Hessian fly Avirulence gene loss‐of‐function defeats plant resistance without compromising the larva's ability to induce a gall tissue

Plant pathogen effectors encoded by Avirulence (Avr) genes benefit the pathogen by promoting colonization and benefit plants that have a matching resistance (R) gene by constituting a signal that triggers resistance. The Hessian fly, Mayetiola destructor (Say) (Diptera: Cecidomyiidae), resembles a plant pathogen in showing R/Avr interactions. Because of these interactions, a wheat plant with the H13 resistance gene can be resistant or susceptible depending on the genotype of the larva that attacks the plant, being resistant if attack comes from a larva with a functional vH13 gene, but susceptible if attack comes from a larva with a non‐functional vH13 gene. In this study we asked: does this susceptible interaction involving plants with H13 look like susceptible interactions with plants lacking H13? Possibly, the H13 plant attacked by a larva with a non‐functional vH13 is induced to partial rather than complete resistance. Or the larva, lacking its vH13‐encoded effector, is compromised in its ability to induce susceptibility, which includes forcing the plant to create a gall nutritive tissue. Responses of epidermal cells to larval attack were explored using imaging techniques (light microscopy, scanning and transmission electron microscopy). Whole‐organism responses were investigated by measuring the growth of plants and larvae. No evidence was found for partial resistance responses by H13 plants or for a compromise in the ability of vH13 loss‐of‐function larvae to induce susceptibility. It appears that disrupting vH13 function is sufficient for overcoming the induced resistance mediated by the H13 gene.     

Oviposition behaviour of Dasineura brassicae on a high- versus a low-quality Brassica host

The oviposition behaviour of the brassica pod midge, Dasineura brassicae Winn. (Diptera: Cecidomyiidae), on a preferred host, Brassica napus L. (summer oilseed rape) was compared to that on a nonpreferred, less suitable host for larval growth, Brassica juncea (L.) Coss & Czern (brown mustard). The experiments were done under field conditions with wild females.The number of landing females was significantly higher on B. napus than on B. juncea, indicating host differences in olfactory and/or visual stimuli. After landing, the behaviour differed in that females stayed longer and laid more egg batches on B. napus than on B. juncea plants. The probability that oviposition would occur after landing and the potentially adjustable egg batch size were similar on the high- and the low-quality host.A larger egg load on B. napus than on B. juncea can thus be attributed mainly to a higher landing rate and more repeated ovipositions occurring on B. napus.

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Comportement de ponte de Dasineura brassicae sur des Brassica de qualites élevée et basse

Résumé La comparaison porte sur le comportement de ponte de D. brassicae Winn. (Dept. Cecidomyiidae) sur Brassica napus L., hôte préféré, et sur B. juncea L., hôte non-préféré, qui convient moins au développement larvaire. Les expériences réalisées en champ ont porté sur des femelles sauvages.Le nombre de femelles qui atterrissent sur B. napus est significativement plus élevé que sur B. juncea, ce qui indique des différences entre les stimuli olfactif et visuel des plantes-hôtes. Aprés atterrisage, le comportement diffère en ce que les femelles restent plus longtemps et déposent plus de pontes sur B. napus que sur B. juncea. La probabilité pour que la ponte suive l'atterrissage et les tailles des ooplaques potentiellement ajustables sont semblables sur les hôtes de qualité élevée ou basse.Une charge supérieure en oeufs sur B. napus que sur B. juncea peut ainsi être principalement attribuée à un taux d'atterrissage plus élevé et à une plus grande fréquence de ponte sur B. napus.

     

The effect of fluctuating asymmetry and leaf nutrients on gall abundance and survivorship

Fluctuating asymmetry (FA) is defined as small and random deviations from perfect symmetry in otherwise bilaterally symmetrical traits. Usually, plants under stress have a higher nutritional quality and are preferred by insect herbivores. Here, we examined the relationship among leaf FA of Bauhinia brevipes (Fabaceae), nutrients and the occurrence of Schizomyia macrocapillata (Cecidomyiidae: Diptera). We evaluated whether: (i) FA was related to S. macropillata abundance and survivorship; (ii) FA correlated with the levels of foliar nutrients (macro- and micronutrients, and organic carbon); and (iii) S. macropillata abundance was related to leaf nutrients. The results showed a positive relationship between FA and gall abundance. S. macrocapillata survivorship was five times higher in B. brevipes individuals with high FA levels, but this difference was not significant. The influence of nutrients in B. brevipes FA was negligible, except for foliar nitrogen, which was 7.3% higher in plants with low FA levels. The abundance of S. macrocapillata was negatively related to nitrogen levels, but gall survivorship was not affected by this nutrient. We found evidence for a causal relationship between FA and gall occurrence, since S. macropillata gall oviposition occurs in young undeveloped leaves, thus mature leaves show an increase in FA. Nonetheless, in this system, neither FA nor nitrogen influenced gall survivorship.     

Phylogeny of the Baldratiina (Diptera: Cecidomyiidae) inferred from morphological, ecological and molecular data sources, and evolutionary patterns in plant-galler relationships

The phylogeny of the gall-midge subtribe Baldratiina (Diptera: Cecidomyiidae) was reconstructed from molecular (partial sequence of the mitochondrial 12S rDNA), morphological and ecological data sets, using 16 representative species of most of the genera. The morphological and ecological data were combined in a single character matrix and analyzed separately from the molecular data, resulting in an eco-morphological cladogram and a molecular cladogram. Attributes of galls and host associations were superimposed on the molecular cladogram in order to detect possible trends in the evolution of these traits. The cladograms resulting from the two independent analyses were statistically incongruent, although both provide evidence for the monophyly of the genera Baldratia and Careopalpis and the paraphyly of the genera Stefaniola and Izeniola. The results suggest a minor impact of the morphological characters traditionally used in the classification of the Baldratiina, whereas ecological data had a major impact on the phylogenetic inference. Mapping of gall and host attributes on the molecular cladogram suggests that multi-chambered stem galls constitute the ancestral state in the subtribe, with several subsequent shifts to leaf galls. It is concluded that in contrast to other studied groups of gall insects, related baldratiine species induce different types of galls, attesting to speciation driven by gall-type shifts at least as often as host shifts.     

Description,phenology and biology of Zelostemma chionochloae Buhl sp. nov., a platygastrid parasitoid of Eucalyptodiplosis chionochloae (Diptera: Cecidomyiidae) in New Zealand

Abstract

A platygastrid wasp that feeds on the snow tussock flower midge in the inflorescences of New Zealand snow tussock grasses (Chionochloa spp.) is formally described. Zelostemma chionochloae is a specialist natural enemy of Eucalyptodiplosis chionochloae Kolesik which is the most ubiquitous and sophisticated seed predator of Chionochloa. Z. chionochloae is a koinobiont parasitoid and some larvae enter prolonged diapause inside their host for at least 2 years. Methods for adult rearing are described. The phenology of Z. chionochloae is highly synchronised with its host even after 2 years in diapause. Parasitism levels were found to differ between years and elevations, while sex ratios differed among years. Z chionochloae probably suffers inter‐specific competition with another host‐specific hymenopteran parasitoid (Gastrancistrus sp.) which also parasitises E. chionochloae.     

Monitoring virulence in Asian rice gall midge populations in India

The Asian rice gall midge, Orseolia oryzae (Wood‐Mason) (Diptera: Cecidomyiidae), is a major pest of rice [Oryza sativa L. (Poaceae)] in India. Breeding resistant varieties and their cultivation has been the main approach to manage this pest. However, the breakdown of resistance conferred by the major genes, deployed one at a time, through evolution of virulent biotypes has become a major setback to this approach. Development of polymerase chain reaction‐based molecular markers for eight of the 10 resistance genes and their possible use in marker‐assisted selection has enabled breeders to pyramid resistance genes for achieving durable resistance. However, the choice of resistance genes needs to be made with a better understanding of the virulence composition of the pest populations in the target area and the genetics of plant resistance and insect virulence, as the rice–gall midge interaction is a gene‐for‐gene one. We adopted a single‐female test and coupled it with a modified F₂ screen test to note the virulence composition of gall midge populations and estimated the frequency of virulence alleles for adaptation at three pest endemic locations in India, namely, Warangal, Ragolu, and Raipur. Results on biotype composition showed heterogeneous pest populations in all the tests and at all the locations. Tests at Warangal repeated after 8 years showed a rapid increase in frequency of the virulence allele conferring adaptation to the plant resistance gene Gm2 as compared to that of the allele for adaptation to the resistance gene Gm1. This is probably the first direct measurement of a durability parameter of plant genes conferring insect resistance. Results supported earlier observations that sex‐linked virulence against Gm2 makes it less durable. The sex ratio did not deviate from the expected 1:1 ratio at Warangal, but at Ragolu females outnumbered males.     

New gall midge taxa of the subfamilies porricondylinae and lasiopterinae (Diptera,Cecidomyiidae) from the Rovno amber

Five new gall midge taxa of the subfamilies Porricondylinae and Lasiopterinae are described from the Late Eocene Rovno amber: Adsumyia integra gen. et sp. nov. (Dicerurini), Gratomyia inexigentis gen. et sp. nov. (Holoneurini), Winnertzia recusata sp. nov. (Winnertziini), Kovaleviola injusta gen. et sp. nov., and Spungisiola insuperabilis gen. et sp. nov. (Brachineurini).     

The adult head morphology of the hessian fly Mayetiola destructor (diptera,cecidomyiidae)

The adult head of the Hessian fly Mayetiola destructor was examined and described in detail. Morphological features are evaluated with respect to phylogenetic implications and possible effects of miniaturisation. Preserved groundplan features of Diptera are the orthognathous orientation of the head, the vestiture of small microtrichia (possible autapomorphy), filiform antennae inserted frontally between the compound eyes, the presence of a clypeolabral muscle (possible autapomorphy), the presence of labellae (autapomorphy), and the presence of only one premental retractor. Potential synapomorphies of the groups assigned to Bibionomorpha are the origin of M. tentorioscapalis medialis on the frons and the loss of M. craniolacinialis. Further apomorphies of Cecidomyiidae identified in Mayetiola are the unusually massive anterior tentorial arm, the absence of the labro‐epipharyngeal food channel, the absence of the lacinia, and the presence of antennal sensilla connected by a seta, a feature not known from any other group of Diptera. The very large size of the compound eyes (in relation to the entire head surface) and the complete loss of ocelli are possible effects of miniaturization. The large size of the brain (in relation to the cephalic lumen), the unusual shape of the optic lobes, and the absence of the frontal ganglion as a separate structure are probably also linked with size reduction. J. Morphol. 274:1299–1311, 2013. © 2013 Wiley Periodicals, Inc.     

Rampant host- and defensive phenotype-associated diversification in a goldenrod gall midge

Natural selection can play an important role in the genetic divergence of populations and their subsequent speciation. Such adaptive diversification, or ecological speciation, might underlie the enormous diversity of plant-feeding insects that frequently experience strong selection pressures associated with host plant use as well as from natural enemies. This view is supported by increasing documentation of host-associated (genetic) differentiation in populations of plant-feeding insects using alternate hosts. Here, we examine evolutionary diversification in a single nominal taxon, the gall midge Asteromyia carbonifera (O.S.), with respect to host plant use and gall phenotype. Because galls can be viewed as extended defensive phenotypes of the midges, gall morphology is likely to be a reflection of selective pressures by enemies. Using phylogenetic and comparative analyses of mtDNA and nuclear sequence data, we find evidence that A. carbonifera populations are rapidly diversifying along host plant and gall morphological lines. At a broad scale, geography explains surprisingly little genetic variation, and there is little evidence of strict co-cladogenesis with their Solidago hosts. Gall morphology is relatively labile, distinct gall morphs have evolved repeatedly and colonized multiple hosts, and multiple genetically and morphologically distinct morphs frequently coexist on a single host plant species. These results suggest that Asteromyia carbonifera is in the midst of an adaptive radiation driven by multitrophic selective pressures. Similar complex community pressures are likely to play a role in the diversification of other herbivorous insect groups.