Role of dung beetle feeding mechanisms in limiting the suitability of species as hosts for the nematode Spirocerca lupi

Various species of dung beetle serve as intermediate hosts after ingesting the embryonated eggs (11–15 × 30–37 µm) of Spirocerca lupi (Spirurida: Spirocercidae) in dog faeces. The feeding mechanisms of coprophagous dung beetles restrict the size of the food particles they can ingest and hence may determine which species can be efficient vectors for S. lupi. In this study, we aimed to exclude certain dung beetle species as possible hosts of S. lupi based on whether or not they ingested latex beads of known diameters mixed into fresh cattle dung. We found that the majority (11/14) of species tested can potentially serve as intermediate hosts of S. lupi because their mouthparts allow the passage of food particles larger than the minimum size range of the eggs of this parasite.     

Potential of Salix as phytoextractor for Cd on moderately contaminated soils

Biomass production and Cd uptake in Salix (willow) is generally high. The aim of this study was to quantify the amounts of Cd in different plant and soil compartments in commercial Salix stands grown on different soil types and to use these data for estimation of the long-term effects of Cd removal by Salix at stem harvest on the soil Cd content by calculating Cd balances. Ten commercial short rotation willow coppice stands, planted with clone 78183 of Salix viminalis (L.) were investigated in order to include three different soil types with respect to pH. Stands with high stem biomass production generally had lower Cd concentrations in the plant and grew on more alkaline soils with low Cd availability when compared to stands with low stem biomass production. The highest output of Cd by Salix is therefore not necessarily achieved by stands with the highest yields or the highest Cd concentrations, as both these parameters have to be considered. The net removal of Cd from the plough layer by the Salix crop under different conditions varied between 2.6 and 16.5 g Cd ha^–1 year^–1. The long-term effects of Salix cultivation on soil Cd content, i.e. after 6–7 cutting cycles (25 years), were calculated and we reached the conclusion that there is a high potential in Salix to remove significant amounts of Cd at stem harvest. Salix can therefore presumably be used to counteract Cd pollution of agricultural soils in Sweden provided that the Cd in furnace ashes is taken care of.     

Oviposition and larval performance of Rabdophaga terminalis on Salix spp. with special consideration to bud size of host plants

Females of the gall midge Rabdophaga terminalis (H. Loew) (Diptera: Cecidomyiidae) are very selective in their choice of host plants at oviposition. In preference trials, eggs were laid almost exclusively on S. alba and S. fragilis. One single oviposition occurred on S. viminalis but none on S. triandra, S. daphnoides or S. smithiana. Significantly more eggs were laid on S. alba than on S. fragilis. No differences were detected between clones of the same species regarding oviposition in laboratory trials. Within the species of S. alba, larger buds were preferred. However, this did not explain the preference of S. alba to S. fragilis. There was agreement between plant species selected by the females and survival of the larvae. No galls developed when eggs were transferred to species that were not oviposited on. There was no difference between S. alba and S. fragilis in larval growth, but after two weeks of development there was a significantly higher proportion of larvae in cocoons and pupae on S. alba. There was a negative linear relationship between weight of larvae and larval number per gall, indicating larval competition. The negative slope was steeper for S. alba than for S. fragilis when larvae were weighed after two weeks of development. There were some discrepancies between laboratory and field data on infestation of S. alba and S. fragilis. Higher infestation levels were related to denser stands in the field.

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Résumé Etude de la ponte et des performances larvaires de Rabdophaga terminalis (Diptera; Cecidomyiidae) sur plusieurs espèces de saules avec examen particulier de l'influence de la taille des bourgeons.La ponte et les performances larvaires de la cécidomyie galliforme, Rabdophaga terminalis (H. Loew) ont été étudiées sur plusieurs espèces et clones de saules cultivés en Suède. Les femelles sélectionnent avec soin les plantes hôtes lors de la ponte. Dans des essais préférentiels, les oeufs ont été pondus presque exclusivement sur S. alba et S. fragilis; une ponte a été observée sur S. viminalis et aucune sur S. triandra, S. daphnoïdes ou S. smithiana. Significativement plus d'oeufs ont été pondus sur S. alba que sur S. fragilis. Les essais au laboratoire n'ont pas permis de déceler des différences entre clones de la même espèce. Chez S. alba, les plus gros bourgeons étaient préférés, mais ceci ne permet pas d'expliquer la préférence pour S. alba par rapport à S. fragilis. Il y a coïncidence entre les plantes choisies par les femelles et al survie des larves; il n'y avait pas développement de galles quand des oeufs étaient transférés sur des espèces qui n'avaient pas reçu de pontes. La croissance larvaire sur S. alba et S. fragilis ne présentait pas de différences, mais après 2 semaines de développement il y avait significativement plus de larves en cocons et pupes sur S. alba. La corrélation entre le poids des larves et le nombre de larves par cellule était linéaire et négative, ce qui indique une compétition larvaire; la pente était plus raide pour S. alba que pour S. fragilis quand les larves étaient pesées au bout de 2 semaines de développement. Il y a eu quelques discordances entre les résultats au laboratoire et les données de terrain sur la contamination de S. alba et S. fragilis. Les plus fortes contaminations étaient observées à l'extérieur sur pépinières denses.

     

The influence of glucosinolates and sugars on feeding by the cabbage stem flea beetle,Psylliodes chrysocephala

Agar was used as an artificial substrate to investigate the feeding behaviour of the cabbage stem flea beetle,Psylliodes chrysocephala L. (Coleoptera: Chrysomelidae), an important pest of winter oilseed rape (Brassica napus) in Europe. Both glucosinolates and sugars stimulated feeding when added to agar. The amount of feeding that occurred was affected by the type and concentration of glucosinolate and surgar and also by combinations of components. Although glucosinolates were potent feeding stimulants forP. chrysocephala, they were not a prerequisite for feeding, nor does it seem likely that glucosinolate profiles are used by this species to discriminate amongst cruciferous plants at the gustatory level.     

Resistance of three wild tuber-bearing potatoes to the Colorado potato beetle

The resistance of Solanum okadae Hawkes & Hjert. (PI 458367), Solanum oplocense Hawkes (PI 473368), and Solanum tarijense Hawkes (PI 414150) to the Colorado potato beetle, Leptinotarsa decemlineata (Say) (Chrysomelidae: Chrysomelini), was studied. In replicated field trials all three accessions showed a high level of resistance to the beetle. No significant genetic variability between genotypes of the same species was found. Results from host acceptance behavior experiments, suitability for larval development tests, foliage consumption tests, and adult survival and oviposition tests supported the hypothesis that the mode of resistance differs between the three wild Solanum species. Solanum okadae and S. oplocense affected host acceptance and consumption. Because the beetle reacted differently to these two species it was hypothesized that the antifeedant chemical(s) differed in nature or quantity. S. tarijense contrasted with the other two species by affecting mostly adult colonization and oviposition.     

Genetic and soil-nutrient effects on the abundance of herbivores on willow

The effects of soil-nutrient environment, plant genotype, and the interaction between the two on the resistance of the willow, Salix sericea, to insect species in a diverse herbivore community was measured. We found that soil-nutrient environment influenced plant growth and the abundance of most herbivores of S. sericea. However, environmental effects on herbivore abundance were often modified by plant genetics; the abundance of four of seven herbivores exhibited significant genotypeby-environment interaction effects. Pure genotype effects were mostly small and non-significant. The effects of fertilization differed among herbivores. Several herbivores were more abundant on fertilized plants, one was less abundant, and the abundance of others did not change. We found that feeding guild was a poor predictor of herbivore response. Finally we found significant phenotypic and genetic correlations among growth rate, internode length, and the abundances of several herbivores.     

Performance of leaf beetle larvae on sympatric host and non-host plants

Studies asking the ability of insects to utilize novel host plants often use novel hosts that are allopatric with the insect population under investigation. However, since the outcomes of species interactions are often site-specific, such studies cannot tell us whether a plant would actually be used by a given insect population if the plant grew sympatrically with it. We therefore performed a quantitative genetics experiment to analyse the performance of larvae of the leaf beetle Oreina elongata Suffrian (Coleoptera: Chrysomelidae, Chrysomelinae) on two host and three non-host plants, collected from a site where insects and plants co-occur in the Western Alps. When raised on the non-host Petasites albus (L.), larvae were able to survive equally well as on the two hosts, Adenostyles alliariae (Gouan) and Cirsium spinosissimum (L.), whereas they did not survive on the two other non-hosts, Peucedanum ostruthium (L.) and Rumex alpinus L. On P. albus, growth rate was slightly lower and development time slightly longer than on the two hosts. We found a genotype by environment interaction only for growth rate but not for development time and survival. However, the shape of the reaction norms of growth rates suggests that it is unlikely that selection could favour the inclusion of P. albus into the host range of the study population.     

The influence of plant species on attraction and host acceptance inCotesia glomerata (Hymenoptera: Braconidae)

Females of the larval parasitoidCotesia glomerata (L.) use plant-associated cues to locate their lepidopteran host,Pieris rapae L. In this study we investigated the influence of four host plant species,Brassica oleracea var.acephala (‘Vates’ kale),Tropaeolum majus (nasturtium),Lunaria annua (honesty), andCleome spinosa (spider flower), on two components of the host selection process inC. glomerata, namely, attraction and host acceptance. Choice tests in a flight tunnel showed that parasitoids were attracted to some host plant species more than to others in the absence of host larvae.B. oleracea was the most attractive plant species, followed byL. annua, T. majus, andC. spinosa. In previous studies it was shown thatB. oleracea carries highly suitable hosts forC. glomerata and that, in the field, parasitization rates on this plant were the highest. When host larvae were reared on the four host plant species and then transferred to a common substrate (B. oleracea var.capitata, cabbage), plant species that had served as diet for the hosts did not have a significant effect on acceptance for parasitization. Thus, parasitoids were attracted to host plant species differentially, but they did not discriminate among host larvae based on the dietary history of their hosts. ForC. glomerata, it appears that phytochemistry mediates host selection more by influencing parasitoid attraction than it does by affecting host acceptance.     

Wild species of Nicotiana as a new source of tobacco resistance to the tobacco hornworm Manduca sexta

Sixteen species of Nicotiana were examined for resistance to second instar larvae of the tobacco hornworm, Manduca sexta (L.). The tests were designed so as to discriminate between antibiosis and nonpreference. High levels of antibiosis resistance were observed in several wild species such as N. gossei and species in the Repandae section. Several other species, such as N. excelsior, showed antibiosis that appeared to be due to a different mechanism than the alkaloid-trichome exudate based resistance of the above species. The data indicate that these species of Nicotiana may be used as a new source of resistance to larvae of M. sexta.

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D'espèces sauvages de Nicotiania comme nouvelle source de résistance du tabac à Manduca sexta

Résumé La résistance aux chenilles de second stade de Manduca sexta L. a été examinée chez seize espèces de Nicotiana. Les essais ont été conçus pour distinguer absence d'appétance et antibiose. Plusieurs espèces sauvages comme N. gossei et les espèces de la section Repandae ont présenté un niveau élevé d'antibiose. D'autres espèces, comme N. excelsior ont présenté une antibiose vraisemblablement due à un mécanisme différent de la résistance des espèces précédentes provoquée par un exsudat alcaloïde des trichomes. Les résultats indiquent que ces espèces de Nicotiana peuvent être utilisées comme nouvelle source de résistance aux chenilles de M. sexta.

     

Interspecific and intraspecific variation in the performance of three pest aphid species on five grain legume hosts

The suitability of five grain legume species (narrow-leafed lupin, chickpea, faba bean, field pea, lentil) as hosts for three aphid species (green peach aphid, cowpea aphid, bluegreen aphid) was evaluated by measuring the mean relative growth rate (MRGR) and survivorship of nymphs over a 5 day period. For each aphid species, intraspecific (interclonal) variation was also determined by independently measuring the performance of 30 clones collected from a variety of hosts and from different parts of the Western Australia (WA) wheatbelt. The suitability of the grain legumes varied among aphid species. Chickpea was not a suitable host for any of the aphids tested. Averaged over all clones, lentil and faba bean were the most suitable hosts for cowpea aphid, and narrow-leafed lupin was the most suitable host for green peach aphid. Field pea was a suitable host for all three species, but only at a suboptimal level. Cowpea aphid showed the greatest amount of intraspecific variation, with significant variation in MRGR among clones on all hosts except chickpea and significant variation in survivorship on chickpea and lupin. For green peach aphid, there was significant variation in MRGR among clones on field pea and lupin, but in survivorship on lupin only. Bluegreen aphid clones showed significant variation only for MRGR on faba bean and lupin. There were positive correlations in performance of green peach aphid clones on faba bean and lentil, and of cowpea aphid clones on faba bean and lentil. Bluegreen aphid clones showed a negative correlation in performance on field pea and faba bean. These results show the importance of screening cultivars against a wide variety of aphid clones when assessing aphid susceptibility in breeding programmes. The implications of these results on the adaptability of parthenogenetic aphids are discussed.     

Prefeeding Behavior of the Crucifer Flea Beetle, Phyllotreta cruciferae, on Host and Nonhost Crucifers

The prefeeding behaviours of adult crucifer flea beetles, Phyllotreta cruciferae (Coleoptera: Chrysomelidae: Alticinae), were determined on seedlings of the host plant, Brassica napus, and compared to behaviors on seedlings of the nonhost crucifers, Crambe abyssinica, Sinapis alba, and Camelina sativa. Three stages of prefeeding behaviour, i.e., acclimation, stimulation, and initial feeding, were distinguished through observation of filmed beetles. Both antennal and tarsal chemoreceptors are important in determination of host plant quality by the crucifer flea beetle. The results of this study suggest that the sequence of prefeeding behaviors plays a crucial role in the onset of feeding. Differences in time spent on plant tissue and the frequency and duration of prefeeding behaviors provide insight into possible mechanisms of resistance to flea beetles in the non-Brassica crucifers. The nonpreferred hosts C. abyssinica and S. alba contain deterrent phytochemicals that partially inhibit feeding. These deterrent compounds appear to be volatile in nature in S. alba but nonvolatile in C. abyssinica. CFB resistance in the nonhost C. sativa may result from either the presence of repellent or the absence of stimulatory volatile phytochemicals.     

Influence of initial egg density and host size on the development of the gregarious parasitoid <Emphasis Type="Italic">Bracon hebetor</Emphasis> on three different host species

Bracon hebetor (Say) (Hymenoptera : Braconidae) is a gregarious parasitoid that attacks a variety of important lepidopterous pests of stored product and in the field. In this study the effect of host species, size and larval competition on parasitoid size, survival and development were investigated. In laboratory studies, wasp eggs at a range of densities, were placed on larvae of different weight of three Lepidoptera host species namely Adoxophyes orana (Fischer von Röslerstamm, Tortricidae), Plodia interpunctella (Hubner, Pyralidae) and, Lobesia botrana(Dennis & Schiffermueller, Tortricidae). On A. orana survival of immature parasitoids was very low at all densities and different host weights. On L. botrana survival progressively reduced as egg density increased at both host weights examined for this host. Survival on P. interpunctella was significantly affected by egg density but not by host weight. Initial egg density had a significant effect on the size of emerging adults from each rearing host. Smaller adult parasitoids emerged as egg density per larva increased. Larval host weight of P. interpunctella and A. orana had a significant effect on the size of emerging adult parasitoids mainly at the higher egg densities used in these experiments. The above results of host quality on fitness of parasitoid are discussed.     

Increase in feeding stimulants as the primary mechanism by which SO2 enhances performance of Mexican bean beetle on soybean

Relative consumption rate (RCR) and relative growth rate (RGR) were significantly higher for larvae of the Mexican bean beetle fed leaves from plants fumigated with SO₂. The insects grew faster primarily because they ate faster, rather than as a result of change in nutritional value of affected host tissue. Soluble carbohydrate content of fumigated or glutathione-treated leaves was much higher than that of corresponding control leaves, and concentrations of sucrose, fructose, and glucose, major feeding stimulants for this insect, were increased 40–50% by the treatments; soluble protein was unchanged (fumigated leaves) or significantly lower (glutathione-treated leaves) than controls. Feeding choice assays using filter-paper discs demonstrated that the beetles can discriminate clearly and respond to differences in sugar content of the magnitude produced by exposure to the pollutant. Thus, the primary mechanism by which SO₂ increases performance of Mexican bean beetle on soybean appears to be increase in foliar concentration of stimulatory sugars, which, at least in part, would be a consequence of the pollutant interfering with phloem loading and translocation of sugar from affected leaves.

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Résumé Les taux de consommation relative (RCR) et de croissance relative (RGR) sont significativement supérieurs chez les larves d'E. varivestis après fumigation des feuilles de soja par SO₂. L'étude de la relation entre RCR et RGR a révélé que les insectes se sont développés davantage, avant tout parce qu'ils ont consommé plus, et non pas par modification de la valeur nutritive des tissus de l'hôte. La teneur en carbohydrates solubles des feuilles traitées au glutathion on ayant subi une fumigation était bien supérieure à celle des témoins; les concentrations de sucrose, fructose et glucose, principaux phagostimulants de cet insecte avaient augmenté de 40 à 50%; la teneur en protéine soluble était inchangée (cas de la fumigation) ou significativement réduite (cas des feuilles traitées au glutathion). Des expériences de choix avec des disques de papier filtre ont montré que les insectes pouvaient distinguer nettement des différences de concentration en sucres, du même ordre d'importance que celles provoquées par le polluant, et y répondre. Ainsi, la cause primaire par laquelle SO₂ augmente les performances d'E. varivestis sur soja semble être l'augmentation de la concentration foliaire en sucres stimulateurs, ce qui serait, au moins en partie, la conséquence de l'interférence du polluant avec la charge du phloème et le transfert du sucre à partir des feuilles atteintes.

     

The role of lignin as a defence against the spruce bark beetle Dendroctonus micans: effect on larvae and adults

Summary The role of lignin as a physical defence against Dendroctonus micans was investigated in laboratory feeding experiments. The effect of lignin is dose-dependent, reducing larval survival, growth rate, and weight, as well as affecting gallery construction. Adults lay fewer eggs in lignified bark and also tend to construct abnormal galleries. The distribution of lignin in trees suggests a role in defence against bark beetles that feed in the thicker bark on the lower bole.     

Establishment of the Amplified Fragment Length Polymorphism (AFLP) technique for genotyping of pollen beetle (Meligethes aeneus) - a noxious insect pest on oilseed rape (Brassica napus)

In order to conduct studies concerning genetic variability of pollen beetles (Meligethes aeneus), a genotyping protocol was established. No genome information is available for pollen beetles so the amplified fragment length polymorphism (AFLP) technique was chosen since it does not depend on any prior sequence information of the samples and also is a sensitive and robust technique. However, several modifications were needed in order to adapt the method for analysis of pollen beetles. Basic modifications included (i) alterations of DNA purification, (ii) use of two six-cutter restriction enzymes, (iii) and modified PCR conditions. This protocol resulted in a favourable number of fragments of an appropriate size range for standard gel analysis by a DNA sequencer applicable to a single insect and even body parts enabling different assays to be conducted on a single specimen. Pollen beetles from different areas of Sweden were analysed to verify the reproducibility and efficacy of the protocol as well as for phenetic analysis. The high reproducibility of the modified AFLP protocol allows it to be used as a reliable tool for genotype analysis of pollen beetles.     

The influence of nutritional and genetic factors on larval performance of the cinnabar moth, Tyria jacobaeae

In a laboratory experiment using full-sibs, 60% of the variation in pupal weight of the monophage Tyria jacobaeae L. (Lepidoptera, Arctiidae) could be explained by variation in the nitrogen concentration of the food plant, Senecio jacobaea L. and only 4% by variation in sugar concentration. Larval weight and growth rates of young and old larvae were also positively correlated with nitrogen and sugar concentration. Developmental time was negatively correlated with nitrogen concentration. In a second experiment full-sib families differed significantly in larval weight at day 7, mortality, growth rate and developmental time. Pupal weight did not differ significantly among families, but was positively correlated with nitrogen concentration of Senecio. Larval performance was not significantly influenced by concentrations of sugars or alkaloids. We conclude that larval performance of Tyria during most of the larval period is mainly determined by genetic factors, but pupal weights are primarily determined by nitrogen concentration of the food plant.     

The effect of stem diameter on European corn borer behavior and survival: potential consequences for IRM in Bt-corn

The ability of non-crop plants to support complete development of insect pests is an important factor for determining the impact of those plants on resistance management programs for transgenic crops. We assessed the effect of one physical factor, plant stem diameter, on the ability of plants to support full development of the European corn borer (ECB), Ostrinia nubilalis Hübner (Lepidoptera: Crambidae), the target pest of transgenic Bt-corn. In the field, European corn borer larvae were significantly more likely to tunnel and survive in plants with larger stem diameters. Larvae were 40× more likely to survive on corn, the largest plant tested, compared to many of the smaller plants. In the laboratory, larvae were more likely to survive in and less likely to abandon the largest diet-filled artificial stems that varied only in stem diameter. In conditions simulating those that an ECB larvae would encounter upon abandoning a host, larvae survived up to three weeks and were able to locate corn as a new host with a significantly higher frequency than would be expected if they were foraging randomly. These results indicate that the probability of ECB larval survival to maturity on a plant other than corn is relatively low and thus these smaller stemmed non-corn plants may not make a substantial contribution to the pool of susceptible adults. Conversely, since more mature larvae are not as susceptible as neonates, any larvae that partially develop on non-corn plants and subsequently colonize Bt-corn may not be exposed to a lethal dose of the toxin. Since some proportion of the individuals that survive could be partially resistant heterozygotes the presence of non-corn host plants could facilitate the development of resistant ECB populations.