F2n/R16R2 (1), b) primers rp1-rp2 followed by rp3-rp4, allowing amplification of fragments of ribosomal protein rpl22 and rps3 genes (3), and c) primers AYsecYF1/AYsecYR1 (2) for amplification of the secY gene. The phytoplasma was detected in all tested insects as well as in all six symptomatic and four out of six asymptomatic plant samples (10 out of 12 plant samples from Bogatynia were positive). No amplification products were detected in negative control samples from Wrocław or in water blanks. The fact that we detected the pathogen in some asymptomatic plants indicated that a low concentration may have been present prior to the development of disease symptoms. Amplicons representing three genetic loci were sequenced in an AbiPrism 3100 Genetic Analyzer apparatus (Applied Biosystems, USA), at the Maria Skłodowska Memorial Cancer Center and Institute of Oncology, Warsaw, Poland. To avoid sequencing errors, all DNA samples were sequenced twice in both directions. The obtained sequences were nearly identical, and representative sequences of 16S rDNA fragments (Accession Nos. KF774297, KF774298, and KF774299), secY gene (KJ394481, KJ394482, and KJ394483) and ribosomal protein gene (KJ394484, KJ394485, and KJ394486), isolated from two plants and one insect, were deposited in GenBank. BLAST analysis of the sequenced 16S rDNA fragments revealed that tested strains shared more than 99% sequence identity with the sequences of phytoplasmas from the aster yellows group (e.g., KJ556903, KJ494330, and KJ491100). The same analysis performed for ribosomal proteins and secY genes confirmed the highest identity (99%) of analyzed sequences with those of 'Candidatus Phytoplasma asteris' (HM626105 and KC354611, respectively). The impact of the detected phytoplasma in the regional ecosystem and the role of L. junci as a possible vector of this pathogen are being assessed.

Review of historical outbreaks of the nun moth with respect to host tree species

Lymantria monacha (L.) is a polyphagous pest feeding on coniferous and deciduous trees in Eurasia. The review presents an exhaustive overview of the nun moth outbreaks in Czech forests from 1784 to 2010 in terms of host tree species. This paper is unique because the majority of utilized sources have never been published formally. At least 22 genera of host trees, shrubs and herbs were recorded in the Czech Republic. On the other hand, two genera were evaluated as non-hosts and four genera as indifferent. The nun moth defoliated mainly coniferous forests (almost 90% of all recorded outbreaks with known data on host trees) in the Czech Republic. Forests with a mixture of coniferous and deciduous trees were defoliated nine times less frequent, and only an insignificant portion was recorded in pure deciduous forests. Although the host range is wide, the nun moth has defoliated predominantly spruce forests (almost 70% of all records with known data on host trees). Mixed coniferous (with a mixture of spruce, pine, larch, fir) forests were attacked three times less frequently than the spruce forests. Pine and larch forests were defoliated to a small extent. Defoliations were sorted also according to the intensity. The spatial distribution of recorded outbreaks is shown in maps.

Impact of areawide integrated pest management strategies on pests of pigeonpea and yield in Marathwada region of Maharashtra, India

Pigeonpea [Cajanus cajan (L.) Millsp.] is an important legume crop of southern Maharashtra, providing high quality protein and animal feed. Insect pests feeding on flowers and pods of this crop are the most important biotic constraint affecting yield to the tune of 60 per cent. Hitherto, focus of pest management research has been on podborer, Helicoverpa armigera (Hubner). With large scale cultivation of transgenic cotton in Maharashtra and climatic changes, pest scenario has changed requiring more attention on leaf webber, Maruca and pod fly. Hence, area wide implementation of Integrated Pest Management (IPM) in pigeopea was implemented during 2010-11 and 2011-12 covering 5 taluks benefitting 2449 farmers of 8 villages. It was observed that use of pesticides based on the “e-Pest monitoring and its subsequent decision support tools” enabled to manage pests with judicious use of pesticides. The pest infestation (pod borer, pod fly, plume moth, flower webber, etc.,) were significantly low as compared to non-IPM with appreciable high population of natural enemies (coccinellids, chrysopa and spiders) were also observed under IPM fields. Timely dissemination of advisories and action has resulted in higher grain yield of 9.89 q/ha and lower grain damage 5.69 per cent as compared to non-IPM (13.79 per cent).

Wpływ biostymulatorów Asahi SL i Siapton 10 L na zdolność roślin ogórka do tolerancji uszkodzeń wywołanych żerowaniem wciornastka zachodniego (Frankliniella occidentalis Pergande)

Summary The studies were conducted on cucumber cultivar Aramis, treated and not treated with biostimulants: Asahi SL and Siapton 10 L in the glasshouse of the Warsaw University of Life Sciences and in the Laboratory of Entomology Department. Plants were cultivated in two glasshouse chambers and western flower thrips (Frankliniella occidentalis Pergande) was introduced to one of the chambers. The aim of the study was to evaluate if application of biostimulants to cucumber crop can increase the level of plant tolerance to thrips. Intensity of growth, photosynthesis and yield were compared in the plants treated and not treated with biostimulants. Cucumber plants tolerated injuries caused by thrips. They accelerated the growth and photosynthesis intensity in the first 4 weeks of pest feeding. This phenomenon was more evident in the plants treated with biostimulants, especially with Siapton 10 L. The yield was not significantly affected by thrips and biostimulants after 4 as well as after 6 weeks of thrips feeding.

Prevalence of Endosymbionts in Polish Populations of Leptinotarsa decemlineata (Coleoptera: Chrysomelidae).

Colorado potato beetle (CPB, Leptinotarsa decemlineata Say) (Coleoptera: Chrysomelidae) is one of the most serious insect pest feeding on wild and cultivated Solanaceae plants. This pest poses a significant threat to potato crops. CPB originated from North America but has become widespread and has adapted in new localizations. Currently, it is reported in many countries worldwide. Endosymbiotic bacteria might have an influence on insect adaptation to new conditions. They are known to play a role in invasiveness of insect hosts and to facilitate colonization of new niches; however, information on endosymbionts of the CPB is very limited. In this study, we screened CPB populations collected from 20 evenly distributed locations in Poland for the presence of Arsenophonus, Cardinium, Wolbachia, and Flavobacterium. We found the presence of Flavobacterium in the studied insects. Little is known about CPB–endosymbionts interactions, thus this study may provide a reference for future studies in this subject.

RNAi-Based Strategy for Asian Citrus Psyllid (Diaphorina citri) Control: A Method to Reduce the Spread of Citrus Greening Disease

Citrus greening disease is a serious bacterial disease of citrus worldwide and is vectored by the Asian citrus pysllid (Diaphorina Citri).  The only effective control strategy includes vigorous control of the psyllid, primarily through heavy reliance on pesticides. As a more sustainable and environmentally friendly method of psyllid control, we evaluated a RNA interference (RNAi) approach based on psyllid oral uptake of dsRNA molecules that target specific psyllid genes.  This approach is based on the finding that cellular uptake of dsRNAs, that match the sequence of essential genes, results in down regulation of those genes and can lead to cell/organism death.  These dsRNA molecules were introduced into the psyllids through feeding on citrus engineered to express the dsRNA using a Citrus tristeza virus as a paratransgenesis vector.  Increased toxicity was observed when adult psyllids were fed on citrus producing dsRNA targeting either gut protease genes.  No increased psyllid toxicity was observed in psyllids fed on citrus producing green fluorescent protein (GFP) dsRNA.  Toxicity related to specific psyllid gene knockout will be discussed.  These results suggest that RNAi-based control may be a viable alternative to current pesticide use for control of psyllids and all phloem feeding pests.

<b>Severe Damage of <i>Moringa Oleifera</i> Lam. Leaves by <i>Ulopeza Phaeothoracica</i> Hampson (Lepidoptera: Crambidae) in Ungogo Local Government Area, Kano State, Nigeria: A Short Communication</b>

The work was carried out at a location (110 58`N and 8026`E) in Ungogo Local Government area of Kano State, Nigeria with objective of identifying an unfamiliar larva feeding on Moringa leaves and to describe its nature of damage. The leaf feeding larvae were sampled and reared through to pupation and to adulthood in the Entomology laboratory, Crop Protection Department, Faculty of Agriculture, Bayero University, Kano, Kano State. The adults that emerged were identified to beUlopeza phaeothoracica Hampson. On the larval feeding, it was observed that damage caused was very severe on a heavily infested young Moringa tree at the study location. In conclusion, the study revealed that U. phaeothoracica is a leaf feeding pest of M. oleifera and that its activity could be of serious concern especially on young trees of Moringa, kept under poor management conditions.Keywords: Damage, Moringa, Ungogo, Kano

Complete mitochondrial genome sequence of a phytophagous ladybird beetle, Henosepilachna pusillanima (Mulsant) (Coleoptera: Coccinellidae)

Ladybird beetles are generally considered as agriculturally beneficial insects, but the ladybird beetles in the coleopteran subfamily Epilachninae are phytophagous and major plant feeding pest species which causes severe economic losses to cucurbitaceous and solanaceous crops. Henosepilachna pusillanima (Mulsant) is one of the important pest species of ladybird beetle. In this report, we sequenced and characterized the complete mitochondrial genome of H. pusillanima. For sequencing of the complete mitochondrial genome, we used the Ion Torrent sequencing platform. The complete circular mitochondrial genome of the H. pusillanima was determined to be 16,216 bp long. There were totally 13 protein coding genes, 22 transfer RNA, 2 ribosomal RNA and a control (A + T-rich) region estimated to be 1690 bp. The gene arrangement and orientations of assembled mitogenome were identical to the reported predatory ladybird beetle Coccinella septempunctata L. This is the first completely sequenced coleopteran mitochondrial genome from the beetle subfamily Epilachninae from India. Data generated in this study will benefit future comparative genomics studies for understanding the evolutionary relationships between predatory and phytophagous coccinellid beetles.

A potential spider natural enemy against virus vector leafhoppers in agricultural mosaic landscapes – Corroborating ecological and behavioral evidence

We intended to establish the potential for interaction between the wheat dwarf virus (WDV) vector leafhopper Psammotettix alienus – a dominant sap feeding pest in cereal fields, and the spider Tibellus oblongus – a dominant predator of grassy field margins. The relationship is important, because with the senescing and harvest of cereals P. alienus migrates to alternative host species, grasses. We analyzed the potential of T. oblongus to be an effective natural enemy of P. alienus by studying the probability of their co-occurrence seasonally and at the habitat and microhabitat scale. By gathering data from long term research (1994–2011) in six agricultural regions of Hungary, we assembled 96 one-year-long datasets obtained by suction sampling from the four key habitats of the agricultural landscape mosaic. The analysis showed that both in space and time the spider has the potential to prey on P. alienus. T. oblongus populations can reach considerable densities and represent high dominance among other spiders in the habitats of the leafhopper. Given this co-occurrence pattern, we devised laboratory experiments to study whether P. alienus is included among the preferred prey types of T. oblongus and to ascertain whether prolonged feeding has no adverse effects and provides the nutrients for growth. P. alienus proved to be both a preferred prey type and one that can be utilized for growth by the spider. This study collected the circumstantial ecological and direct laboratory feeding trial proofs that T. oblongus can be an important biological control agent against the leafhopper pest P. alienus.

Induction of phenolic acids and metals in Arachis hypogaea L. plants due to feeding of three lepidopteran pests

The feeding of lepidopteran pests, Amsacta albistriga W., Aproaerema modicella D. and Spilosoma obliqua W., caused feeding stress in the Arachis hypogaea L. plants. As a common defensive response, the plant exhibited variations in the primary and secondary metabolic contents. Groundnut plant antioxidative enzymes such as peroxidase, superoxide dismutase, polyphenol oxidase, catalase and phenyl ammonia lyase exhibited alterations to confer resistance against the pest. Phenolic compounds, namely coumaric acid, chlorogenic acid, resveratrol, epicatechin, ferulic acid and caffeic acid, showed active defensive role in groundnut plant against the pest feeding through their significant presence in Fourier transform infrared spectroscopy, high-performance liquid chromatography and gas chromatography studies. Changes in metal contents like iron, magnesium, zinc, potassium and calcium were also reported through atomic absorption studies, indicating their defensive role against the biotic stress caused on groundnut by the three lepidopteran pests. The present study can further assist in recognizing the importance of these specific phenolic acids and metals of groundnut in its pest management.

Genetic structure of Curculio elephas Gyll. (Coleoptera, Curculionidae) in Greece: an important pest of sweet chestnut

The weevil, Curculio elephas (Coleoptera, Curculionidae), is one of the most abundant and widespread chestnut feeding pests in Greece. Together with the tortricid moths Cydia splendana and C. fagiglandana (Lepidoptera, Tortricidae), C. elephas greatly affect chestnut production. This weevil occurs in a continuous range throughout Greece; however, its population structure is unknown. Information concerning its population structure could help in the future control of this pest. A 790 bp portion of the mitochondrial Cytochrome Oxidase I gene was sequenced for 160 C. elephas larvae from ten populations. Compared to other Curculio species haplotype diversity with 31 haplotypes and nucleotide diversity with six nucleotide substitutions was low. The Bayesian inference of phylogeography in concert with nested clade analysis revealed a loose geographic distribution of genetic diversity that was likely the joint effect of isolation by distance and gene flow. In addition, population indices and Bayesian-based calculations showed that the populations of C. elephas in Greece are at the phase of expansion. Dating the phylogeny suggests about 300,000 years before present as the start of divergence among the populations of C. elephas in Greece.

Leucothyreus femoratus(Coleoptera: Scarabaeidae): Feeding and Behavioral Activities as an Oil Palm Defoliator

Leucothyreus femoratus Burmeister (Coleoptera: Scarabaeidae) is an important insect pest of oil palm plantations, because larvae and adults feed on plant roots and leaves, respectively. This suggests the necessity of comprehending the pest's feeding and behavioral habits for pest management. Food consumption and injury to leaves of Elaeis guineensis Jacq. (Arecales: Arecaceae, African oil palm) by adults of L. femoratus in Colombia were studied. Locomotion of adults was evaluated with respect to 6 behaviors, i.e., emergence, hiding in the ground, walking, flying, feeding, and mating. In addition, larvae were collected from the roots of other plants found in the oil palm plantation in order to determine possible alternative hosts. Leaf consumption per adult L. femoratus was 13 mm2/day/insect (χ2 = 19.33, P < 0.0001). Leaf injury was in the form of squares or rectangles and cumulative defoliation reached 15.5% in 60 days. The insect showed predominantly nocturnal feeding and mating (χ2 = 95.53, P < 0.05; χ2 = 207.01, P < 0.05, respectively). Larvae of L. femoratus were found in abundance on the roots of Croton trinitatis Millsp. (Euphorbiaceae, road side croton) and Imperata cilindrica (L.) P. Beauv. (Poaceae, cogon grass). The feeding habits of larvae and adults of this insect may be main factors in their adaptation to oil palm plantations. The understanding of the feeding habits and behaviors of L. femoratus are important to define strategies for the management of their populations in oil palm plantations.

Występowanie omacnicy prosowianki (Ostrinia nubilalis Hbn.) w zależności od zasobności gleby w azot oraz od formy nawozu azotowego

Summary The aim of the study was to monitor the occurrence of European corn borer on maize plants depending on soil content of nitrogen and forms of nitrogen fertilizer. A significant influence of weather conditions on damage of maize plants caused by caterpillars was observed. It was shown that the percentage of plants with symptoms of pest feeding increased together with an increase in the level of applied nitrogen ranging from 0 to 100 kg N/ha. Maize fertilization with slow-release fertilizers significantly decreased the percentage of plants damaged by the pest in comparison with fast-release nitrogen fertilizers. ES Paroli „stay-green” cultivar revealed a significantly lower susceptibility to European corn borer feeding in comparison with ES Palazzo cultivar.

Geographic distribution of chestnut feeding insects in Greece

Greece has been traditionally considered as a chestnut-producing country; yet, chestnut production has experienced a dramatic decline in the last decades, mainly due to chestnut blight Cryphonectria parasitica and chestnut feeding pests. Though chestnut blight is partially under control, little attention has been granted on chestnut feeding pests in Greece. Two species are described as major pests, i.e., Cydia splendana and Curculio elephas, without any information regarding their distribution. This study aimed to identify species diversity that feed on chestnuts trees using genetic markers and further to obtain insight into their distribution. Besides C. splendana and C. elephas, three additional species were determined namely Cydia fagiglandana, Curculio glandium as well as a Curculio sp. that has never been genetically determined before. The distribution of these species was inhomogeneous in Greece. These results demonstrate clearly the need for a carefully planned pest management approach adapted to the local mixture of chestnut feeding pests of each area rather than one general approach.

Sources of resistance in primary synthetic hexaploid wheat (Triticum aestivum L.) to insect pests: Hessian fly, Russian wheat aphid and Sunn pest in the fertile crescent

Hessian fly, Mayetiola destructor (Say), Russian wheat aphid (RWA), Diuraphis noxia (Kurdjumov), and Sunn pest, Eurygaster integriceps (Puton), are among the most important insect pests of wheat in North Africa, West and Central Asia. Host plant resistance is the most economical, environmentally friendly and practical means of controlling insect pests. Through field and greenhouse screening, several sources of resistance to Hessian fly, RWA and Sunn pest have been identified in wheat and its wild relatives. To further broaden the genetic base of resistance to these pests, 914 fixed lines of synthetic hexaploid wheat (SHW) commonly designated as primary synthetic wheat were evaluated for resistance to Hessian fly, RWA and Sunn pest. The initial screenings for RWA and Sunn pest were carried out in the field at Tel Hadya, Aleppo, Syria, and for Hessian fly in the greenhouse at Tel Hadya during the 2009 and 2010 seasons. Promising accessions from the initial screening for Hessian fly, RWA and Sunn pest were evaluated for confirmation in replicated trials in the greenhouse and field. Fifteen SHWs showed high levels of resistance to Hessian fly and four showed moderate resistance. A wheat line derived from the cross (Triticum turgidum/T. dicoccoides) also showed a high level of resistance to Hessian fly. The level of resistance to RWA in SHW was considerably lower; only one SHW and one durum wheat ‘Altar 84’ exhibited a high level of resistance, while four SHW were moderately resistant. There were 21 SHW genotypes and one durum wheat ‘Langdon’ found resistant to Sunn pest feeding at the vegetative stage. Crosses between these potentially novel resistance sources and elite bread wheat were initiated. Genetic and genomic studies using these accessions are ongoing to identify and characterize the resistance genes and reveal potentially new resistance genes, which will be useful in breeding programs to develop wheat germplasm with multiple resistances to these pests.

Dispersal and spatial distribution of western corn rootworm larvae in relation to root phenology

1 Despite the increasing economic importance of root feeding pests such as the western corn rootworm (WCR) Diabrotica virgifera virgifera, basic parameters about their below ground biology are only partly understood. The present study investigated the dispersal and distribution of WCR larvae in the maize root system during their development at two growth stages of maize (BBCH 13–14 and BBCH 17–18). 2 Dispersal of the WCR larvae increased as they developed; the larvae moved off their original place of emergence and into deeper soil layers. Overall, changes in the horizontal distribution of the larvae were more extensive than changes in the vertical distribution. 3 The spatial analysis of distance indices revealed that the larvae had an aggregative distribution throughout their development. The feeding site of larvae in the root system was determined by the stage of larval development. Initially, WCR larvae started feeding in close proximity to their emergence location and moved to more developed root tissue towards the end of their development. 4 Differences in root phenology mainly influenced the distribution of the larvae at the end of their development, when larvae exhibited increased vertical movement at a later growth stage of maize. 5 The mechanisms of these distributional changes and the implications for the management of WCR larvae are discussed, especially with regard to chemical control, because fewer larvae are expected to be targeted at a later growth stage of maize.

Changes in leaf tissues of common horse chestnut (Aesculus hippocastanum L.) colonised by the horse-chestnut leaf miner (Cameraria ochridella Deschka and Dimić)

The present study, conducted during the period 2010- 2011, involved morphological observations and anatomical investigations of horse chestnut (&lt;i&gt;Aesculus hippocastanum&lt;/i&gt; L.) leaves with symptoms of damage caused by feeding of larvae of the horse-chestnut leaf miner (&lt;i&gt;Cameraria ohridella&lt;/i&gt; Deschka &amp; Dimić). Leaves were collected from trees growing in the city of Lublin (Poland). Microscopic slides were prepared from fresh and fixed plant material. Leaf anatomical features were examined by light microscopy in order to determine the mechanical barrier for feeding pests. Changes were also observed during the progressive damage of the leaf tissues caused by the larvae. Selected developmental stages of the pest are presented in the paper. It has been shown that very thin blades of the mesomorphic leaves of &lt;i&gt;Aesculus hippocastanum&lt;/i&gt; produce a poorly developed mechanical barrier in which the following elements can be included: the presence of collenchyma and idioblasts with druses of calcium oxalate, few non-glandular trichomes found close to the leaf veins as well as relatively thin outer walls of the epidermal cells. The cells containing tannins and the oil cells found in the mesophyll may form a physiological barrier. However, foraging leaf miner larvae feed only on the palisade and spongy parenchyma cells, leaving undamaged the cells with tannins as well as the idioblasts with calcium oxalate crystals and oils. The feeding of the pest in the leaf mesophyll leads to the death of the epidermis on both sides of the lamina and to drying of the parts of the leaves in the area of the mines.