Identification of aphids of Aphis frangulae-group living on Lamiaceae species through DNA barcode.

The genus Aphis frangulae-group living on Lamiaceae includes several postulate species, which are morphologically indistinguishable. As a consequence, identification is possible only on the basis of the host plant or life cycle. This study tested the utility of a fragment (614 bp) of mitochondrial cytochrome oxidase 1 (COI) with the aim of identifying the species and/or to confirm the previous classification based on host plant and data reported in the literature. Although the general nucleotide variability found was rather low, the analysis enabled the separation and identification of all the specimens collected. In some cases, the lack of nucleotide variability among postulated taxa indicates the limits of identification based on biological traits. Consequently, based on the molecular analysis, the postulate species A. symphyti, A. stachydis and A. lamiorum should be regarded as synonymous of A. frangulae.

Interannual variation in leaf expansion and outbreak of a teak defoliator at a teak stand in northern Thailand.

The leaf area index (LAI) is a key factor affecting tree growth in forests. Following the outbreak of a defoliator, the LAI declines, serving as a useful indicator in forest management. In this study, daily radiative transmittance from above the canopy, which decreases exponentially with increasing LAI, was measured in a teak plantation (Tectona grandis L. f.) in northern Thailand from March through July in 2001-2008. Volumetric soil moisture was also measured at depths of 0.1, 0.2, 0.4, and 0.6 m. The negative logarithmic value of the ratio of daily downward solar radiation on the forest floor to that above the canopy (NLR; -ln[Sb decrease/Sdecrease]), was calculated as an indicator of leaf flush and subsequent leaf expansion. The NLR data indicated that leaf expansion began in late March and continued to the beginning of May during all eight years (with the day the leaves began to expand defined as D(B)). In addition, the peak in NLR values (NLR(P)), corresponding to the lowest value of a 99% confidence interval, occurred in July. The day when NLR first reached NLR(P) was defined as D(P), which always occurred in June, 31-85 days after D(B). The NLR indicated an increase in the population of Hyblaea puera (a teak defoliator) that was associated with greatly decreased leaf areas during two growth periods (D(B)-D(P)): the earliest D(B)-D(P) in 2001 and the second-earliest D(B)-D(P) in 2008. In almost all cases, soil moisture data indicated that leaf expansion occurred after increases in soil moisture at depths of 0.1-0.4 m even without increases at 0.6 m; in contrast, increases in shallow soil moisture (0.1-0.2 m) were insufficient to trigger leaf expansion at the stand level. Periods of soil drought at 0.1-0.4-m soil depths inhibited leaf expansion, resulting in prolongation of the interval between D(B) and D(P) during those years in which the D(B)'s occurred chronologically close to one another. Moreover, when drought did not limit leaf expansion, the D(B)-D(P) growth periods characterized by earlier D(B)'s tended to be longer than those with later D(B)'s.

[Antagonistic mechanisms of trichoderma spp. against Phytophthora nicotianae].

Antagonistic mechanisms of Trichoderma viride M3, Tv04-2, and T. harzianum ThB, were studied against Phytophthora nicotianae, the pathogen of stem blight disease on Schizonepeta tenuifolia by dual-culture, hydrolase activity, volatile and nonvolatile substances. Results indicated that competitive, mycoparasitism and antagonism were the antagonistic mechanisms of three Trichoderma spp. against P. nicotianae. Hydrolase activity showed that M3 was the highest for beta-1, 3-glucanases activity while ThB was the highest for proteases activity among the three T. strains, and they could produce volatile and non-volatile substances, also.

Effect of silicon-based fertilizer applications on the reproduction and development of the citrus mealybug (Hemiptera: Pseudococcidae) feeding on green coleus.

Mealybugs are major insect pests of greenhouses, interiorscapes, and conservatories because they feed on a wide-range of horticultural crops. Furthermore, mealybugs are difficult to regulate with insecticides due to the presence of a nearly impervious protective waxy covering, which means that alternative management strategies are required. As such, this study, involving two replicated experiments, was designed to determine the value of applying silicon-based fertilizers, as potassium silicate, to coleus, Solenstemon scutellarioides (L.) Codd, plants as a way to prevent outbreaks of the citrus mealybug, Planococcus citri (Risso) (Hemiptera: Pseudococcidae). The first experiment evaluated the effects of different application methods (foliar and drench), at 50 ppm silicon, using the commercially-available product, ProTek 0-0-3 The Silicon Solution. The second experiment entailed applying the silicon-based fertilizer as a drench to the growing medium at different rates (0, 100, 400, 800, and 1,600 ppm silicon). We determined the effects of the silicon-based fertilizer treatments on citrus mealybug life history parameters including number of eggs laid by the adult female, body size, and developmental time from first instar to ovipositing adult female. Furthermore, we used a plant alkaline fusion technique to assess the concentration (milligrams per kilogram or ppm) of silicon in the coleus plant tissues at variable time intervals (days). In general, this technique involved dry-ashing plant tissue in a muffle furnace, followed by alkaline fusion and then colormetric analysis. The silicon-based fertilizer application treatments, in both experiments, did not negatively affect any of the citrus mealybug life history parameters measured. In the first experiment, citrus mealybug female egg load ranged from 199.5 (drench application) to 219.4 (combination spray and drench application), and developmental time (days) from first instar crawler to ovipositing female ranged from 34.2 (combination spray and drench application) to 35.7 (drench application). For the second experiment, citrus mealybug female egg load ranged from 223.1 (1,600 ppm silicon) to 249.2 (800 ppm silicon). Developmental time from first-instar crawler to ovipositing female ranged from 35.0 (400 ppm silicon) to 36.6 (800 ppm silicon). Our results indicate that coleus is a silicon "rejector," and as such, applications of silicon-based fertilizers may not benefit dicot plants such as coleus as much as monocot plants in regards to avoiding insect pest outbreaks because dicots tend not to accumulate sufficient quantities of silicon.

[Taxonomy and evolution of the genus Pratylenchoides (Nematoda: Pratylenchidae)].

The amended diagnosis of the genus Pratylenchoides and list of its valid species with synonyms are given. All the efficient diagnostic characters are listed. Modern taxonomic standard for the description of Pratylenchoides species is proposed; it may be used also in taxonomic databases. Tabular and text keys for all species of the genus are given. Five following groups are considered within the genus Pratylenchoides. The group arenicola differs from other groups in the primitive adanal bursa type; the groups magnicauda, crenicauda, ritteri, and megalobatus differ from each other in the position of cardium along the body axis in relation to the pharyngeal gland nuclei, pharynx types are named according to the stages of its evolution from the primitive tylenchoid pharynx (cardium situated posteriorly) to the advanced hoplolaimoid one (cardium situated anteriorly). Diagnoses and species compositions of the groups are given. Basing on the matrix of species characters, the dendrogram has been generated for all species of Pratylenchoides and for all characters (UPGMA, distance, mean character difference, random, characters ordered). Taking in view that the PAUP software gives equal weights to all characters, including the most important ones which define the prognostic species groups, the separate dendrograms for each prognostic species group were generated using the same above mentioned tree parameters. On the base of the records of Pratylenchoides species the matrices of plant host ranges, geographic distribution, and preferred soil-climatic conditions were developed. The dendrograms of the faunal similarities were generated using these matrices, with conclusions on a possible origin and evolution of the genus. The genus evolved from the flood lands with swampy soils and prevalence of dicotyledons (herbaceous Lamiaceae and woody Salicaceae families) to the forest mainland communities with balanced humidity and predominance of herbaceous Poaceae and Fabaceae with woody Fagaceae, Betulaceae, and Oleaceae. The leading factor of the evolutional adaptation to soil-climatic conditions was the factor of humidity, but its significance gradually decreased with the host change to more advanced plant taxa adapted to the communities with more dry balanced humidity. The genus took its origin on the south shores of Laurasia in the Cainozoe. Later, when Hindistant and Arabian Peninsula joined with Laurasia creating the Himalayas barrier, the Pratylenchoides spp. distributed by two branches: the northern one moved into Central Asia, East Europe and North America, and the south branch came into Indo-Malaya, West Asia and the north of Africa. The remnants of the ancient species groups remain in West Europe and East Asia. In the North America the genus gave an origin to its sister genus Apratylenchoides, which spread to the south up to Antarctica; another advanced branch spread in the North America reaching Alaska.

Population dynamics of the Teak defoliator (Hyblaea puera Cramer) in Nilambur teak plantations using Randomly Amplified Gene Encoding Primers (RAGEP).

BACKGROUND: The Teak defoliator (Hyblaea puera) is a pest moth of teak woodlands in India and other tropical regions (e.g. Thailand) and is of major economic significance. This pest is of major concern as it is involved in complete defoliation of trees during the early part of the growing season. Defoliation does not kill teak trees, but it results in huge amount of timber loss. Teak defoliator outbreaks are a regular annual feature in most teak plantations in India and it is extremely difficult to predict the exact time and place of occurrence of these outbreaks. Evidence from the study of the population dynamics of H. puera indicated habitual, short range movements of emerging moth populations, suggesting that these populations have spread to larger areas, generation after generation, affecting the entire teak plantations. We were therefore interested in investigating the temporal and spatial relationship among various population groups in Nilambur, Kerala (India) and address the cause of outbreak at the landscape level. RESULTS: The populations were classified into 'endemic', 'epicenter' and 'epidemic' populations based on the time of occurrence and size of infestation. We devised a novel method of screening nuclear and mitochondrial DNA polymorphisms using Randomly Amplified Gene Encoding Primers (RAGEP). We have used this method extensively to evaluate the species specificity, reproducibility and to discriminate among the three different characterised populations of teak defoliator. CONCLUSIONS: This method also allowed us to comment with some certainty that the endemic teak defoliator, H. puera do not play a major role in contributing to large-scale infestations. With respect to the hypotheses put forward regarding the origin of outbreaks of the moth, this study confirms the role of migration in outbreak causation, while negating the belief that endemic populations aggregate to cause an epidemic.

Antifeedant/insecticidal terpenes from asteraceae and labiatae species native to Argentinean semi-arid lands.

To validate the potential as added-value resources of Asteraceae and Labiatae species of Argentinean semi-arid lands, we have selected 13 of their major terpenoids belonging to several chemical classes and tested their insect antifeedant and toxic activity on the herbivorous insects Spodoptera littoralis and Leptinotarsa decemlineata. The antifeedant effects of the test compounds were structure- and species-dependent. The most active antifeedant to L. decemlineata was the eudesmane sesquiterpene gamma-costic acid (13), followed by the labdane diterpene 2alpha,3alpha-dihydroxycativic acid (8), the clerodane diterpenes 6-acetylteucjaponin B (5), bacchotricuneatin A (1), bartemidiolide (7), butanolide (4), and the sesquiterpenes ilicic acid (11) and tessaric acid (10) (eudesmane and eremophilane type, respectively). S. littoralis was only affected by the clerodanes and showed the strongest response to salviarin (3) and 5, followed by hawtriwaic acid (6) and 12-epi-bacchotricuneatin A (2). Orally injected S. littoralis larvae were negatively affected by 5. Most of the diterpenes had selective cytotoxic effects to insect-derived Sf9 cells with the clerodane 1 being the most active, followed by the eudesmane costic acid (12), the only cytotoxic sesquiterpene. None of these compounds was cytotoxic to mammalian CHO cells.

The impact of host plant on the abundance and function of symbiotic bacteria in an aphid.

The black-bean aphid Aphis fabae bears populations of coccoid symbiotic bacteria Buchnera spp. at 2.0-3.2 x 10(7)cells mg(-1)aphid mass and rod-shaped secondary symbionts of uncertain taxonomic affiliation at 0.1-0.6 x 10(7)cells mg(-1)aphid mass. Buchnera provides essential amino acids, supplementing the poor supply in the aphid diet of plant phloem sap. Comparison of the performance of A. fabae containing and experimentally deprived of their bacteria showed that the bacteria caused increased larval mass of aphids reared on Chenopodium album and Papaver dubium plants, but not when reared on Lamium purpureum. In the aphids reared on L. purpureum, the density of the bacteria, especially the secondary symbionts, was significantly elevated, and bacterial-mediated production of the essential amino acid threonine was reduced, even though the essential amino acid content of phloem exudates from L. purpureum had a low threonine content. It is proposed that the shortfall in threonine, possibly compounded by the high density of secondary symbionts, may contribute to the poor performance of the aphids on L. purpureum. This study offers the first evidence to suggest plant-mediated interference with the nutritional function of symbiotic bacteria in any phytophagous insect.

Phytoseiid mites on peppermint and effectiveness of Neoseiulus fallacis to control Tetranychus urticae (Acari: Phytoseiidae, Tetranychidae) in arid growing regions.

The humid-adapted species Neoseiulus fallacis (German) was the most common phytoseiid mite collected in either humid (> 100 cm annual rainfall) or arid (20-45 cm annual rainfall) mint growing regions of Washington, Oregon, Montana, Idaho, and California during 1991-1995. In experimental field plots, this predator gave excellent biological control of Tetranychus urticae Koch on mint grown under arid conditions in central Oregon when evaluated by an insecticide check method or by the caging of mites. N. fallacis is effective as a predator in arid areas probably because regular irrigation creates a humid environment in the canopy. The selective miticide propargite, when used in combination with predators, was effective at reducing high spider mite populations to below the treatment threshold faster than did N. fallacis alone.

The effect of waste water reuse in irrigation on the contamination level of food crops by Giardia cysts and Ascaris eggs.

In Marrakech, raw sewage has been used for farming purposes for several decades for many types of crops. This study aimed to determine the contamination level of Giardia cysts and Ascaris eggs for crops designated for human consumption. Collected crops in irrigated fields were turnip, marrow, squash, potatoes, pepper and eggplant. Field trials were also carried out on four crops, coriander, carrots, mint and radish, using three water types for irrigation, i.e. raw waste water, treated waste water (sedimentation and 16 days retention) and fresh water. Giardia cysts were detected at a level of 5.1 cysts/kg in potatoes, while Ascaris eggs were observed in numbers varying between 0.18 eggs/kg in potatoes and 0.27 eggs/kg in turnip. Field trials confirmed that irrigation of crops by raw waste water leads to contamination. Giardia and Ascaris were isolated in coriander at concentrations of 254 cysts/kg and 2.7 eggs/kg, respectively; mint was also highly contaminated with numbers reaching 96 cysts/kg and 4.63 eggs/kg. Carrots and radish were contaminated and respective numbers observed for Giardia were 155 and 59.1 cysts/kg; Ascaris was discovered in numbers of 0.7 and 1.64 eggs/kg, respectively. However, cultures irrigated with treated waste water and fresh water were free from contamination. Cysts and eggs on coriander persisted for a maximum of 8 days.