Carabid populations in field beans and their effect on the population dynamics of Sitona lineatus (L.)

The abundance and diversity of potential carabid predators of Sitona lineatus (L.) in field beans were monitored between 1980 and 1983. The absolute abundance of the large predatory species was determined in mark-recapture experiments and a radio-labelling technique was used to estimate the level of predation in the field. Using previously published population data for S. lineatus, the importance of predation in the population dynamics of the weevil was estimated. The mortality of weevil larvae due to predation varied from 0.6%– 10.5% while that of adult weevils varied from 2.6%– 23.8%. It appeared that carabids played a significant role in the population dynamics of S. lineatus and, in years when abundant, could reduce the population of larvae and overwintering adults by more than 30%.     

Chemical stimulation of productivity and pathogenicity of entomopathogenic nematodes

Under laboratory conditions, the treatment of Steinernema carpocapsae and Heterorhabditis bacteriophora entomopathogenic nematodes with either Mg or Mn(II) ions produced an increase in their productivity and pathogenicity against Sitona lineatus weevil, pupae, and larvae. Copyright 1999 Academic Press.     

Notes on chromosome numbers and C-banding patterns in karyotypes of some weevils from central Europe (Coleoptera, Curculionoidea: Apionidae, Nanophyidae, Curculionidae)

Chromosome numbers and C-banding patterns of sixteen weevil species are presented. The obtained results confirm the existence of two groups of species with either a small or large amount of heterochromatin in the karyotype. The first group comprises twelve species (Apionidae: Oxystoma cerdo, Eutrichapion melancholicum, Ceratapion penetrans, Ceratapion austriacum, Squamapion flavimanum, Rhopalapion longirostre; Nanophyidae: Nanophyes marmoratus; Curculionidae: Centricnemus (=Peritelus) leucogrammus, Sitona humeralis, Sitona lineatus, Sitona macularis, Sitona suturalis). In weevils with a small amount of heterochromatin, tiny grains on the nucleus during interphase are visible, afterwards appearing as dark dots during mitotic and meiotic prophase. The second group comprises four species from the curculionid subfamily Cryptorhynchinae (Acalles camelus, Acalles commutatus, Acalles echinatus, Ruteria hypocrita) which possess much larger heteropycnotic chromosome parts visible during all nuclear divisions. The species examined have pericentromeric C-bands on autosomes and on the X chromosome.     

Parasitism of the lucerne pest Sitona discoideus Gyllenhal (Coleoptera: Curculionidae) and non-target weevils by Microctonus aethiopoides Loan (Hymenoptera: Braconidae) in south-eastern Australia, with an assessment of the taxonomic affinities of non-target hosts of M. aethiopoides recorded from Australia and New Zealand

Abstract  The braconid parasitoid Microctonus aethiopoides Loan has been released in Australia and New Zealand for biological control of the lucerne pest Sitona discoideus Gyllenhal. In New Zealand, the parasitoid attacks a number of endemic weevil species. A survey of Curculionoidea found in and near lucerne in south-eastern Australia was carried out to investigate whether similar non-target parasitism was occurring, and to relate this to levels of parasitism found in the target host, S. discoideus . Some of the original M. aethiopoides release sites were particularly targeted in the survey of 25 sites in Victoria, New South Wales and South Australia. Almost 2500 weevils were collected, of which over 90% were S. discoideus , with the remaining 197 other weevils comprising 29 species found at 15 of the 25 sites. Parasitism of S. discoideus by M. aethiopoides occurred at 12 lucerne sites, with levels ranging from 0 to 25%. A single incidence of parasitism of a species of an Australian native weevil Prosayleus sp. by M. aethiopoides was recorded. No parasitism of any other weevil species was observed. The taxonomic affinities between Sitona and native Australian and New Zealand weevils are discussed, concluding that non-target host range in M. aethiopoides may be determined more by ecological factors than by taxonomic affinities among its hosts.     

Field parasitism of nontarget weevil species (Coleoptera: Curculionidae) by the introduced biological control agent Microctonus aethiopoides Loan (Hymenoptera: Braconidae) over an altitude gradient

The parasitoid, Microctonus aethiopoides Loan (Hymenoptera: Braconidae) was introduced into New Zealand in 1982 to control the alfalfa pest, Sitona discoideus Gyllenhal (Coleoptera: Curculionidae). Studies have shown that a number of nontarget weevil species are attacked in the field by this parasitoid. A field study was carried out to investigate nontarget parasitism by M. aethiopoides over an altitudinal sequence from the target host habitat (alfalfa) into native grassland. Three locations were selected for the study, and at each, the alfalfa growing in the valley floor was sampled annually for parasitism of the target pest that ranged between 17 and 78%. At progressively higher altitudes, three further grassland sites at each location were sampled monthly during spring to autumn for up to 6 yr. Weevil densities were estimated, species identified, and dissections carried out to determine reproductive status and parasitism. Almost 12,000 weevils were collected during the study, which were identified as 36 species in total from the three locations. Eight weevil species were found to be parasitized, including S. discoideus, the target host that was found at all sites. Parasitism of nontarget species was approximately 2% overall but varied with location, site, and season. Substantial nontarget parasitism was found at only one of the locations, with up to 24% parasitism of a native weevil, Nicaeana fraudator Broun (Coleoptera: Curculionidae), recorded. Another species, Irenimus egens (Broun) (Coleoptera: Curculionidae), was also found at this location at similar population densities but was attacked far less by M. aethiopoides. Results are discussed in relation to weevil phenology.     

Chemical stimulation of the virulence of entomopathogenic fungi

The effect of magnesium and manganese ions on the virulence of Beauveria bassiana, Metarhizium anisopliae, Paecilomyces farinosus, and Paecilomyces fumosoroseus entomopathogenic fungi was tested. The virulence of entomopathogenic fungi to Sitona lineatus (L) weevil, pupae and larvae, was increased by tested metal ions. Mg ions increased the virulence of B. bassiana against S. linatus (L) weevils 100%. The fungi exhibited various sensitivity to these metal ions.     

The occurrence and effects of red clover necrotic mosaic virus in red clover (Trffbliumpratense)

In 1976, red clover necrotic mosaic virus (RCNMV) was identified in red clover variety trials at the Scottish Colleges of Agriculture and at the trial centres of the National Institute of Agricultural Botany (NIAB) in Northumberland, Dyfed, Devon and Cambridge. In 1977, RCNMV was also found in two commercial crops of red clover in South Wales. The only previous finding of this virus in Britain was in 1971.
In red clover leaves RCNMV causes veinal chlorosis, often followed by severe necrosis and deformation; the plants become stunted. All cultivars tested were infected either in field or glasshouse experiments and three of the four most susceptible cultivars were tetraploids. Yield losses in cv. Hungaropoly averaged 57% over three cuts. RCNMV was transmitted manually but not through seed or by aphids {Acyrthosiphon pisum and Myzus persicae) or weevils (Apion spp. and Sitona lineatus). Seedlings became infected when grown in pots containing RCNMV-infected plants or soil from infected sites, and the roots of infected test seedlings contained an Olpidium sp. which may be the vector.
White clover mosaic virus (WCMV), also common in red clover at some sites, was less damaging than RCNMV and in a glasshouse experiment decreased yield by only 22%. An unidentified seed-borne virus with spherical particles c. 33 nm in diameter was the only virus detected in clover seedlings screened for RCNMV.     

Feeding preferences of the weevils Sitona gressorius and Sitona griseus on different lupin genotypes and the role of alkaloids

The weevils Sitona gressorius and Sitona griseus are specialist herbivores on lupins in Europe. The adult weevils feed on the leaves, and the larvae on the root nodules of the plants. This causes severe damage to lupin crops. In the present study, the feeding preferences of lupin weevil adults on different lupin genotypes were examined with respect to a possible effect of lupin alkaloids on host selection. A total of 12 genotypes from the species Lupinus albus, L. angustifolius, L. luteus, and L. nanus were grown in a field experiment and the feeding damage on the leaves caused by naturally occurring lupin weevil adults was estimated. Additionally, a feeding choice test with S. gressorius adults was performed to examine feeding preferences under laboratory conditions. A gas chromatographic analysis provided information on the alkaloid content and profiles in the leaves of the tested lupin genotypes. In the field experiment, significant differences in the extent of the feeding damage within the 12 lupin genotypes were observed. The dual-choice feeding bioassay did not show discrimination of lupin species, but two L. angustifolius genotypes were significantly less affected than the standard L. luteus “Bornal”. The alkaloid analysis revealed large contrasts in alkaloid concentrations and profiles in the leaves of the tested genotypes. Correlation analysis with the results from the field and laboratory did not indicate a significant influence of the total foliar alkaloid content on the extent of weevil feeding.     

Response of Pisum sativum (Fabales: Fabaceae) to Sitona lineatus (Coleoptera: Curculionidae) infestation: effect of adult weevil density on damage, larval population, and yield loss

Sitona lineatus L. (Coleoptera: Curculionidae) is an invasive pest in North America and its geographical range is currently expanding across the Canadian prairies. Adults and larvae of S. lineatus feed upon the foliage and root nodules, respectively, of field pea, Pisum sativum L. (Fabales: Fabaceae), and may contribute to economic losses when population densities are high. Integrated pest management (IPM) programs that incorporate economic thresholds should be used to manage S. lineatus populations in a sustainable manner. The impact of nitrogen fertilizer on field pea yield and the relationships between adult weevil density and above- and below-ground damage and yield were investigated in southern Alberta, Canada using exclusion cages on field pea plots. In each cage, 32 field pea plants were exposed to weevil densities ranging from zero to one adult weevil per plant. Nitrogen-fertilized plants yielded 16% more than unfertilized plants. Nitrogen-fertilized plants had fewer root nodules than unfertilized plants, but fertilizer had no effect on foliar feeding by S. lineatus. Adult density affected foliar feeding damage, with increases in above-ground damage associated with increases in S. lineatus density. Adult density did not affect root nodule damage, larval density, foliar biomass or seed weight. Overall, these results indicate that terminal leaf damage may be used to estimate adult weevil density but cannot be used to predict larval density or yield loss. Further research is required to better understand the impact of larval damage on yield and determine if economic thresholds can be developed using data from large-scale production systems.     

Spatial and temporal distribution of blackflies (Diptera: Simuliidae) in the Itatiaia National Park, Brazil

The distribution of the blackfly larval taxocenoses of different altitudes in the Itatiaia National Park (located in the southeast of Rio de Janeiro state, Brazil 44 degrees 34' - 44 degrees 42' W, 22 degrees 16' - 22 degrees 28' S) was investigated on four campaigns, one in each season of 2003. On each campaign 60 samples were collected, using 30 x 30 cm wooden quadrats, distributed at four sites: Taquaral, Véu da Noiva, Três Picos and Brejo da Lapa. The winter and spring campaigns included two additional sampling sites: Alsene and Agulhas Negras. A total of 3578 larvae and 292 pupae were sampled, representative of six species: Simulium clavibranchium Lutz, S. subnigrum Lutz, S. rappae Py-Daniel, S. incrustatum Lutz, S. stellatum Gil-Azevedo, Figueiró & Maia-Herzog and Lutzsimulium pernigrum Lutz 1910. The highest larvae abundance and diversity were reported at the intermediate altitude site, Brejo da Lapa. Principal Components Analysis (PCA) revealed that L. pernigrum, S. stellatum and S. incrustatum were associated with the smaller breeding sites, the first two species being associated with sunny sites, while S. incrustatum occurred in sites with little sunlight.     

Adult polyphagous coleopterans overwintering in cereal boundaries: winter mortality and susceptibility to the entomopathogenic fungus Beauveria bassiana

Autumn-collected Bembidion lampros and Agonum dorsale were kept outdoors under semi field conditions to determine winter mortality. On three occasions (autumn, mid-winter and late winter) sub-samples of the population were incubated in the laboratory at room temperature and mortality was recorded. Generally the mortality was low in autumn and mid-winter, not exceeding 5%. A more pronounced post-winter mortality of up to 30% was observed at the end of hibernation. Only a negligible number were infected by the entomopathogenic fungi Beauveria bassiana and Paecilomyces farinosus. Infection experiments with B. bassiana isolates from Sitona lineatus, Tachyporus hypnorum and three species of ground beetles showed a similarly low susceptibility of B. lampros and A. dorsale to B. bassiana and, although Tachyporus spp. showed a distinct mycophagy and a significantly higher mortality, this could not be related to mycosis.     

Interaction between Sitona lepidus and red clover lines selected for formononetin content

Adult clover root weevil Sitona lepidus show a feeding preference for white clover Trifolium repens over red clover Trifolium pratense. The effects on S. lepidus of three red clover T. pratense lines, selected for high, medium, or low levels of the isoflavone formononetin in foliage, were compared in three experiments using white clover as a control. In a no‐choice slant board experiment, weevil larval weights were greater for larvae feeding on white clover roots than those feeding on roots of the red clovers. The effect of larval root herbivory on plant growth was similar for all four clovers. Following root herbivory, a large increase in root and shoot formononetin levels was observed in the high‐formononetin selection of red clover but little change in the low‐formononetin red clover. In a no‐choice experiment with sexually mature female adult weevils feeding on foliage of the four clovers, all the red clovers had increased weevil mortality. Female weevils eating the high‐formononetin red clover laid fewer eggs than weevils eating white clover. The red clover diet caused a large accumulation of abdominal fat and/or oil in the weevils, whereas weevils feeding on white clover did not accumulate fat/oil. When sexually immature adult weevils were given a choice of foliage from all four clovers, white clover was eaten preferentially, and the low‐formononetin red clover was preferred to the high‐formononetin red clover. The results suggest that formononetin and associated metabolites in red clover may act as chemical defences against adult S. lepidus and that distribution in forage legumes can be manipulated by plant breeding to improve root health.     

Incidence and severity of pest and disease damage to white clover foliage at 16 sites in England and Wales

From 1985 to 1987, leaves of white clover ( Trifolium repens ) cv. Grasslands Huia were examined for damage by pests and fungal diseases on seven occasions at up to 16 sites in England and Wales. Pest damage was recorded at all sites on all sampling dates. Over all sampling dates, the mean number of leaves damaged by slugs ranged from 23% to 67%, and that by weevils ( Sitona spp.) ranged from 3% to 62%. Also, up to 30% of leaves were damaged by other, unidentified pests. At individual sites, total pest damage frequently exceeded 90% of leaves. The area of leaf damaged by pests ranged from 2 - 12%. Fungal diseases were recorded in July and September but not in May, and were more prevalent in September 1985 than in September 1986 or 1987. Black blotch ( Cymadothea trifolii ) was the most frequently recorded disease, and the mean number of leaves damaged ranged from 4% to 21%. The mean area of leaves covered by lesions was 1–2%. Infections by viruses were assessed on two occasions, using indicator plants and electron microscopy, and only a very low incidence of arabis mosaic virus and red clover necrotic mosaic virus was recorded.     

Infectivity and reproductive potential of the Oswego strain of Heterorhabditis bacteriophora associated with life stages of the clover root curculio,Sitona hispidulus

The infectivity and reproductive potential of the entomopathogenic nematode Heterorhabditis bacteriophora (Oswego strain), at different concentrations, was studied. Seventy to 80.0% mortality to late instar larvae of the clover root curculio, Sitona hispidulus, and 40.0-76.0% mortality to pupae, was observed at concentrations of 15-100 infective juveniles. There were no significant differences in mortality among nematode concentrations. LC(50) levels of 4.0 and 21.4 nematodes were determined for clover root curculio larvae and pupae, respectively. Nematodes did not cause significant mortality to adult or first instar clover root curculio. H. bacteriophora was able to complete its development and reproduce in 74.0-95.0% of clover root curculio late instar larvae and pupae. Reproductive potential in curculio larvae and pupae ranged from 0 to 7040 infective juveniles per host. Larvae exposed to 100 nematodes had a reproductive potential significantly higher than in those larvae exposed to 15 and 50 nematodes. Reproductive potential in pupae decreased with an increased nematode dose, indicating potential crowding effects. Host larval and pupal mass were positively correlated with nematode progeny production.     

Population dynamics of the white pine weevil, Pissodes strobi, infesting jack pine, Pinus banksiana, in Ontario, Canada

1. Eight generations of white pine weevil, Pissodes strobi (Peck) , infesting the terminal shoots of young jack pine trees, were sampled as larvae, pupae, and adults between 1988 and 1995.
2. The density of adult weevils increased rapidly for the first 3 years of the study, then declined in the next 4 years. Between-generation rates of change in density of weevils were related to mean number of weevils produced per terminal shoot of the host tree. Net increases in population density followed years in which a relatively high number of weevils emerged per terminal shoot and vice versa.
3. The mean number of weevils emerging per terminal shoot was determined by survival of weevils between the end of the larval stage and the successful emergence of adult weevils.
4. There was no clear relationship between survival of the post-feeding stages of the weevil and rates of parasitism or bird predation on these same stages. There was, however, a strong negative relationship between survival of weevils within the terminal shoot and the abundance of the facultative dipteran predator Lonchaea corticis Taylor.
5. The relationship among generational rates of change in populations, survival, and predation was evident irrespective of the age of the trees infested, suggesting that population dynamics of the weevil may be influenced as much by local predation pressure as by physical and biotic changes associated with growth of the young host trees.     

Life history ofSmicronyx guineanus andSm. Umbrinus (Col.: Curculionidae) onStriga hermonthica (Scrophulariaceae)

The life history ofSmicronyx guineanus andSm. umbrinus, weevils attackingStriga hermonthica, was studied in Burkina Faso, West Africa. Field experiments were conducted in 1992 and 1993 at Kaya, in fields of sorghum (Sorghum bicolor (L.) Moench and pearl millet (Pennisetum americanum (L.) K. Schum. (syn.P. typhoides (Burm.) Stapf &; Hubb). The weevils are univoltine; the adults emerge in late August, mate and eggs are laid in the ovary ofStriga inflorescence. Larval feeding in the ovary causes galling and prevents seed production. The main damage toStriga seed capsule is caused by the larvae of at least twoSmicronyx species. Last-instar larvae drop to the soil and bury themselves to a depth of 1–15 cm, pupate and enter into dormancy. Most pupae are found in the upper 5–10 cm of the soil. The pupal period lasts from late October to late July. In May, we found 75.6% of pupae against 24.4% of adults in dormancy.     

Observations on the biology and ecology of Apion vorax (Coleoptera: Apionidae), a vector of broad bean stain and broad bean true mosaic viruses

In spring 1974 and 1975 many adult Apion vorax were found at Rothamsted in woods bordering fields that had been cropped with field beans (Vicia faba) the previous season. The weevils were most common on bramble (Rubus spp.), dog's mercury (Mercurialis perennis) and nettle (Urtica dioica). A decrease in the woodland population in May coincided with the appearance of the weevil on field bean crops in neighbouring areas. In laboratory feeding tests, adult weevils fed more on field bean leaves than on leaves of plants on which they were common in woodlands, and they fed more on field beans in May than at other times of the year. No difference was observed in the feeding of male and female weevils. Many A. vorax were caught on sticky traps in woodlands at Rothamsted in 1975, particularly in April and May, but very few were caught on sticky traps in bean crops. The numbers of A. vorax recorded on the upper foliage of bean crops at Rothamsted in June each year from 1970 to 1980 ranged from 0 to 10 per 10-m row. Eggs, larvae and pupae of A. vorax were found in field bean flowers collected from field crops. The larvae were feeding on the tips of the pistils and stamens. Adult weevils that emerged in mid-June from the flowers of autumn-sown beans mated and produced a second generation when caged on glasshouse-grown plants. Some Apion larvae, possibly A. vorax, were found inside flowers of common vetch (Vicia sativa). The name ‘bean flower weevil’ is considered a suitable common name for A. vorax.     

Partial application of insecticide to broad bean (Vicia fabae) as a means of controlling bean aphid (Aphis fabae) and bean weevil (Sitona lineatus)

The effects upon the nature of insect pest attack of treating only a certain proportion (0%, 25%, 50%, 75% and 100%) of the plants in a field bean (Vicia fabae) stand, with a systemic insecticide (aldicarb as Temik 10G, Rhone Poulenc Drugs Ltd; 10% a.i.) were assessed. Numbers of both the black bean aphid (Aphis fabae) and the bean weevil (Sitona lineatus) were proportionally reduced on untreated plants in plots with an increasing proportion of insecticide treated plants. A similar response was also observed with bean weevil leaf damage scores.
It is postulated that the observed effects are due to a reduction in insect numbers per plot brought about by redistribution of insects after initial invasion. Insects initially alighting on untreated plants later migrate to treated plants and either die or leave the plot altogether. This resulted in proportionally fewer insects on the untreated plants than would be expected.     

Cultivated and wild host plants supporting populations of the cabbage root fly

To determine the relative importance of different potential host plants for supporting populations of the cabbage root fly, wild and cultivated crucifers were sampled for pupae at four locations during 1971-3. In addition, eighty-three species of Cruciferae native to or naturalized in the British Isles were inoculated with cabbage root fly eggs in a glasshouse to determine which species could support the larvae. In the field, most pupae (28-7/plant) were collected from untreated cauliflowers. Fewer pupae (i-7–8-6/plant) were obtained from untreated crops of Brussels sprout, cabbage and swede. Applications of chlorfenvinphos reduced populations to two or less pupae per plant on all crops. Of five common weed species sampled, only Raphanus raphanistrum produced as many pupae as certain of the untreated brassica crops. Pupae did not occur in samples from Capsella bursa-pastoris but Sisymbrium officinale, Thlaspi arvense and Sinapis arvensis usually supported low numbers. In the glasshouse, only forty-four of the eighty-three cruciferous species tested supported larval development. Most pupae were obtained from 12-wk-old plants of Barbarea intermedia. B. stricta, Brassica napus, Cochlearia officinalis and R. raphanistrum and from 24-wk-old plants of Brassica rapa, Erysimum aureum, Cochlearia anglica and C. officinalis. Plant age considerably affected pupal production. Plants within a genus often gave similar results, pupae not being recovered from any of the Diplotaxis or Arabis species tested, or from young plants of Erysimum spp. In other families, Reseda lutea and R. luteola supported larval development, but the widely-separated Plantago major did not. Arguments for and against the removal of cruciferous weeds from the vicinity of cruciferous crops are discussed.     

Behavioural Acceptability of Sitona lepidus (Coleoptera: Curculionidae) to the Parasitoid Microctonus aethiopoides (Hymenoptera: Braconidae) Using the Pathogenic Bacterium Serratia marcescens Bizio

Microctonous aethiopoides Loan has been introduced into New Zealand to control the lucerne pest Sitona discoideus Gyllenhal (Coleoptera: Curculionidae). Sitona lepidus Gyllenhal (Coleoptera: Curculionidae) a pest of clover ( Trifolium spp.), has recently established in New Zealand. Laboratory experiments to test the potential of M. aethiopoides to parasitize S. lepidus has resulted in very low levels of parasitism. To investigate whether there were behavioural or physiological barriers to successful parasitism, two experiments were conducted using the insect pathogenic bacterium. Serratia marcescens Bizio as a marker for parasitoid ovipositor penetration. Firstly, M. aethiopoides 'treated' with S. marcescens were exposed to weevils and rapid weevil mortality was used to indicate ovipositor penetration. Up to 50% mortality of S. lepidus occurred, which was comparable with mortality observed in the permissive host Listronotus bonariensis . Dissection of S. lepidus exposed to parasitoids treated with distilled water showed that ca. 21% contained parasitoid eggs of which 98% were nonviable. In the second experiment, exposure periods of 24, 48 and 72 h to S. marcescens -treated parasitoids produced an increase in S. lepidus mortality of 14, 28 and 38%, respectively. There was 3% successful parasitoid development in weevils exposed for 72 h to parasitoids treated with distilled water. M. aethiopoides has been shown to develop successfully in a wide range of non-target weevil species both in the laboratory and field. Possible reasons for poor survival of M. aethiopoides immature stages in S. lepidus are discussed.