Susceptibility of plants to attack by wireworms (Agriotes spp.)

In laboratory tests, larvae of Agriotes spp. were presented with a choice between seedlings of test plants, and of wheat, which is known to be susceptible. Some plants, e.g. onion, were as susceptible as wheat to wireworm attack whilst others (mustard, cabbage, French marigold, clover and flax) were less often attacked, partly because they are small and are shallow sown. All pea and bean plants exposed to wireworms were attacked but most tolerated attack and continued to grow.     

Toxicity of 1,3-dichloropropene and fosthiazate to wireworms (Agriotes spp.)

Wireworms (Agriotes spp.) are sporadic but increasingly important pests of potatoes, sugar beet and cereals. Whilst effective chemical control is possible, the granular organophosphates normally require high rates of application and the seed dressings containing lindane (gamma‐HCH) have been withdrawn from use. The soil fumigant 1,3‐dichloropropene (1,3‐D as Telone II) and the granular nematicide fosthiazate (Nemathorin 10G) are currently used for the control of potato cyst nematodes. We investigated the effects of both of these chemicals on wireworms. Air‐vapour phase toxicities for 1,3‐D against wireworm were LD₅₀ 2.74 mg.litre.day and LD₉₉ 5.05 mg.litre.day. The in vitro soil phase toxicity was LD₉₉ 8.15 mg.litre.day. 1,3‐D soil phase activity against wireworm may be associated more with air‐vapour phase than a soil‐water phase activity. In glasshouse experiments 16.0 mg.litre.day of 1,3‐D gave 75% control. Fosthiazate, which is applied at approximately 2 μg g^?1 of soil for potato cyst nematode control, achieved an LC₅₀ at 3.20 μg g^?1. In both in vitro and glasshouse studies 1,3‐dichloropropene showed high toxicity to wireworm at dosages below the current commercial application rate for potato cyst nematode control and fosthiazate also showed useful efficacy. These chemicals may therefore prove to be valuable additional tools for limiting initial wireworm plant damage or reducing wireworm populations.     

The effects on soil fauna of insecticides tested against wireworms (Agriotes spp.) in wheat

The organophosphorus insecticides Bayer 38156 (O-ethyl S-p-tolyl ethyl phosphonodithioate), trichloronate, Stauffer N 2790 (O-ethyl S-phenyl ethyl phosphonodithioate), thionazin and fenitrothion were compared with aldrin, dieldrin and γ-BHC for their effects on soil fauna, particularly wire-worms, and on crop yields in 1964 and 1965. At 1·5 lb active ingredient/acre, none of the organophosphates had as great an effect on wireworms as an aldrin spray at 2·25 lb a.i./acre or a dieldrin seed dressing at 2·25 lb a.i./acre. Some treatments significantly increased and some significantly decreased numbers of mites and Collembola. Except for Allolobophora chlorotica in plots treated with Bayer 38156, earthworm numbers were greater in plots sprayed with Bayer 38156 or aldrin, or sown with dieldrin-dressed seeds, than in untreated plots. In May 1964, one month after sowing, untreated plots had significantly fewer plants than plots sprayed with aldrin, trichloronate or Bayer 38156, or sown with γ-BHC or dieldrin-dressed seeds, but yields from untreated plots at harvest were high for such a large wireworm population and did not differ significantly from yields of treated plots in either year. The persistence of thionazin and Bayer 38156 in treated plots was measured by a bioassay using Collembola. Bayer 38156 was detected in plots 1 month after spraying but not after 6 months. Thionazin left detectable residues 1 month after spraying in the two acid plots but not in the two alkaline plots. More frequent samples taken from thionazin-treated plots in 1965 showed a similar pattern of persistence, and laboratory tests, using soil mixed with various amounts of powdered calcium carbonate, confirmed that thionazin persisted longer in more acid soils.     

The biology and management of wireworms (Agriotes spp.) on potato with particular reference to the U.K.

1 This paper reviews and interprets relevant work on the biology and management of wireworms (Agriotes spp.) within the context of potato production in Europe, with particular reference to the U.K. Although the review concentrates on Agriotes spp., the extensive world literature on other Elateridae of economic importance is also drawn upon. 2 Possible reasons for the apparent increase in the importance of wireworms on the potato crop are discussed, followed by a review of wireworm biology, risk assessment techniques (soil sampling, bait trapping and adult pheromone trapping), crop damage, and cultural, biological and chemical control methods. 3 It is clear that the process of site risk assessment followed by appropriate control measures (usually insecticide use) will remain the mainstay of wireworm management programmes. However, there is considerable scope for adopting new risk assessment techniques, such as pheromone trapping of adult beetles. 4 These control measures will need to be underpinned by a greater understanding of wireworm biology, particularly adult dispersal. Factors affecting the initiation and maintenance of wireworm populations in individual fields also require further study. The current use of insecticides could also be optimized by a better appreciation of the interactions between insecticide use, potato variety choice and harvest dates.     

Laboratory and field evaluation of entomopathogenic nematodes for control of Agriotes obscurus (L.) (Coleoptera: Elateridae)

The susceptibility of the dusky wireworm, Agriotes obscurus (L.) (Coleoptera: Elateridae), to different species and strains of entomopathogenic nematodes was tested in a virulence assay in the laboratory. Larvae were exposed to different nematode doses of 50 and 100 IJs/cm². At a dose of 50 IJs/cm², only a commercial strain Heterorhabditis bacteriophora Poinar and the native strain Steinernema carpocapsae (Weiser) B14 caused increased mortality compared with the control (11.1% and 13.3% mortality, respectively). At the higher dose tested, all strains (except Steinernema sp. D122) were virulent to A. obscurus larvae. Steinernema carpocapsae B14 caused higher mortality of wireworm (75.6%) and was used for the assay conducted in cages, with a dose of 100 IJs/cm², in field conditions. The results showed that S. carpocapsae B14 controlled 48.3% of A. obscurus larvae, demonstrating that some entomopathogenic nematodes have the potential to control larvae of A. obscurus. However, further work is needed to improve their efficacy.     

Horizontal migration of click beetle (Agriotes spp.) larvae depends on food availability

It is generally thought that soil animals face specific foraging conditions because movement through soil is highly energy consuming. The hypothesis tested here is that root‐feeding click beetle larvae (wireworms, Agriotes spp.; Coleoptera: Elateridae), to minimize energy loss, only migrate horizontally through soil when located in food‐depleted surroundings. Larvae were placed at either end of a root density gradient created by the grass Holcus lanatus L. (Poaceae), and their position in the gradient was recorded after 12 days of migration. Larval migration depended on the food situation at the starting point, with larvae moving from food‐depleted to food‐rich areas, but not leaving food‐rich areas. Larvae spread further around food‐rich areas when together with conspecifics than when being alone, presumably to avoid cannibalism. Food density‐dependent migration may have to be taken into account when using trap‐crops to control Agriotes larvae. Success may depend on the timing of trap‐crop establishment relative to the target crop to generate an effective food gradient.     

The effects of insecticides on the biting behaviour of wireworms (Agriotes spp.)

Filter-paper discs soaked in nutrient were used to study how insecticides affect the biting behaviour of wireworms. When wireworms were buried in soils treated with 3.7 ppm aldrin, Bayer (38156¹), N 2790 or thionazin they stopped biting several days or weeks before they died. Three out of ten wireworms slowly recovered their biting ability after being buried for 4 days in soil containing 3.7 ppm -BHC. Biting behaviour was little affected when wireworms were confined to soils containing insecticides known to be not very toxic to wireworms.Nutrient discs treated with thionazin or -BHC were bitten less often than discs containing nutrient alone. Those treated with nutrient and aldrin were bitten almost as often as nutrient discs but the wireworms later stopped biting and died.

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Die wirkungen von insektiziden auf das fressverhalten von drahtwürmern (Agriotes spp.)

Zusammenfassung Um den Einfluß von Insektiziden auf das Freßverhalten von Drahtwürmern zu prüfen, wurden auf zweierlei Weise Filtrierpapierscheiben benutzt, die mit dem Nährstoff vollgesogen waren: a) durch Zumischen der Insektizide in den Boden, so daß die Drahtwürmer ihrer Kontaktwirkung nicht entgehen konnten (Bodenbehandlung), b) durch Aufbringen der Insektizide auf die Nährscheiben selbst (Scheibenbehandlung).Drahtwürmer hörten einige Tage oder Wochen vor ihrem Tode auf zu fressen, wenn sie in Böden vergraben waren, die mit 3,7 ppm Aldrin, Bayer 38156 (O-ethyl-S-p-totyl-ethyl phosphonodithioate), N 2790 (O-ethyl-S-phenyl-ethyl-phosphonodithioate) oder Thionazin behandel waren. 3 von 10 Drahtwürmern gewannen ihre Freßfähigkeit langsam wieder, nachdem sie für 4 Tage in Boden vergraben gewesen waren, der mit 3,7 ppm -BHC behandelt war. Die Freßfähigkeit wurde wenig beeinflußt, wenn die Drahtwürmer in Boden eingeschlossen wurden, der Bromophos, Dichlofenthion, Ethion oder RD 14838 (3-isopropylphenyl N-acetyl N-methylcarbamate) enthielt, von denen keines sehr giftig für Drahtwürmer ist.Wenn die Insektizide den Nahrungsscheiben zugefügt wurden, wurden die mit Thionazin oder -BHC behandelten Scheiben weniger oft befressen als diejenigen, die nur die Nahrung enthielten. Mit Nahrungsstoffen und Aldrin behandelte Scheiben wurden bereitwillig befressen, aber die Drahtwürmer hörten später zu fressen auf und starben.

     

Note on the effect of wireworms of the genera Agriotes and Corymbites on crop yields

Experiments were made to illustrate the regular falling off of yield of crops due to increasing wireworm populations under controlled conditions. The genus Corymbites was shown to cause as much damage as Agriotes; Athous was less harmful. The damage caused to various cereals by Agriotes is contrasted.     

Needle nematodes (Longidorus spp.) and stubby-root nematodes (Trichodorus spp.) harmful to sugar beet and other field crops in England

Longidorus attenuatus produces galls at the tips of roots of field crops, including sugar beet, growing in alkaline, sandy soils in eastern England. L. elongatus produces similar, but often larger, galls on the roots of sugar beet and other crops in sandy soils in the W. Midlands and in Fen peats. Trichodorus spp. cause ‘stubby root’ of sugar beet and can feed on many field crops. Seven species of Trichodorus were found in sandy soils in eastern England. L. attenuatus, L. elongatus and Trichodorus spp. aggregate around roots and stunt sugar beet and other crop plants. L. attenuatus is commoner below plough depth than in the topsoil, whereas T. cylindricus, T. pachy-dermus and T. anemones are more abundant in the topsoil. These nematodes cause some forms of ‘Docking disorder’.     

Vegetative reproduction and chemical control with post-emergent herbicides of field bindweed (Convolvulus arvensis L.)

It is clearly seen from data that roots of Convolvulus arvensis L. have more and less intensive regenerative period during growing season. The more intensive period is in autumn, because in that time roots culminate nutrients, carbohydrate as starch and sugar. The less intensive regenerative or shoot-growing period is in spring, called "late spring bud dormancy". Experiments were conducted to get more information and further details about the regenerative capacity of roots close to and far from the collar of Convolvulus arvensis L. Root segments closer to collar have an intensive regenerative capacity than those ones further to collar. By data of Bakke et al. (1939) is well known, roots exhumed from deep soil layers are able to create shoots with low intensity. So finally we can exclaim that regenerative capacity is decreasing further to collar. Using mechanical weed control it is sufficient to till the upper layer of soil, but many times. Chemical treatments are most effective in the integrated weed control. It is clearly seen that auxin-type herbicide such as 2,4-D, fluroxipir, MCPA. dicamba give the best result. They gave 95% weed control effect used them separately or in combination with other herbicides. Combination of Banvel 480 S (dicamba) and Logran 75 WG (triasulfuron) introduced 95% weed control effect. Only one time got absolutely 100% weed control effect, in the case of Glyphosate active substance. Caused total plant destruction. Excellent result was given with the application of Pledge 50WP (flumioxazin). Herbicides mentioned above are absolutely allowed to take an important and significant part in chemical plant protection against Convolvulus arvensis L. Other herbicides like Granstar 75DF (tribenuron-methyl), Basis 75DF (rimsulfuron + tifensulfuron-methyl) and Huszár (jodosulfuron-methyl-sodium + mefenpir-diethyl) are not so effective against Convolvulus arvensis L., as compared to the previous ones.     

Large scale Agriotes spp. click beetle (Coleoptera: Elateridae) invasion of crop land from field margin reservoirs

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Socially flexible female choice and premating isolation in field crickets (Teleogryllus spp.)

Social influences on mate choice are predicted to influence evolutionary divergence of closely related taxa, because of the key role mate choice plays in reproductive isolation. However, it is unclear whether females choosing between heterospecific and conspecific male signals use previously experienced social information in the same manner or to the same extent that they do when discriminating among conspecific mates only. We tested this using two field cricket sister species (Teleogryllus oceanicus and Teleogryllus commodus), in which considerable information is known about the role of male calling song in premating isolation, in addition to the influence of acoustic experience on the development of reproductive traits. We manipulated the acoustic experience of replicate populations of both species and found, unexpectedly, that experience of male calling song during rearing did not change how accurate females were in choosing a conspecific over a heterospecific male song during playback trials. However, females with acoustic experience were considerably less responsive to male song compared with naïve females. Our results suggest that variation in the acoustic environment affects mate choice in both species, but that it may have a limited impact on premating isolation. The fact that social flexibility during interspecific mate discrimination does not appear to operate identically to that which occurs during conspecific mate discrimination highlights the importance of considering the context in which animals exercise socially flexible mating behaviours. We suggest an explanation for why social flexibility might be context dependent and discuss the consequences of such flexibility for the evolution of reproductive isolation.     

Medical Students in Canadian Universities: Report of Statistics, 1966-67

Enrolment in the 13 Canadian medical schools in 1966-67 reached a new high of 4230, an increase of 5.1% over 1965-66. The percentage of women among medical students (12.1%) was close to that of the preceding three years. There has been a levelling off in the decline of students from outside Canada in 1966-67, when 9.5% of medical students were non-Canadian. The decline had been primarily in the number of American students, which continues. The number of students from Commonwealth countries has shown a steady increase during the eight-year period under review; in 1966-67, they make up nearly one-half of all non-Canadian students. It was noted that 18.5% of overseas students came to Canada under governmental or intergovernmental sponsorship. Of the Canadian students, 94% came from the “home” provinces of the medical schools.     

Genetic divergence and ecological specialisation of seed weevils (Exapion spp.) on gorses (Ulex spp.)

Abstract.  1. Reproductive isolation of sympatric populations may result from divergent selection of populations in different environments, and lead to ecological specialisation. In Brittany (France), the gorse Ulex europaeus (Fabaceae, Genisteae), may be encountered in sympatry with one of the two other gorse species present: U. gallii and U. minor . A recent study based on morphological identification of seed predators of gorse has shown that two weevil species (Curculionoidea, Apionidae) infest gorse pods at different seasons and have different host ranges: Exapion ulicis infests U. europaeus in spring, whereas E. lemovicinum infests U. gallii and U. minor in autumn. Weevil populations may thus have diverged in sympatry.
2. As morphological identification of weevils is often difficult and some of the characters used may exhibit individual or environmental variation, mitochondrial and nuclear sequences of weevils collected within pods of the three gorse species in 10 populations of Brittany were used to reconstruct their phylogeny.
3. The results reveal that species differentiation based on morphological characters is confirmed by the two molecular data sets, showing that E. ulicis and E. lemovicinum are distinct species, and suggesting the absence of host races. Finally, E. ulicis was able to use U. gallii and U. minor pods in spring in some years in some populations, which appeared to depend on the availability of pods present during its reproductive period.
4. Divergence between E. ulicis and E. lemovicinum may have resulted from temporal isolation of reproductive periods of weevil populations followed by specialisation of insects to host phenology.     

Mixed species flocking of tits (Parus spp.): a field experiment

Summary We tested two general models of flocking behaviour, namely the antipredation model and foraging efficiency model on mixed-species tit flocks (Parus spp.). After food addition the size of mixed-species flocks was significantly less than in the control samples. In the presence of extra food significantly more birds were observed either in monospecific flocks or solitary, than during the control observations. In the presence of a living predator the birds foraged in larger mixed-specifies flocks than during the control observations. In addition, the social behaviour of Great Spotted Woodpecker, Middle Spotted Woodpecker and Nuthatch shifted to mixed-specific flocking. The size of monospecific flocks was independent of both treatments. The density of birds increased significantly after food addition, while in the predator presence the birds tended to leave the forest. These results support the view that both the antipredation model and foraging efficiency model seem to be valid for mixed-species flocking. However, in the case of monospecific flocks, the territory maintenance could be the most important factor.     

Rapid identification of cyst (Heterodera spp., Globodera spp.) and root-knot (Meloidogyne spp.) nematodes on the basis of ITS2 sequence variation detected by PCR-single-strand conformational polymorphism (PCR-SSCP) in cultures and field samples

Cyst and root-knot nematodes show high levels of gross morphological similarity. This presents difficulties for the study of their ecology in natural ecosystems. In this study, cyst and root-knot nematode species, as well as some ectoparasitic nematode species, were identified using the second internal transcribed spacer (ITS2) sequence variation detected by polymerase chain reaction-single-strand conformational polymorphism (PCR-SSCP). The ITS2 region was sufficiently variable within the taxa investigated to allow species to be separated on the basis of minor sequence variation. The PCR primers used in this study were effective for 12 species with three genera within the Heteroderinae (Globodera pallida, G. rostochiensis, Heterodera arenaria/avenae, H. ciceri, H. daverti, H. hordecalis, H. mani, H. schachtii, H. trifolii, Meloidogyne ardenensis, M. duytsi and M. maritima). However, pathotypes of Globodera pallida and G. rostochiensis could not be distinguished. The method was tested at two coastal dune locations in The Netherlands (one in the lime-poor dunes of the north and one in calcareous dunes of the south) to determine the population structure of cyst nematodes. At each site, cyst nematodes were associated with three plant species: two plant species on the foredune (Elymus farctus and Ammophila arenaria) and one plant species occurring further inland (Calamagrostis epigejos). Two species of cyst nematodes, H. arenaria and H. hordecalis, were found. H. arenaria associated with vigorous A. arenaria and H. hordecalis in association with degenerating A. arenaria and C. epigejos. The field survey demonstrated that in coastal dunes abiotic factors may be the important affecting the distribution of cyst nematodes.