Oviposition choice and larval survival of Dasineura marginemtorquens (Diptera: Cecidomyiidae) on resistant and susceptible Salix viminalis

Abstract.

• 1 Substantial intraspecific variation exists in Salix viminalis resistance to the gall midge Dasineura marginemtorquens. Earlier work has found this variation to have a large genetic component. Willow clones are stable in their resistances between midge generations and different nutrient levels in both field and laboratory culture.
• 2 This study reports the results of laboratory experiments on female oviposition choice and larval survival on potted plants from clones that are very different in resistance as determined in field studies.
• 3 In choice experiments using pairs of plants, the average female midge did not prefer susceptible willow clones over resistant ones for oviposition. In about one third of the replicates, midges actually laid more eggs on the resistant clone. Further work is necessary to examine the nature of variation among midges in discrimination of these plant types.
• 4 Resistance is manifested as great differences in larval survival. Six days after oviposition survival was 92% on susceptible plants but only 6% on resistant ones. Galls developed on all of the susceptible plants, while in 73% of the resistant plants galls were not even initiated.
• 5 The plant traits causing resistance are enigmatic. Larval behaviour suggests that resistant plants interfere with feeding behaviour. On resistant plants, most larvae wander for more than 24 h without initiating any galls before dying. On susceptible plants many first instar larvae begin feeding and initiate galls within this period.

     

A rapid hypersensitive response associated with resistance in the willow Salix viminalis against the gall midge Dasineura marginemtorquens

Great genotypic variation in resistance against the gall midge Dasineura marginemtorquens Bremi (Diptera: Cecidomyiidae) exists within its willow host Salix viminalis L. (Salicaceae). In some resistant genotypes larvae die within 40 h after attempting to initiate galls. The present study tested the hypothesis that the hypersensitive response (HR) is involved in incompatible interactions between D. marginemtorquens and S. viminalis. By means of UV/blue light and visible light microscopy, we verified a rapidly (within 12 h after egg hatch) spreading cell death of an HR-type due to larval attack in resistant willow genotypes. Twelve h after egg hatch, the cell death had spread up to six cell layers in resistant S. viminalis genotypes whereas in susceptible genotypes only up to two cell layers were affected. In the groups of dead cells on the resistant genotypes accumulation of phenolics was observed within 24 h after egg hatch. The rapidity of the cell death induction, the early local accumulation of phenolic compounds, and the strong association of the cell death with larval mortality suggest that the formation of dead cells in resistant willow genotypes should be interpreted as a true HR.     

Dasineura ingeris sp.n. (Diptera: Cecidomyiidae) on Salix viminalis in Sweden, including comparisons with some other Dasineura species on Salix

Infestations of an undescribed gall midge species were discovered in Southern Sweden in biomass plantations and nurseries of Salix viminalis L. Terminal leaf buds are damaged and side shoots subsequently develop. This midge, Dasineura ingeris sp.n., closely resembles three other species occurring on Salix: D.terminalis (H. Loew) on S.alba L. and S.fragilis L.; D.iteobia (Kieffer) recorded from S.caprea L. and S.cinerea L.; and D.schreiteri (Stelter) (= comb.n. for Rabdophaga schreiteri Stelter) originally found as an inquiline in the galls of another gall midge, Dasineura rosaria (H. Loew), on S.repens L. No qualitative differences in morphology were observed between these four gall midge species, but results of morphometric analyses show significant differences between all of them. In oviposition preference trials, which included host plants of all four midge species, D.ingeris laid eggs mainly on S. viminalis, D.schreiteri preferably on S.repens , and D.iteobia exclusively on S.caprea. In larval performance trials D.ingeris produced many galls on S. viminalis , one gall also on S.caprea , but no galls on either S.alba or S.repens.     

Olfactory responses and sensilla morphology of the blackcurrant leaf midge Dasineura tetensi

Olfactory responses of Dasineura tetensi (Rubs) (Diptera; Cecidomyiidae) to leaf volatiles of blackcurrant (Ribes nigrum) were tested in a 4-way olfactometer. Newly emerged virgin females showed no response to the leaf volatiles emitted from a blackcurrant shoot. Newly emerged males (which are known to respond to a pheromone released by the female) also showed no response to the leaf volatiles. Two hours after mating females responded positively, indicating that leaf volatiles may play a role in host plant finding. Scanning (SEM) and transmission (TEM) electron microscopy of the antennae of D. tetensi showed that males and females share five sensillum types; sensilla chaetica (mechanoreceptors), sensilla trichodea, sensilla basiconica, uniporous peg sensilla and circumfila (chemoreceptors). The sensilla chaetica and sensilla trichodea resemble those found on other insects. Sensilla basiconica were found on all antennal subsegments except the tip. These are multiporous receptors with five unbranched dendrites filling the lumen. Small peg sensilla located on the tips of both male and female antennae may function as contact-chemoreceptors. The circumfila, which are a unique type of sensilla found only on cecidomyiid antennae, form loops around each of the antennal subsegments, being attached to the surface by a series of stalks. TEM revealed that each stalk consisted of one sensillum containing a single highly branched dendrite. The distal regions of the walls of each sensillum are fused together to form the circumfila. Circumfila have multiporous walls and a lumen filled with multiple branches of dendrites. Their structure suggests that they are important olfactory receptors in both the male and female.     

Hypersensitive reaction and induced resistance in rice against the Asian rice gall midge Orseolia oryzae

Rice seedlings of the resistant variety Phalguna showed premature tillering, browning of central leaf, and tissue necrosis at the apical meristem following artificial infestation with avirulent biotype 1 of the Asian rice gall midge, Orseolia oryzae (Wood-Mason) (Diptera: Cecidomyiidae). Tissue necrosis representing a typical hypersensitive reaction (HR), accompanied by maggot mortality, was observed within 4 days after infestation. However, reinfestation of secondary tillers subsequent to HR in primary tiller, did not lead to HR in secondary tillers though maggot mortality was seen. Artificial infestation with the weed gall midge O. fluvialis did not result in HR either in gall midge susceptible TN 1 or resistant Phalguna rice varieties. Resistance in Phalguna against the virulent biotype 4 could be induced by either prior, simultaneous, or subsequent infestation with the avirulent biotype 1. The duration of effectiveness of such induced resistance varied with the sequence and time lag between infestations.     

Inheritance of resistance against biotype 2 of the Asian rice gall midge, Orseolia oryzae

The inheritance of resistance in the rice cultivars Phalguna, ARC5984, ARC 5158, Veluthacheera, and T1477 to the Asian rice gall midge biotype 2 was studied under both natural and artificial infestation conditions against the susceptible cultivars Jaya and IR20. A single recessive gene in Veluthacheera and two recessive complementary genes in T1477 control resistance. Phalguna and ARC5984 possess a single dominant gene while ARC5158 has a single dominant and a single recessive gene for resistance. Allelism studies showed that genes for resistance in Veluthacheera and T1477 are allelic but non-allelic to the resistance genes in Phalguna and ARC5984, which are allelic to each other. Genes for resistance in ARC5158 are allelic to resistance genes of the other four donors. There was no cytoplasmic inhibition of resistance by the susceptible parents.     

Intracellular resistance correlates with initial stage of frost hardening in willow (Salix viminalis)

Distributed model parameters of shoots of five clones of willow ( Salix viminalis ) were examined with electrical impedance analysis at the end of the growing season and with cold acclimation. The parameters were compared with regard to frost hardiness, linoleic (18:2) and linolenic (18:3) fatty acids, unsaturation/saturation ratio of fatty acids and dry weight content. The intracellular resistance (r_i) correlated best with changes in frost hardiness. The value of r_i rose from 1–2 Ω m in non-hardened to about 12 Ω m in hardened samples. In the initial stages of frost hardening, a linear relationship was found between r_i and frost hardiness and levels of 18:2 fatty acid, and an inverse relationship between r_i and levels of 18:3 fatty acid. The unsaturation/saturation ratio of fatty acids rose fairly rapidly in the initial stage of hardening. The dry weight content increased stepwise during the experimental period, and less steadily than r_i. In addition, equivalent circuit parameters changed in the prehardening phase, and were probably connected with cell differentiation and lignification. Frost hardiness by the visual method and by extracellular resistance, determined after controlled freezing tests, correlated well in the initial stages of hardening until about − 10°C but deviated upon further hardening.     

Terpenes associated with resistance against the gall wasp,Leptocybe invasa,in Eucalyptus grandis

Leptocybe invasa is an insect pest causing gall formation on oviposited shoot tips and leaves of Eucalyptus trees leading to leaf deformation, stunting, and death in severe cases. We previously observed different constitutive and induced terpenes, plant specialized metabolites that may act as attractants or repellents to insects, in a resistant and susceptible clone of Eucalyptus challenged with L. invasa. We tested the hypothesis that specific terpenes are associated with pest resistance in a Eucalyptus grandis half‐sib population. Insect damage was scored over 2 infestation cycles, and leaves were harvested for near‐infrared reflectance (NIR) and terpene measurements. We used Bayesian model averaging for terpene selection and obtained partial least squares NIR models to predict terpene content and L. invasa infestation damage. In our optimal model, 29% of the phenotypic variation could be explained by 7 terpenes, and the monoterpene combination, limonene, α‐terpineol, and 1,8‐cineole, could be predicted with an NIR prediction ability of  .67. Bayesian model averaging supported α‐pinene, γ‐terpinene, and iso‐pinocarveol as important for predicting L. invasa infestation. Susceptibility was associated with increased γ‐terpinene and α‐pinene, which may act as a pest attractant, whereas reduced susceptibility was associated with iso‐pinocarveol, which may act to recruit parasitoids or have direct toxic effects.     

Endogenous Gibberellins in Elongating Shoots of Clones of Salix dasyclados and Salix viminalis

Elongating shoots of rapidly growing clones of Salix viminalis L. (clone 683-4) and Salix dasyclados Wimm. (clone 908) harvested in early August were analyzed for endogenous gibberellins (GA). Distribution of GA-like activity, determined by Tan-ginbozu dwarf rice microdrop bioassay after reverse phase C₁₈ high performance chromatography, was similar for both species. For S. dasyclados, combined gas chromatography-selected ion monotoring (GC-SIM) yielded identifications of GA₁, GA₈, GA₁₉, GA₂₀, and GA₂₉. Identifications of GA₄ and GA₉ were also made using co-injections of known amounts of [17, 17-²H₂]GAs. By bioassay, the main activity was GA₁₉-like in both species. Gibberellin A₁, GA₁₉, and GA₂₀ concentrations were approximated by GC-SIM using co-injections of known amounts of [17,17-²H₂]GAs. Both bioassay and GC-SIM results indicated very high concentrations of GA₁₉ and GA₂₀ (about 6000 nanograms per kilogram fresh weight shoot tissue using GC-SIM: 800 ng using bioassay), compared to the concentration of GA₁ (about 130 nanograms per kilogram fresh weight using either GC-SIM or bioassay).     

Identification of AFLP markers linked to a resistance gene against pine needle gall midge in Japanese black pine

Bulked segregant and AFLP analyses of two mapping populations (R17 × S6 and R17 × S1) were used to identify markers linked to Rpgm, the only known gene responsible for resistance to pine needle gall midge in Pinus thunbergii Parl. Rpgm was found to be bracketed by ACCC/CCTTT ₁₉₀ on one side at a distance of 6.6 cM and ACGT/CCCGC ₂₅₀ at 15.3 cM on the other side. The segregation of these markers was analyzed in two other families in order to determine their phase and transferability. One of the two additional resistant parents carried ACCC/CCTTT ₁₉₀ in the homozygous state while the marker was in coupling (plus marker allele linked with an R allele) in a resistant parent, R17. The marker ACGT/CCCGC ₂₅₀ was in a repulsion phase in R17 and was not detected in the other two resistant pine trees. Out of four AFLP markers identified, only ACGT/CCAAT ₂₉₀ was transferable in all resistant trees tested, although its phase was opposite for different trees. These results indicate that in applying those markers to select resistant trees, the phase state of the markers in each resistant tree with respect to Rpgm needs to be considered.Communicated by D.B. Neale     

Nitrate Supply and the Biophysics of Leaf Growth in Salix viminalis

The influence of nitrogen on leaf area development and the biophysicsof leaf growth was studied using clonal plants of the shrubwillow, Salix viminalis grown with either optimal (High N) orsub-optimal (Low N) supplies of nitrate. Leaf growth rate andfinal leaf size were reduced in the sub-optimal treatment andthe data suggest that in young rapidly growing leaves, thiswas primarily due to changes in cell wall properties, sincecell wall extensibility (% plasticity) was reduced in the LowN plants. The biophysical regulation of leaf cell expansion also differedwith nitrogen treatment as leaves aged. In the High N leaves,leaf cell turgor pressure (P) increased with age whilst in theLow N leaves P declined with age, again suggesting that foryoung leaves, cell wall plasticity limited expansion in theLow N plants. Measurements of cell wall properties showed thatcell wall elasticity (%E) was not influenced by nitrogen treatmentand remained constant regardless of leaf age. Key words: Salix, cell wall extensibility, nitrogen nutrition, biophysics of leaf growth     

P-protein and inclusion bodies in root protophloem of Salix viminalis

The formation of P-protein in the protophloem of 9- to 14-day-old adventitious roots of Salix viminalis was studied. In immature sieve elements a finely granular material was present. This was considered to be nascent P-protein. Small aggregations of tubular P-protein were observed 17 cells from the first "cleared" sieve element. In older cells the bodies were up to 7 μm long. Nondispersed and disaggregating P-protein bodies were present in mature sieve elements. P-protein bodies were also observed in parenchyma cells adjoining mature sieve elements. In addition, inclusion bodies of unknown origin are described. They had a granular content and were most often found in mature sieve elements.     

Abscisic Acid and the Photoperiodic Induction of Dormancy in Salix viminalis L

A series of growth room experiments was carried out aiming to establish the role of abscisic acid on dormancy of Salix viminalis L. The inhibitor content and abscisic acid levels of extracts from roots, sap, leaves, and apical tissues of willow were measured using biological assay and gas-liquid chromatography.     

Fetuin-null mice are protected against obesity and insulin resistance associated with aging

alpha2-HS glycoprotein (AHSG), also known as fetuin-A, inhibits insulin receptor autophosphorylation and tyrosine kinase activity in vitro and in vivo. Earlier we have shown that fetuin-null (KO) mice demonstrate improved insulin sensitivity and resistance to diet-induced obesity. Since aging is associated with insulin resistance and impaired glucose handling, we tested the hypothesis that fetuin-null (KO) mice are resilient to changes in insulin sensitivity associated with aging. Aged (80-week-old) fetuin-null mice were leaner and demonstrated significantly lower body weights compared to age- and sex-matched wild-type (WT) littermates. Leanness in aged fetuin KO mice was accompanied by a significant increase in dark-onset energy expenditure, without marked alteration of respiratory quotient. In comparison to WT mice, fetuin KO mice demonstrated a lower fasting insulin resistance index, and significantly lower blood glucose and insulin levels, following a 4h fast. Interestingly, despite significantly decreased insulin levels during a glucose tolerance test, aged fetuin-null mice demonstrated a similar glucose excursion as WT mice, indicative of improved insulin sensitivity. Analysis of aldehyde-fuchsin stained pancreas from aged fetuin KO mice indicated no difference in islet beta-cell size or number. An insulin tolerance test confirmed the increased insulin sensitivity of aged fetuin KO mice. Further, compared to WT mice, aged fetuin-null mice demonstrated increased skeletal muscle and liver IR autophosphorylation and TK activity. Taken together, this study suggests that the absence of fetuin may contribute to the improvement of insulin sensitivity associated with aging.     

Sex determination and sex ratio in the dioecious shrub Salix viminalis L.

 Various ecological factors (e.g. herbivory, difference between males and females in colonising ability) have been invoked to explain female-biased sex ratios in populations of willow species. It was implicitly assumed that genetic factors would lead to a balanced sex ratio in the absence of ecological disturbances. In an experiment carried out in a homogeneous environment and in the absence of herbivores the progeny sex ratio of 13 crosses of basket willow (Salix viminalis L.) was observed to range from extreme female bias to extreme male bias. The observed sex ratio cannot be explained by the presence of sex chromosomes without assuming that additional loci are also involved in the sex determination. Alternatively, the sex ratios in this study can be explained by a sex determination mechanism governed by multiple independent loci. Received: 1 February 1996 / Accepted: 14 June 1996