Doppler radar detection of exceptional mass-migration of aphids into Finland

Our objective was to detect mass migrations of insects of economic significance by insect traps and a Doppler weather radar. Migrants were sampled by suction traps, tow nets and light traps in the Helsinki region. We used radar to observe the migrating insects, and trajectories to backtrack mass migrations of aphids (Homoptera, Aphididae) in spring 1988. The aphid migrations were clearly observed in trap catches and by radar. The first migration, mainly involving Euceraphis betulae, occurred on 18 May and was tracked back to northern Poland. The second migration, mainly of Rhopalosiphum padi (a serious pest of small-grain cereals), occurred 3 days later and was tracked back to a large area covering Latvia and western Russia south of St Petersburg. The third migration included both E. betulae and R. padi, and took place on 30 May. It originated from Estonia. Neither trap nor radar data provide exact quantitative information on migrations. Trapping efficiency depends strongly on wind speed and insect size. Radar echo intensity is very strongly related to the sizes of insects in the large volume of air measured, and the sizes are not known accurately. Weather data, especially temperature, can be used in predicting the development of aphids, and air-parcel trajectories in estimating the source areas of migrants. These methods for forecasting aphid migrations, combined with radar observations, are useful for warning purposes and to intensify insect trapping. This would contribute to more efficient agricultural pest management. Received: 11 March 2000 / Revised: 24 April 2000 / Accepted: 26 April 2000     

Diapause termination and egg hatch in the bird cherry aphid, Rhopalosiphum padi

Conclusion TastePROBE is a convenient and flexible electronic circuit designed to record action potentials from taste sensilla of insects. It facilitates the recording of slow potentials arising in taste sensilla, improves the signal to noise ratio, and preserves spike shapes. This new amplifier design combines excellent signal to noise ratio with complete compatibility as regards existing electrophysiological equipment.DC recordings have higher information content than filtered recordings. With DC recordings, spike shapes are not modified and thus better sorting is possible. Moreover, slow variations in the transepithelial potential (i.e. less than 10 Hz) are preserved. Both aspects are of considerable importance when studying the physiology of taste receptors.     

Host plant selection by migrant Rhopalosiphum padi in autumn and the occurrence of an intermediate morph

Alate female Rhopalosiphum padi (L.) were trapped alive in suction traps in autumn, 1986–1988. Alate exules and gynoparae were identified by the morph of their offspring. Gynoparae largely replaced alate exules in September indicating that most of the population were holocyclic even in southern England where the primary host, Prunus padus L., is scarce. However, a few alate exules occurred throughout the autumn indicating that a proportion of the population is anholocyclic. A morph intermediate between alate exules and gynoparae occurred at low frequency throughout the autumn. Alate exules and gynoparae preferred barley and P. padus, respectively, on which to settle and larviposit; gynoparae were less selective than exules possibly due to an incomplete physiological switch from a preference for Gramineae to P. padus on which the sexual cycle is completed. Intermediate individuals preferred to settle on P. padus, but their virginoparous and oviparous nymphs were produced on barley and P. padus respectively. Intermediate morphs maintained under continuous short day conditions (L12 : D12) produced mainly apterous virginoparae with males occurring at the end of their reproductive live; intermediates occurred occasionally amongst the apterae. It is proposed that intermediates are a programmed component of the morph structure and have the potential to contribute to both the holocyclic and anholocyclic portions of the population.

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Résumé Des femelles de R. padi L. ont été capturées vivantes dans des pièges a succion en 1986–88. Les ailés exules et les gynopares ont été identifiés par le morphe de leurs descendants. Les gynopares ont remplacé généralement les ailés exules en septembre, ce qui montre que la majorité de la population est holocyclique même dans le sud de l'Angleterre où l'hôte primaire, Prunus padus L., est rare. Cependant, quelques ailés exules se maintiennent pendant l'automne montrant qu'une partie de la population est anholocyclique. Au cours de l'automne, on observe un morphe intermédiaire entre les ailés exules et les gynopares. Les exules ailés et les gynopares préfèrent respectivement l'orge et P. padus, sur lesquels ils s'installent et produisent des larves; les gynopares étaient moins sélectifs que les exules, peut-être par suite d'une rupture physiologique incomplète de leur préférence pour l'orge sur laquelle ils se développent rendant moins impérative leur attraction par P. padus sur lequel leur cycle sexuel est complet. Les individus intermédiaires préfèrent s'établir sur P. padus, mais leur larves virginipares et ovipares sont produites respectivement sur oreg et sur P. padus. Les morphes intermédiaires maintenus en jours courts (L12/N12) ont donné surtout des virginipares aptères les mâles apparaissant à la fin de leur vie; des intermédiaires sont apparus occasionnellement parmi les aptères. Les intermédiaires seraient une composante programmée de la structure polymorphe et contribueraient à la fois à l'apparition des fractions holocyclique et anholocyclique de la population.

     

Aerial flow of barley yellow dwarf viruses and of their vectors in western France

During the years 1989–1992 cereal aphids were caught alive in a low level (1.5 m high) suction trap operated in Le Rheu (Brittany, France) and tested for BYDV transmission. In most cases comparisons with data collected simultaneously by a 12.2 m suction trap operating in the same site resulted in good relationships between weekly catches at both heights. Results from transmission tests showed that: (i) the two main BYDV vectors were Rhopalosiphum padi and Metopolophium dirhodum during the years of experiment; (ii) PAV and MAV were the commonest viruses and RPV was relatively scarce; (iii) during spring M. dirhodum appeared to be the most important MAV vector and nearly as good a PAV vector as R. padi; (iv) during autumn R. padi was the only vector of the three viruses with mixed transmission allowing it to transmit also MAV probably by heteroencapsidation. To give an indication of the risk of infection, infectivity indices were calculated by multiplying the numbers of aphids caught by the 12.2 m suction trap by the proportion that were infective. These infectivity indices agreed with field records of primary infections.     

The development and multiple uses of a standardised bioassay method to select hypocrealean fungi for biological control of aphids

A technically standardised bioassay method was designed, evaluated and used to assess virulence and host range of hypocrealean fungi against aphids. A track mounted sprayer was used to apply conidia because hand held versions of the same sprayer can be used for field applications, thereby allowing the outcome from laboratory experiments to predict activity in the field accurately. Eighteen fungal isolates were assessed in single concentration bioassays against the black bean aphid Aphis fabae Scopoli. Isolates comprised commercially available mycoinsecticides (based on Beauveria bassiana and Lecanicillium longisporum) and isolates of B. bassiana, Lecanicillium spp., Paecilomyces fumosoroseus and Metarhizium anisopliae. Aphid mortality was in excess of 80% for 15 isolates, and HRI 1.72 (L. longipsorum), Z11 (P. fumosoroseus), Mycotech strain GHA (B. bassiana) and ARSEF 2879 (B. bassiana) were studied further. Multiple concentration bioassays identified HRI 1.72 as the most virulent isolate against A. fabae with significantly smaller LC₅₀ and LT₅₀ values compared to other isolates. A precise LC₅₀ value (2.95 × 10² conidia ml⁻¹) was calculated for HRI 1.72 using a second multiple concentration assay with smaller concentrations of conidia. The four isolates were applied at a single concentration (1 × 10⁸ conidia ml⁻¹) against Myzus persicae, A. fabae, Acyrthosiphon pisum, Metopolophium dirhodum, Sitobion avenae and Rhopalosiphum padi. A ranking of aphid susceptibility was obtained, such that S. avenae > M. persicae, A. pisum, A. fabae > R. padi. Results indicate the importance of standardising bioassay methods to reduce bioassay variability without compromising the ability to use the bioassay to investigate fungus–host interactions under varying abiotic and biotic conditions.     

Effects of host plant drought stress on the performance of the bird cherry-oat aphid, Rhopalosiphum padi (L.): a mechanistic analysis

Abstract.  1. The growth (increase in height and leaf number) of four grass species was reduced by a −0.5 MPa drought stress, but the performance of an associated herbivore, Rhopalosiphum padi (L.), was not affected consistently. The intrinsic rate of increase of R. padi was reduced by drought stress on three grass species, including Dactylis glomerata (L.), but was unaffected on Arrhenatherum elatius (L.). Therefore, there is no general relationship in the effect of plant drought on an insect herbivore, even among closely related host plant species.
2. Drought stress increased the quality of plant phloem sap, as indicated by increased sieve element osmotic pressure and essential amino acid concentrations. Thus, diet quality could not account for the reduced performance of R. padi under drought stress. The concentration of essential amino acids in the phloem of well-watered A. elatius was, however, lower than that of well-watered D. glomerata , correlating with the decreased performance of aphids on well-watered A. elatius .
3. There were no differences in aphid feeding duration between watering treatments or plant species but sap ingestion rates were reduced significantly under drought stress.
4. Using the measure of dietary amino acid concentrations and the estimate of sap ingestion, the essential amino acid flux through aphids was calculated. Compared with the flux through aphids feeding on well-watered D. glomerata , there was a reduction in aphids feeding on drought-stressed D. glomerata and drought-stressed A. elatius due to lower sap ingestion rates. The flux through aphids on well-watered A. elatius was also reduced due to low phloem essential amino acid concentrations. Thus, the performance of an aphid is correlated with the availability and accessibility of essential amino acids.     

Towards an understanding of how phloem amino acid composition shapes elevated CO2‐induced changes in aphid population dynamics

1. The performance of foliage feeders tends to decrease under elevated CO₂, but the responses of phloem‐feeding insects have been much more equivocal. As phloem tissues are less accessible than whole‐plant tissues, much less is known about how phloem composition is altered under elevated CO₂ and the mechanisms driving changes in aphid performance. 2. In this study, the plant mechanisms underlying the performance of Rhopalosiphum padi aphids on Hordeum vulgare (barley) grown under ambient (390 ppm) and elevated (700 ppm) CO₂ were examined. We used aphid stylectomy to sample pure phloem from plants in CO₂‐controlled conditions and high‐performance liquid chromatography to analyse phloem samples for amino acid concentrations. 3. Aphid abundance significantly increased by 127% under elevated CO₂. Consequently, plant biomass decreased under elevated CO₂ in trials with herbivores present, possibly due to the increased herbivore load, but increased when aphids were absent. The intrinsic rate of population increase (r_m) was significantly higher under elevated CO₂; however, there were no statistically significant effects on aphid fecundity or development time. The concentration of individual amino acids tended to increase, although these increases were statistically significant in only a few cases. A principal components analysis revealed that the relative abundance (mol %) of those amino acids considered essential for aphids tended to increase under elevated CO₂. 4. These results indicate that CO₂ may affect nutrient translocation in plants in ways that are contrary to predictions about nitrogen metabolite responses to CO₂. Such plant biochemical responses may underlie observations of improved phloem feeder performance under elevated CO₂.     

禾谷缢管蚜鞣化激素基因克隆及功能分析

【目的】探讨禾谷缢管蚜 Rhopalosiphum padi （Linnaeus）鞣化激素基因的发育表达模式及功能。【方法】采用转录组测序得到禾谷缢管蚜鞣化激素基因bursicon-α 和 bursicon-β cDNA序列。通过实时荧光定量PCR方法,分析该基因的发育表达模式。利用RNA干扰（RNA interference, RNAi）介导 bursicon-α 和bursicon-β 沉默,分析鞣化激素的功能。【结果】序列分析结果显示,禾谷缢管蚜鞣化激素α亚基基因（bursicon-α）cDNA序列开放阅读框为480 bp,编码159个氨基酸残基;β亚基基因（bursicon-β）cDNA序列开放阅读框为417 bp,编码138个氨基酸残基。时序表达分析表明,鞣化激素两个亚基基因在禾谷缢管蚜整个发育期均有表达,以1龄若蚜期表达量最高;成蚜有翅个体中表达量显著高于无翅个体。RNAi介导的 bursicon-α 和 bursicon-β 沉默均能显著抑制禾谷缢管蚜成蚜表皮的黑化。【结论】研究结果表明,鞣化激素在禾谷缢管蚜体壁黑化中发挥着重要作用。该结果为进一步研究鞣化激素在蚜虫生长发育过程中的生理功能提供了基础资料。     

Pitfall-trap catches of the carabid beetle Pterostichus melanarius, in relation to gut contents and prey densities, in insecticide treated and untreated spring barley

During large-scale field experiments in 1981 and 1982, designed to assess the effects of the insecticides Fenitrothion and Sumicidin (Fenvalerate) on beneficial arthropods in spring barley, significant increases in pitfall-trap catches of Pterostichus melanarius (Illiger) were observed in treated plots compared to untreated controls, several weeks after treatment. Significantly more female P. melanarius were caught in treated plots during these post-treatment increases. Corresponding decreases were observed in prey populations following treatments. Individual female P. melanarius from treated plots had significantly fewer of their gut areas full of solid (arthropod) food when compared to those from untreated control plots.Earlier workers observed both faster recapture rates in pitfalls and higher mobility in hungry carabid beetles. The following hypothesis is suggested: reducing prey populations by the application of insecticides results in hungrier carabid beetles with consequently higher activity. Since pitfall-trap catch is determined not only by population size but also activity, it is argued that pitfall-trap catches alone cannot give a true measure of the effects of insecticides on carabid populations in the field.

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Relations entre les captures de Pterostichus melanarius (Col.; Carabidae) dans des trappes, le contenu de l'intestin, et la densité de proies, dans des parcelles d'orge de printemps traitées ou non

Résumé Au cours d'essais à grande échelle, effectués en 1981 et 1982, sur orge de printemps, pour évaleur l'effet des insecticides Fenitrothion et Sumicidine (fenvalerate) sur les arthropodes utiles, un accroissement significatif des captures, dans des trappes pièges de Barber, de Pterostichus melanarius (Illiger) a été observé plusierus semaines après le traitement dans les lots traités par rapport aux lots témoins. Significativement plus de femelles de P. melanarius ont été capturées dans les parcelles traitées pendant cette période d'accroissement après traitement.Une diminution correspondante dans les populations de proies a été observée à la suite des traitements.Chaque femelle de P. melanarius des parcelles traitées avait une fraction significativement moins importance de son intestin remplie d'aliments solides (arthropodes) que celles des parcelles non traitées.Des auteurs précédents avaient observé des taux de capture plus rapides dans les trappes et ne plus grande mobilité des carabes affamés. La réduction des populations proies par l'application d'insecticides affamerait les carabes dont l'activité serait par suite plus élevée. Comme le taux de captures dans les trappes est dû à la fois à la taille de la population et à son activité, on en déduit que la capture par trappes seule ne peut donner une image exacte de l'effet des insecticides sur les populations de carabes dans les champs.